@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Land and Food Systems, Faculty of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Cruickshank, John Johnston"@en ; dcterms:issued "2010-05-11T21:49:56Z"@en, "1985"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The objective of this study was to investigate the effects of cage density and excess vitamin D₃ on the incidence and severity of leg abnormalities in broiler chickens. In addition, sequential morphometric and radiographic characteristics of leg bone development were described in normal and abnormal broilers in an attempt to develop a pattern recognition for leg abnormalities in poultry. Twisted leg, characterized by a progressive medial (varus) or lateral (valgus) deviation of the distal tibiae was the predominant leg abnormality observed. Lateral deviations were more common than medial deviations (92% and 8%, repectively) and it occurred equally on the right and left leg. The incidence of twisted leg was considerably higher in cages than on litter (21% vs 4%, respectively). High density and excess dietary vitamin D₃ resulted in a significant increase in the incidence of twisted leg. Differences in incidence could not be explained through differences in body weight or feed consumption. However, broilers fed the excess vitamin D₃ consumed more but gained less body weight, suggesting a metabolic stress may have been involved. High density appeared to increase the severity of the disorders, while excess vitamin D₃ had no effect on severity. Morphometric and radiographic comparisons of tibiae from normal broilers and those with twisted leg suggested that the development of twisted leg may be related to a structural abnormality in the distal tibiae; namely shallow distal condyle grooves. Changes in tibiae morphology associated with the progression of the disorder appeared as functional adaptations to the deformation rather than the primary cause of the bone deviations themselves. Sequential radiography of tibae from clinically normal broilers revealed a high incidence of tibial dyschondro-plasia in the proximal metaphyses at 3, 4 and 5 weeks (60%, 20% and 20%, respectively). It was concluded that tibial dyschondroplasia may be more common than it is realized."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/24601?expand=metadata"@en ; skos:note "MORPHOMETRIC AND RADIOGRAPHIC CHARACTERIZATION OF LEG DISORDERS IN BROILER CHICKENS BY JOHN JOHNSTON CRUICKSHANK B.Sc.(Agr.)» The U n i v e r s i t y of B r i t i s h Columbia, 19 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of P o u l t r y Science) We accept t h i s t h e s i s as conforming to the r e q u i j e d standard THE UNIVERSITY OF BRITISH COLUMBIA August 1985 © J o hn Johnston Cruickshank, 1985 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f CAJM02 The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date ABSTRACT The o b j e c t i v e of t h i s s t u d y was to i n v e s t i g a t e t h e e f f e c t s of cage d e n s i t y and e x c e s s v i t a m i n Dg on the i n c i d e n c e and s e v e r i t y of l e g a b n o r m a l i t i e s i n b r o i l e r c h i c k e n s . In a d d i t i o n , s e q u e n t i a l morphometric and r a d i o -g r a p h i c c h a r a c t e r i s t i c s of l e g bone d e v e l o p m e n t were d e s c r i b e d i n normal and abnormal b r o i l e r s i n an attempt to d e v e l o p a p a t t e r n r e c o g n i t i o n f o r l e g a b n o r m a l i t i e s i n p o u l t r y . T w i s t e d l e g , c h a r a c t e r i z e d by a p r o g r e s s i v e m e d i a l (varus) or l a t e r a l (valgus) d e v i a t i o n of the d i s t a l t i b i a e was t h e p r e d o m i n a n t l e g a b n o r m a l i t y o b s e r v e d . L a t e r a l d e v i a t i o n s were more common than medial d e v i a t i o n s (92% and 8%, r e p e c t i v e l y ) and i t o c c u r r e d e q u a l l y on the r i g h t and l e f t l e g . The i n c i d e n c e of t w i s t e d l e g was c o n s i d e r a b l y higher i n cages than on l i t t e r (21% vs 4%, r e s p e c t i v e l y ) . High d e n s i t y and excess d i e t a r y v i t a m i n Dg r e s u l t e d i n a s i g n i f i c a n t i n c r e a s e i n the i n c i d e n c e of t w i s t e d l e g . D i f f e r e n c e s i n i n c i d e n c e c o u l d not be e x p l a i n e d t h r o u g h d i f f e r e n c e s i n body weight or f e e d consumption. However, b r o i l e r s fed the excess vitamin Dg consumed more but g a i n e d l e s s body w e i g h t , s u g g e s t i n g a m e t a b o l i c s t r e s s may have been i n v o l v e d . High d e n s i t y a p p e a r e d t o i n c r e a s e t h e s e v e r i t y of the d i s o r d e r s , w h i l e excess v i t a m i n Dg had no e f f e c t on s e v e r i t y . i i i M o rphometric and r a d i o g r a p h i c c o m p a r i s o n s of t i b i a e from normal b r o i l e r s and t h o s e w i t h t w i s t e d l e g suggested t h a t the development of t w i s t e d l e g may be r e l a t e d t o a s t r u c t u r a l abnormality i n the d i s t a l t i b i a e ; namely shallow d i s t a l c o n d y l e g r o o v e s . C h a n g e s i n t i b i a e m o r p h o l o g y a s s o c i a t e d with the p r o g r e s s i o n of the d i s o r d e r appeared as f u n c t i o n a l a d a p t a t i o n s to the d e f o r m a t i o n r a t h e r than the primary cause of the bone d e v i a t i o n s themselves. S e q u e n t i a l radiography of t i b a e from c l i n i c a l l y normal b r o i l e r s r e v e a l e d a h i g h i n c i d e n c e of t i b i a l dyschondro-p l a s i a i n the proximal metaphyses at 3, 4 and 5 weeks (60%, 20% and 20%, r e s p e c t i v e l y ) . I t was c o n c l u d e d t h a t t i b i a l d y s c h o n d r o p l a s i a may be more common than i t i s r e a l i z e d . TABLE OF CONTENTS Page ABSTRACT 1 1 LIST OF TABLES v i LIST OF FIGURES v i i LIST OF APPENDIX TABLES i x ACKNOWLEDGEMENTS x I GENERAL INTRODUCTION 1 II LITERATURE REVIEW 3 AVIAN SKELETON 3 S k e l e t a l Development 3 Gross Anatomy of the Chicken Leg 5 LEG ABNORMALITIES IN POULTRY 8 GENETIC ETIOLOGIES 10 T i b i a l Dyschondroplasia 10 Chondrodystrophy 12 R i c k e t s 13 S p o n d y l o l i s t h e s i s 15 Long Bone D i s t o r t i o n 16 NUTRITIONAL ETIOLOGIES 18 T i b i a l Dyschondroplasia 18 Chondrodystrophy 18 R i c k e t t s 21 S p o n d y l o l i s t h e s i s 23 Long Bone D i s t o r t i o n 25 ENVIRONMENTAL/MANAGERIAL ETIOLOGIES 26 SPECIFIC PATHOGENS 29 I I I EFFECT OF EXCESS VITAMIN Do AND CAGE DENSITY ON THE INCIDENCE OF LEG ABNORMALITIES IN BROILER CHICKENS 32 I n t r o d u c t i o n 32 M a t e r i a l s and Methods 34 R e s u l t s and D i s c u s s i o n 36 i v V Page IV SEQUENTIAL MORPHOMETRY AND RADIOGRAPHY OF THE TIBIAE FROM NORMAL BROILER CHICKENS AND THOSE WITH TWISTED LEG 51 I n t r o d u c t i o n 51 M a t e r i a l s and Methods 54 R e s u l t s and D i s c u s s i o n 59 V SUMMARY AND CONCLUSIONS 82 VI LITERATURE CITED 85 VII APPENDIX 94 LIST OF TABLES Table Page 3 .1 Composition of Experimental D i e t s 35 3.2 Main E f f e c t s of Vitamin D 3 and Cage Density on the S e v e r i t y of Leg A b n o r m a l i t i e s 43 4 .1 R a d i o l o g i c a l Techniques used to X-ray the T i b i a e of B r o i l e r Chickens.. 57 v i LIST OF FIGURES F i g u r e Page 1.0 The Gross Anatomy of the Chicken Leg 7 3.1 Normal and Abnormal Chicks at 5 Days 38 3.2 Moderate Medial (Varus) Bending of the D i s t a l T i b i o t a r s u s and Proximal Tarsometatarsus at 28 Days 39 3.3 Incidence of Leg A b n o r m a l i t i e s (ILA) i n B r o i l e r s Fed C o n t r o l L e v e l s (400 ICU/kg feed) or High L e v e l s (4000 ICU/kg feed) of Vitamin D3 i n the Diet 40 3.4 Incidence of Leg A b n o r m a l i t i e s (ILA) i n B r o i l e r s Reared i n High Density (340 cm^/bird) or Low Density (680 cm 2/bird) Cages 41 3.5 Feed Consumption (FC) of B r o i l e r s Reared i n High Density (340 cm^/bird) or Low Density (680 cm^/bird) Cages 44 3.6 Body Weight (BWT) of B r o i l e r s Reared i n High Density (340 cm^/bird) or Low Density (680 cm 2/bird) Cages 45 3.7 Body Weight (BWT) of B r o i l e r s Fed C o n t r o l L e v e l s (400 ICU/kg feed) or High L e v e l s (4000 ICU/kg feed) of Vitamin Dg i n the D i e t 48 3.8 Feed Consumption (FC) of B r o i l e r s Fed C o n t r o l L e v e l s (400 ICU/kg feed) or High L e v e l s (4000 ICU/kg feed) of Vitamin D3 i n the Diet 49 4.1 Morphometric c r i t e r i a and methodology used to measure the t i b i a e 55 4.2 T o t a l Leg A b n o r m a l i t i e s , P r o p o r t i o n with Twisted Leg and F l o c k M o r t a l i t y over the Six Week T r i a l 60 4.3 P r o g r e s s i o n of T y p i c a l U n i l a t e r a l Valgus Deformation 61 4.4 P r o g r e s s i o n of T y p i c a l B i l a t e r a l Varus Deformation 62 v i i v i i i A.5 S e q u e n t i a l Radiography of B r o i l e r Chickens Showing Normal T i b i a l Growth and Development 64 4.6 P r o g r e s s i o n of B i l a t e r a l Varus Deformity as seen with S e q u e n t i a l Radiography 65 4.7 P r o g r e s s i o n of U n i l a t e r a l Valgus Deformity as seen with S e q u e n t i a l Radiography 66 4.8 A n t e r o p o s t e r i o r Radiographs of the L e f t T i b i a e from C l i n i c a l l y Normal B r o i l e r Chickens Revealed S u b c l i n i c a l Dyschondroplasia i n the Proximal Metaphyses 68 4.9 L a t e r a l Radiograph of L e f t T i b i a e of C l i n i c a l l y Normal B r o i l e r Chickens at 4 weeks Revealing S u b c l i n i c a l Dyschondroplasia 69 4.10 L o n g i t u d i n a l S e c t i o n s Through Proximal Metaphyses Revealing Abnormal Masses of C a r t i l a g e T y p i c a l of Dyschondroplasia 70 4.11 Body Weight (BWT) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 71 4.12 T i b i a l Length ( T i b . L ) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 73 4.13 Condyle Groove Depth (CGD) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 74 4.14 Condyle Groove Width (CGW) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 76 4.15 T i b i a l Diameter (TD) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 77 4.16 Percent C o r t i c a l Thickness (PCT) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg (TL) 78 4.17 Percent Ash (PASH) of Normal (N) B r o i l e r s and Those A f f e c t e d with Twisted Leg 80 LIST OF APPENDIX TABLES Table Page I Regression A n a l y s i s of P r o d u c t i o n Parameters f o r D i e t Over B i r d Age 95 II Regression A n a l y s i s of P r o d u c t i o n Parameters f o r Density Over B i r d Age 96 I I I A n a l y s i s of Variance on S e v e r i t y Scores of Leg A b n o r m a l i t i e s 97 IV Regression A n a l y s i s of Body Weight and Morphometric Parameters 98 V Main E f f e c t Means of Vitamin D3 and Cage Density on P r o d u c t i o n Parameters 100 VI Mean Values f o r Morphometric Parameters, T i b i a l Ash, and % C o r t i c a l Thickness 101 i x ACKNOWLEDGMENTS I wish to express my s i n c e r e g r a t i t u d e to Dr. J . S. Sim f o r i n i t i a t i n g t h i s s t u d y and f o r h i s support and guidance t h r o u g h o u t . T h a n k s a r e a l s o i n o r d e r t o D r . R.C. F i t z s i m m o n s , Dr. K.M. Cheng, Dr. J.H. Robinson, Dr. D. L i and Dr. J.W. Knickerbocker f o r t h e i r v a l u a b l e suggestions as committee members. Many p e o p l e have c o n t r i b u t e d to the s u c c e s s of t h i s s t u d y . A s s i s t a n c e f r o m t h e s t a f f and s t u d e n t s i n t h e Department of P o u l t r y S c i e n c e , and i n p a r t i c u l a r R. Soong, G. S c h i e r m a n , H. Song, and M. Newcombe i s g r a t e f u l l y a cknowledged. T e c h n i c a l a s s i s t a n c e provided by C. Hutch and the s t a f f of the Radiology Department at the U n i v e r s i t y of B r i t i s h Columbia Acute Care U n i t i s much a p p r e c i a t e d . I w o u l d a l s o l i k e t o t h a n k my w i f e Pam f o r h e r u n y i e l d i n g support and encouragement throughout t h i s study. F i n a l l y , I would l i k e to d e d i c a t e t h i s t h e s i s to my p a r e n t s who have a l w a y s encouraged me i n my s c h o l a s t i c endeavors. F i n a n c i a l s u p p p o r t was provided by A g r i c u l t u r e Canada and the B r i t i s h Columbia M i n i s t r y of A g r i c u l t u r e and Food. V CHAPTER ONE GENERAL INTRODUCTION P o u l t r y p r o d u c t i o n i n Canada, and g e n e r a l l y throughout the world i s c a r r i e d out p r i m a r i l y i n a h i g h l y s p e c i a l i z e d , e f f i c i e n t branch of the farming i n d u s t r y . S t a t i s t i c s Canada (1983) r e v e a l s the a n n u a l d o m e s t i c p r o d u c t i o n of p o u l t r y meat has been i n c r e a s i n g i n recent years and exceeded 430.2 tonnes, with farm cash r e c e i p t s t o t a l l i n g over 608.2 m i l l i o n d o l l a r s . However, l e g a b n o r m a l i t i e s are one of the major areas of c o n c e r n f o r the p o u l t r y i n d u s t r y , w i t h numerous r e p o r t s c i t i n g them as c o s t i n g the p o u l t r y i n d u s t r y m i l l i o n s of d o l l a r s . Leg a b n o r m a l i t i e s r e p r e s e n t l o s s e s f o r t h e p r o d u c e r i n terms of i n c r e a s e d m o r t a l i t y and m e d i c a t i o n c o s t s , and a l s o l o s s e s i n terms of c a r c a s s condemnation and down g r a d i n g a t t h e t i m e of p r o c e s s i n g . As a r e s u l t , numerous s t u d i e s have been conducted, w i t h v a r y i n g d e g r e e s of s u c c e s s , i n an attempt to r e s o l v e the l e g a b n o r m a l i t y problem i n p o u l t r y . Much re s e a r c h work i n the area of p o u l t r y l e g abnormal-i t i e s has centered on the c h a r a c t e r i z a t i o n of the v a r i o u s l e g d i s o r d e r s . The t e r m i n o l o g y used i n d e s c r i b i n g these a b n o r m a l i t i e s has sometimes l e d to c o n f u s i o n , w i t h s e v e r a l q u a l i t a t i v e t e r m s b e i n g u s e d t o d e s c r i b e a p a r t i c u l a r d i s o r d e r . Despite t h i s c o n f u s i o n , s e v e r a l general c a u s a t i v e f a c t o r s have been repo r t e d c o n t r i b u t i n g to the e t i o l o g i e s of the l e g a b n o r m a l i t i e s . They i n c l u d e the f o l l o w i n g : G e n e t i c a l , 1 2 N u t r i t i o n a l , P a t h o l o g i c a l , and E n v i r o n m e n t a l / M a n a g e r i a l . T h e r e f o r e , t h e p u r p o s e o f t h e p r e s e n t s t u d y was t o i n -v e s t i g a t e t h e e f f e c t s o f a n u t r i t i o n a l f a c t o r ( V i t a m i n Dg) and a m a n a g e r i a l f a c t o r ( c a g e d e n s i t y ) on l e g a b n o r m a l i t i e s i n p o u l t r y . I n a d d i t i o n , s e q u e n t i a l m o r p h o m e t r i c a n d r a d i o g r a p h i c c h a r a c t e r i s t i c s o f l e g bone d e v e l o p m e n t were d e s c r i b e d i n n o r m a l and a b n o r m a l b r o i l e r s i n an a t t e m p t t o d e v e l o p a p a t t e r n r e c o g n i t i o n f o r l e g a b n o r m a l i t i e s i n p o u l t r y . 3 CHAPTER TWO LITERATURE REVIEW AVIAN SKELETON The a v i a n s k e l e t o n f u n c t i o n s i n s u p p o r t , p r o t e c t i o n , locomotion, m i n e r a l h o m e o s t a s i s and has been a r b i t r a r i l y d i v i d e d i n t o two major components; the a x i a l s k e l e t o n and the a p p e n d i c u l a r s k e l e t o n (Koch, 1973). The a x i a l s k e l e t o n c o n s i s t s of the s k u l l , v e r t e b r a l column, r i b s and sternum. The a p p e n d i c u l a r s k e l e t o n c o n s i s t s of t h e p e c t o r a l and p e l v i c g i r d l e s with t h e i r a s s o c i a t e d limbs. L i g h t n e s s and s t r e n g t h are major themes e x h i b i t e d by most a s p e c t s of the a v i a n s k e l e t o n ( F e d u c c i a , 1975). The s k e l e t o n i s l i g h t e n e d by extensions of the e x t e n s i v e a i r sac system. These a i r s a c s r e p l a c e bone marrow i n many of the limb bones, p a r t s of the s k u l l , v e r t e b r a l column and p e l v i c g i r d l e and r e p r e s e n t a f u n c t i o n a l a d a p t a t i o n to the b i r d s r e l a t i v e l y h i g h m e t a b o l i c r a t e and consequent demand f o r great amounts of oxygen (Romer and Parsons, 1977). Strength and r i d g i d i t y are a t t a i n e d by f u s i o n , and o f t e n d e l e t i o n of bones, and occur to a great extent i n the bones of the wing and p e l v i c limb (Koch, 1973). S k e l e t a l Development The a v i a n s k e l e t a l s y s t e m mesoderm. The d i f f e r e n t i a t i o n of d e v e l o p s from the p r i m i t i v e embryonic me s o d e rm-4 de r i v e d c e l l s (mesenchymal c e l l s ) to bone can o c c u r by one of two r o u t e s ; t r a d i t i o n a l l y d e s c r i b e d as e i t h e r ( i ) i n t r a -membranous o s s i f i c a t i o n or ( i i ) e n d o c h o n d r a l o s s i f i c a t i o n (Moore, 1973). ( i ) F i r s t , i f there i s a d i r e c t development of bone f r o m t h e c o n d e n s a t i o n and d i f f e r e n t i a t i o n of mesenchyme i n t o osteogenic c e l l s , the mechanism i s r e f e r r e d to as intramembranous o s s i f i c a t i o n . Bones formed from t h i s model i n c l u d e the f r o n t a l , p a r i e t a l , temporal, and part of the c a l v a r i u m of the s k u l l , part of the mandible; the f a c i a l b o n es and the c l a v i c l e s ( B o r y s e n k o and B e r i n g e r , 1984). ( i i ) Second, i f an i n t e r v e n i n g h y a l i n e c a r t i l a g e model p r e -c e d e s the f o r m a t i o n of bone from mesenchymal c e l l s , the mec h a n i s m i s r e f e r r e d t o as e n d o c h o n d r a l o r i n t r a -c a r t i l a g i n o u s o s s i f i c a t i o n . Bones formed from t h i s model i n c l u d e the m a j o r i t y of bones of the a x i a l p o r t i o n of the s k e l e t o n and a l l t h e bones of the a p p e n d i c u l a r p o r t i o n (Borysenko and B e r i n g e r , 1984). I t i s through t h i s p r o c e s s of e n d o c h o n d r a l osteogenesis that the limb bones develop i n the chicken ( F e l l , 1925; Wolbach and Hegsted, 1952). The young c h i c k has an immature s k e l e t o n at hatching ( R i d d e l l , 1981). Remnants of t h e c a r t i l a g i n o u s model p e r s i s t i n the m e t a p h y s i s of the l o n g bones as cones of c a r t i l a g e u n t i l 11-14 days p o s t - h a t c h i n g ( L u f t i , 1967), when t h e y a r e g r a d u a l l y r e p l a c e d by bone (Wise and J e n n i n g s , 1973). Continued l o n g i t u d i n a l growth of bone i n both b i r d s and mammals i s dependent upon the a c t i v i t y of two a c t i v e l y p r o l i f e r a t i n g bands of c a r t i l a g e c e l l s , one s i t u a t e d at each 5 end of the bone known as growth c a r t i l a g e s or e p i p h y s e a l growth p l a t e s (Wise and Jennings, 1973). The e n t i r e sequence of e n d o c h o n d r a l bone f o r m a t i o n o c c u r s i n a h i g h l y organized columnar continuum i n the e p i -physeal growth p l a t e ( R e d d i , 1981). There has been con-s i d e r a b l e v a r i a t i o n i n the terminology used to d e s c r i b e the avian growth p l a t e . Using the terminology of R i d d e l l (1981) the a v i a n growth p l a t e may be d i v i d e d i n t o four zones. (1) The zone of p r o l i f e r a t i o n which l i e s immediately adjacent to the e p i p h y s i s and f u n c t i o n s as the germinal l a y e r f o r the e p i p h y s e a l growth c a r t i l a g e ( B r i g h t o n , 1978); (2) The p r e -h y p e r t r o p h i c ( o r m a t u r a t i o n zone by o t h e r s ) r e p r e s e n t s a t h i n t r a n s i t i o n zone between the zone of p r o l i f e r a t i o n and ( 3 ) , the zone of h y p e r t r o p h y , where i n i t i a l c a l c i f -i c a t i o n of the c a r t i l a g e m a t r i x o c c u r s ; ( 4 ) , The zone of o s s i f i c a t i o n . I t i s i n the f o u r t h zone that bone r e p l a c e s the h y p e r t r o p h i c c a r t i l a g e . Growth i n width i s accomplished i n t y p i c a l endochondral f a s h i o n as new bone i s l a i d down on the p e r i o s t e a l s u r f a c e and resorbed on the endosteal s u r f a c e of the bone (Borysenko and B e r i n g e r , 1984). Gross Anatomy of the Chicken Leg There i s l i t t l e d i f f e r e n c e i n the gross anatomy of the c h i c k e n as d e s c r i b e d by v a r i o u s i n v e s t i g a t o r s . T h e r e f o r e , t h e f o l l o w i n g b r i e f d e s c r i p t i o n i s a c o m p i l a t i o n o f i n f o r m a t i o n gathered from Koch (1973), Feduccia (1975), and R i d d e l l (1981), except where s p e c i f i c a l l y noted. 6 The l e g of the c h i c k e n c o n s i s t s of a femur, t i b i a , f i b u l a , t a r s o m e t a t a r s u s , and p h a l a n g e s ( F i g u r e 1 ) . The femur, or t h i g h bone, a r t i c u l a t e s p r o x i m a l l y w i t h the a c e t -abulum of the p e l v i c g i r d l e . The proximal end of the femur has a prominent t r o c h a n t e r l a t e r a l to and extending s l i g h t l y above the head of the femur. T h i s t r o c h a n t e r (Trochanter major) i s covered with c a r t i l a g e , which remains i n c o n t a c t w i t h the a n t e t r o c h a n t e r of the a c e t a b u l a r rim. The femoral s h a f t i s s l i g h t l y bent and at i t s d i s t a l end, two d i s t i n c t l y s e p a r a t e c o n d y l e s , t h e m e d i a l and l a t e r a l c o n d y l e s , a r t i c u l a t e with the t i b i a and f i b u l a , r e s p e c t i v e l y . The t i b i a i s the l a r g e s t of the l e g bones. P r o x i m a l l y the t i b i a i s c h a r a c t e r i z e d by two prominent c o n d y l e s f o r a r t i c u l a t i o n w i t h the femur and by l a r g e c n e m i a l c r e s t s which have the o r i g i n s of important e x t e n s o r m u s c l e s . The l a t e r a l segment of the upper d i a p h y s i s e x h i b i t s a r i d g e f o r the attachment of the much red u c e d f i b u l a . D i s t a l l y the e p i p h y s i s i s c h a r a c t e r i z e d by a t r o c h l e a with two prominent condyles f o r a r t i c u l a t i o n w i t h the t a s o m e t a t a r s u s . These c o n d y l e s r e p r e s e n t f u s e d t a r s a l bones, and f o r that reason the t i b i a of b i r d s i s a l s o c a l l e d the t i b i o t a r s u s . The f i b u l a i n b i r d s i s t y p i c a l l y g r e a t l y reduced; long, t h i n , f u s e d i n s e v e r a l p l a c e s w i t h the t i b i a , and always s h o r t e r than the t i b i a . D i s t a l e l e m e n t s o f t h e t a r s a l b o nes f u s e d u r i n g embryonic development w i t h the e l o n g a t e d m e t a t a r s a l s ( I I , I I I , IV) so t h a t a s i n g l e bone, the t a r s o m e t a t a r s u s or 7 FIGURE 1.0 The G r o s s Anatomy of the C h i c k e n Leg. A, R i g h t femur, t i b i o t a r s u s , f i b u l a of c h i c k e n ; c r a n i a l v i e w . B, L e f t t a r s o m e t a t a r s u s , and phalanges of chicken; c r a n i a l view. I , Femur; a, t r o c h a n t e r major; b, head of femur; c, l a t e r a l c o n d y l e ; d, medial condyle; e, t r o c h l e a ; I I T i b i o t a r s u s ; f, inner cnemial c r e s t ; g, medial condyle; h, l a t e r a l c o n d y l e ; i , t r o c h l e a ; I I I , F i b u l a ; I V , T a r s o m e t a t a r s u s ; j , d o r s a l metatarsal groove; k, metatarsal 1; 1, t r o c h l e a f o r d i g i t s I I , I I I , IV (from l e f t to r i g h t ) with t h e i r r e s p e c t i v e p h a l -anges (from F e d u c c i a , 1975). 8 \"running bone\" i s formed. The m e t a t a r s u s I i s r u d i m e n t a r y and f u s e d w i t h the m e t a t a r s u s I I . P r o x i m a l l y , the t a r s o -m e t a t a r s u s has two a r t i c u l a t i o n s u r f a c e s where t h e two d i s t a l t i b i a l c o n d y l e s i n s e r t , and p o s t e r i o r l y has two p r o t r u s i o n s f o r the i n s e r t i o n of the tendons of the t o e s . T h i s r e g i o n i s o f t e n r e f e r r e d t o as t h e h y p o t a r s u s . D i s t a l l y , the tarsometatarsus c a r r i e s three l a r g e t r o c h l e a e f o r a r t i c u l a t i o n w i t h the phalanges I I , I I I , and IV. Post-e r i o r l y , at the d i s t a l end of the t a r s o m e t a t a r s u s i s the r u d i m e n t a r y m e t a t a r s u s I which a r t i c u l a t e s with the short p o s t e r i o r l y d i r e c t e d toe I, c o n s i s t i n g of t h r e e p h a l a n g e s . Toes I I , I I I , and IV, which correspond i n l o c a t i o n to t h e i r r e s p e c t i v e t r o c h l e a e , have three, f o u r , and f i v e p h a l a n g e s , r e s p e c t i v e l y . LEG ABNORMALITIES IN POULTRY Leg a b n o r m a l i t i e s cause s i g n i f i c a n t economic l o s s f o r the p o u l t r y i n d u s t r y ; causing death or c u l l i n g of more than 1% of the b i r d s i n many co m m e r c i a l b r o i l e r c h i c k e n f l o c k s and more than 4% of the b i r d s i n many commercial male turkey f l o c k s ( R i d d e l l , 1981; N a t i o n a l T urkey F e d e r a t i o n , 1971). However, not a l l b i r d s a f f e c t e d with l e g a b n o r m a l i t i e s are c u l l e d or d i e . Many are processed. However, the p r o c e s s i n g of c r i p p l e d b i r d s i s not g e n e r a l l y p r o f i t a b l e because of d e p r e s s e d g r o w t h and d o w n g r a d i n g ( N a t i o n a l T u r k e y F e d e r a t i o n , 1971). 9 During the past twenty years, progress has been made i n t h e c l a s s i f i c a t i o n of the t y p e s of l e g a b n o r m a l i t i e s i n p o u l t r y . Recent and comphrehensive reviews on common t y p e s o f l e g a b n o r m a l i t i e s i n c l u d e t h o s e of N a i r n and Watson (1972), Wise (1975; 1978), R i d d e l l (1978; 1981). G e n e r a l l y , l e g a b n o r m a l i t i e s i n p o u l t r y are b r o a d l y c l a s s i f i e d i n t o i n f e c t i o u s and n o n i n f e c t i o u s d i s e a s e s and encompass many d i f f e r e n t d i s o r d e r s a f f e c t i n g the n e r v o u s , m u s c u l a r and s k e l e t a l s y s t e m s . E t i o l o g i c a l f a c t o r s have been b r o a d l y c l a s s i f i e d by P i e r s o n and H e s t e r (1982) and J u l i a n (1981) as g e n e t i c , n u t r i t i o n a l , p a t h o l o g i c a l , or e n v i r o n m e n t a l / managerial. P o t e n t i a l g e n e t i c and n u t r i t i o n a l f a c t o r s have been ex-t e n s i v e l y s t u d i e d r e l a t i n g to the major l e g a b n o r m a l i t i e s of concern to the p o u l t r y i n d u s t r y . T h e r e f o r e , i n t h i s review, these l e g a b n o r m a l i t i e s which i n c l u d e t i b i a l d y s c h o n d r o -p l a s i a , c h o n d r o d y s t r o p h y , r i c k e t s , s p o n d y l o l i s t h e s i s and long bone d i s t o r t i o n , were r e v i e w e d on the b a s i s of t h e i r g e n e t i c a n d n u t r i t i o n a l p r e d i s p o s i t i o n s . E n v i r o n -mental/managerial f a c t o r s and s p e c i f i c i n f e c t i o u s pathogens ( b a c t e r i a , v i r u s e s , m y c o p l a s m a ) i n v o l v e d w i t h l e g a b n o r m a l i t i e s were a l s o d i s c u s s e d s e p a r a t e l y . I t i s im-portant to r e a l i z e that more than one e t i o l o g i c a l f a c t o r may be i n v o l v e d i n e l i c i t i n g a p a r t i c u l a r l e g abnormality. 10 GENETIC ETIOLOGIES In r e s p o n s e to the demands of the producers, p o u l t r y breeders have sought p r i m a r i l y to improve growth r a t e and f e e d e f f i c i e n c y of meat type b i r d s . However, many re s e a r c h workers f e e l that t h i s s o r t of b r e e d i n g s t r a t e g y may have caused the i n c r e a s e i n s k e l e t a l d e f o r m i t i e s i n modern meat-type b i r d s (Wise and Jennings, 1972; Poulous et a l . , 1978). The i m p o r t a n c e of g e n e t i c s with r e s p e c t to the i n c i d e n c e of l e g a b n o r m a l i t i e s h a s a l s o b e e n shown by n u m e r o u s r e s e a r c h e r s who have e s t a b l i s h e d s t r a i n s showing high or low i n c i d e n c e o f v a r i o u s l e g d i s o r d e r s t h r o u g h s e l e c t i v e b r e e d i n g programs ( R i d d e l l , 1973, 1976; Khan et a l . , 1977; A u s t i c et a l . , 1977; Sheridan et a l . , 1974, 1976). T i b i a l Dyschondroplasia T i b i a l d y s c h o n d r o p l a s i a i s a c a r t i l a g e a b n o r m a l i t y c h a r a c t e r i z e d by a mass of a v a s c u l a r h y p e r t r o p h i c c a r t i l a g e s i t u a t e d i n the metaphysis beneath the proximal t i b i o t a r s a l and l e s s commonly the d i s t a l t i b i o t a r s a l and p r o x i m a l t a r s o m e t a t a r s a l growth p l a t e s . I t was f i r s t d e s c r i b e d i n b r o i l e r chickens by Leach and Nesheim (1965), and i n t u r k e y by McCapes (1 9 6 7 ) . I t has a l s o been termed osteochondrosis by O l s s o n (1978), and f o c a l o s t e o d y s t r o p h y by McCapes (1967) . C l i n i c a l l y , a f f e c t e d b i r d s tend to squat and are o f t e n 11 r e l u c t a n t to move. These b i r d s have an awkward g a i t which i s a s s o c i a t e d w i t h an e n l a r g e m e n t of the p r o x i m a l t i b i o -t a r s u s w i t h marked a n t e r i o r and l a t e r a l bowing ( R i d d e l l , 1975). The i n c i d e n c e of lameness due to t i b i a l dyschondro-p l a s i a v a r i e s from l e s s than 1% i n b r o i l e r f l o c k s (Hemsley, 1970) to 4-40% i n severe cases ( S i l l e r , 1970). However sub-c l i n i c a l t i b i a l d y s c h o n d r o p l a s i a may be more common than t h o u g h t w i t h f r e q u e n c i e s of 26% or more ( R i d d e l l et a l . , 1971; Poulous et a l . , 1978). The i n c i d e n c e and s e v e r i t y of t i b i a l d y s c h o n d r o p l a s i a can be changed through g e n e t i c s e l e c t i o n . Leach and Nesheim (1965) e s t a b l i s h e d the h e r i t a b l e nature of t h i s d i s e a s e by mating s e l e c t e d s i r e s and dams to d e v e l o p two s t r a i n s of b r o i l e r s : one d e m o n s t r a t i n g a h i g h i n c i d e n c e (41%) and another showing a low i n c i d e n c e (16%) of t i b i a l d y s c h o n d r o -p l a s i a . S i m i l a r l y , S h e r i d a n et a l . (1974; 1976) s e l e c t e d f o r a h i g h i n c i d e n c e of t i b i a l d y s c h o n d r o p l a s i a i n A u s t r a l i a n meat c h i c k e n s . T h e i r i n v e s t i g a t i o n s i n d i c a t e d that t i b i a l d y s c h o n d r o p l a s i a may be a s s o c i a t e d w i t h a major sex l i n k e d r e c e s s i v e gene. R i d d e l l et a l . (1971) and Prasad et a l . (1972) were unable to show a d i f f e r e n c e between sexes i n t h e i r s u s c e p t i b l i t y to the development of t i b i a l dyschon-d r o p l a s i a . However, Edwards (1983) was a b l e to show a s i g -n i f i c a n t d i f f e r e n c e due t o sex w i t h m a l e s showing an i n c i d e n c e of 49% and females 31%. T h i s d i f f e r e n c e may have been due to the males f a s t e r growth r a t e . R i d d e l l (1975), and P o u l o u s et a l . (1978) showed t h a t t h e i n c i d e n c e of 12 t i b i a l d y s c h o n d r o p l a s i a i n growing c h i c k e n s s i g n i f i c a n t l y d i m i n i s h e d when t h e growth r a t e was r e d u c e d by d i e t a r y m a n i p u l a t i o n s . Breed d i f f e r e n c e s a l s o e x i s t i n terms of s u s c e p t i b i l i t y to t i b i a l d y s c h o n d r o p l a s i a . While t i b i a l d y s c h o n d r o p l a s i a i s w e l l documented i n b r o i l e r and turke y f l o c k s ( R i d d e l l , 1978) White Leghorns are not a f f l i c t e d with t h i s abnormality ( R i e l a n d et a l . , 1978). Chondrodystrophy C h o n d r o d y s t r o p h y as i t s name suggests i s a l e g abnorm-a l i t y m a n i f e s t e d t h r o u g h abnormal c a r t i l a g e development. I t has a l s o been t e r m e d p e r o s i s by many p a t h o l o g i s t s . However, N a i r n and Watson (1972) and l a t e r Wise ( 1 9 7 5 ) s u g g e s t e d t h a t the use of the term p e r o s i s be d i s c o n t i n u e d i n avian pathology. They argued that p e r o s i s meant d i f f e r e n t t h i n g s to d i f f e r e n t p e o p l e . Wise (1975) def i n e d chondro-dystrophy as a g e n e r a l i z e d d i s o r d e r of the growth p l a t e s of l o n g b ones s u c h t h a t l i n e a r g r o w t h i s i m p a i r e d , w h i l e m i n e r a l i z a t i o n and a p p o s i t i o n a l g r o w t h r e m a i n n o r m a l . C l i n i c a l l y , t h i s impairment r e s u l t s i n shortened, thickened, long bones and o f t e n secondary varus or v a l g u s d e f o r m a t i o n o f t h e l e g s ( R i d d e l l , 1 9 8 1 ) . D i s p l a c e m e n t o f t h e gastrocnemius tendon o f f i t s i n t e r c o n d y l o i d groove at the t i b i o t a r s a l - t a r s o m e t a t a r s a l j o i n t ( hock) o f t e n occurs i n severe cases ( N o r r i s and S c o t t , 1965). S e v e r a l n u t r i t i o n a l d e f i c i e n c i e s , i n c l u d i n g t h o s e of manganese, c h o l i n e , b i o t i n , n i c o t i n i c a c i d and z i n c 13 i n t e r f e r e w i t h normal development of g r o w t h p l a t e s and i m p a i r l i n e a r growth of bones ( R i d d e l l , 1978). Wise et a l . (1973a) c o r r o b o r a t e d t h i s d e s c r i p t i o n and . f u r t h e r s t a t e d t h a t c h o n d r o d y s t r o p h y was s p e c i f i c a l l y r e l a t e d to a s e l e c t i v e s l o w i n g of the m i t o t i c r a t e o f p r o l i f e r a t i n g c h o n d r o c y t e s i n the growth p l a t e s . H i s t o p a t h o 1 o g i c a l l y , these chondrocytes appear abnormal. They were re d u c e d i n number, swollen, and the amount of i n t e r v e n i n g c a r t i l a g e was i n c r e a s e d ( R i d d e l l , 1978). N o r r i s and S c o t t (1965) found l i t t l e or no impairment of m i n e r a l i z a t i o n of the long bones and thus surmised that chondrodystrophy p r i m a r i l y a f f e c t e d l i n e a r growth and not a p p o s i t i o n a l growth (growth i n width). Although c h o n d r o d y s t r o p h y i s g e n e r a l l y a c c e p t e d as a l e g a b n o r m a l i t y p r e c i p i t a t e d by n u t r i t i o n a l d e f i c i e n c i e s , many i n v e s t i g a t o r s have c i t e d e v i d e n c e f o r a g e n e t i c b a s i s i n i t s p r o d u c t i o n . E a r l y s t u d i e s by Asmundson (1942, 1944) and Lamoreux (1942) demonstrated t h a t c h o n d r o d y s t r o p h y was c l e a r l y a h e r i t a b l e t r a i t i n b r o i l e r c h i c k e n s . More r e c e n t l y , Gaffney (1975) working with turkey embryos, found c h o n d r o d y s t r o p h y to be i n h e r i t e d as a s i n g l e , autosomal, r e c e s s i v e l e t h a l with the i n c i d e n c e of p h e n o t y p i c a l l y normal and abnormal progeny f i t t i n g a 3:1 r a t i o . S t i l l f u r t h e r evidence of i n h e r i t e d chondrodystrophy i n l a r g e and medium s t r a i n s of t u r k e y s has r e c e n t l y been p r o v i d e d by N e s t o r (1978). R i c k e t s R i c k e t s i s a disease of growing b i r d s c h a r a c t e r i z e d by 14 poor m i n e r a l i z a t i o n of o s t e o i d and e p i p h y s e a l c a r t i l a g e ; w h e r e a s i n a d u l t s i t i s known as o s t e o m a l a c i a (Jubb and Kennedy, 1970). C l i n i c a l signs are most o f t e n e n c o u n t e r e d between two and three weeks of age (Wise, 1978) and i n c l u d e a r e l u c t a n c e to walk, poor f e a t h e r i n g and o f t e n a s t u n t e d a p pearance ( N a i r n and Watson, 1972). M i n e r a l i z a t i o n of the bone i s impaired and thus bones bend r a t h e r than break w i t h a snap, and e p i p h y s e a l growth p l a t e s are o f t e n enlarged and widened ( R i d d e l l , 1 9 8 1 ) . T h i s o f t e n f a c i l i t a t e s ' t h e development of a bowed appearance most n o t i c e a b l e at the proximal ends of the t i b i o t a r s u s (Wise, 1975). The cause of r i c k e t s has g e n e r a l l y been a t t r i b u t e d to n u t r i t i o n a l d e f i c i e n c i e s e s p e c i a l l y d e f i c i e n c i e s of calcium, p h o s p h o r u s , v i t a m i n Dg or c o m b i n a t i o n s t h e r e o f ( R i d d e l l , 1978). However, A u s t i c et a l . (1977) demonstrated the r o l e of g e n e t i c s e l e c t i o n i n i t s p r o d u c t i o n . T h e i r s t u d i e s i n v o l v e d a s e x - l i n k e d dwarf s t r a i n o f c h i c k e n s , h i g h l y s u s c e p t i b l e to r i c k e t s and a c o n t r o l s t r a i n r e a r e d under i d e n t i c a l c o n d i t i o n s . The r e s u l t s i n d i c a t e d t h a t even when o p t i m a l l e v e l s of c a l c i u m , phosphorus, and vi t a m i n Dg were p r o v i d e d , the c o n t r o l s had s i g n i f i c a n t l y g r e a t e r bone m i n e r a l i z a t i o n than d w a r f s . However, low l e v e l s of two of the n u t r i e n t s s i g n i f i c a n t l y d e c r e a s e d bone ash i n dwarfs but not i n the c o n t r o l s . Consequently they suggested that the g r e a t e r s u s c e p i b i 1 i t y of the dwarfs to r i c k e t s may be due to an a l t e r a t i o n i n the r a t e of d e p o s i t i o n or r e s o r p t i o n of bone m i n e r a l , w i t h the dwarfs b e i n g more s e n s i t i v e to 15 marginal d e f i c i e n c i e s . No r e f e r e n c e was made to a p o t e n t i a l g e n e t i c a b n o r m a l i t y i n n u t r i e n t a b s o r p t i o n i n the dwarf s t r a i n . T h i s p o s s i b i l i t y i s strengthened and perhaps should be g i v e n f u r t h e r c o n s i d e r a t i o n i n p o u l t r y as over 30 causes of r i c k e t s have been i d e n t i f i e d i n man (Dent and Stamp, 1977) and some i n c l u d e many malabsorption syndromes. S p o n d y l o l i s t h e s i s S p o n d y l o l i s t h e s i s i s a locomotory d i s t u r b a n c e r e s u l t i n g from a n e u r a l impairment to the lower l i m b s . R i d d e l l and H o w e l l (1972) c h a r a c t e r i z e d the d i s e a s e as a d i s t o r t i o n and/or d i s p l a c e m e n t of t h e s i x t h and s e v e n t h t h o r a c i c v e r t e b r a . T h i s d e f o r m a t i o n causes p o s t e r i o r p a r a l y s i s due to compression of the s p i n a l cord (Wise, 1970). C l i n i c a l l y , most b i r d s with s p o n d y l o l i s t h e s i s assume a h o c k - s i t t i n g p o s t u r e . However, due to t h e p o s t e r i o r p a r a l y s i s they are commonly unable to move, except with the a i d of t h e i r wings. No a b n o r m a l i t i e s i n e p a x i a l musculature or f a i l u r e of i n t e r s p i n u o u s l i g a m e n t s were found i n the deformed r e g i o n of the s p i n a l c o r d i n s p o n d y l o l i s t h e s i s (Wise, 1970). However degenerative changes i n l e g muscles a t t r i b u t e d to d e n e r v a t i o n were r e p o r t e d by Khan e t a l . ( 1 9 7 7 ) . S u b c l i n i c a l s p o n d y l o l i s t h e s i s without damage to the s p i n a l cord i s a p p a r e n t l y common i n b r o i l e r c h i c k e n s (Wise, 1973; Khan et a l . , 1977) . There i s a h e r e d i t a r y p r e d i s p o s i t i o n to s p o n d y l o l i s -t h e s i s . R i d d e l l (1973) bred b r o i l e r s t h a t had r e c o v e r e d 16 from c l i n i c a l s p o n d y l o l i s t h e s i s and r a i s e d the i n c i d e n c e of c l i n i c a l s p o n d y l o l i s t h e s i s to 9% i n t h r e e g e n e r a t i o n s . S i m i l a r i l y , Khan et a l . (1977) were able to m a i n t a i n a h i g h i n c i d e n c e (58-66%) of s p o n d y l o l i s t h e s i s through four suc-c e s s i v e g e n e r a t i o n s of b r o i l e r progeny. O s b a l d i s t o n and Wise (1967) were the f i r s t to d e s c r i b e s p o n d y l o l i s t h e s i s i n b r o i l e r c h i c k e n s . They f e l t t h a t weaknesses i n the t h o r a c i c v e r t e b r a e may have been s p e c i f i c a l l y s e l e c t e d f o r or r e s u l t e d from undue m e c h a n i c a l s t r e s s imposed by m a j o r , g e n e t i c a l l y induced changes i n body conformation ( r e d i s t r i -b u t i o n of body mass). T h i s concept i s supported i n p a r t by more r e c e n t r e s e a r c h (Wise, 1973). By a r t i f i c i a l l y slowing the growth r a t e e a r l y i n the b i r d s l i f e , Wise (1973) was a b l e to c o m p l e t e l y p'revent i t s development r e g a r d l e s s of subsequent growth r a t e s . Long Bone D i s t o r t i o n L ong bone d i s t o r t i o n i s a g e n e r a l form of o s t e o d y s -trophy. Oteodystrophy by d e f i n i t i o n i s d e f e c t i v e bone forma-t i o n and i s used i n t h i s review as i t was by R i d d e l l (1981) to emphasize that a b n o r m a l i t i e s of the long bones i n p o u l t r y may r e s u l t from d e f e c t i v e c o r t i c a l bone formation as opposed to abnormal c a r t i l a g e formation (chondrodystrophy). S e v e r a l terms have been c o i n e d to d e s c r i b e these o s t e o d y s t r o p h i e s and i n c l u d e \" t w i s t e d l e g \" , \"bowed l e g \" , and \" v a r u s - v a l g u s d e f o r m a t i o n \" , t o name a few. Wise (1978) warned t h a t although the above a b n o r m a l i t i e s are a s s o c i a t e d w i t h g r o s s 17 d e f o r m i t i e s of the l e g s k e l e t o n , there may be j u s t i f i c a t i o n f o r s e p a r a t i n g them i n t o i n d i v i d u a l d i s e a s e s i n the f u t u r e when more i s known. However, F e r g u s o n et a l . (1974) con-s i d e r e d t h a t they were a l l m a n i f e s t a t i o n s of the same syn-drome and i n t h a t l i g h t w i l l be t r e a t e d as such i n t h i s review. I n i t i a l l y , O s b a l d i s t o n and Wise (1967) and l a t e r Nairn and Watson (1972), Wise (1975), and Haye and Simons (1978) used the term \" t w i s t e d l e g \" to d e s c r i b e a l e g a b n o r m l a l i t y w i t h which no c h o n d r o d y s t r o p h y had been a s s o c i a t e d i n b r o i l e r c h i c k e n s . T h e l e s i o n was u n i l a t e r a l and c h a r a c t e r i z e d by a l a t e r a l t w i s t i n g and outward b e n d i n g of the d i s t a l end of the t i b i o t a r s u s . The gastrocnemius tendon was not always d i s p l a c e d and the e p i p h y s e a l growth p l a t e s were n o r m a l . More r e c e n t l y R a n d a l l and M i l l s (1981) and J u l i a n (1984) have i n t r o d u c e d the term \"varus-va1gus d e f o r -m a t i o n s \" i n an attempt to a t t a i n a more p r e c i s e d e s c r i p t i o n of the d i s o r d e r . However t h e i r d e s c r i p t i o n s , f o r the most p a r t , were i d e n t i c a l to those used under the terra \" t w i s t e d l e g \" . Howver, Rand a l l and M i l l s (1981) argued t h a t \" t w i s t e d l e g \" was an i n a c c u r a t e term as no t w i s t , i n the sense of a r o t a t i o n about the long a x i s of a bone, was i n v o l v e d . The i n c i d e n c e of t w i s t e d l e g i n b r o i l e r s has been shown by Haye and Simons (1978) to be i n f l u e n c e d by g e n e t i c s . T h e i r r e s u l t s showed that s t r a i n d i f f e r e n c e s e x i s t i n terms of s u s c e p t i b i l i t y to t w i s t e d l e g and t h a t sex d i f f e r e n c e s a l s o e x i s t , w i t h the i n c i d e n c e f o r males being twice that 18 f o r females. B u f f i n g t o n et a l . (1975), working with turkeys, d e s c r i b e d the i n c i d e n c e of bowed l e g and l e s s f r e q u e n t l y r o t a t e d t i b i a s were more f r e q u e n t i n males than f e m a l e s . Somes ( 1969) i d e n t i f i e d an autosomal r e c e s s i v e gene i n one s t r a i n of chickens which was r e s p o n s i b l e f o r t w i s t e d t i b i o -t a r s a l and b e n t t a r s o m e t a t a r s a l bones. A l l homozygote r e c e s s i v e b i r d s were found a f f e c t e d to v a r y i n g d e g r ees i n e i t h e r one or both l e g s . NUTRITIONAL ETIOLOGIES The n u t r i e n t requirements f o r most c l a s s e s of p o u l t r y a r e w e l l d o c u m e n t e d ( N a t i o n a l R e s e a r c h C o u n c i l , 1981). Research has shown a wide range of d i e t a r y f a c t o r s to be i m p o r t a n t i n n o r m a l d e v e l o p m e n t and g r o w t h o f bone. Consequently, d u r i n g the p a s t s e v e r a l y e a r s , the r o l e of n u t r i t i o n i n the p r e v e n t i o n and/or p r o d u c t i o n of p o u l t r y l e g a b n o r m a l i t i e s has been a t o p i c of i n t e n s e s t u d y . C u r r e n t and comphrehensive reviews i n c l u d e those of Sauveur (1984), P i e r s o n and Hester (1982), and Wise (1978). T i b i a l Dyschondroplasia A l t h o u g h the cause of t i b i a l d y s c h o n d r o p l a s i a has been s t r o n g l y l i n k e d to g e n e t i c s , many n u t r i t i o n a l f a c t o r s have a l s o been i m p l i c a t e d i n i t s e t i o l o g y . I t has been suggested that r a p i d growth may be an e t i o l o g i c a l f a c t o r i n t i b i a l d y s c h o n d r o p l a s i a ( S i l l e r , 1970; P o u l o u s et a l . , 1978). 19 Poulous et a l . (1978) o b s e r v e d c o n s i s t e n t l y t h a t d i e t a r y treatments which decreased growth r a t e reduced the i n c i d e n c e of t i b i a l d y s c h o n d r o p l a s i a . R i d d e l l (1975a) d e m o n s t r a t e d t h a t slowed growth d e c r e a s e d the i n c i d e n c e of t i b i a l dys-c h o n d r o p l a s i a , but no s i g n i f i c a n t c o r r e l a t i o n c o u l d be seen between the r a t e of bone growth and development of t i b i a l d y s c h o n d r o p l a s i a i n i n d i v i d u a l c h i c k e n s . He t h e r e f o r e s u g g e s t e d t h a t growth r a t e may be no more than a c o n t r i b -u t i n g f a c t o r i n t i b i a l d y s c h o n d r o p l a s i a . In a d d i t i o n , when l o o k i n g at the r a t e of growth of i n d i v i d u a l bones, Church and Johnson (1964) and R i d d e l l ( 1 9 7 5 a ) f o u n d t h a t t h e p r o x i m a l end of the t i b i o t a r s u s had the f a s t e s t growth r a t e and the proximal tarsometatarsus had the second f a s t e s t r a t e of growth when compared with other growth p l a t e s i n the same b i r d . T h i s may e x p l a i n the more common o c c u r r e n c e of dys-c h o n d r o p l a s i a at the p r o x i m a l ends of the t i b i o t a r s u s and the t a r s o m e t a t a r s u s . In t e r m s of body w e i g h t , no e v i d e n c e was found by R i d d e l l (1975b) to s u p p o r t the h y p o t h e s i s t h a t e x c e s s i v e weight on the proximal t i b i o t a r s u s to be the primary f a c t o r i n the p a t h o g e n e s i s of t i b i a l d y s c h o n d r o p l a s i a . However bowing of the t i b i o t a r s u s and a compensatory t h i c k e n i n g of the concave c o r t e x appeared to be a d i r e c t r e s p o n s e t o weight bearing ( R i d d e l l , 1975b). Metaphyseal c a p i l l a r y t u n n e l i n g has been shown to be i m p o r t a n t i n n o r m a l e n d o c h o n d r a l bone f o r m a t i o n i n the r e g i o n of the growth p l a t e s ( B r i g h t o n , 1978). I t has been 20 suggested ( R i d d e l l , 1981) t h a t the d e l a y e d d e g r a d a t i o n of c a r t i l a g e i n t i b i a l d y s c h o n d r o p l a s i a might be l i n k e d to an absence of c a p i l l a r y t u n n e l i n g . However no e v i d e n c e as to whether the p r i m a r y l e s i o n was i n the development of the c a r t i l a g e or i n the m e t a p h y s e a l b l o o d s u p p l y c o u l d be e l i c i t e d from the l i t e r a t u r e . S i l l e r (1970) and Wise and Jennings (1972) have s u g g e s t e d t h a t the m e t a p h y s e a l b l o o d s u p p l y may f a i l due to e x c e s s i v e p r e s s u r e on the growth p l a t e s i n r a p i d l y g r o w i n g b i r d s and t h u s c a u s e t i b i a l d y s c h o n d r o p l a s i a . T h i s h y p o t h e s i s i s f u r t h e r supported by R i d d e l l (1975) who produced a d e f e c t t h a t was g r o s s l y and h i s t o l o g i c a l l y s i m i l a r to the d e f e c t i n n a t u r a l cases of t i b i a l d y s c h o n d r o p l a s i a by sur g i c a 1, i n t e r f er ence w i t h the m e t a p h y s e a l blood supply i n b r o i l e r c h i c k e n s . These s t u d i e s i n d i c a t e t h a t r a p i d growth and e x c e s s i v e w e i g h t may be c o n t r i b u t i n g f a c t o r s i n t h e d e v e l o p m e n t o f t i b i a l d y s c h o n d r o p l a s i a i n p o u l t r y . S e v e r a l m i n e r a l s have been i m p l i c a t e d as e t i o l o g i c a l f a c t o r s i n t i b i a l d y s c h o n d r o p l a s i a . I t i s now w e l l e s t a b l i s h e d t h a t m e t a b o l i c a c i d o s i s i n d u c e d by ammonium c h l o r i d e (Leach and Nesheim, 1972) or by a simple e x c e s s of c h o r i d e r e l a t i v e t o s o d i u m and p o t a s s i u m (Sauveur and Mongin, 1974) i n c r e a s e d the i n c i d e n c e of t i b i a l d y s c h o n d r o -p l a s i a . S a u v e u r e t a l . ( 1 9 7 8 ) r e v e a l e d t h a t c h r o n i c metabolic a c i d o s i s d i d i n f a c t a l t e r r e n a l m e t a b o l i s m of v i t a m i n Dg i n r a c h i t i c c h i c k s by reducing the c o n v e r s i o n of 25(0H)D 3 i n t o 1-25(0H) 2 Dg. However, t h e r e i s no e v i d e n c e 21 of r i c k e t s i n b i r d s a f f e c t e d w i t h t i b i a l d y s c h o n d r o p l a s i a ( R i d d e l l , 1981). T h e r e f o r e , i t i s d i f f i c u l t to e x p l a i n the e f f e c t of a high c h l o r i d e d i e t on the i n c i d e n c e of t i b i a l d y s c h o n d r o p l a s i a by i n t e r f e r e n c e with v i t a m i n Dg metabolism. I t has been claimed f o r many years that n e i t h e r calcium n o r p h o s p h o r u s l e v e l i n t h e d i e t was r e l a t e d t o t h e i n c i d e n c e of t i b i a l d y s c h o n d r o p l a s i a ( L e a c h and Nesheim, 1965). Recent s t u d i e s by Edwards and Veltman (1983) and L i l b u r n et a l . (1983) have provided new evidence i n d i c a t i n g t h a t c a l c i u m and phosphorus l e v e l s i n the d i e t are major n u t r i e n t f a c t o r s i n f l u e n c i n g t h e e x p r e s s i o n o f t i b i a l d y s c h o n d r o p l a s i a . They concluded that the l e v e l s of calcium and phosphorus i n the r a t i o n a r e of g r e a t i m p o r t a n c e i n p r o d u c i n g a n d / o r p r e v e n t i n g t i b i a l d y s c h o n d r o p l a s i a i n b r o i l e r s . The r e s u l t s c l e a r l y i n d i c a t e d that the Ca:P r a t i o was a f a c t o r i n c a u s i n g t i b i a l d y s c h o n d r o p l a s i a , w i t h c o n s i s t e n t r e s u l t s showing a lower i n c i d e n c e when the Ca:P r a t i o was i n c r e a s e d , e i t h e r by a d d i t i o n a l c a l c i u m or by reducing a v a i l a b l e phosphorus i n the d i e t . In f a c t , Edwards and V e l t m a n n ( 1 9 8 3 ) f o u n d h i g h p h o s p h o r u s l e v e l s t o accentuate the development of the l e s i o n . They s u g g e s t e d t h a t the h i g h phosphorus l e v e l may be a c t i n g s i m i l a r to the h i g h c h l o r i d e l e v e l u p s e t t i n g the a c i d - b a s e b a l a n c e and p r e c i p i t a t i n g the t i b i a l d y s c h o n d r o p l a s i a c o n d i t i o n . Chondrodystrophy As p r e v i o u s l y m e n t i o n e d , many p r i m a r y n u t r i t i o n a l 22 d e f i c i e n c i e s have been shown t o i n t e r f e r e w i t h n o r m a l development of growth p l a t e s and cause c h o n d r o d y s t r o p h i c symptoms i n p o u l t r y . T h e s e i n c l u d e d e f i c i e n c i e s o f manganese (Wilgus et a l . , 1936; Wolbach and Hegsted, 1953), z i n c ( O ' D e l l and Savage, 1957; Young et a l . , 1958), c h o l i n e ( J u k e s and B i r d , 1942), n i a c i n ( B r i g g s et a l . , 1943), f o l i c a c i d ( D a n i e l et a l . , 1946) and p y r i d o x i n e ( G r i e s and S c o t t , 1972). Wise et a l . (1973a),in an attempt to provide a u n i f y i n g hypothesis to e x p l a i n why a l l the above d e f i c i e n c i e s might r e s u l t i n c h o n d r o d y s t r o p h y , s u g g e s t e d t h a t they a l l may i n t e r f e r e with normal p r o l i f e r a t i o n of c h o n d r o c y t e s . T h i s c o n c l u s i o n was based on h i s a b i l i t y to produce a s i m i l a r l e s i o n i n the zone of p r o l i f e r a t i o n of the growth p l a t e s of the t u r k e y u s i n g i r r a d i a t i o n of the hock j o i n t to depress m i t o s i s of chondrocytes. The r e d u c t i o n i n the c a p a c i t y of the e p i p h y s e a l c a r t i l a g e f o r growth was a l s o a s s o c i a t e d with ( i ) a l a c k of columnar arrangement of c h o n d r o c y t e s ( i i ) an i n c r e a s e i n amount of m a t r i x i n the zone of p r o l i f e r a t i o n and ( i i i ) s m a l l e r than normal zone of hypertrophy. In other s t u d i e s ( L e a c h , 1967; 1971) i t was d e m o n s t r a t e d t h a t i n manganese d e f i c i e n c y i n the chicken there was a r e d u c t i o n i n the e x t r a c e l l u l a r matrix, namely i n the c h o n d r o i t i n sulphate and that the primary s i t e of manganese a c t i o n appeared to be i n v o l v e d i n the enzyme systems i n v o l v e d i n the s y n t h e s i s of c h o n d r o i t i n s u l p h a t e . The r e s u l t s of Wise et a l . (1973a) working with d e f i c i e n c i e s of c h o l i n e and n i c o t i n i c a c i d , and 23 and those of Westmoreland and H o e k s t r a (1969) s u p p o r t the c o n c e p t t h a t the d i s t a n c e of the chondrocyte from i t s blood s u p p l y i s of i m p o r t a n c e i n t h e p a t h o g e n e s i s of c h o n -d r o d y s t r o p h y as l e s i o n s were present i n those areas of the p r o l i f e r a t i v e zone f u r t h e s t away f r o m t h e d e s c e n d i n g e p i p h y s e a l v e s s e l s . C h o n d r o d y s t r o p h y , l i k e t i b i a l d y s c h o n d r o p l a s i a , has been s a i d to be a s s o c i a t e d with r a p i d growth r a t e . I t has been o b s e r v e d c o n s i s t e n t l y t h a t d i e t a r y t r e a t m e n t s which decrease growth r a t e u s u a l l y reduce the i n c i d e n c e of t h e s e a b n o r m a l i t i e s ( P o u l o u s et a l . , 1978). The growth r a t e and feed e f f i c i e n c y of b r o i l e r c h i c k e n s has been d r a s t i c a l l y improved a l t h o u g h recommendations f o r mineral and v i t a m i n requirements have changed l i t t l e over the past twenty y e a r s (Summers et a l . , 1978). T h e r e f o r e , i t seems l i k e l y , or at l e a s t t h e p o t e n t i a l e x i s t s t h a t m i n o r n u t r i t i o n a l d e f i c i e n c i e s may r e s u l t from the r a p i d growth of t o d a y s modern b i r d s and i t i s these minor n u t r i t i o n a l d e f i c i e n c i e s t h a t cause chondrodystrophy ( R i d d e l l , 1981; Poulous et a l . , 1978). R i c k e t s R i c k e t s i s g e n e r a l l y c o n s i d e r e d to be the r e s u l t of a d e f i c i e n c y of v i t a m i n Dg, c a l c i u m , or p h o s p h o r u s or an i m b a l a n c e of t h e s e n u t r i e n t s . F i e l d outbreaks of r i c k e t s are r a r e l y diagnosed i n p o u l t r y (with perhaps the e x c e p t i o n of t u r k e y s ) and many cases may be due to simple feed-mixing 24 e r r o r s (Wise, 1975; N a i r n and Watson, 1972). In g e n e r a l , d e s c r i p t i o n s of r i c k e t s i n the f i e l d agree with d e s c r i p t i o n s of r i c k e t s i n experimental c h i c k e n s . Groth and F r e y (1966) produced e x p e r i m e n t a l r i c k e t s i n fowl with d e f i c i e n c i e s of c a l c i u m , phosphorus and v i t a m i n Dg and d e s c r i b e d the p a t h o l -o g i c a l changes p r o d u c e d . V i t a m i n Dg or calcium d e f i c i e n t d i e t s produced a s i m i l a r syndrome, but i f t h e s e b i r d s were fed a phosphorus d e f i c i e n t d i e t a syndrome d i f f e r i n g i n some p a t h o l o g i c a s p e c t s r e s u l t e d . C a l c i u m and v i t a m i n Dg d e f i c i e n c y were a s s o c i a t e d w i t h d i s o r g a n i z a t i o n of the growth p l a t e a r c h i t e c t u r e . The zone of p r o l i f e r a t i o n i n the e p i p h y s e a l c a r t i l a g e was t h i c k e n e d , i r r e g u l a r and only a small zone of h y p e r t r o p h y was p r e s e n t . There was l i t t l e p r o v i s i o n a l c a l c i f i c a t i o n of the h y p e r t r o p h i c c a r t i l a g e and reduced v a s c u l a r i n v a s i o n . The u s u a l o r d e r l y l o n g i t u d i n a l arrangement of bony s p i c u l e s i n the r e g i o n of the metaphysis was d i s r u p t e d and r e p l a c e d by f i b r o u s t i s s u e . In r e s p o n s e to low b l o o d calcium l e v e l s , h y p e r p l a s i a of the p a r a t h y r o i d i s a p a t h o l o g i c a l f e a t u r e o f r i c k e t t s a s s o c i a t e d w i t h calcium or v i t a m i n D d e f i c i e n c i e s ( R i d d e l l , 1981). T h i s may not be s u r p r i s i n g s i n c e the main e s t a b l i s h e d r o l e of v i t a m i n Dg i s to s t i m u l a t e calcium b i n d i n g p r o t e i n and hence calcium a b s o r p t i o n from the gut (Wise, 1975). P h o s p h o r u s d e f i -c i e n c i e s , however, produced no d i s r u p t i o n of the growth p l a t e a r c h i t e c t u r e but d e l a y e d the c a l c i f i c a t i o n of t h e h y p e r t r o p h i c c a r t i l a g e as e v i d e n c e d by an i n c r e a s e d t h i c k e n i n g of the growth p l a t e (Groth and Frey, 1966). 25 S p o n d y l o l i s t h e s i s Wise (1973) and Khan et a l . (1977) have emphasized the importance of g e n e t i c s i n the e t i o l o g y of s p o n d y l o l i s t h e s i s . However, growth r a t e was a l s o shown to be a c o n t r i b u t i n g f a c t o r by W ise ( 1 9 7 3 ) . He d e m o n s t r a t e d t h a t s e v e r e r e s t r i c t i o n i n the growth r a t e i n b r o i l e r s f o r the f i r s t week p o s t - h a t c h i n g completely p r e v e n t e d the development of s p o n d y l o l i s t h e s i s r e g a r d l e s s of the s u b s e q u e n t r a t e of growth. Long Bone D i s t o r t i o n L i t t l e e v i d e n c e as to a p o t e n t i a l n u t r i t i o n a l e t i o l o g y i n the p r o d u c t i o n and/or p r e v e n t i o n of long bone d i s t o r t i o n c o u l d be d i s c e r n e d from the l i t e r a t u r e . Haye and Simons (1978) found that feed r e s t r i c t i o n reduced the o c c u r e n c e of \" t w i s t e d l e g \" i n b r o i l e r s as body weight was lower than when the b i r d s were a l l o w e d a d l i b i t u m a c c e s s t o t h e d i e t . However, Cook et a l . (198A) addressed the independent e f f e c t of body weight on the s e v e r i t y of l e g a b n o r m a l i t i e s ( v a r u s -v a l g u s d e f o r m i t i e s ) i n p o u l t r y . In o r d e r to make the i n f l u e n c e of body weight independent of g e n e t i c , n u t r i t i o n a l and e n v i r o nme n t a 1/ma na g e r i a 1 e f f e c t s , they i n c r e a s e d body weight by h a r n e s s i n g s t e e l w e i g h t s on the backs of c h i c k s and p o u l t s . They c o n c l u d e d that the s k e l e t a l s t r u c t u r e of the fowl i s capable of s u p p o r t i n g a load g r e a t e r than normal weight as a r t i f i c i a l w eight l o a d i n g had no e f f e c t on the s e v e r i t y of l e g a b n o r m a l i t i e s . U n f o r t u n a t e l y , no attempt was 26 made to evaluate the e f f e c t of a r t i f i c i a l weight l o a d i n g on t h e i n c i d e n c e o f l e g a b n o r m a l i t i e s . A l t h o u g h s l i g h t l y d i f f e r e n t , these r e s u l t s are s t i l l i n general agreement with the view that f a s t growing b i r d s have more l e g a b n o r m a l i t i e s than those that grow more s l o w l y ( R i d d e l l , 1983; Hulan et a l . , 1979). H u l a n e t a l . (1979) were u n a b l e to d e m o n s t r a t e any e f f e c t of a d d i t i o n a l minerals and vitamins to v a r i o u s groups o f b r o i l e r s i n which \" t w i s t e d l e g \" was o c c u r r i n g . Wise (1978) concluded g e n e t i c s , e n v i r o n m e n t and f e e d appear to have an i n f l u e n c e ; however simple n u t r i e n t d e f i c i e n c e s could not be i m p l i c a t e d i n the e t i o l o g y of \" t w i s t e d l e g \" . ENVIRONMENTAL/MANAGERIAL ETIOLOGIES Many r e s e a r c h workers and c o m m e rcial p r o d u c e r s have s u g g e s t e d t h a t e n v i r o n m e n t a l and m a n a g e r i a l f a c t o r s may i n f l u e n c e the o c c u r r e n c e of l e g a b n o r m l a i t i e s i n p o u l t r y ( P i e r s o n and H e s t o r , 1982; W i l s o n et a l . , 1984; Haye and Simons, 1978). U n f o r t u n a t e l y , much of the p u b l i s h e d work h a s l a c k e d s p e c i f i c i t y by l u m p i n g a l l f o r m s of l e g a b n o r m a l i t i e s together or has been d i r e c t e d more towards the e l i m i n a t i o n of bone breakage during p r o c e s s i n g . L i g h t i n g regimes are known to i n f l u e n c e the o c c u r r e n c e of l e g a b n o r m a l i t i e s i n p o u l t r y . B u c k l a n d et a l . (1973; 1976) demonstrated t h a t t u r k e y s grown i n c o n t i n u o u s l i g h t h ad s i g n i f i c a n t l y more l e g a b n o r m a l i t i e s t h a n t h o s e 27 s u b j e c t e d to i n t e r m i t t e n t l i g h t i n g s c h e d u l e s . They moni-to r e d plasma c o r t i c o s t e r o i d l e v e l s as an i n d i c a t o r of s t r e s s and c o n c l u d e d t h a t r a i s e d c o r t i c o s t e r o i d l e v e l s i n bi'rds r a i s e d under c o n t i n u o u s l i g h t r e f l e c t e d a more s t r e s s f u l l i g h t i n g system. However, no attempt was made to r e l a t e c o r t i c o s t e r o n e l e v e l s to the i n c i d e n c e of l e g a b n o r m a l i t i e s and no c a u s a l r e l a t i o n s h i p between e l e v a t e d c o r t i c o s t e r o n e l e v e l s to the i n c i d e n c e of l e g a b n o r m a l i t i e s could be found i n the l i t e r a t u r e . S i m i l a r work on b r o i l e r s by W i l s o n et a l . (1984) confirmed Buckland et a l . ' s (1973; 1976) r e s u l t s . They showed that those b i r d s grown under continuous i l l u m i n -a t i o n had s i g n i f i c a n t l y more, and more s e v e r e l e g ab-n o r m a l i t i e s t h a n t h o s e b i r d s u n d e r i n t e r m i t t e n t i l l u m i n a t i o n . I n c r e a s e d b i r d a c t i v i t y under i n t e r m i t t e n t i l l u m i n a t i o n was h e l d as a p a r t i a l e x p l a n a t i o n f o r t h e stronger l e g s . B r o i l e r s r e a r e d i n cages show a h i g h e r f r e q u e n c y of l e g a b n o r m a l i t i e s than b i r d s reared on l i t t e r (Reece et a l . , 1971). S t u d i e s by Haye and Simons (1978) found a higher i n c i d e n c e of \" t w i s t e d l e g \" ( l o n g bone d i s t o r t i o n ) w i t h b r o i l e r s i n cages than on l i t t e r . The type of cage f l o o r was a l s o found to have a s i g n i f i c a n t e f f e c t , w i t h b r o i l e r s r e a r e d on m e t a l w i r e and p e r f o r a t e d sheets having more l e g problems than t h o s e r e a r e d on p l a s t i c mats and p l a s t i c c o v e r e d w i r e . Andrews e t a l . ( 1 9 7 4 ) a l s o f o u n d t h a t i n c i d e n c e v a r i e d with type of cage f l o o r i n g . T h i s d i f f e r e n c e was e x p l a i n e d by d i f f e r e n c e s i n movement, w i t h the b i r d s 28 being a b l e to walk more e a s i l y and get more e x e r c i s e on the p l a s t i c or p l a s t i c - c o v e r e d wire f l o o r i n g . R e s u l t s of s t u d i e s on cage s i z e and l o c a t i o n of water suggested that a l a c k of e x e r c i s e i n c r e a s e s the i n c i d e n c e of l e g a b n o r m a l i t i e s . R o denhoff and Dammrich (1971) showed that fewer l e g a b n o r m a l i t i e s occurred when b i r d s moved about more. T h i s l a c k of e x e r c i s e hypothesis i s f u r t h e r s u p p o r t e d by r e s e a r c h on bone breakage during p r o c e s s i n g between caged and f l o o r reared b i r d s . Numerous r e p o r t s have shown t h a t b i r d s r e a r e d on t h e f l o o r have g r e a t e r bone b r e a k i n g s t r e n g t h s ( s t r o n g e r bones) and fewer broken bones d u r i n g p r o c e s s i n g (Meyer and Sunde, 1974; Merkley, 1981; Anderson et a l . , 1979). The g e n e r a l c o n l u s i o n s drawn from t h e s e s t u d i e s was t h a t more e x e r c i s e was necessary to reduce the i n c i d e n c e of broken bones during p r o c e s s i n g of c a g e - r e a r e d b i r d s . I t i s u n f o r t u n a t e that none of these s t u d i e s r e l a t e d the i n c i d e n c e of broken bones at p r o c e s s i n g to the i n c i d e n c e of l e g a b n o r m a l i t i e s during p r o d u c t i o n . Rowland et a l . (1971) and S i e g a l et a l . (1973) have shown environmental temperature w i l l i n f l u e n c e bone s t r e n g t h as high ambient temperatures augmented a d e p r e s s i o n i n bone s t r e n g t h a s s o c i a t e d w i t h the c o n f i n e m e n t of b r o i l e r s to c a g e s . However, the d e p r e s s i o n of bone s t r e n g t h a t t h e h i g h e r t e m p e r a t u r e may have been due to d e p r e s s e d f e e d i n t a k e c a u s i n g a m a r g i n a l d e f i c i e n c y o f c a l c i u m o r p h o s p h o r u s . T h i s may be l i k e l y , e s p e c i a l l y s i n c e Rowland et a l . (1967) found that i n c r e a s i n g l e v e l s of e i t h e r m i n e r a l 29 i n c r e a s e d bone s t r e n g t h . High environmental temperature was a l s o shown by Reece et a l . (1971) to i n c r e a s e the i n c i d e n c e of l e g a b n o r m a l i t i e s . SPECIFIC PATHOGENS S p e c i f i c p a t h o g e n s s u c h as b a c t e r i a , v i r u s e s , or s p e c i e s of Mycoplasma when l o c a l i z e d i n or around a j o i n t , or i n bone or c a r t i l a g e may cause l e s i o n s l e a d i n g to l e g a b n o r m a l i t i e s or lameness i n b i r d s . P i e r s o n and H e s t o r (1982) ranked the l e g a b n o r m a l i t i e s produced by i n f e c t i o u s a g e n t s to be of the most concern to the turkey and b r o i l e r i n d u s t r i e s , f o l l o w i n g l e g a b n o r m a l i t i e s of a n u t r i t i o n a l n a t u r e . The major pathogenic c o n d i t i o n s c u r r e n t l y known to produce lameness i n f o w l are v i r a l a r t h r i t i s , b a c t e r i a l s y n o v i t i s / o s t e o m y e l i t i s , and turkey syndrome 196-5. S e p t i c e m i c i n f e c t i o n s by b a c t e r i a , m y c o p l a s m a or v i r u s e s a r e t h o u g h t t o be t h e p r i m a r y c a u s e of t h e development of t h e s e d i s o r d e r s , but i n most c a s e s t h e i n i t i a l r o u t e of e n t r y remains u n d e t e r m i n e d ( P i e r s o n and Hestor, 1982). The c a u s a t i v e agent i n v i r a l a r t h r i t i s i s a r e o v i r u s while the commonest i n f e c t i n g b a c t e r i a i n s y n o v i t i s or o s t e o m y e l i t i s are Staphylococcus aureus and E s c h e r i c h i a c o l i (Wise, 1982). A r t h r i t i s and s y n o v i t i s i n p o u l t r y are inflammations of the dense connective t i s s u e membranes l i n i n g the a r t i c u l a r c a p s u l e s , tendon s h e a t h s and bursae of d i a r t h r i t i c j o i n t s 30 ( O l s o n et a l . , 1956). O s t e o m y e l i t i s i s an i n f l a m m a t o r y c o n d i t i o n of the e p i p h y s e a l and metaphyseal r e g i o n s of the l o n g bones and may o c c u r s e p a r a t e l y o r t o g e t h e r w i t h s y n o v i t i s ( N a i r n , 1973; Wise, 1982). C l i n i c a l lameness i s secondary and develops when the degrees of t i s s u e damage and s w e l l i n g become such that they impair a r t i c u l a t i o n (Olson et a l . , 1956; Wise, 1975). In some f l o c k s , minor o u t b r e a k s of o s t e o m y e l i t i s were c o n f i n e d to the v e r t e b r a l column, u s u a l l y i n the r e g i o n of the 5-7 t h o r a c i c v e r t e b r a e (Wise, 1971). The consequence was the c o l l a p s e of one or more v e r t e b r a l bodies with subsequent s p i n a l c o r d damage and p a r a p l e g i a , t y p i c a l of s p o n d y l o l i s t h e s i s . Turkey Syndrome 1965 (TS65) i s an i n f e c t i o u s c o n d i t i o n t h a t d e v e l o p s i n young t u r k e y s at 2-4 weeks of age, and u s u a l l y a p p e a r s t o be a s s o c i a t e d w i t h e a r l y mycoplasma i n f e c t i o n , normally Mycoplasma m e l e a g r i d i s i n f e c t i o n (Wise e t a l . , 1973b; 1 9 7 4 ) . The h i s t o l o g i c a l changes i n the growth p l a t e s of long bones of t u r k e y p o u l t s w i t h TS65 are i d e n t i c a l to t h o s e seen i n c a s e s of c h o n d r o d y s t r o p h y of d i e t e t i c o r i g i n d e s p i t e the f a c t t h a t the syndrome i s not caused by a p r i m a r y n u t r i t i o n a l d e f i c i e n c y (Wise, 1982). The mechanism by w h i c h t h e m y c o p l a s m a s c a u s e t h e l e g a b n o r m a l i t i e s i s o b s c u r e . However, i t has been p o s t u l a t e d by Wise (1978) that the mycoplasma may cause a b l o c k to the p r o p e r n u t r i t i o n of the growth p l a t e s of long bones. TS65 i s now of d e c l i n i n g i m p o r t a n c e as v e r t i c a l t r a n s m i s s i o n ( i n f e c t e d o v i d u c t t o egg) of M. m e l e a g r i d e s has been 31 c o n t r o l l e d by e r a d i c a t i o n or by a n t i b i o t i c d i p p i n g of eggs (Wise, 1978). CHAPTER THREE EFFECT OF EXCESS VITAMIN D3 AND CAGE DENSITY ON THE INCIDENCE OF LEG ABNORMALITIES IN BROILER CHICKENS INTRODUCTION A comphrehensive r e v i e w of the l i t e r a t u r e has shown a v a r i e t y of f a c t o r s c o n t r i b u t e to l e g a b n o r m a l i t i e s i n p o u l t r y . The e t i o l o g i e s and pathogeneses of these abnormal-i t i e s are complex and o f t e n poorly d e f i n e d . Few abnormal-i t i e s c an be a t t r i b u t e d t o a s i n g l e f a c t o r . Most l e g problems are p r o b a b l y due to the i n t e r a c t i o n of s e v e r a l f a c t o r s i n v o l v i n g n u t r i t i o n , environment, g e n e t i c s and/or p a t h o l o g y ( P i e r s o n and H e s t o r , 1982; N a i r n and Watson, 1972). I t has been claimed that h e r e d i t a r y p r e d i s p o s i t i o n s to l e g a b n o r m a l i t i e s are w i d e s p r e a d i n commercial b r o i l e r s t r a i n s and t h a t s t r e s s f a c t o r s d e r i v e d e i t h e r from the environment or n u t r i t i o n may t r i g g e r the c l i n i c a l s i g n s of l e g a b n o r m a l i t i e s (Sim and Cruickshank, 1985). Wilson et a l . (1984) working with b r o i l e r s and Buckland et a l . (1973; 1976) w orking w i t h t u r k e y s demonstrated that b i r d s grown under continuous l i g h t i n g had s i g n i f i c a n t l y more l e g ab-n o r m a l i t i e s than t h o s e b i r d s under i n t e r m i t t e n t l i g h t i n g . High environmental t e m p e r a t u r e was shown by Reece et a l . (1971) to i n c r e a s e the i n c i d e n c e of l e g a b n o r m a l i t i e s and b r o i l e r s reared i n cages have shown a h i g h e r i n c i d e n c e of le g a b n o r m a l i t i e s than those reared on l i t t e r o(Reece et a l . 32 33 1971; Haye and Simons, 1978). S i m i l a r i l y , d u r i n g the past s e v e r a l years the r o l e of n u t r i t i o n i n the pre v e n t i o n and/or p r o d u c t i o n of a v i a n l e g a b n o r m a l i t i e s has been a t o p i c of i n t e n s e study. Vitamin Dg has emerged as one of the n u t r i e n t s to be of paramount i m p o r t a n c e i n e m b r y o n i c c h i c k d e v e l o p m e n t (Sunde and Deluca, 1978), normal post-hatch bone growth and develop-ment ( Y u i l e et a l . , 1967), and calcium and phosphorus meta-bolism ( S o a r e s , 1984). D e f i c i e n c i e s of V i t a m i n Dg have been e x t e n s i v e l y s t u d i e d and g e n e r a l l y r e s u l t i n r i c k e t s ; a disease of growing b i r d s c h a r a c t e r i z e d by poor m i n e r a l i z -a t i o n o f o s t e o i d and e p i p h y s e a l c a r t i l a g e ( J u b b and Kennedy, 1970). A l t h o u g h many p o t e n t i a l s t r e s s f a c t o r s have been i d e n t i f i e d , l i t t l e r e s e a r c h has been p u b l i s h e d on t h e e f f e c t s o f d e n s i t y or v i t a m i n Dg o v e r n u t r i t i o n on the i n c i d e n c e of l e g a b n o r m a l i t i e s . These two a r e a s a r e of p a r t i c u l a r i n t e r e s t s i n c e r o u t i n e p o u l t r y p r o d u c t i o n i n v o l v e s r e a r i n g b i r d s under i n t e n s i v e c o n d i t i o n s . They are c r o w d e d ( e s p e c i a l l y a t b r o o d i n g ) and a r e f e d d i e t s s upplemented w i t h n u t r i e n t s much i n e x c e s s of r e q u i r e d l e v e l s . T h e r e f o r e , the o b j e c t i v e of the present study was to i n v e s t i g a t e the e f f e c t s of cage d e n s i t y and e x c e s s v i t a m i n Dg on t h e i n c i d e n c e a nd s e v e r i t y o f l e g a b n o r m a l i t i e s i n b r o i l e r c h i c k e n s . 34 MATERIALS AND METHODS Animals and Experimental Design: One h u n d r e d and e i g h t y , d a y - o l d c o m m e r c i a l Hubbard b r o i l e r c o c k e r e l s were p u r c h a s e d from a l o c a l c o m m e r cial h a t c h e r y ( C e n t e n n i a l H a t c h e r y , A l d e r g r o v e B.C.). Chicks were randomly d i v i d e d i n t o d e n s i t i e s of e i t h e r t e n (680 c m ^ / b i r d ; low d e n s i t y ) or t w e n t y (340 c m ^ / b i r d ; h i g h d e n s i t y ) c h i c k s per cage. They were housed i n e l e c t r i c a l l y h e a t e d and t h e r m o s t a t i c a l l y c o n t r o l l e d Petersime b a t t e r y brooders with r a i s e d wire f l o o r s . A b a s a l d i e t c o n t a i n i n g 22% p r o t e i n , 2879 ME/kg was f o r m u l a t e d to meet NRC (1977) n u t r i e n t r e q u i r e m e n t s f o r b r o i l e r c h i c k e n s u s i n g ground c o r n , ground wheat, and soybean meal as the major f e e d s t u f f s ( T a b l e 3 . 1 ) . Two l e v e l s of v i t a m i n Dg (500,000 ICU/g) were i n c o r p o r a t e d i n t o the b a s a l d i e t to s u p p l y e i t h e r 400 ICU/kg f e e d or 4000 ICU/ kg f e e d . Feed and water were p r o v i d e d ad l i b i t u m throughout the 4 week experimental p e r i o d . The e x p e r i m e n t o was a 2 f a c t o r i a l arrangement with three r e p l i c a t i o n s , two b i r d d e n s i t i e s , and two l e v e l s of v i t a m i n Dg. P r o d u c t i o n Data: Weekly f e e d c o nsumption, body weight and i n c i d e n c e of l e g a b n o r m a l i t i e s were recorded f o r f o u r weeks. I n c i d e n c e was d e f i n e d as the percentage of b i r d s i n each cage demon-35 Table 3.1 Composition of Experimental D i e t s INGREDIENTS GroundCorn 31.0 Ground Wheat 30.0 Soybean Meal 28.2 Meatmeal 5.0 Animal Tallow 3.5 Limestone 0.6 Calcium multiphosphate 0.7 Vitamin mix 1 » 2 0.5 M i n e r a l mix 3 0.5 C a l c u l a t e d A n a l y s i s : Crude P r o t e i n (%) 22.00 M e t a b o l i z a b l e Energy (kcal/kg) 2878.90 Calcium (%) 0.97 A v a i l a b l e Phosphorus (%) 0.71 Methionine (%) 0.44 Ly s i n e (%) 1.17 Su p p l i e s per kg of c o n t r o l d i e t : v i t a m i n A, 8,800 IU; vi t a m i n Do, 400 ICU; vi t a m i n E, 21.9 IU; vi t a m i n Bi 2» 0.03 mg; r i b o f l a v i n , 13.2 mg; pantothenic a c i d , 15.8 mg; n i a c i n , 44 mg; c h o l i n e 475 mg. S u p p l i e s per kg of excess v i t a m i n D3 d i e t : as c o n t r o l d i e t except v i t a m i n D3, 4000 ICU. S u p p l i e s per kg of d i e t : manganese, 30 mg; z i n c , 97 mg; copper, 25 mg. 36 s t r a t i n g a t l e a s t some k i n d o f l e g a b n o r m a l i t y . In a d d i t i o n , on days 21 and 28 of the experiment, the s e v e r i t y of each l e g abnormality was e v a l u a t e d u s i n g the f o l l o w i n g s c o r i n g system: C h i c k s w i t h a s l i g h t d e f o r m i t y (awkward g a i t , r e l u c t a n c e to move) were s c o r e d as 1; th o s e w i t h a moderate d e f o r m i t y (moderate bending, bowing, r o t a t i o n of t i b i o t a r s u s ) as 2 and those with s e v e r e d e f o r m i t i e s as 3. A s i m i l a r s c o r i n g system was used by J u l i a n (1984) i n h i s c l a s s i f i c a t i o n of l e g a b n o r m a l i t i t e s . S t a t i s t i c a l A n a l y s i s The r e s p o n s e s of body weight, feed consumption and the i n c i d e n c e of l e g a b n o r m a l i t i e s to e i t h e r t h e l e v e l o f v i t a m i n Dg i n the d i e t or cage d e n s i t y were compared by r e g r e s s i o n a n a l y s i s over b i r d age ( S t e e l and T o r r i e , 1980). S e v e r i t y d a t a were s u b j e c t e d to an a n a l y s i s of v a r i a n c e (ANOVA) f o r 2^ f a c t o r i a l a r rangements ( S t e e l and T o r r i e , 1980) and Duncan's m u l t i p l e range t e s t was used f o r mean se p a r a t i o n s (Duncan, 1955). A r c s i n t r a n s f o r m a t i o n s on the data i n percentages were performed before s t a t i s t i c a l a n a l -yses ( S t e e l and T o r r i e , 1980). The s t a t i s t i c a l a n a l y s e s were c o n d u c t e d with the a i d of the \"General L i n e a r Models\" and \" A n a l y s i s of V a r i a n c e \" p r o c e d u r e s of the S t a t i s t i c a l A n a l y s i s System (SAS, 1982) at the U n i v e r s i t y of B r i t i s h Columbia Computer Center. 37 RESULTS AND DISCUSSION Leg a b n o r m a l i t i e s were f i r s t observed at 5 days of age. At t h i s age the a b n o r m a l i t i e s c o n s i s t e d m e r e l y of an awkward s t a n c e , or the b i r d s showed a r e l u c t a n c e to move, o f t e n r e s o r t i n g to a h o c k - s i t t i n g p o s i t i o n ( F i g u r e 3.1). L a t e r , at 14-28 days the gross c l i n i c a l s i g n s were t y p i c a l of the valgus and varus d e f o r m i t i e s d e s c r i b e d by R a n d a l l and M i l l s (1981) and J u l i a n ( 1 9 8 4 ) . The a b n o r m a l i t i e s progressed from s l i g h t l a t e r a l ( v a l g u s ) or m e d i a l ( v a r u s ) b e n d i n g o f t h e d i s t a l t i b i o t a r s u s and p r o x i m a l t a r s o m e t a t a r s u s to a more s e v e r e c o n d i t i o n of t h e same d e f o r m i t y ( F i g u r e 3.2). The a b n o r m a l i t i e s were most o f t e n u n i l a t e r a l , with no predominance shown between the r i g h t and l e f t l e g . There were no s i g n i f i c a n t i n t e r a c t i o n s (p>0.05) between d i e t and d e s i t y and t h e r e f o r e the main e f f e c t s were a n a l -yzed f o r the r e g r e s s i o n a n a l y s i s . The main e f f e c t s of d i e t and cage d e n s i t y on the i n c i d e n c e of l e g a b n o r m a l i t i e s are shown i n f i g u r e 3.3 and 3.4 r e s p e c t i v e l y . A s i g n i f i c a n t l i n e a r i n c r e a s e i n the i n c i d e n c e of the l e g a b n o r m a l i t i e s was o b s e r v e d w i t h r e s p e c t to b i r d age (p< 0.05), with the two l e v e l s of v i t a m i n Dg showing d i f f e r e n t r e s p o n s e s . The excess v i t a m i n Dg caused a sharper r i s e i n the i n c i d e n c e of l e g a b n o r m a l i t i e s when compared w i t h the c o n t r o l d i e t . F i g u r e 3.4 shows t h e i n c i d e n c e o f l e g a b n o r m a l i t i e s i n c r e a s e d q u a d r a t i c a l l y with r e s p e c t to cage d e n s i t y . The F i g u r e 3.1 Normal and Abnormal Chicks at 5 Days. The b i r d on the r i g h t i s normal. The b i r d on the l e f t shows s l i g h t medial (varus) bending of the d i s t a l t i b i o t a r s u s and proximal tarsometatarsus. 39 F i g u r e 3.2 Moderate Medial T i b i o t a r s u s and 28 Days. (Varus) Bending of the D i s t a l Proximal Tarsometatarsus at 40 F i g u r e 3.3 Incidence of Leg A b n o r m a l i t i e s (ILA) i n B r o i l e r s Fed C o n t r o l L e v e l s (400 ICU/kg feed) or High L e v e l s (4000 ICU/kg f e e d ) of V i t a m i n D 3 i n the D i e t . The equations f o r the l i n e s are: C o n t r o l , ILA= 0.71X ( ± 0.16) High, ILA= 0.97X (± 0.16) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). I n t e r c e p t s are not s i g n i f i c a n t l y d i f f e r e n t from zero (p> 0.05). + Standard E r r o r of Estimate. r=0.72 (p<0.05). 41 gure 3.4 Incidence of Leg A b n o r m a l i t i e s (ILA) i n B r o i l e r s Reared i n High Density (340 cm 2/bird) or Low Density (680 cm 2/ b i r d ) Cages. The equations f o r the l i n e s are: High, ILA= 2.31X - 0.05X 2 ( + 0.6) (+0.02) Low, ILA= 1.11X - 0.0067X 2 (± 0.6) (+ 0.02) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). I n t e r c e p t s are not s i g n i f i c a n t l y d i f f e r e n t from zero (p> 0.05). +Standard E r r o r of Estimate. r=0.74 (p<0.05). 42 two cage d e n s i t i e s a l s o produced s i g n i f i c a n t l y d i f f e r e n t r e s p o n s e s (p< 0.05). The high d e n s i t y caused a more r a p i d i n c r e a s e i n the i n c i d e n c e of l e g a b n o r m a l i t i e s as compared to the low d e n s i t y ; however by the end of the t r i a l both showed a s i m i l a r i n c i d e n c e of l e g a b n o r m a l i t i e s . The main e f f e c t s of d i e t and d e n s i t y on the s e v e r i t y of the l e g a b n o r m a l i t i e s a r e shown i n t a b l e 3.2. D i e t showed no s i g n i f i c a n t e f f e c t on the s e v e r i t y of the l e g a b n o r m a l i t i e s at e i t h e r 21 or 28 days. However, the h i g h d e n s i t y showed a t r e n d towards i n c r e a s i n g the s e v e r i t y of the l e g a b n o r m a l i t i e s , and at 28 d a y s t h i s d i f f e r e n c e approached s i g n i f i c a n c e (p=0.08). The i n i t i a l i n c r e a s e i n the i n c i d e n c e of l e g abnormal-i t i e s w i t h the b i r d s r e a r e d i n the high d e n s i t y cages i s not e x p l a i n e d through d i f f e r e n c e s i n body weight or f e e d c o n s u m p t i o n . R i d d e l l ( 1 9 8 3 ) and H u l a n et a l . (1979) repor t e d that f a s t e r growing b i r d s have more l e g abnormal-i t i e s than slower growing b i r d s . In t h i s experiment, those b i r d s reared under high d e n s i t y cages showed a s i g n i f i c a n t d e p r e s s i o n i n feed consumption and body weight ( F i g u r e s 3.5 and 3.6, r e s p e c t i v e l y ) , yet s t i l l responded w i t h i n c r e a s e d l e g a b n o r m a l i t i e s . The sharp i n i t i a l r i s e i n the i n c i d e n c e of l e g a b n o r m a l i t i e s i n the h i g h d e n s i t y c a g e s , t o g e t h e r w i t h the p l a t e a u observed around 21 days suggests that i n -creased d e n s i t y may be i n i t i a l l y d e t r i m e n t a l to the c h i c k s , but may be b e n e f i c i a l l a t e r on. Haye and Simons (1978) found that b i r d s f o r c e d to walk f u r t h e r f o r f e e d and water had lower i n c i d e n c e s of l e g 43 Table 3.2 Main E f f e c t s of Vitamin Dg and Cage Density on the S e v e r i t y of Leg A b n o r m a l i t i e s . Age (Days) D i e t 1 Density I n t e r a c t i o n C o n t r o l High Low High D i e t * D e n s i t y 21 1.6 1.7 1.4 1.9 NS 28 1.6 1.9 1.4 2.1* NS C o n t r o l , 400 ICU v i t a m i n Dg/kg feed; High, 4000 ICU vi t a m i n Dg/kg feed. High, 340 cm 2 / b i r d ; Low, 680 c m 2 / b i r d . NS denotes a n o n s i g n i f i c a n t i n t e r a c t i o n (p>0.05). D i f f e r e n c e approached s i g n i f i c a n c e (p=0.08). 44 8 0 0 700-600 -0) z o & a (A z o u Q w ui 500-4 0 0 -300-200-l O O -DENSITY -• LOW A HIGH -r 14 T 21 T 28 AGE (days ) F i g u r e 3.5 Feed Consumption (FC) of B r o i l e r s Reared i n High Density (340 cm 2/bird) or Low Density (680 cm 2/bird) Cages. The equations f o r the l i n e s a re: High, FC= 23.6X (± 0.6) Low, FC= 25.9X ( ± 0 . 6 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). ±Standard E r r o r of Estimate. r=0.99 (p<0.05). 45 AGE (DAYS ) F i g u r e 3.6 Body Weight (BWT) of B r o i l e r s Reared i n High Density (340 cm 2/bird) or Low Density (680 cm^/bird) Cages. The equations f o r the l i n e s are: High, BWT= 20.81 + 12.85X +0.69X 2 ( ± 1 6 . 2 ) ( ± 2 . 7 ) ( ± 0 . 0 9 ) Low, BWT= 18.27 + 12.46X +0.84X 2 ( ± 1 6 . 2 ) ( ± 2 . 7 ) ( ± 0 . 0 9 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). I n t e r c e p t s are not s i g n i f i c a n t l y d i f f e r e n t (p> 0.05). ±Standard E r r o r of Estimate r=0.99 (p<0.05). 46 l e g a b n o r m a l i t i e s . S i m i l a r i l y , W i l s o n et a l . ( 1 9 8 4 ) found b r o i l e r s p r o v i d e d w i t h more fe e d i n g space showed more l e g a b n o r m a l i t i e s than t h o s e g i v e n l e s s f e e d i n g s p a c e . They s u g g e s t e d t h a t b i r d s g i v e n more f e e d i n g space had to compete l e s s f o r feed and t h e r e f o r e r e c i e v e d l e s s e x e r c i s e which may have r e s u l t e d i n more l e g problems. R e s u l t s from Simons (1982) f u r t h e r s u b s t a n t i a t e s t h i s suggestion i n that b i r d s r e a r e d under i n t e r m i t t e n t l i g h t showed i n c r e a s e d a c t i v i t y and fewer l e g a b n o r m a l i t i e s than t h o s e r e a r e d under continuous l i g h t . The p r e c i s e manner i n w h i c h the i n c r e a s e d d e n s i t y caused the i n i t i a l s h arp r i s e i n l e g a b n o r m a l i t i e s i s u n c l e a r . However i t has been r e p o r t e d c o n s i s t e n t l y that the i n c i d e n c e of l e g a b n o r m a l i t i e s i n cages i s grea t e r than that on l i t t e r (Reece et a l . , 1971; Haye and Simons, 1978), and t h a t the type of f l o o r i n g was i m p o r t a n t w i t h w i r e f l o o r s p r o d u c i n g more l e g problems than f l o o r s made of p l a s t i c mats or p l a s t i c c o v e r e d w i r e . These d i f f e r e n c e s were a t t r i b u t e d to d i f f e r e n c e s i n movement, with the b i r d s having more d i f f i c u l t y walking on the wire f l o o r s (Andrews et a l . , 1974; Haye and Simons, 1978). C a s u a l o b s e r v a t i o n s from t h i s e x p e r i m e n t showed an i n c r e a s e d a c t i v i t y l e v e l i n t h e h i g h d e n s i t y c a g e s ; e s p e c i a l l y when f e e d i n g . Perhaps the i n c r e a s e d a c t i v i t y l e v e l a s s o c i a t e d w i t h t h e h i g h d e n s i t y i n i t i a l l y accentuated the d i f f i c u l t y i n w a l k i n g on the wir e c a g e s . T h e r e f o r e , c h i c k s may have been f o r c e d to move on the wire 47 f l o o r when they were l e a s t able and thus s t r e s s e d the hock j o i n t . L a t e r on, when the c h i c k s were b e t t e r able to walk on t h e w i r e f l o o r s , t h e i n c r e a s e d a c t i v i t y may have p r o v i d e d s u f f i c i e n t e x e r c i s e to s t r e n g t h e n the l e g bones and reduce l e g a b n o r m a l i t i e s . The t r e n d o b s e r v e d toward i n c r e a s e d s e v e r i t y of t w i s t e d l e g i n the high d e n s i t y cages may be e x p l a i n e d , i n p a r t , by i n c r e a s e d m e c h a n i c a l a g g r a -v a t i o n of e x i s t i n g l e g a b n o r m a l i t i e s . Both body weight and f e e d consumption appeared to be s e n s i t i v e to e x c e s s v i t a m i n Dg . Those b i r d s fed the high l e v e l s of v i t a m i n Dg c o n s i s t e n t l y showed d e p r e s s e d body weights d e s p i t e e l e v a t e d feed consumption ( F i g u r e s 3.7 and 3.8 r e s p e c t i v e l y ) . T h i s , together with the sharper r i s e i n the i n c i d e n c e of l e g a b n o r m a l i t i e s f o r the b i r d s fed the high l e v e l of vi t a m i n Dg may suggest that a d i e t a r y induced m e t a b o l i c s t r e s s may be c o n t r i b u t i n g to the e t i o l o g i e s of the a b n o r m a l i t i e s . C o m p e t i t i o n among the f a t - s o l u b l e v i t a m i n s f o r ab-s o r p t i o n and t r a n s p o r t has been demonstrated, with a marked i n c r e a s e i n the d i e t a r y l e v e l of one causing a d e f i c i e n c y of one or more of the other f a t - s o l u b l e v i t a m i n s ( S c o t t et a l . , 1 9 8 2 ) . M a r c h e t a l . (1973) r e p o r t e d t h a t e x c e s s vi t a m i n E (2200 IU/kg feed) i n c r e a s e d the r e q u i r e m e n t f o r both v i t a m i n D and K; with a f f e c t e d b i r d s showing depressed growth and bone c a l c i f i c a t i o n . I n t e r e s t i n g l y , h y p o v i t a m i n -o s i s A s u p p r e s s e s e n d o c h o n d r a l bone growth (Wolbach and H e g s t e d , 1952), and h y p o v i t a m i n o s i s E c a u s e s myopathy A8 Fi g u r e 3.7 Body Weight (BWT) of B r o i l e r s Fed C o n t r o l L e v e l s (A00 ICU/kg feed) or High L e v e l s (A000 ICU/kg feed) of Vitamin D 3 i n the D i e t . The equations f o r the l i n e s a re: High, BWT= 19.56 + 11.81X +0.80X 2 ( ± 2 0 . 3 ) ( ± 3 . A ) ( ± 0 . 1 1 ) C o n t r o l , BWT= 19.53 + 13.50X +0.73X 2 ( ± 2 8 . 7 ) ( ± 3 . A ) ( ± 0 . 1 1 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). I n t e r c e p t s are not s i g n i f i c a n t l y d i f f e r e n t (p> 0.05). ±Standard E r r o r of Estimate. r=0.99 (p<0.05). 49 V I T A M I N D 3 • » CONTROL AGE (days) F i g u r e 3.8 Feed Consumption (FC) of B r o i l e r s Fed C o n t r o l L e v e l s (400 ICU/kg feed) or High L e v e l s (4000 ICU/kg feed) of Vitamin D 3 i n the D i e t . The equations f o r the l i n e s a re: High, FC= 25.4X ( ± 0 . 6 ) C o n t r o l , FC= 24.2X ( ± 0 . 6 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p< 0.05). ±Standard E r r o r of Estimate. r=0.99 (p<0.05). 50 ( n u t r i t i o n a l m uscular d y s t r o p h y ) of the b r e a s t and l e g muscles (NRC, 1984). I t may be t h a t excess vitamin Dg i n t h i s experiment may have caused an i n c r e a s e i n the r e q u i r e -ment f o r t h e s e o t h e r f a t - s o l u b l e v i t a m i n s and thus any t o x i c e f f e c t of the excess v i t a m i n Dg on growth or l e g ab-n o r m a l i t i e s may appear secondary to d e f i c i e n c i e s of these v i t a m i n s . However, f u r t h e r r e s e a r c h i s needed to d e l i n e a t e t h e m e t a b o l i c s t r e s s o f e x c e s s v i t a m i n Dg on bone development. CHAPTER FOUR SEQUENTIAL MORPHOMETRY AND RADIOGRAPHY OF THE TIBIAE FROM NORMAL BROILER CHICKENS AND THOSE WITH TWISTED LEG INTRODUCTION A m e d i a l or l a t e r a l d e v i a t i o n of the s h a f t of the d i s t a l t i b i o t a r s a l bone i s one of t h e most common l e g a b n o r m a l i t i e s i n b r o i l e r c h i c k e n s ( J u l i a n , 1984). I t was i n i t i a l l y termed t w i s t e d l e g by O s b a l d i s t o n and Wise (1967) and l a t e r by N a i r n and Watson (1972) and Haye and Simons (1978). More r e c e n t l y R a n d a l l and M i l l s (1981) and J u l i a n (1984) have s u g g e s t e d the term varus-valgus deformation to d e s c r i b e the abnormality. The syndrome i s seen i n most b r o i l e r f l o c k s , w i t h an i n c i d e n c e of 5 % not being unusual (Wise, 1975). C l i n i c a l l y , the a b n o r m a l i t y i s u s u a l l y u n i l a t e r a l , although both legs may be i n v o l v e d and t h e g a s t r o c n e m i u s t e n d o n may be d i s p l a c e d o f f the d i s t a l t i b i a l c o n d y l e s ( R i d d e l l , 1981). The a b n o r m a l i t y has been o b s e r v e d as e a r l y as f i v e d ays ( J u l i a n , 1984;), but i s more f r e q u e n t l y n o t i c e d a f t e r 2 weeks of age ( R i d d e l l , 1981). The i n c i d e n c e o f t w i s t e d l e g has been shown to be i n f l u e n c e d by g e n e t i c a l f a c t o r s . Haye and Simons (1978) r e p o r t e d i t more p r e v a l e n t i n males than i n f e m a l e s and found the i n c i d e n c e v a r i e d between b r o i l e r s t r a i n s . Sim and Cruickshank (1985) found the i n c i d e n c e of twisted l e g v a r i e d between b r o i l e r s t r a i n s and a l s o w i t h i n s t r a i n depending on 51 52 from which b r e e d e r farm the h a t c h i n g eggs were s u p p l i e d . Somes ( 1969) i d e n t i f i e d an autosomal r e c e s s i v e gene i n one s t r a i n of c h i c k e n w h i c h was r e s p o n s i b l e f o r t w i s t e d t i b i o t a r s a l and bent t a r s o m e t a t a r s a l bones. S e v e r a l i n v e s t i g a t o r s have a l t e r e d the i n c i d e n c e of l e g a b n o r m a l i t i e s t h r o u g h m a n i p u l a t i o n s of the e n v i r o n m e n t . Continuous l i g h t i n g r egimes ( B u c k l a n d et a l . , 1973; 1976; Wilson et a l . , 1984), cage r e a r i n g (Reece et a l . , 1971; Haye and Simons, 1978), type of cage f l o o r (Haye and S i m o n s , 1978; Andrews et a l . , 1974) and high environmental temper-ature (Reece et a l . , 1971), have been shown to i n c r e a s e the i n c i d e n c e of l e g a b n o r m a l i t i e s . Reduced e x e r c i s e a s s o c i a t e d with decreased a c t i v i t y has been held p a r t i a l l y r e s p o n s i b l e f o r the i n c r e a s e d i n c i d e n c e i n these s t u d i e s . Wise (1978) and P o u l o u s et a l . (1978) s u g g e s t e d t h a t r a p i d i l y g r o w i n g bones a r e s u b j e c t t o d e f o r m i t y when abnormal f o r c e s are a p p l i e d t o them and t h a t s k e l e t a l deformity may be found i n many b r o i l e r s p o s s i b l y as a r e s u l t of i m b a l a n c e s between m u s c l e mass and s k e l e t a l f r a m e . Moreover, the evidence f o r p o t e n t i a l g e n e t i c p r e d i s p o s i t i o n to t w i s t e d l e g , t o g e t h e r w i t h the a b i l i t y to i n c r e a s e the i n c i d e n c e of t w i s t e d l e g t h r o u g h e n v i r o n m e n t a l f a c t o r s suggests that there may be a s t r u c t u r a l d e f e c t i n the t i b i a e w h i c h may be a t l e a s t p a r t i a l l y r e s p o n s i b l e f o r t h e d i s o r d e r . T h e r e f o r e , t h i s experiment was designed to compare the t i b i a e of normal b r o i l e r c h i c k e n s w i t h t h o s e e x h i b i t i n g 53 t w i s t e d l e g i n a n a t t e m p t t o d e v e l o p a p a t t e r n r e c o g n i t i o n f o r t h i s l e g d i s o r d e r . Q u a l i t a t i v e d i f f e r e n c e s w e r e d e t e r m i n e d u s i n g c o n v e n t i o n a l r a d i o g r a p h y a n d q u a n t i t a t i v e d i f f e r e n c e s w e r e d e t e r m i n e d u s i n g s e q u e n t i a l m o r p h o m e t r y . 54 MATERIALS AND METHODS F i v e h u n d r e d , d a y - o l d c o m m e r c i a l Hubbard b r o i l e r c o c k e r e l s were h o u s e d c o n v e n t i o n a l l y on h e m l o c k wood s h a v i n g s f o r s i x weeks. C h i c k s had ad l i b i t u m a ccess to water and a standard commercial b r o i l e r s t a r t e r r a t i o n (23% minimum crude p r o t e i n ) . A l l b i r d s were wing-banded and weighed on day 1 and each week t h e r e a f t e r f o r s i x weeks. The b i r d s were o b s e r v e d d a i l y , and m o r t a l i t y and the i n c i d e n c e of l e g a b n o r m a l i t i e s recorded. Those b i r d s showing signs of lameness were put i n t o a separate pen ( w i t h i n the same barn) f o r ease of i d e n t i f i c a t i o n and o b s e r v a t i o n . Morphometry W e e k l y m o r p h o m e t r i c c o m p a r i s o n s of the t i b i a e from normal b r o i l e r c h i c k e n s and t h o s e w i t h t w i s t e d l e g were made s t a r t i n g at two weeks. Because t h e r e was no way of determining when and how many b i r d s at a given age would be showing s i g n s of t w i s t e d l e g , a v a r i a b l e number of abnormal b i r d s (1-7), and at l e a s t e i g h t normal b i r d s were randomly s a m p l e d each week f o r m o r p h o m e t r i c a l c o m p a r i s o n . These b i r d s were weighed and then k i l l e d by c e r v i c a l d i s l o c a t i o n . T i b i a e were r e m o v e d , c l e a n e d of s u r r o u n d i n g t i s s u e and measured. Measurements i n c l u d e d t i b i a l l e n g t h , d i s t a l con-d y l e groove depth, d i s t a l condyle groove width, diameter at m i d s h a f t ( F i g u r e 4 . 1 ) . M e d i a l c o r t i c a l t h i c k n e s s , and l a t e r a l c o r t i c a l t h i c k n e s s were a l s o measured to c a l c u l a t e % 55 TIBIAL LENGTH CONDYLE GROOVE WIDTH % CORTICAL THICKNESS=LCT +MCT/TIBIAL DIAMETER AT MIDSHAFT F i g u r e 4.1 Morphometric c r i t e r i a and methodology used to measure the t i b i a e . LCT, l a t e r a l c o r t i c a l t h i c k n e s s ; MCT, medial c o r t i c a l t h i c k n e s s ( f i g u r e of t i b i a adapted from Feduccia, 1975). 56 c o r t i c a l t h i c k n e s s ( B a r n e t t a n d N o r d i n , 1 9 5 9 ) . A l l measurements were made using d i a l c a l i p e r s s e n s i t i v e to 0.01 mm. Radiography R o u t i n e m e d i o l a t e r a l and a n t e r o p o s t e r i o r radiographs were taken of a l l t i b i a e sampled f o r the morphometrical com-p a r i s o n s . In a d d i t i o n , four b i r d s were randomly s e l e c t e d at the beginning of the experiment f o r s e q u e n t i a l r a d i o g r a p h y of t h e i r t i b i a e . S i m i l a r i l y , b i r d s showing sig n s of tw i s t e d l e g were s e q u e n t i a l l y radiographed as the abnormality became a p p a r e n t . A n t e r o p o s t e r i o r and m e d i o l a t e r a l x - r a y s of the t i b i a e of these l i v e b i r d s were taken once a week. An Acoma p o r t a b l e x-ray u n i t (model PX-30) was used with Kodak X-Omat TL x-ray f i l m and f a s t tungstate i n t e n s i f y i n g screens. Auto-m a t i c p r o c e s s i n g of the x - r a y s was generously provided by t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a A c u t e C a r e U n i t , Radiology Laboratory. X - r a y s of l i v e c h i c k s were o b t a i n e d by p l a c i n g them e i t h e r on t h e i r backs ( f o r a n t e r o p o s t e r i o r view) or on t h e i r s i d e s ( f o r m e d i o l a t e r a l view), and tap i n g t h e i r t i b i a e down to a piece of p l e x i g l a s s . The c h i c k s r e l a x e d when s e c u r e l y t a p e d so e x c e l l e n t f i l m s c o u l d be made. The r a d i o l o g i c a l techniques used are shown i n t a b l e 4.1. Bone Ash Determination: S u b s e q u e n t t o t h e m o r p h o m e t r y , t i b i a l a s h was 57 Table 4.1 R a d i o l o g i c a l Techniques used to X-ray the T i b i a e of B r o i l e r Chickens. Radiographs were taken with an Acoma p o r t a b l e x-ray u n i t (model PX-30), Kodak X-Omat TL Ready Pack F i l m , and f a s t tungstate i n t e n s i f y i n g s creens. P o s i t i o n B i r d Age Tube c u r r e n t Voltage Exposure (Weeks) (m i l l i a m p s ) ( k i l o v o l t s ) (seconds) A n t e r o p o s t e r i o r 2 20 60 0.63 3 20 60 0.80 4 20 50 1.00 5 20 60 1.00 6 20 60 1.00 M e d i o l a t e r a l 2 20 60 0.53 3 20 60 0.63 4 20 50 0.80 5 20 60 0.80 6 20 60 1.00 58 determined by a s h i n g d r i e d t i b i a e (24 h r s . a t 90 C) i n a muffle furnace f o r 5-7 hours at 600 C. S t a t i s t i c a l A n a l y s i s The morphometrica1 c r i t e r i a were compared over b i r d age by r e g r e s s i o n a n a l y s i s using body weight as a c o v a r i a t e . A r c s i n t r a n s f o r m a t i o n s on t h e d a t a i n p e r c e n t a g e s was performed b e f o r e s t a t i s t i c a l a n a l y s e s ( S t e e l and T o r r i e , 1980). The s t a t i s t i c a l analyses were conducted with the a i d of the \"General L i n e a r M o d e l s \" and \" A n a l y s i s of V a r i a n c e \" p r o c e d u r e s from the S t a t i s i c a l A n a l y s i s System (SAS, 1982) at the U n i v e r s i t y of B r i t i s h Columbia Computer Center. RESULTS AND DISCUSSION Twisted l e g was by f a r the predominant l e g a b n o r m a l i t y o b s e r v e d , c o n t r i b u t i n g to over 75% of a l l l e g d i s o r d e r s . The i n c i d e n c e of t w i s t e d l e g was 0.04% a t one week and i n c r e a s e d s t e a d i l y to 5.4% at s i x weeks ( F i g u r e 4.2). Other l e g a b n o r m a l i t i e s o b s e r v e d were n o n - s p e c i f i c . C l i n i c a l s i g n s of the s e a b n o r m a l i t i e s i n c l u d e d swollen, b r u i s e d t i b -i o t a r s a l - t a r s o m e t a t a r s a l (hock) j o i n t s and were most o f t e n a s s o c i a t e d w i t h r u n t e d b i r d s . For t h i s r e a s o n they were excluded from the r a d i o g r a p h i c and morphometric comparisons. M o r t a l i t y i n c r e a s e d from 2% at one week to 5% at the end of the s i x weeks ( F i g u r e 4.2). No m o r t a l i t y c o u l d be d i r e c t l y a t t r i b u t e d to l e g a b n o r m a l i t i e s . However, one of the runts d i s p l a y i n g n o n s p e c i f i c s i g n s of lameness died at 4 weeks. T h e r e f o r e , i t would appear t h a t t w i s t e d l e g r e p r e -sents a c h r o n i c problem. C l i n i c a l s i g n s of t w i s t e d l e g were f i r s t observed at one week. T y p i c a l l y , the deformity was s l i g h t at t h i s age and c o n s i s t e d e i t h e r of s l i g h t v a r u s ( m e d i a l ) or v a l g u s ( l a t e r a l ) d e f o r m a t i o n of the d i s t a l t i b i a e . Most b i r d s showed the a b n o r m a l i t y u n i l a t e r a l l y ; although Ra n d a l l and M i l l s (1981) r e p o r t e d b i l a t e r a l d e f o r m a t i o n s were most common. The d e v i a t i o n s were more f r e q u e n t l y l a t e r a l than medial (92% l a t e r a l ; 8% medial) and occurred e q u a l l y on the r i g h t and l e f t l e g s . F i g u r e s 4.3 and 4.4 show the p r o g r e s s i o n of the 59 60 |\"*\"| Total Leg Abnormalities ^ Proportion with Twisted Leg — Mortality • 1 1 1 1 I AGE (Weeks) .2 T o t a l Leg A b n o r m a l i t i e s , P r o p o r t i o n with Twisted Leg and Flock M o r t a l i t y over the Six Week T r i a l . 61 Figu r e 4.3 P r o g r e s s i o n of T y p i c a l U n i l a t e r a l Valgus Deformation. A, deformity at 2 weeks; p o s t e r i o r view; B, at 4 weeks; p o s t e r i o r view; C, at 6 weeks; a n t e r i o r view. The l a t e r a l deformation at two weeks was s l i g h t , with the chick assuming an awkward stance. However, as the deformity developed, p r o g r e s s i v e l a t e r a l bending of the d i s t a l t i b i a e made locomotion i n c r e a s i n g l y d i f f i c u l t . At s i x weeks, when the deformation was most severe, the b i r d s could only use the abnormal hock f o r support and thus the p o s t e r i o r aspect of the hock was of t e n s e v e r e l y b r u i s e d , swollen, and presum-ably more s u s c e p t i b l e to secondary i n f e c t i o n . (,1 A 62 F i g u r e 4.4 P r o g r e s s i o n of T y p i c a l B i l a t e r a l Varus Deformation. Deformity at 3 weeks (A) and 6 weeks (B); p o s t e r i o r views. The b i l a t e r a l varus c o n d i t i o n developed with a p r o g r e s s i v e medial bending of the d i s t a l t i b i a e a s s o c i a t e d with some outward r o t a t i o n of the a n t e r i o r s u r f a c e . The proximal tarsometa-t a r s u s was r o t a t e d inwards r e s u l t i n g i n a \"bow legged\" stance which made movement d i f f i c u l t . A 63 u n i l a t e r a l v a l g u s and the b i l a t e r a l v a r u s d e f o r m a t i o n s t y p i c a l of t w i s t e d l e g , r e s p e c t i v e l y . As the d e f o r m i t y progressed, the b i r d s movement became i n c r e a s i n g l y hindered. B i r d s would p r e f e r e n t i a l l y s i t on t h e i r hocks. When fo r c e d to move, a f f e c t e d b i r d s would h e s i t a t e and then walk w i t h a l i m p . In s e v e r e c a s e s of u n i l a t e r a l valgus deformations, b i r d s would use the abnormal hock f o r support i n s t e a d of the t a r s o m e t a t a r s u s ( F i g u r e 4.3c). Subsequently, the p o s t e r i o r aspect of the hock j o i n t was o f t e n s e v e r l y b r u i s e d , swollen, and presumably more s u s c e p t i b l e to secondary i n f e c t i o n . By the end of the s i x week t r i a l , 75% of the b i r d s s h o w i n g sign s of t w i s t e d l e g had d i s p l a c e d gastrocnemius tendons. S e q u e n t i a l r a d i o g r a p h s of t i b i a e from n o r m a l b i r d s ( F i g u r e 4.5) were compared with those from b i r d s d i s p l a y i n g b i l a t e r a l varus ( F i g u r e 4.6) or u n i l a t e r a l v a l g u s ( F i g u r e 4.7) deformations. Both forms of t w i s t e d l e g developed from a s l i g h t d e v i a t i o n or t o r s i o n of the d i s t a l t i b i a e . Adaptive remodeling, as evidenced by p r o g r e s s i v e bowing of the t i b i a e and compensatory t h i c k e n i n g of the c o r t e x on the w e i g h t b e a r i n g s i d e was a c h a r a c t e r i s t i c r a d i o g r a p h i c f e a t u r e of t w i s t e d l e g . These changes i n the bone are most l i k e l y a f u n c t i o n a l a d a p t a t i o n and a p p e a r t h e r e s u l t o f t h e p r o g r e s s i v e n a t u r e of the d e f o r m a t i o n s r a t h e r t h a n t h e primary cause of the bone d e v i a t i o n s themselves. S e q u e n t i a l r a d i o g r a p h y of t h e t i b i a e s a m p l e d f o r morphometry showed s u b c l i n i c a l s i g n s of d y s c h o n d r o p l a s i a i n many of the proximal metaphyses of c l i n i c a l l y normal b i r d s . 64 F i g u r e 4.5 S e q u e n t i a l Radiography of B r o i l e r Chickens Showing Normal T i b i a l Growth and Development. A, r i g h t and l e f t t i b i a e at 2 weeks; B, at 4 weeks; C, r i g h t and l e f t t i b i a e at 6 weeks; ( A n t e r o p o s t e r i o r v i e w s ) . The broken f u s e i n B was simply used f o r s c a l e . 65 F i g u r e 4.6 P r o g r e s s i o n of B i l a t e r a l Varus Deformity as seen with S e q u e n t i a l Radiography. A, r i g h t and l e f t t i b i a e at 2 weeks; B, at 4 weeks; C, at 6 weeks; ( A n t e r o p o s t e r i o r views ). No t i c e the p r o g r e s s i v e bending (LT) and outward r o t a t i o n of the d i s t a l t i b i a e (H). An apparent inward r o t a t i o n of the proximal tarsometatarsae i s a l s o shown. Regions of thickened cortex represent an attempt to strenghten the bone on the s i d e that i s c a r r y i n g the most weight ( J u l i a n , 1984) and represent s i t e s of adaptive remodeling ( C a r t e r , 1984). 66 a Figure 4.7 P r o g r e s s i o n of U n i l a t e r a l Valgus Deformity as seen with S e q u e n t i a l Radiography. A, two r i g h t t i b i a e at 3 weeks; B, abnormal r i g h t t i b i a at 4 weeks; C, r i g h t t i b i a at 6 weeks; ( A n t e r o p o s t e r i o r views). Notice the p r o g r e s s i v e l a t e r a l d e v i a t i o n of the d i s t a l t i b i a e and compensatory remodeling of the t i b i a e p a r t i c u l a r i l y on the weight bearing (concave) s i d e s (—>). T h i s adaptive or s t r u c t u r a l remodeling of bone ( C a r t e r , 1984; Rubin, 1984) i s an attempt to strengthen bone and hence r e s i s t f u n c t i o n a l s t r a i n s . An outward r o t a t i o n of a f f e c t e d t i b i a e i s a l s o observed at 4 and 6 weeks. A s s o c i a t e d with t h i s deformation of the t i b i a e i s a p r o g r e s s i v e inward r o t a t i o n of the tarsometatarsae. 67 S i x t y percent of the b i r d s sampled at 3 weeks, and twenty p e r c e n t of the b i r d s sampled at four and f i v e weeks showed r a d i o g r a p h i c s i g n s of d y s c h o n d r o p l a s i a ( F i g u r e 4 . 8 ) . R a d i o l u c e n t r e g i o n s i n the proximal metaphysis corresponded to r e g i o n s of r e t a i n e d c a r t i l a g e and gave the appearance of a widened j o i n t space. A n t e r o p o s t e r i o r bowing of the t i b i a e was a l s o pronounced i n a f f e c t e d b i r d s as s e e n w i t h t h e l a t e r a l r a d i o g r a p h s ( F i g u r e 4.9). T h e r e f o r e , i t would appear that t i b i a l d y s c h o n d r o p l a s i a may be more common than i s c l i n i c a l l y r e a l i z e d . There was no r a d i o g r a p h i c evidence of d y s c h o n d r o p l a s i a i n any of the d i s t a l t i b i a e of a f f e c t e d b i r d s . S p l i t t i n g the proximal t i b i a l metaphyses l o n g i t u d i n a l l y ( a f t e r morphometry) confirmed the r a d i o g r a p h i c d i a g n o s i s of d y s c h o n d r o p l a s i a . Abnormal masses of u n c a l c i f i e d c a r t i l a g e were r e t a i n e d i n the metaphyses of a f f e c t e d b i r d s ( F i g u r e 4.10) and c o r r e s p o n d e d to the r a d i o l u c e n t r e g i o n s on the r a d i o g r a p h s . T h e s e b i r d s w ere n o t i n c l u d e d i n t h e m o r p h o m e t r i c c o m p a r i s o n . There was no d y s c h o n d r o p l a s i a d e t e c t e d r a d i o g r a p h i c a 11y or by s p l i t t i n g t h e t i b i a e l o n g i t u d i n a l l y i n any of the d i s t a l metaphyses. B i r d s showing c l i n i c a l s i g n s o f t w i s t e d l e g were c o n s i s t e n t l y l i g h t e r and g e n e r a l l y i n poorer c o n d i t i o n than normal b i r d s . Pronounced d i f f e r e n c e s i n body weight were e v i d e n t w i t h b i r d s s h o w i n g s e v e r e d i s o r d e r s and were e s p e c i a l l y e vident a f t e r f i v e weeks ( F i g u r e 4.11). 6 8 F i g u r e 4 . 8 A n t e r o p o s t e r i o r Radiographs of the L e f t T i b i a e from C l i n i c a l l y Normal B r o i l e r Chickens Revealed S u b c l i n i c a l Dyschondroplasia i n the Proximal Metaphyses (-^~). A, 3 weeks; B, 4 weeks. Radiolucent regions corresponded to regions of r e t a i n e d u n c a l c i f i e d c a r t i l a g e and thus make the j o i n t space appear enlarged. 69 4T F i g u r e 4.9 L a t e r a l Radiograph of L e f t T i b i a e of C l i n i c a l l y Normal B r o i l e r Chickens at 4 weeks Revealing S u b c l i n i c a l Dyschondroplasia. T i b i a on the l e f t appears normal. T i b i a on the r i g h t shows a d i s -t i n c t r a d i o l u c e n t r e g i o n i n the proximal meta-physis , and pronounced a n t e r o p o s t e r i o r bowing. F i g u r e A .10 L o n g i t u d i n a l S e c t i o n s Through Proximal Meta-physes Revealing Abnormal Masses of C a r t i l a g e T y p i c a l of Dy s c h o n d r o p l a s i a . Abnormal C a r t -i l a g e appears as opaque plugs i n the proximal metaphyses ( ) . A, 3 weeks; B, k weeks. T 3 4 AGE (Weeks) F i g u r e 4.11 Body weight (BWT) of normal (N) b r o i l e r s and those a f f e c t e d with t w i s t e d l e g ( T L ) . The equations of the l i n e s a r e : N, BWT= -45.89 + 121.86X + 35.8X 2 ( ± 1 2 1 . 3 ) ( ± 6 8 . 3 ) ( ± 8 . 5 ) TL, BWT= -1563.88 + 974.2X - 84.7X 2 ( + 389.9) ( ± 1 9 1 . 2 ) ( ± 2 1 . 9 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p<0.05). ± Standard E r r o r of Estimate r= 0.99 (p<0.05) 72 S e q u e n t i a l m o r p h o m e t r y on t h e t i b a e f r o m n o r m a l c h i c k e n s and t h o s e a f f e c t e d w i t h t w i s t e d l e g r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s (p<0.05) i n the growth p a r a m e t e r s measured. F i g u r e 4.12 shows the r e g r e s s i o n l i n e of t i b i a l l e ngth over b i r d age. T i b i a l lengths were c o n s i s t a n t l y s h o r t e r i n t h e b i r d s a f f e c t e d w i t h t w i s t e d l e g d e s p i t e the normal appearance of t h e i r growth p l a t e s . I t i s p o s s i b l e that these d i f f e r e n c e s were the r e s u l t of the p r o g r e s s i v e bending of the d i s t a l t i b i a e r a t h e r than any r e a l d i f f e r e n c e i n a c t u a l t i b i a l l e n g t h . F i g u r e 4.13 shows that the depth of the d i s t a l condyle groove i n c r e a s e d w i t h age f o r both n o r m a l and a f f e c t e d b i r d s . However, t h o s e b i r d s a f f e c t e d with t w i s t e d l e g had c o n s i s t e n t l y more s h a l l o w d i s t a l c o n d y l e g r o o v e s . T h i s d i f f e r e n c e may have been important i n the i n i t i a l develop-ment of the d i s o r d e r ; e s p e c i a l l y when one c o n s i d e r s t h e e t i o l o g i e s of a n a l a g o u s d e f o r m i t i e s i n other s p e c i e s . For example, a s i m i l a r l e g abnormality ( p a t e l l a r l u x a t i o n ) has been d e s c r i b e d i n toy breeds of dogs (Pedersen et a l . 1981) and l e s s f r e q u e n t l y i n the horse and c a t ( F l e c k n e l l et a l . 1979). T h i s l e g abnormality has been l i n k e d to a s t r u c t u r a l d e f e c t i n the d i s t a l femur. S p e c i f i c a l l y , the p a t e l l a r groove appears unusually f l a t t e n e d and allows the p a t e l l a to disengage m e d i a l l y or l a t e r a l l y . With time the knee j o i n t becomes deformed i n a v a l g u s or varus p o s i t i o n and i s pre-disposed to degenerative changes. R e c u r r i n g d i s l o c a t i o n of 73 90-AGE (Weeks) F i g u r e A.12 T i b i a l L e n g t h ( T i b . L ) o f n o r m a l (N) b r o i l e r s and t h o s e a f f e c t e d w i t h t w i s t e d l e g ( T L ) . The e q u a t i o n s o f t h e l i n e s a r e : N, T i b . L = 32.A + 13.AX - 0.70X 2 ( ± 1 . 9 ) ( ± 1 . 1 ) ( ± 0 . 1 5 ) TL, T i b . L = 28.0 + 15.9X - 1 . 0 7 X 2 ( ± 6 . 8 ) ( ± 3 . 5 ) ( ± 0 . 3 8 ) S l o p e s a r e s i g n i f i c a n t l y d i f f e r e n t ( p < 0 . 0 5 ) . ±Standard E r r o r o f E s t i m a t e . r= 0.99 ( p < 0 . 0 5 ) . AO-AGE (Weeks) F i g u r e 4 .13 Condyle Groove Depth (CGD) of normal (N) b r o i l e r s and those a f f e c t e d with t w i s t e d l e g ( T L ) . The equations of the l i n e s a r e : N, CGD= 1.29 + 0.56X - 0.02X 2 ( ± 0 . 2 6 ) ( ± 0 . 1 5 ) ( ± 0 . 0 1 ) TL, CGD= -0.17 + 1.32X -0.12X2 ( ± 0 . 9 1 ) ( ± 0 . 4 7 ) ( ± 0 . 0 5 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p<0.05). ± Standard E r r o r of Es t i m a t e . r= 0.99 (p<0.05). 75 the p a t e l l a i n humans has a l s o been a t t r i b u t e d to many con-g e n i t a l d i s o r d e r s ; one of which i n v o l v e s f l a t t e n i n g of the l a t e r a l femoral condyles ( H e l f e t and Heywood, 1982). I t may be t h a t a s i m i l a r mechanism i s r e s p o n s i b l e f o r the v a l g u s - v a r u s d e f o r m a t i o n s i n p o u l t r y . P e r h a p s t h e s h a l l o w c o n d y l e groove p r e d i s p o s e s the d i s t a l t i b i a to a s l i g h t displacement of the g a s t r o c n e m i u s tendon and hence uneven t e n s i o n on the c o n d y l e s . With time, t h i s d i s p l a c e -ment may provide s u f f i c i e n t s t r a i n to cause s t r u c t u r a l r e -modeling and hence p r o g r e s s i v e bowing of the d i s t a l t i b i a e . D i f f e r e n c e s i n the growth i n width of the d i s t a l t i b i a l c o n d y l e groove were a l s o observed ( F i g u r e 4.14). In normal b i r d s the growth i n width of the d i s t a l t i b i a e i n i t i a l l y i n -c r e a s e d and t h e n a p p e a r e d to l e v e l o f f a t 5-6 weeks. However, those b i r d s a f f e c t e d with t w i s t e d l e g showed a pro-g r e s s i v e l i n e a r i n c r e a s e . T h i s i n c r e a s e was a s s o c i a t e d with t h e p r o g r e s s i v e b e n d i n g of t h e d i s t a l t i b i a e and a s u b s e q u e n t i n c r e a s e i n t i s s u e on the convex s i d e of the d e v i a t i o n s . The d i a m e t e r of t i b i a e from both normal and abnormal chickens i n c r e a s e d w i t h age, w i t h abnormal b i r d s showing c o n s i s t a n t l y wider diameters ( F i g u r e 4.15). A s s o c i a t e d with the i n c r e a s e i n t i b i a l diameter was a d e c r e a s e i n the p e r -c e n t c o r t i c a l t h i c k n e s s ( F i g u r e 4.16). T h i s decrease was more gradual i n abnormal b i r d s compared w i t h normal b i r d s . These r e s u l t s s u g g e s t t h a t abnormal t i b i a e may have been AGE (Weeks) F i g u r e 4 . 1 4 C o n d y l e G r o o v e W i d t h ( C G W ) o f n o r m a l ( N ) b r o i l e r s a n d t h o s e a f f e c t e d w i t h t w i s t e d l e g ( T L ) . T h e e q u a t i o n s o f t h e l i n e s a r e : N , C G W - 7 . 3 3 + 2 . 3 X - 0 . 2 3 X 2 ( ± 0 . 5 2 ) ( ± 0 . 3 0 ) ( ± 0 . 0 4 ) T L , C G W - 8 . 7 5 + 1 . 3 4 X ( ± 0 . 5 6 ) ( ± 0 . 1 6 ) S l o p e s a r e s i g n i f i c a n t l y d i f f e r e n t ( p < 0 . 0 5 ) . ± S t a n d a r d E r r o r o f E s t i m a t e r = 0 . 9 9 ( p < 0 . 0 5 ) . 7.0-77 AGE (Weeks) F i g u r e A.15 T i b i a l Diameter (TD) of normal (N) b r o i l e r s and those a f f e c t e d wi th t w i s t e d l e g ( T L ) . The e q u a t i o n s o f the l i n e s a r e : N, TD= 1.9 + 0.95X - 0 . 0 8 X 2 ( ± 0 . 3 9 ) ( ± 0 . 2 2 ) ( ± 0 . 0 3 ) T L , TD= 2.9 + 0.55X ( ± 0 . 3 7 ) ( ± 0 . 1 1 ) S lopes are s i g n i f i c a n t l y d i f f e r e n t (p<0.05) . ± S t a n d a r d E r r o r of E s t i m a t e r= 0.99 (p<0.05) . 78 F i g u r e 4.16 P e r c e n t C o r t i c a l T h i c k n e s s (PCT) of normal ( N ) b r o i l e r s and those a f f e c t e d wi th t w i s t e d l e g ( T L ) . The e q u a t i o n s of the l i n e s a r e : N, P C T - 34.84 - 2.61X ( ± 0.B7) ( ± 0 . 5 2 ) T L , PCT« 33.13 - 2.09X ( ± 1 . 5 ) ( ± 0 . 4 5 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p<0.05) . ± S t a n d a r d E r r o r of E s t i m a t e . r « 0.99 (p<0.05).-79 r e a c t i n g i n an adaptive manner to r e d u c e f u n c t i o n a l s t r a i n a s s o c i a t e d with the deformation. P e l l e g r i n o and B l i t z (1983), u s i n g a c h i c k bone model to e v a l u a t e r a d i a l bone growth, found no evidence of bone formation on the endosteal s u r f a c e and no evidence f o r bone r e s o r p t i o n on the p e r i o s t e a l s u r f a c e of the c h i c k t i b i a . T h e r e f o r e , i n order f o r the abnormal t i b i a e to a c q u i r e the t h i c k e n e d c o r t e x r e l a t i v e to the normal ones, t h e r e must have been i n c r e a s e d p e r i o s t e a l bone fo r m a t i o n . At the same time, bone r e s o r p t i o n i n those areas where s t r a i n was engen-dered must have been reduced.. Presumably the c o o r d i n a t i o n of p e r i o s t e a l bone f o r m a t i o n and e n d o s t e a l bone r e s o r p t i o n r e s u l t e d i n an optimum t i b i a l s t r u c t u r e more a b l e to w i t h -stand the f u n c t i o n a l s t r a i n s a s s o c i a t e d with the d e f o r m i t y . T i b i a l ash d e c r e a s e d w i t h age; w i t h a b n o r m a l b i r d s showing a s h a r p e r d e c l i n e than normal b i r d s ( F i g u r e 4.17). T h i s o v e r a l l decrease i n t i b i a l ash may be e x p l a i n e d by the r e l a t i v e d e c r e a s e i n c o r t i c a l bone r e l a t i v e to t r a n s v e r s e diameter of the t i b i a ( P e l l e g r i n o and B l i t z , 1983) or by the r e l a t i v e i n c r e a s e i n s i z e of the c a r t i l a g i n o u s epiphyses. Moreover, the d i f f e r e n c e between normal and abnormal t i b i a e may have been due to the a d d i t i o n a l n o n c a l c i f i e d t i s s u e as-s o c i a t e d with the deformed d i s t a l condyle. R e s u l t s f r o m t h i s e x p e r i m e n t s u g g e s t t h a t t h e development of t w i s t e d l e g i n b r o i l e r s could be r e l a t e d to a s t r u c t u r a l abnormality i n the d i s t a l t i b i a e ; namely shallow 80 F i g u r e 4.17 Percent Ash (PASH) of normal (N) b r o i l e r s and those a f f e c t e d wi th t w i s t e d l e g ( T L ) . The e q u a t i o n s o f the l i n e s a r e : N, PASH= 42.24 - 1.59X ( ± 0 . 4 9 ) ( ± 0 . 2 9 ) T L , PASH= 43.03 - 1.88X , ( ± 0 . 8 8 ) ( ± 0 . 2 5 ) Slopes are s i g n i f i c a n t l y d i f f e r e n t (p<0.05) . ± S t a n d a r d E r r o r of E s t i m a t e . r«= 0.99 (p<0.05) . 81 d i s t a l c o n d y l e g r o o v e s . The s h a l l o w d i s t a l c o n d y l e g r o o v e may p r e d i s p o s e t h e d i s t a l t i b i a e t o a s l i g h t d i s p l a c e m e n t o f t h e g a s t r o c n e m i u s t e n d o n and h e n c e u n e v e n s t r a i n on t h e d i s t a l c o n d y l e s . W i t h t i m e , t h e uneven s t r a i n on t h e d i s t a l t i b i a e and p r o x i m a l t a r s o m e t a t a r s u s p r o d u c e s t h e c h a r a c t e r -i s t i c v a l g u s ( l a t e r a l ) o r v a r u s ( m e d i a l ) d e f o r m a t i o n s . O t h e r c h a n g e s i n t i b i a e m o r p h o l o g y ( d i a m e t e r a t m i d s h a f t , d i s t a l c o n d y l e g r o o v e w i d t h , e t c . ) a p p e a r e d as f u n c t i o n a l a d a p t a t i o n s t o t h e d e f o r m a t i o n r a t h e r t h a n t h e p r i m a r y c a u s e o f t h e bone d e v i a t i o n s t h e m s e l v e s . S e q u e n t i a l r a d i o g r a p h y o f t i b i a e f r o m c l i n i c a l l y n o rmal b r o i l e r s r e v e a l e d a h i g h i n c i d e n c e o f t i b i a l d y s c h o n d r o -p l a s i a i n t h e p r o x i m a l m e t a p h y s e s a t 3 , 4, and 5 w e e k s . I t i s t h e r e f o r e c o n c l u d e d t h a t t i b i a l d y s c h o n d r o p l a s i a may be more common t h a n i t i s r e a l i z e d . CHAPTER FIVE SUMMARY AND CONCLUSIONS A number of l e g a b n o r m a l i t i e s have been d e s c r i b e d i n b r o i l e r chickens which together cause s i g n i f i c a n t economic l o s s f o r t h e p o u l t r y i n d u s t r y ( R i d d e l l , 1981; N a t i o n a l Turkey F e d e r a t i o n . 1971). The e t i o l o g y and p a t h o g e n e s i s of t h e s e d e f o r m i t i e s i s complex and o f t e n poorly d e f i n e d . Few of the l e g a b n o r m a l i t i e s can be a t t r i b u t e d t o a s i n g l e f a c t o r and most a p p e a r t o i n v o l v e an i n t e r a c t i o n of g e n e t i c s , n u t r i t i o n , and environment. The p r e s e n t s t u d y was based on, and s u p p o r t e d , the hypothesis that h e r e d i t a r y p r e d i s p o s i t i o n s to l e g a b n o r m a l -i t i e s are widespread i n commercial b r o i l e r s t r a i n s and that s t r e s s f a c t o r s d e r i v e d e i t h e r f r o m t h e e n v i r o n m e n t or n u t r i t i o n may t r i g g e r t h e c l i n i c a l s i g n s o f l e g a b n o r m a l i t i e s (Sim and Cruickshank, 1985). T w i s t e d l e g , c h a r a c t e r i z e d by a m e d i a l or l a t e r a l d e v i a t i o n of the d i s t a l t i b i a , emerged as the predominant l e g a b n o r m a l i t y i n both t r i a l s . However, the i n c i d e n c e of t w i s t e d l e g i n the b r o i l e r s reared i n cages (under c o n t r o l c o n d i t i o n s ) was 21% at A weeks; c o n s i d e r a b l y higher than the A% (at A weeks) f o r t h o s e r e a r e d c o n v e n t i o n a l l y i n f l o o r pens. The m o r p h o m e t r i c c o m p a r i s o n of t i b i a e from normal 82 83 chickens and those a f f e c t e d w i t h t w i s t e d l e g s u g g e s t t h a t the development of t w i s t e d l e g i n b r o i l e r s may be r e l a t e d to a s t r u c t u r a l a b n o r m a l i t y i n t h e d i s t a l t i b i a e , namely s h a l l o w d i s t a l condyle grooves. The shallow d i s t a l condyle groove may predispose the d i s t a l t i b i a to a s l i g h t d i s p l a c e -ment of the gastrocnemius tendon; with the r e s u l t a n t s t r a i n c o n f e r r i n g t h e v a r u s o r v a l g u s d e f o r m a t i o n s . The p r o g r e s s i o n of the deformity appeared to r e s u l t from normal adaptive remodeling; as evidenced by s e q u e n t i a l r a d i o g r a p h y and morphometry of a f f e c t e d t i b i a e . Cage r e a r i n g of b r o i l e r s was shown i n t h i s s t u d y to i n c r e a s e the i n c i d e n c e of t w i s t e d l e g . I t has a l s o been r e p o r t e d c o n s i s t e n t l y t h a t more e x e r c i s e was n e e d e d t o r e d u c e the i n c i d e n c e of t w i s t e d l e g i n cage-reared b r o i l e r s (Reece et a l . , 1971; Andrews et a l . , 1974; Haye and Simons, 1978). R e s u l t s from t h i s s t u d y are i n general agreement with t h i s h y p o t h e s i s . D i f f i c u l t y i n w a l k i n g a s s o c i a t e d w i t h w i r e f l o o r s (Haye and Simons, 1978: Andrews et a l . , 1974) may c o n t r i b u t e an a d d i t i o n a l s t r a i n on the hock j o i n t and t h u s a g g r a v a t e a n d / o r a c c e n t u a t e any s t r a i n a s s o c i a t e d with shallow d i s t a l condyle grooves. Any b e n e f i t i n i t i a l l y g a i n e d from the i n c r e a s e d a c t i v i t y a s s o c i a t e d with the high d e n s i t y cages i n terms of i n c r e a s e d e x e r c i s e (Rodenhoff and Damrarich, 1971) and i n c r e a s e d t i b i a l bone s t r e n g t h (Meyer and Sunde, 1974) may have been l o s t due to i n c r e a s e d s t r e s s on the hock j o i n t . T h i s was evidenced by the sharp i n i t i a l 84 r i s e i n i n c i d e n c e of t w i s t e d l e g i n the high d e n s i t y c a g e s . L a t e r , the i n c r e a s e d a c t i v i t y may have provided s u f f i c i e n t e x e r c i s e to reduce the i n c i d e n c e of t w i s t e d l e g . The p r e c i s e mannner i n which the e x c e s s v i t a m i n Dg c a u s ed the s h a r p e r r i s e i n the i n c i d e n c e of t w i s t e d l e g r e m a i n s u n c l e a r . However, i t may be that myopathy of the l e g muscles ( a s s o c i a t e d w i t h a v i t a m i n E d e f i c i e n c y ) may h ave p r o d u c e d an e f f e c t s i m i l a r to t h a t a s s o c i a t e d w i t h decreased e x e r c i s e ; namely weaker l e g s and more d i s o r d e r s . However, more r e s e a r c h i s needed to more p r e c i s e l y e x p l a i n t h i s r e s u l t . LITERATURE CITED Anderson, J.O., Warnick, R.E., and N. Nakhata, 1979. E f f e c t of Cage and F l o o r Rearing; D i e t a r y Calcium, Phosphorus, F l o u r i d e , and Energy L e v e l s ; and Temperature on Growing Turkey Performance, the Incidence of Broken Bones and Bone Weight, and Ash. P o u l t r y S c i . 58:1175-1182. Andrews, L.D., Seay, R.L., H a r r i s , G.C, J r . , and G.S. Nelson, 1974. F l o o r i n g M a t e r i a l s f o r Caged B r o i l e r s and T h e i r E f f e c t Upon Performance. P o u l t r y S c i . 53:1141-1146. A u s t i c , R.E., Baker, D.J., and R.K. Cole, 1977. Suscept-a b i l i t y of a dwarf s t r a i n of chickens to r i c k e t t s . P o u l t r y S c i e n c e . 56:285-291. Asmundson, V.S., 1944. I n h e r i t e d s h o r t e n i n g of the long bones i n the turk e y . J . Hered. 35:295-299. Asmundson, V.S., 1942. An i n h e r i t e d micromelia i n the domestic f o w l . J Hered. 33:328-330. B a r n e t t , E. , and B.E.C. Nordin, 1959. The R a d i o l o g i c a l D i a g n o s i s of O s t e o p o r o s i s : A New Approach. C l i n R a d i o l . 9:166-174. Borysenko, M., and T. B e r i n g e r , 1984. C a r t i l a g e and Bone. In: F u n c t i o n a l H i s t o l o g y 2nd Ed., pp 101-121. L i t t l e Brown and Co. Inc. Toronto. B r i g g s , G.M., Luckey, T.D., Tepley, L. J . , Elvehjem, C A . , and C B . Hart, 1943. St u d i e s on n i c o t i n i c a c i d d e f i -c i e n c y i n the c h i c k . J . B i o l . Chem. 148:517- 523. B r i g h t o n , C.T., 1978. S t r u c t u r e and Fu n c t i o n of the Growth P l a t e . C l i n . Orth. R e l . Res. 136:22-32. Buckland, R.B., Bernon, D.E., and A Goldrosen, 1976. E f f e c t of Four L i g h t i n g Regimes on B r o i l e r Performance, Leg Ab n o r m a l i t i e s and Plasma C o r t i c o i d L e v e l s . P o u l t r y S c i . 55:1072- 1076. Buckland, R.B., H i l l , A.T., and D.E. Bernon, 1973. E f f e c t s of four l i g h t i n g regimes on the performance of b r o i l e r s and r o a s t e r s . Can. J . Anim. S c i . 53:21-24. B u f f i n g t o n , D.E., Kleven, S.H., and K.A. Jordan, 1975. The Incidences of l e g and foot a b n o r m a l i t i e s i n Wrolstad White t u r k e y s . P o u l t r y S c i . 54: 457- 461. C a r t e r , D.R., 1984. Mechanical Loading H i s t o r i e s and C o r t i c a l Bone Remodeling. C a c i f . T i s s u e I n t . 36:S19-S24. 85 86 Church, L.E., and L.C. Johnson, 1964. Growth of Long Bones i n the Chicken. Amer. J . Anat. 114(3):521-538. Cook, M.E., P a t t e r s o n , P.H., and M.L. Sunde, 1984. Leg D e f o r m i t i e s : I n a b i l i t y to Increase S e v e r i t y by I n c r e a s i n g Body Weight of Chicks and P o u l t s . P o u l t r y S c i . 63:620- 627. D a n i e l , L . J . , Farmer, F.A., and L.C. N o r r i s , 1946. F o l i c a c i d and p e r o s i s . J . B i o l . Chem. 163: 349-350. Dent, C.E., and Stamp, T.C.B., 1977. Vitamin D, R i c k e t t s and Osteomalacia. In: M e t a b o l i c Bone Disease, Eds., L.V. A v i o l i and S.M. Krane, Academic Press, New York, V o l . 1, pp. 237-305. Duncan, D.B., 1955. M u l t i p l e Range and M u l t i p l e F T e s t s . B i o m e t r i c s 11:1-42. Ed wards, H.M., 1983. E t i o l o g y of T i b i a l Dyschondroplasia i n P o u l t r y . Proceedings 1983 Georgia N u t r i t i o n Conf. f o r the Feed Industry, pp. 103-111. Edwards H.M. J r . , and J.R. Veltaraann J r . , 1983. The Role of c a l c i u m and Phosphorus i n the E t i o l o g y of T i b i a l Dys-c h o n d r o p l a s i a i n Young C h i c k s . J . Nutr. 113: 1568-1575. Fe d u c c i a , A., 1975. Aves Osteology. In: S i s s o n s and Grossman's The Anatomy of the Domestic Animals, 5th Ed., pp. 1790-1801. Ed. R. Getty. W.B. Saunders Co., P h i l a d e l p h i a . F e l l , H.B., 1925. The H i s t o g e n e s i s of C a r t i l a g e and Bone i n the Long Bones of the Embryonic Fowl. J . Morphol. P h y s i o l . 40(3):417-459. Ferguson, A.E., Summers, J.D., L e s l i e , A.J. and H.C. C a r l s o n , 1974. Leg D e f o r m i t i e s i n Chicken B r o i l e r s . Can. Vet. J . 15(7):185-190 F l e c k n e l l , P.A., and J . J . Gruffydd-Jones, 1979. C o n g e n i t a l l u x a t i o n of the p a t e l l a e i n the c a t . F e l i n e P r a c t . 9:18. Gaffney, L . J . , 1975. Chondrodystrophy: An i n h e r i t e d l e t h a l c o n d i t i o n i n turkey embryos. J . Hered. 66:339-343. G r i e s , C.L., and M.L. S c o t t , 1972. The pathology of p y r i d o x i n e d e f i c i e n c y i n c h i c k s . J . Nutr. 102:1259-1268. Groth, W., and H. Frey, 1966. A c o m p a r i t i v e study of the e f f e c t s of d e f i c i e n c y of calcium, phosphorus or vitamin D on the bones, blood and endocrines of the c h i c k . Z b l . Vet. Med. 13A:302-319. 87 Haye, U., and P.CM. Simons, 1978. Twisted Legs i n B r o i l e r s . Br. P o u l t . S c i . , 19:549-557. H e l f e t , A.J., and A.W., Brookes Heywood, 1982. D i s l o c a t i o n s of the P a t e l l a . In: D i s o r d e r s of the Knee. 2nd. ed. Ed. A.J. H e l f e t , J.B. L i p p i n c o t t Co: P h i l . Toronto, pp.347-362. Hemsley, L.A., 1970. A c a r t i l a g e abnormality of b r o i l e r c h i c k s . Vet. Rec. 86:385. Hulan, H.W., Proudfoot, F.G., Ramey, D., and K.B. McRae, 1979. I n f l u e n c e of genotype and d i e t on general per-formance and i n c i d e n c e of l e g a b n o r m a l i t i e s of commercial b r o i l e r s reared to r o a s t e r weight. P o u l t r y S c i . 59:748-757. Jubb, K.V.F., and P.C. Kennedy, 1970. Bones, J o i n t s , and S y n o v i a l S t r u c t u r e s . In: Pathology of Domestic Animals 2nd Ed. pp. 1-90. Academic P r e s s . New York and London. Jukes, T.H., and F.H. B i r d , 1942. Pr e v e n t i o n of P e r o s i s by b i o t i n . Proc. Soc. Exp. B i o l . Med. 49:231-232. Jukes, T.H., 1940. E f f e c t of c h o l i n e and other supplements on p e r o s i s . J . Nutr. 20:445-458. J u l i a n , R.J., 1984. Valgus-Varus Deformity of the I n t e r t a r s a l J o i n t i n B r o i l e r Chickens. Can. Vet. J . 25:254-258. J u l i a n , R.J., 1981. Lameness and Leg Problems. In: Canada Poultryman, March 1981 pp. 6-41. Khan, M.A., Olson, N.O., and D.0. Overman, 1977. Spontaneous s p o n d y l o l i s t h e s i s i n embryonic and a d u l t c h i c k . P o u l t r y S c i . 56:689-697. Koch, T., 1973. Anatomy of the Chicken and Domestic B i r d s . Ed. and Trans. B.H. Skold and L. DeVries. Iowa State U n i v e r s i t y P r e s s , Ames Iowa. Lamoreux, W.F., 1942. H e r e d i t a r y Chondrodystrophy i n the Fowl. J . Hered. 33:275-283. Leach, R.M. J r . , 1971. Role of Manganese i n Mucopolysaccharide Metabolism. Fed. Proc. 30:991-994. Leach, R.M. J r . , 1967. Role of Manganese i n the Syn t h e s i s of Mucopolysaccharides. Fed. Proc. 26:118-120. Leach, R.M., and M.C. Nesheim, 1972. Further s t u d i e s on T i b i a l Dyschondroplasia ( C a r t i l a g e Abnormality) i n young c h i c k s . J . Nutr. 102:1673-1680 88 Leach, R.M., and M.C. Nesheim, 1965. N u t r i t i o n a l , Genetic and M o r p h o l o g i c a l S t u d i e s of an Abnormal C a r t i l a g e Formaation i n Young C h i c k s . J . Nutr. 86:236-244. L i l b u r n M.S., Ngian, K., and J.H. Smith, 1983. The E f f e c t of M i n e r a l and E l e c t r o l y t e Balance on the Incidence of Leg A b n o r m a l i t i e s i n D i f f e r e n t S t r a i n s of Commercial B r o i l e r s . P o u l t r y S c i . 62:1353 ( A b s t r . ) . L u f t i , A.M., 1967. Growth and Development of the upper end of the T i b i a of the fowl ( G a l l u s Domesticus). Ph.D. T h e s i s , the Queen's U n i v e r s i t y of B e l f a s t . March, B.E., Wong, E., S e i e r , L., Sim, J . , and J . B i e l y , 1973. H y p e r v i t a m i n o s i s E i n the Chick. J . Nutr. 103(3): 371-377. McCapes, R.H., 1967. Bone D e f o r m i t i e s . Proc. Western P o u l t . D i s . Conf., Univ. of C a l i f o r n i a , Davis C a l i f o r n i a , USA p.13 Merkley, J.W., 1981. A Comparison of Bone Strengths from B r o i l e r s Reared Under Vari o u s C o n d i t i o n s i n Coops and F l o o r Pens. P o u l t r y S c i . 60:98-106. Meyer, W.A., and M.L. Sunde, 1974. Bone Breakage as A f f e c t e d by Type Housing or an E x e r c i s e Machine f o r Lay e r s . P o u l t r y S c i . 53:878-885. Moore, K.L., 1973. The Developing Human- C l i n i c a l l y O r iented Embryology. W.B. Saunders Co. Toronto. Na i r n , M.E., 1973. B a c t e r i a l O s t e o m y e l i t i s and S y n o v i t i s of the Turkey. Avian D i s . 17:504-517. Nairn, M.E., and A.R.A., Watson, 1972. Leg Weakness of P o u l t r y - A C l i n i c a l and P a t h o l o g i c a l C h a r a c t e r i z a t i o n . Aust. Vet. J . 48:645-655. N a t i o n a l Research C o u n c i l (NRC), 1984. N u t r i e n t Requirements of P o u l t r y 8th. ed. N a t i o n a l Academy of Sci e n c e s , Wash. DC. N a t i o n a l Research C o u n c i l (NRC), 1977. Nut r i e n t Requirements of P o u l t r y 7th. ed. N a t i o n a l Academy of Scie n c e s , Wash. DC. N a t i o n a l Turkey F e d e r a t i o n , 1971. Proc. Symp. Leg Weakness i n Turkeys. Sponsored by the N a t i o n a l Turkey Feder-a t i o n , Iowa State U n i v e r s i t y , Ames. Nestor, K.E., 1978. H e r e d i t a r y Chondrodystrophy i n the Turkey. P o u l t r y S c i . 57:577-580. 89 N o r r i s , L . C , and M.L. S c o t t , 1965. P r o t e i n s , Carbohydrates, F a t s , F i b e r , M i n e r a l s and Water i n P o u l t r y Feeding. In: Diseases of P o u l t r y . Ed. H.E. Bieder, and L.H. Schwarte. 5th. ed. p . 165. The Iowa State U n i v e r s i t y P r e s s , Ames. O' D e l l , B.L., and J.E. Savage (1957). Symptoms of Zinc D e f i c i e n c y i n the Chick. Fed. Proc. 16:394 ( A b s t r . ) . Olson, N.O., Shelton , D.C, B l e t n e r , J.K., Munro, D.A. and G.C. Anderson, 1956. S t u d i e s of I n f e c t i o u s S y n o v i t i s i n Chickens. Am. J . Vet. Res. 17:747-754. Olsson, S.E., 1978. The Nature of Osteochondrosis i n Animals. Acta R a d i o l . , Suppl. 358:9-14. O s b a l d i s t o n , G.W., and D.R. Wise, 1967. S p o n d y l o l i s t h e s i s and Leg Weakness i n the Chicken- A Common A e t i o l o g y . Vet. Rec. 80:320-322. Pearce, L., 1960a. H e r e d i t a r y D i s t a l F o r e l e g Curvature i n the Rabbit. J . Exp. Med. 111:801-822. Pedersen, N.C, P o o l , R.R., and T.R. O'Brien, 1981. N a t u r a l l y O c c u r r i n g A r t h r o p a t h i e s of Animal. In: Diagnosis of Bone and J o i n t D i s o r d e r s . V o l . 1., Ed D.R. Resnick and G. Niwayama. W.B. Saunders Co., P h i l . , London, Toronto. P e l l e g r i n o , E.D., and R.M. B l i t z , 1983. A Chick Bone Model f o r E v a l u a t i n g R a d i a l Bone Growth. I. E f f e c t s of Vitamin D3 D e f i c i e n c y . P o u l t r y S c i . 62:2083-2087. P i e r s o n , F.W., and D.Y. Hester, 1982. F a c t o r s I n f l u e n c i n g Leg A b n o r m a l i t i e s i n P o u l t r y : A Review. World's P o u l t r y S c i . J . 38:5-17. Poulous. P.W. J r . , R i e l a n d , S., Elwinger, K., and S.E. Olsson, 1978. S k e l e t a l L e s i o n s i n the B r o i l e r , with S p e c i a l Reference to Dyschondroplasia (Osteochon-d r o s i s ) . Acta R a d i o l . , Suppl. 358:229-275. Prasad, S., H a i r r , W.T., and J . T. D a l l a s , 1972. Observations of Abnormal C a r t i l a g e Formation A s s o c i a t e d with Leg Weakness i n Commercial B r o i l e r s . Avian Dis. 16:457-461. R a n d a l l , C.J., and C.P.J. M i l l s , 1981. Observations on Leg Deformity i n B r o i l e r s with P a r t i c u l a r Reference to the I n t e r t a r s a l J o i n t . Avian Path. 10:407-431. Reddi, A.H., 1981. C e l l B i o l o g y and Biochemistry of Endochondral Bone Development. C o l l . Res. 1:209-226 9 0 R e e c e , F . N . , D e a t o n , J . W . , M a y , J . D . , a n d K . N . M a y , 1 9 7 1 . C a g e v e r s u s F l o o r R e a r i n g o f B r o i l e r C h i c k e n s . P o u l t r y S c i . 5 0 : 1 7 8 6 - 1 7 9 0 . R e i l a n d , S . , O l s s o n , S . E . , P o u l o u s , P . W . J r . , a n d K . E l w i n g e r , 1 9 7 8 . N o r m a l a n d P a t h o l o g i c a l S k e l e t a l D e -v e l o p m e n t i n B r o i l e r a n d L e g h o r n C h i c k e n s . A c t a R a d i o l . , S u p p l . 3 5 8 : 2 7 7 - 2 9 8 . R i d d e l l , C , 1 9 8 3 , P a t h o l o g y o f t h e S k e l e t o n a n d T e n d o n s o f B r o i l e r C h i c k e n s R e a r e d t o R o a s t e r W e i g h t s . I C r i p p l e d C h i c k e n s . A v i a n D i s . 2 7 ( A ) : 9 5 0 - 9 6 2 . R i d d e l l , C , 1 9 8 1 . S k e l e t a l D e f o r m i t i e s i n P o u l t r y . A d v . V e t . S c . C o m p . M e d . 2 5 : 2 7 7 - 3 1 0 R i d d e l l , C , 1 9 7 8 . C o m m o n N o n i n f e c t i o u s D i s o r d e r s o f t h e S k e l e t o n o n D o m e s t i c C h i c k e n s a n d T u r k e y s . A C o n t i n u i n g E d u c a t i o n P r o g r a m ; A A A P , I n c . R i d d e l l , C , 1 9 7 6 . S e l e c t i o n o f B r o i l e r C h i c k e n s f o r a H i g h a n d L o w I n c i d e n c e o f T i b i a l D y s c h o n d r o p l a s i a w i t h O b -s e r v a t i o n s o f S p o n d y l o l i s t h e s i s a n d T w i s t e d L e g s ( P e r o s i s ) . P o u l t r y S c i . 5 5 : 1 4 5 - 1 5 1 . R i d d e l l , C , 1 9 7 5 . T i b i a l D y s c h o n d r o p l a s i a i n D o m e s t i c P o u l t r y . A C o n t i n u i n g E d u c a t i o n P r o g r a m ; A A A P , I n c . R i d d e l l , C , 1 9 7 5 a . S t u d i e s o n t h e P a t h o g e n e s i s o f T i b i a l D y s c h o n d r o p l a s i a i n C h i c k e n s . I I G r o w t h R a t e o f L o n g B o n e s . A v i a n D i s . 1 9 ( 3 ) : 4 9 0 - 4 9 6 . R i d d e l l , C , 1 9 7 5 b . S t i d i e s o n t h e P a t h o g e n e s i s o f T i b i a l D y s c h o n d r o p l a s i a i n C h i c k e n s . I l l E f f e c t o f B o d y W e i g h t . A v i a n D i s . 1 9 ( 3 ) : 4 9 7 - 5 0 5 . R i d d e l l , C , 1 9 7 5 c . S t u d i e s o f t h e P a t h o g e n e s i s o f T i b i a l D y s c h o n d r o p l a s i a i n C h i c k e n s . I P r o d u c t i o n o f a S i m i l a r D e f e c t b y S u r g i c a l I n t e r f e r e n c e . A v i a n D i s . 1 9 ( 3 ) : 4 8 3 - 4 8 9 . R i d d e l l , C , 1 9 7 3 . S t u d i e s o n S p o n d y l o l i s t h e s i s ( k i n k y - b a c k ) i n B r o i l e r C h i c k e n s . A v i a n P a t h . 2 : 2 9 5 - 3 0 4 . R i d d e l l , C , a n d J . H o w e l l , 1 9 7 2 . S p o n d y l o l i s t h e s i s ( k i n k y -b a c k ) i n B r o i l e r C h i c k e n s i n W e s t e r n C a n a d a . A v i a n D i s . 1 6 : 4 4 4 - 4 5 2 . R i d d e l l , C , H o w e l l , J . , a n d M . M . K a y e , 1 9 7 1 . T i b i a l D y s c h o n d r o p l a s i a i n B r o i l e r C h i c k e n s i n W e s t e r n C a n a d a . A v i a n D i s . 1 5 : 5 5 7 - 5 6 5 . 9 1 R o d e n h o f f , G . , a n d K . D a m r a r i c h , 1 9 7 1 . Z e n t b l . V e t . M e d . 1 8 ( A ) : 2 9 7 - 3 0 9 . R e f . W i s e , D . R . , 1 9 7 8 . N u t r i t i o n -D i s e a s e I n t e r a c t i o n s o f L e g W e a k n e s s i n P o u l t r y . I n : R e c e n t A d v a n c e s i n A n i m a l N u t r i t i o n . E d s . W. H a r e s i g n a n d D . L e w i s , B u t t e r w o r t h s , L o n d o n B o s t o n , 1 9 7 9 p p . 4 1 -4 7 . R o m e r , A . S . , a n d T . S . P a r s o n s , 1 9 7 7 . T h e V e r t e b r a t e B o d y . 5 t h . e d . , W . B . S a u n d e r s C o . P h i l a d e l p h i a p . 3 3 3 . R o w l a n d , 1 . 0 . J r . , D a m r o n B . L . , R o s s , E . , a n d R . H . H a r m s , 1 9 7 1 . C o m p a r i s o n s o f B o n e C h a r a c t e r i s t i c s B e t w e e n F l o o r a n d B a t t e r y G r o w n B r o i l e r s . P o u l t r y S c i . 5 0 : 1 1 2 1 - 1 1 2 4 . R o w l a n d , L . O . J r . , H a r m s , R . H . , W i l s o n , H . R . , R o s s , I . J . a n d J . L . F r y , 1 9 6 7 . B r e a k i n g S t r e n g t h o f C h i c k B o n e s a s a n I n d i c a t i o n o f d i e t a r y C a l c i u m a n d P h o s p h o r u s A d e q u a c y . P r o c . S o c . E x p . B i o l . M e d . 1 2 6 : 3 9 9 - 4 0 1 . R u b i n , C . T . , 1 9 8 4 . S k e l e t a l S t r a i n a n d F u n c t i o n a l S i g n i f i c a n c e o f B o n e A r c h i t e c t u r e . C a l c i f . T i s s u e I n t . 3 6 : S 1 1 - S 1 8 . S a u v e u r , B . , 1 9 8 4 . D i e t a r y F a c t o r s a s C a u s e s o f L e g A b n o r m a l i t i e s i n P o u l t r y - A R e v i e w . W o r l d ' s P o u l t r y S c i . J . 4 0 ( 3 ) : 1 9 5 - 2 0 6 . S a u v e u r , B . f a n d P . M o n g i n , 1 9 7 8 . T i b i a l D y s c h o n d r o p l a s i a , a C a r t i l a g e A b n o r m a l i t y i n P o u l t r y . A n n . B i o l . A n i m . B i o c h . B i o p h y s . 1 8 : 8 7 - 9 8 . S a u v e u r , B . , a n d P . M o n g i n , 1 9 7 4 . I n f l u e n c e o f D i e t a r y L e v e l o f C h l o r i d e , S o d i u m , a n d P o t a s s i u m o n C h i c k C a r t i l a g e A b n o r m a l i t i e s . P r o c . XV W o r l d ' s P o u l t r y C o n g r e s s : 1 8 0 - 1 8 1 . S c o t t , M . L . , N e s h e i m , M . C . , a n d R . L . Y o u n g . 1 9 8 2 . T h e V i t a m i n s . I n : N u t r i t i o n o f t h e C h i c k e n . 3 r d . e d . M . L . S c o t t a n d A s s o c i a t e s I t h a c a , N Y . p p . 1 1 9 - 2 7 6 . S h e r i d a n , A . K . , H o w l e t t , C . R . , a n d E . B . D e l t m a n n , 1 9 7 6 . S e l e c t i o n f o r T i b i a l D y s c h o n d r o p l a s i a i n A u s t r a l i a n M e a t C h i c k e n s . P r o c . A u s t . P o u l t . S t o c k F o o d C o n v e n t i o n , M e l b o u r n e , p p . 1 7 6 - 1 8 1 . S h e r i d a n , A . K . , H o w l e t t , C . R . , a n d J . A . B r u y n , 1 9 7 4 . G e n e t i c a l F a c t o r s I n f l u e n c i n g T i b i a l D y s c h o n d r o p l a s i a i n A u s t r a l i a n M e a t C h i c k e n s . 1 5 t h . W o r l d ' s P o u l t r y C o n g r e s s , New O r l e a n s , p p . 3 4 - 3 5 . S i e g e l , H . S . , D r u r y , L . N . , a n d W . C . P a t t e r s o n , 1 9 7 3 . B o n e C h a r a c t e r i s t i c s a n d G r o w t h o f B r o i l e r s H o u s e d i n P l a s t i c C o o p s o r o n L i t t e r i n M o d e r a t e a n d H i g h T e m p e r a t u r e s . 4 t h . E u r o p . P o u l t r y C o n f . p p . 1 5 9 - 1 6 4 . 92 S i l l e r , W.G., 1970. T i b i a l D y schondroplasia i n the Fowl. J . Path. 101:39-46. Sim, J.S., and J . J . Cruickshank, 1985. C h a r a c t e r i z a t i o n of Leg D i s o r d e r s and E t i o l o g y i n B r o i l e r C h i c k s . Proc. The 3rd. AAAP Animal Science Congress, Seoul, Korea, 1:537-539. Simons, P.CM., 1982. E f f e c t of L i g h t i n g Regimes on Twisted Legs, Feed Conversion and Growth of B r o i l e r Chickens. P o u l t r y S c i . 61:1546 ( A b t r . ) . Soares, J.H., 1984. Calcium Metabolism and I t s C o n t r o l - A Review. P o u l t r y S c i . 63:2075-2083 Somes, R.G., 1969. Genetic P e r o s i s i n the Domestic Fowl. J . Hered. 60:163-166 Summers, J.D., Leeson, S., and A.E. Ferguson, 1978. Performance and Leg C o n d i t i o n s of Caged and F l o o r Reared B r o i l e r s Fed D i e t s D e f i c i e n t i n S e l e c t e d Vitamins and M i n e r a l s . P o u l t r y S c i . 57:506-512. Sunde, M.L., and H.F. DeLuca, 1978. The E s s e n t i a l i t y of Vitamin D m e t a b o l i t e s f o r embryonic Chick Development. Science 200:1067-1069. S t a t i s t i c a l A n a l y s i s System (SAS), 1982. SAS User's Guide: S t a t i s t i c s 1982 E d i t i o n . SAS I n s t i t u t e Inc., USA. S t a t i s t i c s Canada - A g r i c u l t u r e S t a t i s t i c s D i v i s i o n , 1983. Pr o d u c t i o n of P o u l t r y and Eggs. M i n i s t e r of Supply and S e r v i c e s Canada, J u l y , 1984. S t e e l , R.G.D., and J.H. T o r r i e , 1980. P r i n c i p l e s and Procedures of S t a t i s t i c s . 2nd. Ed. McGraw-Hill, New York, NY.. Westmoreland, N., and W.G.Hoekstra, 1969. P a t h o l o g i c a l D e f e c t s i n the E p i p h y s e a l C a r t i l a g e of Z i n c - D e f i c i e n t C h i c k s . J . Nutr. 98:76-82. Wilgus, H.S. J r . , N o r r i s , L . C , and G.F. Heuser, 1936. The r o l e of C e r t a i n Inorganic Elements i n the Cause and Pr e v e n t i o n of P e r o s i s . Science 84:252-253 Wilson, J.L., Weaver, W.D. J r . , Beane, W.L., and J.A. Cherry, 1984. E f f e c t s of L i g h t and Feeding Space on Leg Abnormaities i n B r o i l e r s . P o u l t r y S c i . 63:564-567. Wise, D.R., 1982. S k e l e t a l D i s o r d e r s . In: P o u l t r y D i s e a s e s . 2nd. ed. Eds. R.F. Gordon and F.T.W. Jordan, B a l l i e r e T i n d a l l : London, pp.236-246. 93 Wise, D.R., 1978. N u t r i t i o n - D i s e a s e I n t e r a c t i o n s of Leg Weakness i n P o u l t r y . In: Recent Advances i n Animal N u t r i t i o n Ed., W. Haresign and D. Lewis. Butterworths, London Boston, 1979. pp.41-57. Wise, D.R., 1975. S k e l e t a l A b n o r m a l i t i e s i n Table P o u l t r y -A Review. Avian Path. 4:1-10. Wise, D.R., F u l l e r , M.K., and G.A. Thorton, 1974. Experimental Reproduction of Turkey Syndrome '65 with Mycoplasma M e l e a g r i d i s . Res. Vet. S c i . 17:236-241. Wise, D.R., 1973. The Incidence and E t i o l o g y of Avian S p o n d y l o l i s t h e s i s ( k i n k y - b a c k ) . Res. Vet. S c i . 14:1-10 Wise, D.R., Jennings, A.R., and D.E. Bostock, 1973a. P e r o s i s i n Turkeys. Res. Vet. S c i . 14:167-172. Wise, D.R., Boldero, M.K., and G.A. Thorton, 1973b. The Pathology and E t i o l o g y of Turkey Syndrome '65 (TS '65). Res. Vet. S c i . 14:194-200. Wise, D.R., 1971. S t a p h y l o c o c c a l O s t e o m y e l i t i s of the Avian V e r t e b r a l Column. Res. Vet. S c i . 12:169-171. Wise, D.R., 1970. S p o n d y l o l i s t h e s i s (kinky-back) i n B r o i l e r Chickens. Res. Vet. S c i . 11:447-451. Wise, D.R., and A.R. Jennings, 1973. The Development and Morphology of the Growth P l a t e s of Two Long Bones of the Turkey. Res. Vet. S c i . 14:161-166. Wise, D.R., and A.R. Jennings, 1972. Dyschondroplasia i n Domestic P o u l t r y . Vet. Rec. 91:285-286. Wolbach, S.B., and D.M. Hegsted, 1952. Endochondral bone growth i n the Chick. AMA, Arch Path., 54(1):1-12. Wolbach, S.B., and D.M. Hegsted, 1952. Vitamin A D e f i c i e n c y i n the Duck. S k e l e t a l Growth and C e n t r a l Nervous System. Arch. P a t h o l . 54:548-557. Young, R.J., Edwards, H.M. J r . , and M.B. G i l l i s , 1958. S t u d i e s on Z i n c i n P o u l t r y N u t r i t i o n . 2. Zinc Requirement and D e f i c i e n c y Symptoms of C h i c k s . P o u l t r y S c i . 37:1100-1107. Y u i l e , C.L., Chen, P.S., and H.B. Bosmann, 1967. A n t i r a c h i t i c S t e r o l s i n C h i c k s . Arch. P a t h o l . 83:241-250. 94 APPENDIX 95 T a b l e I R e g r e s s i o n A n a l y s i s of P r o d u c t i o n Parameters f o r D i e t over B i r d Age. Dependant V a r i a b l e Source df Mean Square 1 P>F Body Wei ght Model 5 Diet 1 Day*Diet 2 Day 2 * D i e t 2 E r r o r 54 1397430.679 0.002 30467.467 202542.110 2202.095 634.59 0.00 13.84 45.99 0.0001 0.9993 0.0001 0.0001 Feed Consumption Model D i e t Day*Diet E r r o r 1 2 56 1138350.364 754.657 1707427.600 1211.020 939.99 0.62 1409.91 0.0001 0.4332 0.0001 Incidence of Leg A b n o r m a l i t i e s 2 Model D i e t Day*Diet E r r o r 1 2 56 1408.506 0.013 2008.412 70.974 19.85 0.0001 0.00 0.9890 28.30 0.0001 Type I I I SS were used the model parameters. to c a l c u l a t e the Mean Squares for 2 Data was a r c s i n transformed p r i o r to a n a l y s i s . 96 T a b l e II R e g r e s s i o n A n a l y s i s o f P r o d u c t i o n P a r a m e t e r s f o r D e n s i t y o v e r B i r d A g e . D e p e n d a n t V a r i a b l e S o u r c e d f M e a n S q u a r e 1 P > F B o d y W e i g h t M o d e l 5 D e n s i t y 1 D a y * D e n s i t y 2 D a y 2 * D e n s i t y 2 E r r o r 5 4 1 4 0 5 9 9 5 . 2 8 1 7 . 2 6 3 0 3 4 0 . 2 2 1 0 2 0 3 7 . 1 5 1 4 0 9 . 0 7 9 9 7 . 8 1 0 . 0 1 2 1 . 5 3 7 2 . 4 1 0 . 0 0 0 1 0 . 9 1 0 0 0 . 0 0 0 1 0 . 0 0 0 1 F e e d C o n s u m p t i o n M o d e l 3 D e n s i t y D a y * D e n s i t y E r r o r 5 6 1 1 4 3 9 1 9 . 5 2 1 2 5 3 . 3 7 0 . 0 0 0 1 1 1 5 5 . 7 4 0 . 1 7 0 . 6 8 0 0 2 1 7 1 0 2 8 1 . 4 0 1 8 7 3 . 9 3 0 . 0 0 0 1 9 1 2 . 6 7 I n c i d e n c e o f L e g A b n o r m a l i t i e s ' M o d e l 5 D e n s i t y 1 D a y * D e n s i t y 2 D a y 2 * D e n s i t y 2 E r r o r 5 4 9 0 4 . 4 1 3 . 2 3 6 2 4 . 9 6 2 4 9 . 3 3 6 8 . 1 1 1 3 . 2 8 0 . 0 5 9 . 1 8 3 . 6 6 0 . 0 0 0 1 0 . 8 2 0 0 0 . 0 0 0 4 0 . 0 3 0 0 1 T y p e I I I S S w e r e u s e d t o c a l c u l a t e t h e M e a n S q u a r e s f o r t h e m o d e l c o m p o n e n t s . 2 D a t a w a s a r c s i n t r a n s f o r m e d p r i o r t o a n a l y s i s . 97 T a b l e I I I A n a l y s i s o f V a r i a n c e o n S e v e r i t y S c o r e s o f Leg A b n o r m a l i t i e s . A g e ( D a y s ) S o u r c e d f M e a n S q u a r e F P > F 21 M o d e l 3 0 . 3 5 1 9 0 . 8 1 0 . 5 2 D i e t 1 0 . 3 5 1 9 0 . 0 2 0 . 8 9 D e n s i t y 1 0 . 9 0 7 5 2 . 0 8 0 . 1 8 D i e t * D e n s i t y 1 . 0 . 1 A 0 8 0 . 3 2 0 . 5 8 E r r o r 8 0 . A 3 6 7 28 M o d e l 3 0 . 5 9 6 A 1 . 5 6 0 . 2 7 D i e t 1 0 . 2 A 0 8 0 . 6 3 0 . A 5 D e n s i t y 1 1 .5A08 A . 0 3 0 . 0 8 D i e t * D e n s i t y 1 0 . 0 0 7 5 0 . 0 0 2 0 . 8 9 E r r o r 8 0 . 3 8 2 5 98 T a b l e IV R e g r e s s i o n A n a l y s i s of Body Weight and Morphometric parameters over age wi th body weight as a c o v a r i a t e . Dependant Source df Mean S q u a r e 1 F P>F V a r i a b l e Body Weight T i b i a l Length Condyle Groove Depth Condyle Groove Width T i b i a l Diameter Model 6 22589885. 742 1356. 31 0. 0001 Leg 2 135130. 984 8. 11 0 . 0006 Week*Leg 2 242720. 649 14. 57 0. 0001 Week 2 *Leg 2 268897. 877 16. 14 0 . 0001 E r r o r 87 16655. 443 Model 7 110015. 869 25711. 08 0. 0001 Leg 2 622. 929 145. 58 0 . 0001 Week*Leg 2 333. 374 77. 91 0. 0001 Week 2 *Leg 2 73. 149 17. 10 0 . 0001 BWT 1 301. 782 70. 53 0. 0001 E r r o r 86 4. 279 Model 7 184. 006 2388. 90 0. 0001 Leg 2 0 . 938 12. 18 0 . 0001 Week*Leg 2 0 . 785 10. 20 0. 0001 Week 2 *Leg 2 0 . 295 3. 84 0 . 0254 BWT 1 0. 308 4. 00 0. 0486 E r r o r 86 0 . 077 Model 7 3849. 866 12554. 43 0. 0001 Leg 2 32. 444 105. 80 0. 0001 Week*Leg 2 9. 667 31. 53 0. 0001 Week 2 *Leg 2 5. 366 17. 50 0 . 0001 BWT 1 20. 074 65. 46 0. 0001 E r r o r 86 0 . 307 Model 7 704. 296 3938. 15 0. 0001 Leg 2 2. 994 16. 74 0. 0001 Week*Leg 2 1. 623 9. 07 0. 0003 Week 2 *Leg 2 0 . 665 3 . 72 0 . 0282 BWT 1 9. 091 50. 83 0. 0001 E r r o r 86 0 . 179 99 T a b l e I V , C o n t i n u e d f r o m p r e v i o u s p a g e . R e g r e s s i o n A n a l y s i s o f B o d y W e i g h t a n d M o r p h o m e t r i c p a r a m e t e r s o v e r a g e w i t h b o d y w e i g h t a s a c o v a r i a t e . D e p e n d a n t V a r i a b l e S o u r c e d f M e a n S q u a r e 1 P > F P e r c e n t A s h 2 M o d e l L e g W e e k * L e g BWT E r r o r 2 2 1 88 27274.743 26910.03 4590.285 4528.91 27.622 11.908 1.014 27.25 11.75 0.0001 0.0001 0.0001 0.0009 P e r c e n t C o r t i c a l T h i c k n e s s 2 M o d e l L e g W e e k * L e g BWT E r r o r 2 2 1 88 14691.637 3029.488 44.161 24.492 3.123 4704.19 970.03 14.14 7.84 0.0001 0.0001 0.0001 0.0063 1 T y p e III S S w e r e u s e d t o c a l c u l a t e t h e M e a n S q u a r e s f o r t h e m o d e l p a r a m e t e r s . 2 D a t a w a s A r c s i n t r a n s f o r m e d p r i o r t o a n a l y s i s . 100 Table V. Main E f f e c t Means of Vitamin D3 and Cage Density on Pro d u c t i o n Parameters . Parameter B i r d D i e t 2 D e n s i t y 3 SEM 4 Age (weeks) C o n t r o l Excess Low High Body Weight (g) 1 37.1 36.6 36.9 36.8 0.2 7 148.6 138.7 143.5 143.8 4.4 14 338.1 326.9 338.8 326.1 7.6 21 647.0 645.0 680.6 611.1 18.8 28 966.0 971.7 1018.5 919.2 13.6 Feed Consumption ( g / b i r d ) 7 129.6 117.4 126.3 120.7 4.0 14 292. 7 288.0 298. 5 282. 2 8.8 21 494.3 500.1 530.3 464.2 13.5 28 640.4 669. 5 679. 3 630.6 7.4 % Incidence Leg A b n o r m a l i t i e s 1 0 0 0 0 0 7 5:8 5.8 5.0 6.7 1.4 14 7.5 12.5 8.3 11.7 1.7 21 16.7 15.0 13.3 15.8 3.3 28 13.3 25.0 23.3 19.2 2.9 There were no s i g n i f i c a n t D i e t * D e n s i t y i n t e r a c t i o n s (p>0.05) C o n t r o l s u p p l i e d 400 ICU v i t a m i n D3 /kg f e e d ; E x c e s s s u p p l i e d 4000 ICU vitamin D3 /kg feed. High Density, 340 cm 2 / b i r d ; Low Density, 680 cm 2 / b i r d . +/- Standard E r r o r of the Mean. Table VI Mean Values for Morphometric Parameters, Tibial Ash and % Cortical Thickness (+ Standard Error of the Mean) PARAMETERS MEASURED B i rd Body T i b i a l Condyle Condyle T i b i a l C o r t i c a l T i b i a l Age Weight Length Groove Groove Diameter Th ickness Ash (weeks) (g) (mm) Depth Width (mm) (%) (%) (mm) (mm) N* A* N A N A N 2 337 273 61.07 59.30 2.45 2.10 12.36 11.00 4.34 4.60 26.0 27.2 40.9 39.3 (+/- 6) (+/- 0.27) (+/- 0.02) (+/- 0.09) (+/- 0.05) (+/- 0.3) (+/- 0.3) 3 652 494 75.59 73.32 3.19 2.92 14.60 14.62 5.59 5.87 26.3 23.5 41.3 40.0 (+/- 15) (+/- 0.48) (+/- 0.17) (+/- 0.11) (+/- 0.06) (+/- 0.5) (+/- 0.3) 4 1029 942 89.98 87.87 3.74 3.70 16.81 16.82 6.89 6.50 20.9 20.3 37.5 37.2 (+/- 14) (+/- 0.25) (+/- 0.05) (+/- 0.13) (+/- 0.09) (+/- 0.3) (+/- 0.3) 5 1433 1387 101.70 100.87 4.06 3.97 18.76 19.77 8.38 8.93 20.5 21.2 37.1 35.5 ( + /- 26) (+/- 0.60) (+/- 0.04) (+/- 0.11) (+/- 0.10) (+/- 0.6) (+/- 0.2) 6 1984 1176 116.27 101.80 4.86 4.00 20.49 20.10 9.61 8.62 19.7 18.4 37.7 32.6 (+/- 39) (+/- 0.78) (+/- 0.07) (+/- 0.18) (+/- 0.13) (+/- 0.5) (+/- 0.4) N, normal b i r d s ; A, abnormal b i r d s . "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0096057"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Food Science"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Morphometric and radiographic characterization of leg disorders in broiler chickens"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/24601"@en .