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Morphometric and radiographic characterization of leg disorders in broiler chickens Cruickshank, John Johnston 1985

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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 . 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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 . 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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 . 

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