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Strain differences in embryonic and early chick growth Iton, Laurence Eric 1962

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STRAIN DIFFERENCES IN EMBRYONIC AND EARLY CHICK GROWTH  by LAURENCE ERIC ITON B.S.A., University of B r i t i s h Columbia, 1953  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN AGRICULTURE  i n the Department of Poultry Science  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA AUGUST 1962 ;  In presenting  t h i s thesis i n p a r t i a l f u l f i l m e n t of  the requirements f o r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference  and study.  I further agree that permission  for extensive copying of t h i s thesis f o r scholarly purposes may granted by the Head of my Department or by his  be  representatives.  It i s understood that copying or publication of this thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  Poultry Science  The University of B r i t i s h Columbia, Vancouver 8, Canada. Date  August 13,  1962  ii  ABSTRACT  The  e x t e n t t o w h i c h e g g w e i g h t m o d i f i e s g e n e t i c d i f f e r e n c e s i n body-  w e i g h t o f t h e embryo a n d c h i c k a n d t h e c o r r e l a t i o n b e t w e e n r a t e and p o s t - h a t c h i n g growth r a t e were i n v e s t i g a t e d . i n g the r e l a t i o n s h i p s between chick;  T h i s was  c e n t a g e g r o w t h r a t e o f embryo a n d c h i c k ;  and  b r y o n i c growth r a t e and p o s t - h a t c h i n g growth  c o n d u c t e d on f i v e  o f t h e s t r a i n s were b r e d f o r meat,  (k)  (3) s t r a i n a n d p e r -  s t r a i n s a n d one  mediate type,  The  m a l e s o f one W h i t e L e g h o r n s t r a i n w i t h f e m a l e s o f t h e o t h e r .  Two  Cornish);  a n d one was  s t r a i n - c r o s s was  w e i g h t s w e r e r e c o r d e d f o r o v e r 2,200 e g g s .  em-  strain-cross.  (White Plymouth Rock and White  (White-New H a m p s h i r e ) .  and  rate.  (White Leghorns);  an  inter-  derived from mating Individual  egg  Between n i n e and e i g h t e e n embryos  o f e a c h c a t e g o r y w e r e w e i g h e d f r o m e a c h o f two  c a t e g o r y were weighed  done b y s t u d y -  t h e r e l a t i o n s h i p between  two w e r e b r e d f o r h i g h e g g p r o d u c t i o n ,  e i g h t e e n t h day o f i n c u b a t i o n .  growth  ( l ) e g g w e i g h t a n d b o d y w e i g h t o f embryo  (2) s t r a i n a n d b o d y w e i g h t o f embryo a n d c h i c k ;  T h i s s t u d y was  embryonic  incubators from the n i n t h t o the  Between f i f t e e n and t h i r t y - t h r e e  chicks of  each  a t h a t c h i n g and a t w e e k l y i n t e r v a l s f o r t h r e e weeks.  A n a l y s e s o f v a r i a n c e o f embryonic w e i g h t s , c h i c k w e i g h t s , and  embry-  o n i c o r c h i c k w e i g h t s e x p r e s s e d as p e r c e n t a g e s o f egg w e i g h t were done.  Anal-  y s e s o f v a r i a n c e were a l s o done on e m b r y o n i c Coefficients of correlation  ( r ) between  and p o s t - h a t c h i n g growth  egg w e i g h t and e m b r y o n i c o r  rates.  chick  w e i g h t and a l s o  c o e f f i c i e n t s o f r e g r e s s i o n o f c h i c k w e i g h t on egg w e i g h t were  computed.  c o r r e l a t i o n between  The  was e s t i m a t e d .  embryonic and p o s t - h a t c h i n g growth  rates  iii  From the results of the above tests i t was concluded that:  (l)  Differences i n embryonic weights among the strains were due to differences i n inherent genetic factors;  (2)  Egg weight exerted a temporary measurable  influence on embryonic and chick weight, the effect being greatest at hatching;  (3)  Differences i n post-hatching  growth rate among the strains were  probably due to differences i n n u t r i t i o n a l factors which contributed to a more e f f i c i e n t u t i l i z a t i o n of nutrients by the heavy type chicks; Approximately 65 per cent of the v a r i a t i o n i n post-hatching  and (k)  growth rate to  three weeks of age was dependent on the v a r i a t i o n i n growth rate during the nine- to fourteen-day incubation period.  The estimate of c o r r e l a t i o n bet-  ween growth rate during these two periods was, however, not precise.  viii  ACKNOWLEDGEMENT  The writer wishes to express h i s indebtedness to Mr. Herbert E l l i s who assisted i n weighing and setting eggs, and extracting embryos.  The writer also wishes to express apprec-  i a t i o n f o r the assistance given by Mr. Keith Eccleston who read the manuscript and made valuable suggestions about presentat i o n of the t h e s i s .  iv  TABLE OF CONTENTS  Page  INTRODUCTION  1  REVIEW OF THE L I T E R A T U R E  1  MATERIALS AND METHODS  7  S T A T I S T I C A L METHODS  9  RESULTS AND D I S C U S S I O N  13  CONCLUSIONS  2k  BIBLIOGRAPHY  25  LIST OF TABLES  Table  Page  1  Mean Egg Weights i n Grams  27  2  Mean Embryonic and Chick Weights i n Grams  28  3a  V a r i a b i l i t y of Embryonic Weights  29  3b  V a r i a b i l i t y of Embryonic Weights  31  k  Total Number of Embryos Extracted  33  5a  V a r i a b i l i t y of Chick Weights  3^+  5b  V a r i a b i l i t y of Chick Weights  35  6a  Results of B a r t l e t t ' s Test of Homogeneity of Variance  36  6b  Results of B a r t l e t t ' s Test of Homogenity of Variance  37  7  Analyses of Variance of Embryonic and Chick Weights  38  8  Results of Duncan's New Multiple-Range Test Used On Mean Embryonic and Chick Weights i n Grams  9 10  Analyses of Variance of Egg Weights  39 ^0  Embryonic and Chick Weights Expressed as Percentages of Egg Weight  kl  Results of Tukey's Test f o r Non-Additivity  Analyses of Variance of Embryonic and Chick Weights Expressed as Percentages of Egg Weight  Results of Duncan's New Multiple-Range Test Used On Mean Embryonic and Chick Weights Expressed as Percentages of Egg Weight  C o e f f i c i e n t s of Correlation (r) Between Egg Weight and Embryonic or Chick Weight C o e f f i c i e n t s of Correlation (r) Between Egg Weight and Embryonic or Chick Weight Regression C o e f f i c i e n t s : Grams of Chick Weight On Grams of Egg Weight Results of Tests f o r Linear Relationship Between InW and Time Equations Used to Plot Growth Curves Analyses of Variance of Growth Rates Analyses of Variance of Growth Rates  vii  LIST OF FIGURES  Figure  1  Page  A r i t h - l o g Graphs of Growth Rate Obtained From the Equation: InW = InA + kt  2  52  A r i t h - l o g Graphs of Growth Rate Obtained From the Equation: InW = InA + kt  53  3a  Arithmetic Graphs of Growth Rate  5k  3b  Arithmetic Graphs of Growth Rate  55  ka  Arithmetic Graphs of Growth Rate  56  kh  Arithmetic Graphs of Growth Rate  57  INTRODUCTION  The ultimate size of an organism i s under the joint control of gene t i c and environmental factors.  The study of the comparative effects of gen-  e t i c and environmental influences has posed problems f o r investigators of size inheritance i n many organisms. fowl f o r such studies.  Numerous investigators have used the domestic  Some have confined t h e i r attention to the influence  of environmental factors such as egg weight and hereditary factors such as breed or s t r a i n on body weight.  A large proportion of these investigators  was interested i n the economic implications of the problem e.g. the effect of hatching-egg weight on growth of the chick to f r y e r age. selves with the post-hatching period of development.  They concerned them-  Others, whose interests  were more academic, studied the influence of egg weight and hereditary factors on embryonic growth.  The contributions of both categories of investigators  are b r i e f l y reviewed below.  REVIEW OF THE LITERATURE  One of the e a r l i e s t reports on the influence of egg weight on chick weight was submitted by Halbersleben and Mussehl (1922).  They found the av-  erage weight of the chick at hatching was 6k per cent of i n i t i a l egg weight and, at t h i r t y - f i v e days a f t e r hatching, the chicks from small eggs were approximately the same average weight as were those from large eggs.  (1928)  found the weight of chicks at hatching to be approximately  of egg weight.  Upp  68  per cent  He also found that egg weight and day-old chick weight were  unreliable indices of chick weight at two, four, and twelve weeks of age.  2  Jail  and  Heywang (1930) l i k e w i s e c o n c l u d e d t h a t , r e g a r d l e s s  weight, the percentage chick weight a t hatching too, ial  found that chick weight a t hatching egg  weight.  Byerly  breeds d i f f e r e d l i t t l e  like He  a v e r a g e d a b o u t 68 p e r  They,  cent o f i n i t -  (1930) r e p o r t e d t h a t c h i c k e m b r y o s o f d i f f e r e n t same  size.  " m a j o r d i f f e r e n c e s i n embryo s i z e among e m b r y o s o f  age c o u l d b e s a t i s f a c t o r i l y accounted f o r b y d i f f e r e n c e s i n egg s i z e " .  concluded without  proof  t a i n l y apparent by the Wiley  (l950a) o b t a i n e d  t h a t the  s e v e n t h day  e f f e c t o f e g g s i z e o n embryo s i z e i s c e r o f incubation  s m a l l eggs.  ment o f e m b r y o s a t s e v e n t y - t w o h o u r s , f o u r t e e n found no c o n s i s t e n t d i f f e r e n c e s i n w e i g h t . the  cant e f f e c t on chick s i z e a t hatching.  chicks.  weight on the  Wiley  growth o f Barred  He f o u n d t h a t a h i g h  Kosin  They r e p o r t e d  nineteen  develop-  days and  days o f i n c u b a t i o n has  P l y m o u t h Rock and  space  a signifi-  (1950b) a l s o s t u d i e d t h e  eff-  White Wyandotte This  cor-  t h i r d week a n d c o n t i n u e d t o  chick from hatching  t o twelve  that though egg s i z e f r e q u e n t l y exerted  i n f l u e n c e o n c h i c k growth, b r e e d a n d sex  d i f f e r e n c e s i n the  treme v a r i a t i o n s i n the  precluded  r e l a t i o n s h i p and  weeks  a significant  c h i c k s caused ex-  generalizations.  However,  t h e mean g r o w t h r a t e d e t e r m i n e d b y a c t u a l g a i n i n b o d y w e i g h t o f c h i c k s greater than that o f chicks from  from  l a r g e e g g s was,  i n general,  eggs.  (1961) c a r r i e d o n i n v e s t i g a t i o n s t o f r y e r a g e a n d s t u d i e d t h e  Goodwin  slightly  laid  (1952) s t u d i e d t h e i n f l u e n c e o f e g g  weight on a c t u a l body weight g a i n o f the o f age.  He s t u d i e d t h e  c o r r e l a t i o n existed a t hatching.  eta l .  I n contrast  Plymouth Rocks t h a t  d a y s , and  r e l a t i o n was m a r k e d l y r e d u c e d i n m a g n i t u d e b y t h e diminish subsequently.  1932).  However, he d i d s u g g e s t t h a t  egg s h e l l d u r i n g the l a s t two o r t h r e e  e c t o f egg  (Byerly,  eggs f r o m a s t r a i n o f B a r r e d  l a r g e eggs, and from a n o t h e r t h a t l a i d  in  tends t o be constant.  i n s i z e when d e v e l o p e d i n e g g s o f t h e  L a t e r on he p o s t u l a t e d ,  o f i n i t i a l egg  small  3  relationship between chick size at hatching and growth rate.  He found that  chick weight at hatching exerted an important effect on growth to f r y e r age. Bray and Iton (1962) studied the effect of egg weight on embryonic and posthatching weight of f i v e strains of fowl from the sixth day of incubation to eight weeks a f t e r hatching.  They ranked the strains on the basis of embry-  onic weight and determined the c o r r e l a t i o n between these ranks and rankings of the parents' body weights and egg weights.  They observed that the ranks  of embryonic weights changed from a perfect correlation with parental weight at eleven days of incubation to a perfect c o r r e l a t i o n with egg weight at hatching and returned to a close relationship with parental weights at two weeks after hatching.  They concluded that egg weight exerted a temporary  environmental influence which concealed genetic differences i n embryonic and early post-hatching growth among strains.  The above investigations indicate  that egg weight exerts a pronounced influence on growth during the l a t e stage of incubation and the early post-hatching period.  The evidence they provide  about the influence of egg weight on the early and intermediate stages of embryonic growth i s inconclusive.  Investigation of the effect of breed or s t r a i n on growth has been equally extensive as that of egg weight on growth.  Henderson (1930) measured  the wet weight, dry weight, and t o t a l nitrogen content of Dark Cornish and White Leghorn embryos from four to twenty days of incubation and found l i t t l e difference between the breeds.  Byerly (1930), i n a previously mentioned  study, used embryos of Rhode Island Reds, White Leghorns, and r e c i p r o c a l crosses between the two.  He observed that embryos of Rhode Island Reds and cross-  breds were somewhat heavier than White Leghorn embryos from the tenth day of incubation to hatching.  In eggs of the same weight from the two breeds the  embryo-size difference tended to disappear toward hatching time.  Blunn and  Gregory (1935) measured growth by weight, c e l l counts, and mitotic figure counts at seventy-two hours, fourteen days, and nineteen days of incubation. They observed a consistent difference between White Leghorn and Rhode Island Red embryos i n the rate of c e l l p r o l i f e r a t i o n .  The difference i n the number  of c e l l s per unit volume was less at nineteen days than at fourteen days or at seventy-two hours.  In spite of s i g n i f i c a n t differences i n the rate of  c e l l p r o l i f e r a t i o n , these investigators found no s i g n i f i c a n t breed differences  i n embryonic weights.  Byerly, Helsel, and Quinn (1938);  studied embryos  of White Leghorns, S i l k i e s , Rhode Island Reds, and r e c i p r o c a l crosses of S i l kies and Rhode Island Reds.  They found that during the period from the e l -  eventh to the seventeenth day embryos of heavier parents were, i n general, s l i g h t l y heavier than embryos of l i g h t e r parents, even from eggs of similar weight.  McNary, B e l l , and Moore ( i 9 6 0 ) studied the growth of inbred and  crossbred embryos of White Leghorns, Rhode Island Reds, and New  Hampshires.  They measured growth rate by counting the number of somites present a f t e r t h i r t y - e i g h t hours of incubation.  They also recorded embryo weights after  one week and two weeks of incubation. ferences i n a l l three measurements.  They reported s i g n i f i c a n t genetic d i f Egg weight had l i t t l e e f f e c t on embry-  onic weight because i t explained only 0 . 0 6 per cent of the v a r i a t i o n i n embryonic weight at one week and 3 per cent of the v a r i a t i o n at two weeks of age.  Bray and Iton (1962) likewise observed genetic differences i n embry-  onic weight.  The differences were s i g n i f i c a n t from the tenth day of incub-  5  ation onwards.  It i s evident from the foregoing review that genetic differences i n growth are discernible from the early stages of embryonic development.  These  differences were mostly differences i n actual weight of the embryos or chicks. Few investigators of size inheritance i n poultry have attempted to determine genetic differences i n growth on the basis of the percentage or r e l a t i v e rate of increase i n body weight per unit time.  Those who have attempted such com-  parisons have used mathematical formulae involving either the calculation of differences i n actual weight at two or more periods of time or the f i t t i n g of an equation to the data collected.  Lerner and Asmundson (1932) applied a  formula of the former type to the study of growth rate of Light Sussex, Anconas, and crosses of the two breeds from three to twelve weeks a f t e r hatching.  They obtained s i g n i f i c a n t genetic differences.  Asmundson and Lerner  (l933)> employing the same type of formula, found s i g n i f i c a n t differences between White Leghorn families i n rate of growth from two to eight weeks after hatching.  Other workers have applied variations of the second type of form-  u l a to the study of embryonic growth i n the domestic fowl but these applications were not designed to determine genetic differences i n growth rate i n t h i s species.  For instance, Murray (1925) and Brody (1927) were interested  i n finding l i n e a r equations that would express the r e l a t i v e rate of growth of the chicken embryo.  Byerly (1932) used a similar type of equation to demon-  strate growth rates of embryos from d i f f e r e n t genetic sources but he assumed that the rates of growth of the d i f f e r e n t types of embryos were i d e n t i c a l . Henderson and Penquite (1934) used Brody's equation to compare embryonic rates of chickens with those of turkeys, ducks and geese.  growth  6  The above review of l i t e r a t u r e indicates that both egg weight and inherent  genetic factors influence embryonic and post-embryonic growth. I t  does not, however, indicate c l e a r l y the extent to which egg weight modifies genetic differences.  Neither does i t indicate the extent to which embryon-  i c growth rate and post-embryonic growth rate are correlated. was  undertaken to investigate these problems.  This study  The purpose was to study the  relationships between ( l ) egg weight and body weight of embryo and chick; (2)  s t r a i n and body weight of embryo and chick;  growth rate of embryo and chick;  ( 3 ) s t r a i n and percentage  and (k) the relationship between embryonic  growth rate and post-hatching growth rate.  The fourth aspect of t h i s study may have p r a c t i c a l significance. Exhaustive investigations of t h i s aspect may indicate whether or not there i s a high c o r r e l a t i o n between embryonic growth rate and post-hatching growth rate. I f i t can be established that a high c o r r e l a t i o n exists then evaluation of growth rate of prospective breeding stock can be made on the basis of embryoni c growth rate.  Thus strains that are undesirable  a c t e r i s t i c can be eliminated at the embryonic stage.  with respect to t h i s charThis practice would  have the advantages of reducing rearing costs and accelerating a breeding programme .  7  MATERIALS AND METHODS  Five strains and one strain-cross were used i n t h i s study. The parent stock was part of the f l o c k of The University of B r i t i s h Columbia. The strains were of the following v a r i e t i e s :  White Plymouth Rock, White New  Hampshire, White Cornish, and White Leghorn.  The strain-cross was derived  from the mating of two White Leghorn strains.  For the sake of convenience  a l l s i x categories w i l l hereafter be referred to as strains. designated WR, WH, WC, MH, UBC, and MHxUBC, respectively.  They w i l l be MH and UBC were  White Leghorn strains, and MHxUBC was obtained from mating MH males and UBC females.  WR, WH, and WC were c l a s s i f i e d as heavy or meat types, and the White  Leghorns as l i g h t or egg types.  On the basis of body weight at sexual matur-  i t y , the parent stock was ranked i n the following ascending order of magnitude: MH, UBC, WH, WC, and WR.  Hatching eggs were collected f o r fourteen days.  Eggs were collected  at mid-morning and mid-afternoon periods and stored i n a room at approximately 55°F.  More frequent c o l l e c t i o n s were not made because the a i r temperature of  the hen houses was considered to be low enough to prevent embryonic development. The eggs were weighed d a i l y to the nearest gram.  Table 1 shows the mean egg  weights. The t o t a l egg c o l l e c t i o n of each s t r a i n was divided into twenty-two groups.  In order to minimize differences due to the effect of storage on em-  bryonic development, eggs were assigned at random to these groups i n such a way that, i n general, not more than three eggs from any day were included i n a group.  The twenty-two groups of eggs from each s t r a i n were divided into  8 two subgroups of eleven. Model 29^0 incubators.  One subgroup was incubated i n each of two Jamesway Eggs were set i n eleven trays of each machine.  were s i x sections i n each tray. chosen at random.  There  Eggs from each s t r a i n occupied one section  The trays were numbered consecutively and each was assign-  ed a p o s i t i o n i n the incubator at random.  The numbers determined the order  i n which the trays were withdrawn.  Embryos were weighed from the ninth to the eighteenth day of incubation.  One tray was withdrawn d a i l y from each incubator.  Each developing em-  bryo was removed from i t s s h e l l and separated from i t s extra-embryonic membranes by cutting the yolk stalk at i t s proximal end.  An attempt was made to re-  move as much amniotic f l u i d as possible by placing the embryo momentarily on a paper towel before weighing.  The embryo was then transferred to a balance and  weighed to the nearest one-hundredth of a gram.  The weights of any embryos  showing obvious abnormalities such as deformed beaks or undeveloped eyes were not recorded because the weights of such embryos were considered l i k e l y to bias the r e s u l t s .  Table 2 shows the mean weights of the embryos, Tables 3a and 3b  show the v a r i a b i l i t y of the weights, and Table k shows the number of embryos weighed and the number discarded.  The eleventh tray of eggs i n each incubator was candled on the nineteenth day and the f e r t i l e eggs were transferred to the hatching compartment to hatch i n d i v i d u a l l y .  On the twenty-second day the chicks were removed from  the incubators, wing-banded and weighed to the nearest gram.  The chicks from  both incubators were grouped according to s t r a i n and assigned at random to s i x compartments i n a battery brooder. three weeks of age.  They were weighed at weekly i n t e r v a l s to  Table 2 shows the mean weights of chicks and Tables 5a  and 5b show the v a r i a b i l i t y of chick weights.  9  STATISTICAL METHODS  The experimental design was that of a randomized complete-block with subsampling.  Incubators were considered to be blocks and each developing em-  bryo was considered to be a subsample of an experimental u n i t .  This design  was chosen i n order to determine whether or not there was a s i g n i f i c a n t i n teraction between incubators and strains.  Consequently incubator effects,  s t r a i n effects and incubator-strain effects were considered to be f i x e d and sampling error was used f o r t e s t i n g hypotheses concerning i n t e r a c t i o n and s t r a i n effects. From the ninth day of incubation to the eighteenth day i n c l u s i v e subsamples of nine embryos were selected at random f o r analyses of variance. the twenty-second day s i x chicks were s i m i l a r l y selected.  On  Nine embryos and  s i x chicks were the maximum numbers that could be thus selected i n order to have equal numbers from each s t r a i n .  Analyses of variance were done on embry-  onic weights, egg weights, embryonic weights expressed as percentages of egg weights, and also on growth rates.  Analyses of variance of egg weights were  done on the eggs that yielded the selected embryos or chicks.  The v a l i d i t y of the assumption of homogeneity of variances of the subsamples selected f o r analysis was v e r i f i e d by B a r t l e t t ' s t e s t .  Variances  of embryonic weights were heterogeneous on the tenth, twelfth, and thirteenth days.  Variances of embryonic weights expressed as percentages of egg weights  were heterogeneous on the tenth, thirteenth, and seventeenth days, and variances of egg weights were heterogeneous on the tenth day.  These variances were  1 0  not analyzed.  Analyses of variance were not done on the grand t o t a l of pool-  ed subsamples of egg weights because B a r t l e t t ' s test showed that the variances were heterogeneous.  The alternative approach of conducting separate analyses  of variance on egg weights sub sampled each day was resorted to because variances were homogeneous on every day except the tenth. range test as described by Steel and Torrie  ( i 9 6 0 )  Duncan's new multiplewas used to make comparisons  among s t r a i n means i n a l l analyses of variance where s i g n i f i c a n t differences were indicated.  Tukey's test f o r non-additivity was applied to the embryonic  weights expressed as percentages of egg weights i n order to determine whether or not a transformation was necessary.  Snedecor  ( 1 9 5 6 )  advocates the use of  t h i s test f o r t h i s purpose.  Another method used to examine the data was the determination of the product moment c o e f f i c i e n t s of c o r r e l a t i o n between egg weight and embryonic or chick weight.  From the ninth day of incubation to hatching c o e f f i c i e n t s were  computed separately f o r each s t r a i n and each incubator.  Separate analyses  were done i n order to compare the r e s u l t s obtained from each incubator.  Since  the chicks were separated a f t e r hatching on the basis of s t r a i n and not on the basis of the incubator i n which they were hatched, computation of the c o e f f i c ients on the l a t t e r basis was not j u s t i f i e d f o r the post-hatching period.  For  the c o r r e l a t i o n analyses the weights of a l l embryos and chicks and the weights of the eggs that yielded them were used.  C o e f f i c i e n t s of regression of chick  weight on egg weight were also computed.  A method d i f f e r e n t from those described above was adopted to examine the effect of s t r a i n on embryonic and post-hatching growth rate.  Growth rate  11  i n t h i s report means the percentage increase i n body weight at any instant. The computation of growth rate was based on the exponential function proposed by Brody (1927).  ¥ = Ae  The function i s :  k t  where ¥ = the weight of the embryo or chick at any observation point, t = the time, i . e . the day or week at which the observation was made, e = the base of natural logarithms, k = a constant which when m u l t i p l i e d by 100 gives the percentage growth rate, and A = the weight of the i n d i v i d u a l when t = 0. The parameter A has only t h e o r e t i c a l significance.  I t does not indicate the  actual weight of the zygote at time zero, the instant of f e r t i l i z a t i o n .  Ex-  t r a p o l a t i o n of t h i s value to time zero i s not j u s t i f i e d because the constant was computed from data f o r the ninth day of incubation onwards. The above function was used because i t provided a means of comparing the strains on the basis of percentage increase i n weight rather than on actual increase i n weight per unit time.  The former basis was preferred be-  cause the object of interest was increase per unit weight.  The natural log-  arithm of the function provided the equation, InW = InA -t- kt, from which the curves were plotted on a r i t h - l o g paper. by the method of l e a s t squares.  This equation was f i t t e d to the data  12  Byerly (1932) c r i t i c i z e d Brody's method of f i t t i n g a straight l i n e by inspection to points plotted on a r i t h - l o g paper. i s a poor judge of goodness of f i t . test was  He stated that the  Because of t h i s c r i t i c i s m Student's t  applied to the data to determine whether or not there was  relationship between InW  eye  a linear  and t f o r each s t r a i n .  Differences i n growth rate among the strains were tested for significance by analyzing the variance of rate of growth from day to day i n the case of embryos and from week to week i n the case of chicks.  The variables  to which the analyses of variance were applied were obtained from the equation k ^ lnw~2 - lnWj_ ^ where the subscripts 1 and 2 indicate the weights of the i n t2 " individuals at the beginning (t]_) and at the end (t2) respectively, of the period. tg - tj_ was  equal to unity i n every case.  To determine whether there was  a s i g n i f i c a n t relationship between  growth rate during the embryonic period and growth rate during the three-week post-hatching  period, product moment c o e f f i c i e n t s of c o r r e l a t i o n were comput-  ed for the following time i n t e r v a l s :  ( l ) nine to fourteen days of incubation,  and zero to three weeks a f t e r hatching;  and (2) f i f t e e n to eighteen days of  incubation and zero to three weeks a f t e r hatching.  The f i f t e e n - to  day rather than the fourteen- to eighteen-day period was  chosen because there  were no flexures i n any of the curves during the former i n t e r v a l . rates used i n t h i s analysis are presented i n Table  17.  eighteen-  The growth  13  RESULTS AND DISCUSSION  The results of B a r t l e t t ' s test of homogeneity of variance are presented i n Tables 6a and 6b, and those f o r analyses of variance of embryonic and chick weights are presented i n Table 7-  The l a s t table shows that d i f -  ferences among strains were highly s i g n i f i c a n t at a l l observation points from the ninth to the eighteenth day of incubation, but were not s i g n i f i c a n t on the twenty-second day.  S i g n i f i c a n t differences are indicated i n Table 8.  Embryos of the heavy strains were s i g n i f i c a n t l y heavier than MH embryos from the ninth to the eighteenth day.  This finding i s similar to that  of Bray and Iton (1962), who, working with embryos from the same gene pool, obtained similar s i g n i f i c a n t differences from the tenth to the seventeenth day.  WR embryos were s i g n i f i c a n t l y heavier than MHxUBC embryos from the e l -  eventh to the sixteenth day, and were s i g n i f i c a n t l y heavier than UBC embryos from the fourteenth to the eighteenth day.  ' UBC and MHxUBC embryos were gen-  e r a l l y not s i g n i f i c a n t l y heavier than MH embryos.  The average weights of the meat-type embryos were greater than those of the egg-type embryos on every day f o r which tests were performed except the ninth day of incubation.  The MH s t r a i n which ranked highest i n egg weight  ranked lowest i n embryonic weight on every day except the eighteenth day of incubation.  These results c l e a r l y demonstrate genetic differences i n embry-  onic weight from the eleventh to the eighteenth day of incubation. Table 9 shows the results of analyses of variance of egg weights based on a completely random design.  There were non-significant differences  Ik  on a l l but the eleventh and twelfth days.  Since for the most part there were  no s i g n i f i c a n t differences among egg weights, the s i g n i f i c a n t differences among embryonic weights were attributed to inherent genetic factors that i n f l u e nced growth of the embryos.  This finding i s contrary to Byerly's postulate  that major weight differences among embryos of the same age can be satisfact o r i l y accounted f o r by differences i n egg weight.  Egg weights d i d not d i f f e r s i g n i f i c a n t l y on the eighteenth day or at hatching.  Embryonic weights d i f f e r e d s i g n i f i c a n t l y on the eighteenth day, but  chick weights at hatching did not.  Consequently, i t was  concluded that egg  weight, or, more precisely, yolk weight exerted an influence on embryonic weight between the eighteenth day of incubation and hatching. ted  This was expec-  since yolk absorption occurs during t h i s i n t e r v a l , and according to J u l l  and Heywang (1930) yolk material accounts f o r 15-30  per cent to 19-92  per cent  of chick weight at hatching.  Embryonic weights expressed as percentages i n Table 10. 11.  of egg weights are shown  Results of Tukey's test f o r non-additivity are shown i n Table  This test indicated that the percentages  d i d not require transformation.  Consequently, analyses of variance were conducted on the actual percentages. Table 12 shows that there were genetic differences at a l l ages except at hatching.  On the twelfth day an i n t e r a c t i o n between incubators and strains was  present.  There was no reason to believe that t h i s type of i n t e r a c t i o n would  occur on one day only. error.  Therefore t h i s occurrence was attributed to  sampling  15  Table 13 shows that, except on the twelfth day, embryonic weights expressed as percentages of egg weight were not s i g n i f i c a n t l y d i f f e r e n t among heavy strains on the days f o r which the test was performed.  In contrast there  were s i g n i f i c a n t differences among the l i g h t strains on every day except the f i f t e e n t h and sixteenth.  The heavy strains a l l ranked higher than the l i g h t  ones on every day except the eleventh and twelfth.  The measurements of the  heavy strains were s i g n i f i c a n t l y greater than those of the MH on a l l days, but there were fluctuations i n the significance of the differences among the heavy strains and the other two l i g h t ones. i n measurement.  On a l l days the MH s t r a i n ranked lowest  These results agree substantially with those f o r actual body  weight and manifest genetic differences i n embryonic growth.  In a l l strains  chick weight averaged about 68 per cent of i n i t i a l egg weight. rees with those of Upp Heavy-type  This value ag-  (1928) and J u l l and Heywang (1930).  embryos accounted f o r a s i g n i f i c a n t l y greater percentage  of t h e i r egg weights than MH embryos d i d up to the eighteenth day but there were no s i g n i f i c a n t differences at hatching. the  This evidence suggested that  yolk absorbed by MH embryos towards the end of the incubation period rep-  resented a greater percentage of chick weight than i t d i d i n the heavy strains. This phenomenon indicates either that yolk weight accounted f o r a greater percentage of i n i t i a l egg weight i n the MH s t r a i n than i t d i d i n the heavy ones or that the heavy-type embryos u t i l i z e d a greater percentage of t h e i r yolk p r i o r to the eighteenth day than MH embryos did.  The findings of J u l l and  Heywang (1930) provide evidence to support t h i s conclusion.  These authors  calculated the mean percentage yolk weight of egg weight f o r d i f f e r e n t hens and found s i g n i f i c a n t differences between several pairs of hens.  They also  16  found that there were s i g n i f i c a n t differences i n the rate of assimilation of yolk material by the embryos from d i f f e r e n t White Leghorn hens.  C o e f f i c i e n t s of correlation (r) between egg weight and embryonic or chick weight are presented i n Tables lha and iht.  In at l e a s t one incubator  a l l the strains showed evidence of a consistent increase i n the magnitude of the c o e f f i c i e n t s as hatching time approached.  The trend to consistent i n -  crease i n magnitude began on the thirteenth day of incubation i n the WH strain. In the WE and l i g h t strains i t began on the sixteenth day, and i n the WC s t r a i n on the seventeenth day. c l i n e d thereafter.  The c o e f f i c i e n t s reached a maximum at hatching and de-  A few s i g n i f i c a n t values were obtained before the seven-  teenth day of incubation but were not part of a consistent trend and were therefore considered to have occurred by chance.  A f t e r the seventeenth day s i g n i f -  icant c o r r e l a t i o n existed f o r longer periods i n the heavy strains than i t d i d i n the l i g h t ones.  In the heavy strains c o r r e l a t i o n was s i g n i f i c a n t by at  l e a s t the eighteenth day i n one incubator and continued to be s i g n i f i c a n t at least to the end of the f i r s t week a f t e r hatching.  In contrast, c o r r e l a t i o n  i n the l i g h t strains was s i g n i f i c a n t only at hatching. p o s i t i v e c o e f f i c i e n t s existed f o r a l l strains.  At t h i s stage high  There was thus no difference  i n the duration of the period f o r which s i g n i f i c a n t values existed i n the l i g h t strains but there were differences i n the duration among the heavy strains. S i g n i f i c a n t values f o r WE existed from the seventeenth day of incubation to one week a f t e r hatching.  For WR the correlation was s i g n i f i c a n t from the  eighteenth day of incubation to one week after hatching and f o r WC s i g n i f i c a n t values were indicated from the eighteenth day of incubation to two weeks after hatching.  These results show that significance of the c o r r e l a t i o n between egg  17  weight and embryonic or chick weight was different.among the heavy strains and more pronounced i n these strains than i n the l i g h t ones.  The differences i n the duration of a s i g n i f i c a n t c o r r e l a t i o n may be associated with differences i n the stage of development at which the yolk was absorbed by the embryos and differences i n the rate at which i t was u t i l i z e d by the chicks a f t e r hatching.  Perhaps the yolk of heavy strains started pas-  sing into the i n t e s t i n e at an e a r l i e r stage than i t did i n the l i g h t ones and was  absorbed at a slower rate by the chicks of the heavy s t r a i n s .  Romanoff  (i960) reported that yolk p e r s i s t s for varying periods of time i n d i f f e r e n t chicks.  The periods, he stated, range from two to t h i r t y - f o u r or more weeks.  Table 15 shows the r e s u l t s of the analysis of regression of chick weight on egg weight.  As was expected these r e s u l t s were similar to those of  the c o r r e l a t i o n analysis. significant.  At hatching the c o e f f i c i e n t s of a l l strains were  Thereafter values of the l i g h t strains were non-significant.  At one week of age the WR c o e f f i c i e n t was s i g n i f i c a n t at the 1 per cent l e v e l , whereas the WC and WH c o e f f i c i e n t s were s i g n i f i c a n t at the 5 V  er  cent l e v e l .  At two weeks of age the WC c o e f f i c i e n t was s t i l l s i g n i f i c a n t at the 5 per cent l e v e l , whereas the others were non-significant. at the end of the t h i r d week.  A l l values were non-significant  C o e f f i c i e n t s at hatching  indicated that the i n -  crease i n chick body weight that could be expected per gram increase i n egg weight ranged from an average of 0.66 grams i n the MHxUBC s t r a i n to an average of 0.84 grams i n the WR and MH strains.  According to magnitude of regression  c o e f f i c i e n t the strains ranked i n the following ascending order: WH, UBC, WR, MH.  MHxUBC, WC,  There was thus no obvious relationship between magnitude of  c o e f f i c i e n t and type of chick i . e . meat or egg type.  18  The analyses of variance, c o r r e l a t i o n and regression considered j o i n t l y showed that s i g n i f i c a n t s t r a i n differences i n body weight existed between the ninth and eighteenth days of incubation, that any such differences which might have been present at hatching were almost e n t i r e l y masked by the effect of egg weight and that there were s t r a i n differences i n significance of the relationship between egg weight and body weight to two weeks after hatching.  The results of Student's t test which was applied to show the r e l a tionship between the natural logarithm of body weight and time are presented i n Table 16.  The test showed that there was  these two variables i n each s t r a i n .  a l i n e a r relationship between  Figures 1 and 2 demonstrate growth rate  plotted on a r i t h - l o g paper and Figures 3& "to kt demonstrate curves of growth plotted on arithmetic coordinate paper.  The curves i n Figures 1 and 2 show  f o r each s t r a i n three periods of d i f f e r e n t growth rate between the ninth day of incubation and three weeks a f t e r hatching. period was  calculated as a constant.  The rate of growth during each  For a l l strains except UBC  and MH the  periods occurred between ( l ) the ninth and fourteenth days of incubation; (2) the fourteenth and eighteenth days of incubation; weeks thereafter.  and (3) hatching and three  The second period f o r UBC was d i f f e r e n t ;  ween the fourteenth and seventeenth days of incubation. periods f o r MH were d i f f e r e n t ;  i t occurred bet-  The f i r s t and second  they occurred between the ninth and f i f t e e n t h  days of incubation and between the f i f t e e n t h and eighteenth days of incubation respectively.  These results conform with patterns observed by previous investig-  19  ators.  Brody (1927) found that the r e l a t i v e rate of growth of the chick emb-  ryo tends to remain constant during c e r t a i n i n t e r v a l s . Henderson and Brody (1927) reported that the chicken embryo passes through several d i s t i n c t stages of growth during which the percentage-rate of growth i s constant and that percentage-rate diminishes progressively from stage to stage.  They also stat-  ed that the rates of growth as well as the duration of each stage are influenced by temperature.  Romanoff (1929) suggested that there are at l e a s t three  well-defined cycles of embryonic growth In the chicken; nine and another at sixteen days of incubation.  one of these ends at  He, too, observed that a change  i n incubation temperature can s h i f t the time of occurrence of the cycles.  Hen-  derson (1930) suggested that these stages were more c l o s e l y related to attained weight than to time.  The data of the present  study indicate that the stages  were more c l o s e l y related to time than to weight, because changes i n growth rate occurred on the fourteenth day of incubation i n strains among which there were highly s i g n i f i c a n t differences i n embryonic weight. Growth rates are presented i n Table 17 and r e s u l t s of the of variance of growth rates i n Tables l 8 a and l8b.  analyses  There were no s i g n i f i c a n t  differences i n the rate of embryonic growth among strains or between heavy and l i g h t types, but there were s i g n i f i c a n t differences i n the rate of  post-hatching  growth among strains and highly s i g n i f i c a n t differences between heavy and l i g h t types.  The heavy types considered as a group grew at a s i g n i f i c a n t l y greater  rate than the l i g h t types considered as a group. The evidence so f a r considered indicates that differences i n embryoni c weights were s i g n i f i c a n t but differences i n embryonic growth rates were not  20  significant.  This s i t u a t i o n i s explicable on the basis of the nature of the  growth process.  Reproducing c e l l s tend to reproduce exponentially, i . e . at  a constant percentage rate i n a geometric progression. dividuals d i f f e r i n g i n i n i t i a l weight may  In t h i s manner two i n -  double t h e i r weights i n the same  time i n t e r v a l , but the one with the greater i n i t i a l weight w i l l be the heavi e r at the end of the i n t e r v a l .  Thus minute differences at the beginning w i l l  show up as considerable differences at a l a t e r stage. may,  Differences i n weights  therefore, be simply a r e f l e c t i o n of differences i n the sizes and, by i n -  ference, the weights of zygotes which gave r i s e to the embryos.  There are re-  ports i n d i c a t i n g that differences i n c e l l size may be responsible f o r d i f f e r ences i n t o t a l size of an organism. ers who  have found that body size was  Lerner  (1937)  n a  s  c i t e d a number of work-  roughly proportional to c e l l size.  The existence of s i g n i f i c a n t differences i n embryonic weight and nonexistence of s i g n i f i c a n t differences i n embryonic growth rate may plained i n other ways. the growth rate data was  also be  ex-  For instance i t i s possible that the test applied to not s u f f i c i e n t l y sensitive to detect such differences.  It i s also possible that differences i n growth rate were so small as to be not s i g n i f i c a n t at t h i s stage.  Another factor that might have influenced the re-  sults of the t e s t on embryonic growth rate i s that growth rate was  calculated  on the basis of average weights of d i f f e r e n t groups of embryos rather than on the same individuals from day to  day.  The l a s t factor mentioned above did not exist during the period because growth rate was  post-hatching  computed on the basis of observed weights of the  same individuals throughout t h i s period.  This may be one of the reasons f o r  s i g n i f i c a n t differences being manifest during t h i s period and not during the  21  embryonic period.  But d i f f e r e n t environmental conditions might also have had  a bearing on the magnitude of differences i n growth rate at t h i s stage. example the source of nutrients during the post-hatching  For  period was the ration  fed to the chicks whereas the source of nutrients during the embryonic period was the egg.  I t i s possible that the f a s t e r growing strains u t i l i z e d nut-  r i e n t s from the r a t i o n more e f f i c i e n t l y than the slower growing ones d i d during the post-hatching  period whereas during the embryonic period there was no  difference i n the e f f i c i e n c y of u t i l i z a t i o n of nutrients among the s t r a i n s . Another condition involving differences i n e f f i c i e n c y of u t i l i z a t i o n of nutr i e n t s during the post-hatching  period might have had some influence on the  magnitude of differences i n growth rate.  I t concerns the duration of the per-  iod i n which egg weight was s i g n i f i c a n t l y correlated with chick weight.  The  suggestion was made i n an e a r l i e r discussion that the yolk persisted for a longer period i n the heavy type chicks than i t d i d i n the l i g h t type ones. I f t h i s longer persistence d i d occur then i t i s possible that the yolk material with i t s high f a t content enabled the heavy type chicks to u t i l i z e the protein i n the r a t i o n more e f f i c i e n t l y than the l i g h t ones did.  The s i g n i f i c a n t l y  greater growth rate of the heavy type chicks probably resulted from a more eff i c i e n t u t i l i z a t i o n of protein i n the r a t i o n .  Card (1961) has reported that  during the early post-hatching weeks chicks u t i l i z e protein with increasing eff i c i e n c y as the percentage of f a t i n the diet increases.  There i s , of course,  a l i m i t to the extent to which the percentage of f a t may be increased with bene f i c i a l results.  The f i n a l phase of the i n v e s t i g a t i o n involved the determination of c o e f f i c i e n t s of c o r r e l a t i o n between embryonic growth rate and post-hatching growth rate.  The c o e f f i c i e n t of c o r r e l a t i o n (r) between growth rates f o r the  22  periods nine to fourteen days of incubation and zero to three weeks after hatching  was 0.805.  This value i s s i g n i f i c a n t l y d i f f e r e n t from zero at the 10 per  cent l e v e l , but not at the 5 per cent l e v e l where a value of 0.811 for  significance.  -0.02  and 0-95-  i s required  The 95 per cent confidence l i m i t s f o r t h i s estimate were Approximately  65 per cent of the v a r i a t i o n i n post-hatching  growth rate to three weeks of age was dependent on the v a r i a t i o n i n growth rate during the nine- to fourteen-day incubation period.  However, an estimate of  c o r r e l a t i o n with so wide a confidence i n t e r v a l i s not precise and was therefore considered to be of l i t t l e p r a c t i c a l importance.  A c o e f f i c i e n t of -0.45  was  ob-  tained f o r the periods f i f t e e n to eighteen days of incubation and zero to three weeks a f t e r hatching.  In evaluating the results of t h i s study one must bear i n mind that the sample sizes were small. on an experiment.  Small sample size imposes certain l i m i t a t i o n s  The most important of "these l i m i t a t i o n s are that ( i ) the  smaller the sample size the l e s s accurate i s an estimate of a parameter l i k e l y to be; to  and ( i i ) a test performed on a sample that i s too small i s more l i k e l y  f a i l to detect s i g n i f i c a n t differences than one performed on a sample that  i s large. Another point that must be considered i n evaluating the r e s u l t s i s that an implied assumption i n a l l the tests used to investigate differences i n embryonic weight and growth rate was that the average incubation temperature was optimum f o r a l l the strains. sults could be misleading.  Should t h i s assumption be erroneous the re-  23  If investigation of the c o r r e l a t i o n between embryonic and posthatching growth rates i s to be conducted with a view to applying the results to breeding programmes, the problem of possible differences i n optimum incubation temperature among strains w i l l have to be considered.  The importance  of t h i s consideration suggested i t s e l f when differences i n the time of occurrence of flexures i n the growth curves were observed.  Henderson and Brody  (1927) and others have shown that temperature greatly affects the position of flexures i n the growth curve of the chicken embryo and also i n the value of k, the r e l a t i v e rate of growth.  A unit change i n incubation temperature may  not  a f f e c t embryonic growth of d i f f e r e n t strains to the same extent.  Consequent-  l y i t i s conceivable that, f o r d i f f e r e n t incubation temperatures,  the correla-  t i o n between embryonic and post-hatching growth rates may vary among strains i n such a way  as to complicate interpretation of the r e s u l t s .  Such complica-  tions would have a bearing on any generalizations that may be made about the relationship.  This problem of d i f f e r e n t optimum incubation temperatures  is  a question a r i s i n g from the present study that may warrant further investigation.  2k CONCLUSIONS  The conclusions that can be drawn from the foregoing results applyonly to the embryos and chicks that were used i n t h i s study and to the conditions under which the i n v e s t i g a t i o n was (1)  conducted.  The conclusions are:  Differences i n embryonic weights among the strains from nine to fourteen days of incubation were due to differences i n i n herent genetic f a c t o r s .  (2)  Egg weight exerted a temporary measurable influence on embryonic and chick weight.  This influence was  evident from the  l a s t four or f i v e days of incubation to two weeks a f t e r hatching.  At hatching the e f f e c t of egg weight almost  completely  concealed the effect of s t r a i n on chick weight.  (3)  Differences i n post-hatching growth rate among the strains were probably due to differences i n n u t r i t i o n a l factors which contributed to a more e f f i c i e n t u t i l i z a t i o n of nutrients by the heavy type chicks.  (k)  Approximately 65 per cent of the v a r i a t i o n i n post-hatching growth rate to three weeks of age was  dependent on the var-  i a t i o n i n growth rate during the nine- to fourteen-day i n cubation period.  The estimate of correlation between growth  rate during these two periods was,  however, not precise, i . e .  O the true value of the estimate could not be established withi n narrow l i m i t s .  25  BIBLIOGRAPHY  Asmundson, V.S., and I.M. Lerner. 1933Inheritance of rate of growth i n domestic fowl. I I . Genetic v a r i a t i o n i n growth of Leghorns. Poultry S c i . 12: 250-255. Blunn, C.T., and Paul W. Gregory. 1935The embryo-logical basis of size inheritance i n the chicken. J. Exp. Zool. 70: 397-4l4. Bray, D.F., and E.L. Iton. 1962. The effect of egg weight on s t r a i n d i f ferences i n embryonic and postembryonic growth i n the domestic fowl. (Unpublished). Brody, S. 1927- Growth and development. I I I . Growth rates, t h e i r evaluation and s i g n i f i c a n c e . Univ. Missouri Agric. Exp. Sta. Res. B u l l . 97: 5-70. Byerly, T.C. 1930. The e f f e c t s of breed on the growth of the chick embryo. J. Morph. and Physiol. 50: 341-359ply.  . 1932. Growth of the chick embryo i n r e l a t i o n to i t s food supJ. Exp. B i o l . 9: 15-44.  Byerly, T.C, W.C. H e l s e l , and J.P. Quinn. 1938. Growth i n weight and c e l l number. Genetic e f f e c t s i n the chick embryo and chick. J. Exp. Zool. 78: 185-203Card, L.E. 1961. and Febiger.  Poultry production.  9"th ed., 409 P-  Philadelphia:  Lea  Goodwin, K. 1961. E f f e c t of hatching egg size and chick size upon subsequent growth rate i n chickens. Poultry S c i . 40: 1408. Halbersleben, D.L., and F.E. Mussehl. weight at hatching. Poultry S c i .  1922. Relation of egg weight to chick 1: 143-144.  Henderson, E.W. 1930. Growth and development. XVI. The influence of temperature and breeding upon the rate of growth of chick embryos. Univ. Missouri Agric. Exp. Sta. Res. B u l l . 149: 5-47Henderson, E.W., and S. Brody. 1927- Growth and development. V. The effect of temperature on the percentage-rate of growth of the chick embryo. Univ. Missouri Agric. Exp. Sta. Res. B u l l . 99: 3-HHenderson, E.W., and R. Penquite. 1934. A comparison of embryonic growth rates of chickens, turkeys, ducks and geese. 5"th. World's Poultry Congress. 2: 297-306.  26  J u l l , M.A., and B.W. Heywang. development of the chick.  1930. Yolk assimilation during the embryonic Poultry S c i . 9: 393-404.  Kosin, I.L., H. Abplanalp, J. Gutierrez, and J.S. Carver. 1952. The i n f l u ence of egg size on subsequent early growth of the chick. Poultry S c i .  31: 247-254.  Lerner, I.M. 1937domestic fowl.  Relative growth and hereditary size l i m i t a t i o n s i n the H i l g a r d i a 10: 5H-560.  Lerner, I.M., and V.S. Asmundson. 1932. Inheritance of rate of growth i n domestic fowl. I. Methods and preliminary report on r e s u l t s obtained with two breeds. Scient. Agr. 12: 652-664. McNary, H.W., A.E. B e l l , and C H . Moore, i960. The growth of inbred hybrid chicken embryos. Poultry S c i . 39: 378-384.  and  Murray, H.A. J r . Physiological ontogeny. A. Chicken embryos. I I I . Weight and growth rate as functions of age. J. Gen. Physiol. 9- 39-I+8Romanoff, A.L. 1929Science 70: 484. .  i960.  Cycles i n the prenatal growth of the domestic fowl. The avian embryo.  1305  Co. Snedecor, G.W. 1956. S t a t i s t i c a l methods. Iowa State College Press.  P-  New  York:  5"th ed., 534 p.  The Macmillan Ames:  The  Steel, R.G.D., and J.H. Torrie. i960. P r i n c i p l e s and procedures of s t a t i s t i c s . 481 p. New York: McGraw-Hill Book Co. Upp,  C.W. 1928. Egg weight, day o l d chick weight and rate of growth i n Single Comb Rhode Island Red chicks. Poultry S c i . 7: 151-155-  Wiley, W.H. 1950a. The influence of egg weight on the pre-hatching and post-hatching growth rate i n the fowl. I. Egg weight-embryonic development r a t i o s . Poultry S c i . 29: 570-574. . 1950b. The influence of egg weight on the pre-hatching and post-hatching growth rate i n the fowl. I I . Egg weight-chick weight r a t i o s . Poultry S c i . 29: 595-604.  TABLE 1  MEAN EGG WEIGHTS IN GRAMS WR 62.26  +4.35  WC 60.54  +4.42  WH 62.27  +4.90  UBC 61.73 + 3-75  MH 62.68  +4.42  —j  TABLE 2 MEAN EMBRYONIC AND CHICK WEIGHTS IN GRAMS (AVERAGES OF ALL EMBRYOS AND CHICKS WEIGHED) Days of Incubation 10  11  12  13  WR  1.55  2.52  3-47  5-51  7-29  11.16  WC  1.51  2.37  3-43  5-26  6.91  10.51 12.72  WH  1.52  2.47  3.34  5.01  6.97  10.42  1.54  2.25  3.29  4.65  6.63  9.30  MHxUBC  I.56  2.24  3-20  5-02  6.48  MH  1.35  2.11  3-04  4.20  5.65  UBC  14  15  9  Weeks After Hatching 16  13.78 17.32  17  18  22  I  2  3_  20.72  23-46  43.85  96.08 169.38 264.12  16.29  20.35  23.02  40.33  90.43  174.57 283.62  17.10  20.87  25.10  43-42  89.OO  166.52 261.30  11.88 15.73  19-50  21.46  41.78  80.65  142.12 209.65  10.00  12.21  15-55  19-46  22.84  42.38 76.90  142.76 212.05  9-04  11.66  14.99 18.34  21.47  42.12  140.47 207.06  13.26  79.69  ro  00  TABLE 3a VARIABILITY OF EMBRYONIC WEIGHTS  Day  Incubator No. of Embryos  Mean Wt (GM)  WH  WC  WR Standard Deviation  (GM)  No. of Embryos  Mean Wt  (GM)  Standard Deviation (GM)  No. of Embryos  Mean Wt (GM)  Standard Deviatioi (GM)  9  1 2  13 15  1.44 1.65  +0.17 + .54  10 16  1.47 1.54  +0.19 + .19  18 16  1.39 I.67  +0.18 + .21  10  1 2  15 Ik  2.53 2.52  + .19 + .14  14 15  2.39 2.35  + .22 + .29  14 17  2.54 2.41  + .15 + .15  11  1 2  15 14  3-57 3-37  + .42 + • 25  12 12  3-42 3.43  + .41 + .30  17 17  3.47 3-22  + .26 + .30  12  1 2  12 15  5.74 5-33  + • 47 + .40  11 13  5.65 4.93  + .29 + .56  15 18  5.19 4.86  + .59 + -75  13  1 2  16 15  7.42 7.14  +1.24 + .92  14 13  7.08 6.73  +1.22 + .54  14 18  7-37 6.66  + .92 + .59  Ik  1 2  16 13  11.28 11.01  +0.79 +1 .12  10 13  10.74 10.33  +0.94 + .81  15 17  10.65 10.22  +1.03 +1.27  15  1 2  10 13  13.91 13.68  +1 • 19 + .85  14 13  13-04 12.37  + .92 +1.10  17 16  12.82 13.73  +1.04 +1.07  16  1 2  10 9  17.06 17.62  + • 93  16 13  16.43 l6.ll  +1.31 + .91  15 17  16.74 17.43  +1.74 +1.24  +1.43  TABLE 3a (continued)  Day  Incubator  WE No. of Embryos  Mean Wt (GM)  WC Standard Deviation (GM)  No. of Embryos  Mean Wt (GM)  WH Standard Deviation (GM)  No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  IT  1 2  l4 16  20.66 20.78  +2.01 +1.98  12 10  19-90 20.89  +1.70 +1-75  17 13  21.04 20.64  +1-53 +1.01  18  1 2  15 9  23-97 22.60  +1.07 +2.51  Ik 16  23-25 22.81  +1.11 +1.66  15 17  25-24 24.97  +2.51 +2.24  00 o  TABLE 3b VARIABILITY OF EMBRYONIC WEIGHTS  Day  Incubator  UBC  MHxUBC  No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  MH  No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  9  l  2  10 11  1.48  +0..20  • 19  10 14  1.45 1.65  +0 .11 + •17  12 10  1.26 1.45  10  1 2  12 12  2.21 2.29  ,24 ,21  13 13  2.36 2.,12  +  + ,  .16 •29  11 13  2.03 2.17  11  1 2  9 12  3-32 3-27  + ,  •19 •23  14 11  3..13 3.• 30  +  • 32 .21  13 10  3-22 2.81  12  1 2  13 11  4.74 4.54  + ,  •36 ,18  14 12  5.• 13 4,•89  +  +  • 33 • 31  12 12  4.22 4.18  13  1 2  12 13  6.99 6.30  + , + .  • 71 .67  13 12  6,• 63 6,• 32  +  •25 •92  12 14  6.04 5.32  14  1 2  12 10  9.26 9.36  +1..16  9.• 93 10..06  +  •49 • 73  12 9  9-30 8.69  +  .84  10 12  +  + ,  15  1 2  11 9  II.89  13 12  12.• 33 12..07  +  •71  +1 .24  12 13  12.00 11.35  +  11.87  +1..07 + ,• 57  16  1 2  Ik  16.01 15.37  +1,.24 +1..00  13 11  15.,92 15..11  .61 +1 •51  11 13  15-37 14.68  +1 .42 +1 .04  11  1.60  + , + ,  + ,  + ,  + +  +  +  +0 •19 .08  + + +  + + + + + +  +  +  -15 -13 .18 -23 -55 -49 •39 .60 •79 • 65  • 93 .85  UJ  H  TABLE 3b (continued)  Day  Incubat or  MHxUBC  UBC No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  No. of Embryos  Mean Wt (GM)  17  1 2  13 11  19-53 19.46  +1.47 +1.64  13 13  19.61  18  1 2  9  21.97  +1.96 +2.00  12  23.60  12  21.09  14  19-30 22.20  MH No. of Embryos  Mean Wt (GM)  Standard Deviation (GM)  +1.14 +1.57  12  18.51 18.19  +1.17 +2.13  +2.17 +1.88  13 10  22.29  +I.78 +1.45  Standard Deviation (GM)  13  20.40  ro  TABLE k TOTAL NUMBER OF EMBRYOS EXTRACTED Number Weighed  Number Discarded  WR  269  k  WC  261  3  WH  323  1  UBC  227  0  MHxUBC  2^9  2  MH  237  0  CO  TABLE 5a VARIABILITY OF CHICK WEIGHTS Week  Incubat or  WR No. o f Chicks  Mean Wt (GM)  WH  WC Standard Deviation (GM)  No. of Mean Wt (GM) Chicks  Standard Deviation (GM)  No. o f Mean Wt Chicks (GM)  Standard Deviation (GM)  13 13  44.00 43.69  + 4.91 + 3.31  12 9  41.67 38.56  + 3.96 + 3-37  19 14  43.74 43.00  + 4.62 + 2.45  1  26  96.08  +11.31  21  90.43  +10.19  33  89.OO  + 7.74  2  26  169•38  +19.74  21  17^-57  +20.08  33  166.52  +16.94  3  26  264.12  +28.18  21  283.62  +36.22  33  261.30  ±37-50  0  1 2  OJ  4="  TABLE 5b VARIABILITY OF CHICK WEIGHTS Week  Incubat or No. of Chicks  Mean Wt (GM)  MH  MHxUBC  UBC Standard Deviation (GM)  No. of Chicks  Mean Wt (GM)  Standard Deviation (GM)  No. of Chicks  Mean Wt (GM)  Standard Deviation (GM)  10 8  41.80 41.75  + 3-03 + 3.67  12 9  41.67 43-33  + 1.89 + 2.36  10 6  42.30 41.83  + 2.86 + 3-39  1  IT  80.65  + 7-37  21  76.90  + 7-10  16  79.69  + 5-00  2  17  142.12  +13.56  21  142.76  +15•20  15  140.47  +10.08  3  17  209.65  +24.28  21  212.05  +27.49  16  207.06  +14.71  0  1 2  LO  TABLE 6a RESULTS OF BARTLETT'S TEST OF HOMOGENEITY OF VARIANCE ~  Day  f o r 5 degrees of freedom = 11.1  Embryo or Chick Weight  Embryo or Chick Weight as $ Egg Weight  Egg Weight  1-90  1.33  5-39  9 10  i6.07  11  7-20  12 13  2  2.39  M  154. k6  m  4.23 M  19.89**  10.99  12.15* 2.08 8.73  17.90**  5.39  Ik  9.5+  10.72  3.26  15  1-72  7.13  3-35  16  7-50  0.79  3-55  17  9.96  13.60*  4.06  18  8.36  5-66  3-91  22  3-48  5.18  2.06  AA A  S i g n i f i c a n t at P=0.01 Significant at P=0.05  TABLE 6b RESULTS OF BARTLETT'S TEST OF HOMOGENEITY OF VARIANCE  X  .05  f o r 5 degrees o f freedom = 11.1  X  2  9-14- days incubation  15-18 days incubation  10.59  4.14-  0-3 weeks post-hatching 3-93  TABLE 7 ANALYSES OF VARIANCE OF EMBRYONIC AND CHICK WEIGHTS Source of Variation  Mean Squares  Degrees of Freedom  Day 9  11  14  15  16  17  18  22  0.35  k.69  1.00  3.86  0.01  20.23  1-39  Incubators(i)  1  1. .17  Strains  5  0.  5  0..01  0.19  0.60  1.10  2.59  3.26  6.19  26.92  0.87  1.07  1.63  3.18  4.46  11.62  17.67  14.84  21.40  29.94  I x S  (S)  1 j j jfcfe  o.4o**  Sampling Error  96 „ (6o)  0..03  0.10  Total  107 „  1. • 35  1.04  M #  11.51**  23.49**  11.67**  30.89**  11.12  #  (7D  #  S i g n i f i c a n t at P=0.01 S t a t i s t i c f o r 22nd day.  61.77  51.05  TABLE 8 RESULTS OF DUNCAN'S NEW MULTIPLE-RANGE TEST USED ON MEAN EMBRYONIC AND CHICK WEIGHTS IN GRAMS Age (Days) 9 11 14  15  16  17 18 22  Standard Error of The Mean MH 1.34  1.46  WH 1.54  MHxUBC 1.56  UBC 1.56  3.04  MHxUBC 3.18  UBC 3.28  WH 3-33  3-42  MH 8.95  UBC 9.27  MH  WC  WC  WR 1.56.  +0.04  WR 3-43  +0.08  MHxUBC 10.01  WH 10.30  WC 10.50  WR 11.11  +0.22  MHxUBC 12.18  WC 12.54  WH 13.34  WR 13.69  +0.24  WC 16.48  WH 16.62  WR 17.38  +0.31  MH 11.76  UBC 11.81  MH 15.12  MHxUBC 15-32  MH 18.03  UBC 19.39  MHxUBC 19.81  WC 20.73  WR 20.88  WH 20.98  +0.42  UBC 21.38  MH 21.46  MHxUBC 22.79 .  WC 23.10  WR 23.18  WH 24.92  +0.50  MH 41-75  WH 41-75  UBC 42.17  MHxUBC  WR 44.25  +O.98  UBC 15.82  WC 41.83  42.42  Any values not underscored by the same l i n e are s i g n i f i c a n t l y d i f f e r e n t . Any values underscored by the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t .  TABLE 9 ANALYSES OF VARIANCE OF EGG WEIGHTS  Source of Variation  Degrees of Freedom  Mean Squares Day 11  12  14.54  73.86**  45-13*  21.40  23-93  21.16  10.25  43.47  52.51  6.11  16.89  20.91  18.63  16.24  15.68  16.79  17.45  22.23  25.26  18.88  31-43  94.77  63.76  37-64  39.61  37-95  27.70  65-70  77-77  24.99  9 Strains  13  14  15  16  17  18  22  (5)*  Error  (66)# 107 „ (7D #  AA A #  Significant at P=0.01 S i g n i f i c a n t at P=0.05 S t a t i s t i c f o r 22nd day  TABLE 10 EMBRYONIC AND CHICK WEIGHTS EXPRESSED AS PERCENTAGES OF EGG WEIGHT (AVERAGES OF ALL EMBRYOS WEIGHED) Days of Incubation  22  15  16  17  18  18.10  21.98  27.41  33-30  38.40  68.43  11.36  17.12  20.70  26.32  34.25  37-73  67.44  7-93  11.43  16.80  21.34  27.60  33.62  39.63  68.47  5.49  7-46  10.83  15-04  18.89  25.19  31.59  34.17  67.44  3.56  5.32  8.28  10.52  16.40  20.00  25.27  31.25  36.80  68.73  3.35  4.78  6.69  9.34  14.29  18.62  23.96  29.80  33-43  67.94  9  10  11  12  WR  2.4-7  3.96  5.52  8.92  11.50  WC  2.4-8  3.98  5.63  8.88  WH  2.46  3.98  5.23  UBC  2.49  3.66  MHxUBC  2.49  MH  2.11  13  14  4=-  H  TABLE 11 RESULTS OF TUKEY'S TEST FOR NON ADDITIVITY (EMBRYONIC AND CHICK WEIGHTS EXPRESSED AS PERCENTAGES OF EGG WEIGHT) Mean Squares Degrees of Freedom  Day 9  Error  10  11  12  13  Ik  15  16  17  18  22  • 03  .07  .02  .16  .21  .90  .09  2.52  3.38  3-97  5.19  12.17  96  (6o)# Non-Additivity For Testing  #  1  .01  .01  .08  • 72  95 (59)#  .11  .21  M  .89  S t a t i s t i c f o r 22nd day.  12.  kk  4.82  TABLE 12 ANALYSES OF VARIANCE OF EMBRYONIC AND CHICK WEIGHTS EXPRESSED AS PERCENTAGES OF EGG WEIGHT  Mean Squares  Degrees of Freedom  Source of Variation  Day 11  3.05  Incubators ( i ) Strains  (s)  0.08  10.99  1.71*  17-23*  k.ko  9.76  18  22  28.76  5.80  34.01™  IO6.52*  8.20  2.34  4.23  7.12  15.22  4.07  0.43  0.1  3-35  3-93  5-14  12.32  4.74  3-00  31.81  53.17  48.41  56.03  162.82  22.81  0.05  0.78  Sampling . Error  96 .. (60 F  0.11  Total  107 «(7lF  3-59  S i g n i f i c a n t at P=0.05 S i g n i f i c a n t at P=0.01 S t a t i s t i c f o r 22nd day  16  2.70*  5  A M. #  15  35.85  0.38  I x S  14  38.50*  5  A  12  M  TABLE 13 RESULTS OF DUNCAN'S NEW MULTIPLE-RANGE TEST USED ON MEAN EMBRYONIC AMD CHICK WEIGHTS EXPRESSED AS PERCENTAGES OF EGG WEIGHT Age (Days)  Standard E r r o r o f The Mean  9  MH 3-38  MHxUBC 3.50  UBC 3-66  3.87  WH 4.05  WR 4.08  +0.08  11  MH 4.74  WH 5.18  MHxUBC 5.26  WR 5.38  UBC 5-53  WC 5.60  +0.16  MH 6.52  UBC 7.45  WH 7.80  MHxUBC 8.35  WC 9.01  WR 9.06  +0.23  MH 14.13  UBC 15.09  MHxUBC 16.33  WH 16.71  WC 17.58  WR 17.95  +0.43  15  MH I8.56  UBC 18.62  MHxUBC 19.93  WC 20.69  WH 21.32  WR 21-99  +0.47  16  MH 24.08  MHxUBC 24.98  UBC 25.32  WC 26.75  WH 27.00  WR 27.64  +0.54  MH 33-20  UBC 34.22  MHxUBC 36.86  WR 37-93  WC 38.40  WH 39-30  +0.83  MH 67.51  WH 67.82  WC 68.07  UBC 68.14  MHxUBC 68.85  WR 69.78  +0.62  12 14  18 22  wc  Any values not underscored by the same l i n e are s i g n i f i c a n t l y Any values underscored by the same l i n e are not s i g n i f i c a n t l y  different. different.  TABLE l i m COEFFICIENTS OF CORRELATION (r) BETWEEN EGG WEIGHT AND EMBRYONIC OR CHICK WEIGHT Age  WR Inc 1  9 Days  WC Inc 2  Inc 1  WH Inc 2  -.710*  -•350  .063  10  • 300  -.409  -.480  -.478  11  .340  -.374  -.090  .024  12  • 125  -.196  -.092  -.634*  • 131  .001  -.566*  .036  .291  -.313  .240  .123  -.366  .418  .156  .456  .772*  .652*  .290  .594*  .616*  .811*  .902™  .976™  .197  15  -.062  .450  .760*  16  .360  .094  .325  .076  17  -.236  .225  .091  -.239  • 493  .230  .895™  .887™  t  gl|/7**  .084  .670*  .290  .116  22 (Hatch)  -.068  -.068  11+  .542*  .114  - .172  -.098  -.205  Inc 2  -.440  13  18  .180  Inc 1  :  1 Week  • 501*  • 534*  .419*  2 Weeks  .149  .445*  .261  3  .043  .297  .082  A ML  "  Significant at P=0.05 Significant at P=0.01  TABLE l4b COEFFICIENTS OF CORRELATION (r) BETWEEN EGG WEIGHT AND EMBRYONIC OR CHICK WEIGHT Age  UBC  9 Days  MH  Inc 1  Inc 2  -.170  MHxUBC Inc 1 Inc 2  Inc 1  Inc 2  .186  -.620*  -.275  .068  .176 .125  10  .680*  .356  .040  -.089  -.226  11  .072  .142  -.450  -.178  -.614*  12  .024  -.188  -.061  -.145  .160  .241  13  .100  ..344  .380  .021  .710  .333  14  .297  -.261  -.063  .610  .005  15  • 301  .385  -.018  .229  • 590  16  .158  -.028  .272  .211  .058  .156  17  .291  -.153  .392  .058  .385  .286  18  •549  -•503  .422  - • 353  .410  • 347  22 (Hatch)  A • 910*  .889**t  • 9^5  • 511  .832*  -.4io  .895*^L  Qfy ~| ^^^^  -.440  J  1 Week  .425  .284  -239  2 Weeks  .118  .030  ,181  - .044  .018  • 139  3 A ±k  "  Significant at P=0.05 Significant at P=0.01  ]  TABLE 15 REGRESSION COEFFICIENTS  GRAMS OF CHICK WEIGHT ON GRAMS OF EGG WEIGHT  Age (Weeks)  WR  0  1 2  . go5™ .768  1  WC  1  Incubator  -A-A-  WH  1 2  .746™  UBC  1 2  .856™ .754*  MH  1 2  A &k  Significant at P=0.05 Significant at P=0.01  3_. 245™  .647  .269  ry-i QitM  • 7-Lo  1 2  3  M  2  MHxUBC  2  JV.JL  1.050*  1.719*  2.07  A .A.  .663*  .904  .628  A A  .884  .451  -.301  .403  .087  • 075  .563  .913  . Y04™  .565™  1.271  TABLE 16 RESULTS OF TESTS FOR LINEAR RELATIONSHIP BETWEEN InW AND TIME  t Values Strains  Incubation  9-14  Days  t.05 =  2.776  Periods  Ik-18 Days  t.05 =  4.303  Post-Hatching Period  0-3 Weeks  t.05 = k.303  WR  30.82  10.• 79  11.,02  WC  33.87  9-,88  4l.•57  WH  36.64  18.• 54  13.• 85  UBC  86.81  13.,o6#  12.,72  MHxUBC  36.67  15.• 79  14.•91  MH  22.28  13..69  13.• 50  #  t.  = 0 5  1  2  -  7  1  TABLE 17 EQUATIONS USED TQ PLOT GROWTH CURVES Incubation Period (Days)  9-l4  14-18  Equation  Class WR WC WH 'UBC MH MHxUBC  InW InW InW InW InW InW InW  = InA + kt = -2.9956 + .3868t = -2.97283 + -38lOt = -2.91142 + .3752t = -2.78441 + -3594t = -2.79025 + -35297t = -2.88044 + -3693t  WR WC WH UBC MH MHxUBC  InW InW InW InW InW InW  = -0.01238 + 0.l7744t = -0.42924 + 0.2000t = -0.56522 + 0.2113t = -1.22952 + 0.2477t = -O.56726 + 0.203l6t = -0.63164 + 0.21015t  WR WC WH UBC MH MHxUBC  InW InW InW InW InW InW  = = = = = =  Post-Hatching Period (Weeks)  Growth Rate (100k) D a i l y  38.68 38.10  37.52 35-9^ 35-30 36.93 17.74 20.00  21.13 24.77 20.32 21.02  Weekly  0-3  A  Daily rates i n parentheses  3.87042 3.77720 3.83405 3.79487 3.79728 3-78465  + o.59502t + o.65052t + 0.60099t + 0.54099t + 0.53399t + 0.54500t  59-50; 65.05; 60.10; '54.10; 53-40; 54.50;  (8.50) (9.29) (8.59) (7-73) (7.63) (7-79)  TABLE 18a ANALYSES OF VARIANCE OF GROWTH RATES Source of Variation  Mean Squares  Degrees of Freedom  Period 9-lk Days Incubation  15-18 Days Incubation  0-3 Weeks Post-Hatching  Incubators ( i )  1  .016  .0005  .015  Strains  5  .003  .0009  .068*  5  .001  .0003  .006  48 24  .009  • 0057  .020  .029  .007+  .109  (s)  I xS Sampling Error  a  b  20k a b c  5 9  Total  3 5  215 A a  c  Significant at P=0.05 S t a t i s t i c f o r 9-lk days  c  S t a t i s t i c f o r 15-18 days S t a t i s t i c f o r 0-3 weeks  RESULTS OF DUNCAN'S MULTIPLE-RANGE TEST MH •530  MHxUBC -537  UBC -539  WH -594  WR .609  WC .631  Any values not underscored by the same l i n e are s i g n i f i c a n t l y different Any values underscored by the same l i n e are not s i g n i f i c a n t l y different  TABLE 18b ANALYSES OF VARIANCE OF GROWTH RATES  Source of Variation  Types Error  Total  Mean Squares  Degrees of Freedom  58  a  2l4  c  59* 35 215  Period 9-l4 Days Incubation  15-18 Days Incubation  .008  .0001  • 31*  .007  ,0042  .02  .015  .0043  • 33  b  c  AA a  h c  S i g n i f i c a n t at P=0.01 S t a t i s t i c f o r 9-l4 days S t a t i s t i c f o r 15-18 days S t a t i s t i c f o r 0-3 weeks  0-3 Weeks Post-Hatchins  52  53  Figure 2. Arith-log graphs of growth rate obtained from the equation : InW = In A*  F i g u r « 3 a A r i t h m e t i c graphs of growth rata  55  56  300  POST-HATCHING  AGE(WEEKS]  Figure4a. Arithmetic graphs of growth rate.  57  

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