Abstract:

【Background】 In addition to regulating its own phenotype, the genotype of an individual animal also affects the performance of other animals within a social group through resource allocation or behavioral interaction, and this phenomenon is called an indirect genetic effect. In the animal breeding, if the genetic model harbored the indirect genetic effects, it will not only improve the social relationship between individuals, but also obtain more genetic gains. 【Objective】 In this study, Rugao Yellow Chickens raised in group cages were used as the test animals, and the indirect genetic model was used to evaluate body weight data, aiming to provide a flexible model to select the Rugao Yellow Chickens. 【Method】The body weight data was collected from the breeding group of Rugao Yellow Chickens. The fowls were weighed at the age of 42 days-old, and 11 983 raw data were collected. The data cleaning procedure included: i. removing outlier beyond three standard deviations either side of the mean; ii. eliminate the fowl without marker; iii. get rid of unknown sexed fowls; iv. the fowls with less than 4 records within a social group were also excluded. The pedigree data consisted of 12 208 fowls, including 11 735 chickens with body weight records and 473 chickens without records, 10 560 chickens without progeny and 1 648 with progeny, and the progeny of them included 208 male breeders and 1 440 female breeders. With SPSS software packages, ANOVA was used to test the influence of environmental factors on body weight and determine the factors included in the fixed effects. The classic animal model and indirect genetic model were used to analyze the variance components and genetic parameters of Rugao Yellow Chickens, and to test whether there was a dilution effect on the indirect genetic variance. The genetic model included the general fixed effects, fixed regression terms, additive genetic effects, indirect genetic effects, common environmental effects and residuals. In this study, the fixed regression term included cage sizes, and random terms included additive genetic effects, indirect genetic effects and common environmental effects. The initial value of the dilution parameter was set to 0, and it was step increased to 1.0 in increments of 0.1. After evaluating with AIC and BIC standard, the dilution parameter should be set to 0. Accounting for heterogeneous errors did not alter the estimates of genetic parameters and variance components. Therefore, the homogeneous error was assumed. Using WOMBAT software, estimates of variance components and genetic parameters converged for both classic and indirect genetic models (with or without dilution effect). 【Result】The fixed effects included the combination of laying batch-row-sex level. The significant indirect genetic variance for body weight of 42-day-old Rugao Yellow Chickens was found, for the additive heritability was 0.54±0.02, and the total heritable variation was 0.66±0.06. The corporation relationship between individuals presented in the same cage of Rugao Yellow Chickens. The direction of additive genetic and indirect genetic selection was the same, and the genetic correlation coefficient was 0.41. There was no dilution effect in the indirect genetic variance of Rugao Yellow Chickens. The indirect genetic variances were distinguished between sexes, and so on heritability and genetic correlation coefficient. 【Conclusion】Indirect genetic model could be used for the genetic evaluation and selection of body weight during the rearing period. Compared with those classic animal models, the indirect genetic models could achieve an additional genetic gain.

Key words: Rugao Yellow Chickens, heritability, indirect genetic effect, body weight, cooperation behavior