Section 14 — Animal Genetics and Breeding 



four generations of selection, the response in 

 lines 1 and 2 was in reasonable agreement with 

 expectations, being greatest in each case for 

 the trait under direct selection. In the third line 

 the males showed both an increase in 63-day 

 weight and a decrease in 147-day weight. Fe- 

 males, on the other hand, showed a slightly 

 greater increase than males in 63-day weight, 

 but showed no change from the controls in 

 147-day weight. These results would indicate 

 that the growth pattern can be changed in the 

 desired manner by selection. 



14.34. Selection for Growth Rate and Correlated 

 Responses in Chickens. R. George Jaap (Co- 

 lumbus, U.S.A.). 



The paired mating system suggested for 

 minimum inbreeding in control populations by 

 Gowe, Robertson and Latter^ 1 ) has been used for 

 two random-bred control lines and five lines 

 with random-breeding of growth-selected parents. 

 All lines arose from crossbred ancestry, the 

 two control and two of the selected lines arising 

 from the same base populations. 



In the growth-selected lines, 20 to 25 per cent 

 of each generation has been used for reproduc- 

 tion in 40 paired matings per line. The inbreeding 

 coefficient (F) in the selected lines increased 

 approximately 1.0 per cent per generation. In 

 the random-bred control lines, F has increased 

 slightly less than 0.5 per cent per generation. 

 Little change from inbreeding depression or 

 random gene drift was expected. The present 

 number of generations of selection is 8, 5, 2, 4 

 and 3 for lines G, A, AG, RG and GRL, respec- 

 tively. 



Realized heritability of weight at 8 weeks of 

 age from the first four generations of selection 

 in line G was about 0.4. Recently, those selected 

 lines having most rapid growth rate (A, AG and 

 the last 4 generations of G) have failed to re- 

 spond as rapidly as RG, GRL and the first four 

 generations of G. This slackening of the progress 

 in line G is the first evidence of a plateau in the 

 rate of progress from selection for growth rate 

 in chickens. 



When week body weight was increased 

 by about one-half a pound, the following cor- 

 related responses were observed: Egg produc- 

 tion decreased 5 per cent, egg weight increased 

 2.8 g, eggs became relatively broader in shape 

 and their albumen height increased 0.3 mm. 



1. Poultry Sci. 38, 462-471, 1959. 



14.35. Influence of Feed on the Heritability of Some 

 Chicken Traits. J. P. Boyer, X. de Laage 

 and C. Calet (Jouy-en-Josas, France). 



In May-June 1962 3527 chicks were hatched 

 from 20 sires and 164 dams during 8 weeks — 

 the hatches 1, 3, 5, and 7 received an all mash 

 ration with high energy and a coccidiostat; the 

 hatches 2, 4, 6, and 8 received an usual mash 

 ration. 



At 8 weeks of age, weight, breast angle, keel 

 length, diameter of shank and weight / shank 

 length ratio were appreciated. All data were 

 transformed on a probit scale to avoid the hatch 

 influence. 



Heritabilities of the five characters were esti- 

 mated by hierarchical analysis of variance. 



For males, no great difference was observed 

 between the two regimes; the percent heritability 

 was, for "special" and "usual" ration respec- 

 tively: weight 47.1-48.6, breast angle 38.1-21.3, 

 keel length 59.2-59.2, diameter of shank 68.4- 

 56.6; weight / shank length ratio 46.7-39.6. 



For females, the differences were spectacular 

 ones: weight 67.3-41.5, breast angle 42.3-17.2, 

 keel length 62.1-49.0, diameter of shank 71.4- 

 59.3, weight / shank length ratio 65.5-42.4. 

 It is interesting to note that in all cases, the sire 

 component of variance was greatly increased. 



It is concluded that an appropriate feeding 

 plan permits the manifestation of a genetic 

 sex-linked variability for meat characters. 

 Such an environment is able to facilitate selec- 

 tion. 



It is suggested that the absence of response of 

 males was perhaps caused by a limitation of 

 available energy in ration. 



14.36. Heritability in the Progeny of Hens with 

 Contrasting and Similar Constitution and 

 Productiveness. E. E. Penionzhkevich 

 (U.S.S.R.). 



Investigations that are carried out at the 

 poultry breeding laboratory under the auspices 

 of the author on heretability of productive, 

 exterior and interior characters in farm poultry 

 show hereditary variability of the same characters 

 depending on methods of reproduction (inter- 

 breeding, inbreeding, somatic hybridization), 

 environmental conditions (mainly temperature), 

 various physiological states of the organism, age 

 of parents and selection of parental forms among 

 contrast or similar breeds. 



Progeny is affected by parental forms includ- 

 ing at least two main factors: (a) nutrition during 



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