Genetic heterogeneity of residual variance of hatch weight in Mazandaran native chicken.

1. In current breeding programmes, uniformity of end products and producing animals that are robust to environmental challenges are desirable. Several studies have provided evidence of the presence of genetic heterogeneity of residual variance and proposed that it could be possible to increase uniformity of livestock productions by selection. The present study aimed to define the micro environmental sensitivity of dual-purpose chickens for body weight at hatch. 2. The data set consisted of 24,321 female and 21,547 male chickens' records of hatch weight from 19 consecutive generations of Mazandaran fowl. The statistical analysis was carried out in a two-step approach: first, an animal model was fitted to the data and then, the impact of additive genetic effects on the residual variance of the studied trait was investigated. 3. The estimate of heritability for body weight at hatch was in the range of 0.23-0.25 for female and 0.14-0.16 for male offspring, respectively. The proportion of maternal environmental variance to phenotypic variance ranged from 0.24 to 0.27 for female and 0.17 to 0.24 for male offspring. Heritabilities in females were higher than males. Estimates of the heritability of residual variance ranged between 0.067 and 0.090. The genetic coefficients of variation were high ranging between 0.83 and 0.86. Genetic correlations between hatch weight and its residual variance estimates from bivariate analysis were -0.39 and -0.44 in females and males, respectively. 4. The results suggest that there is an opportunity to simultaneously improve body weight and the uniformity of body weight by selecting for lower residual variance in native chickens.