Genetic Analysis of Kaliber Ratio Traits based on the Information of Autosomal and Sex-linked Chromosomes in Merkhoz Goat

Estimates of genetic and environmental parameters of different component traits related to growth are needed to develop a proper selection program. The Kleiber ratio (KR) is defined as average daily gain as a proportion of metabolic body weight. Most studies conducted in KR ignored the effect of sex-linked chromosomes and assumed that direct genetic effects were influenced by autosomal chromosomes. Therefore, the purpose of this study was to estimate (Co)variance components of both autosomal and sex-Linked chromosomes for KR in Markhoz goat.

In the present study, the data were collected from 1992 to 2014 at Markhoz goat breeding station in Kurdistan province, Iran. The traits were kleiber ratio from birth to weaning (KR1), kleiber ratio from weaning to six months of age (KR2), kleiber ratio from weaning to six months of age (KR2), kleiber ratio from six to nine months of age (KR3) and kleiber ratio from nine to twelve months of age (KR4). The GLM procedure of the SAS software was used to determine significant fixed effects. The model accounting for fixed effects included year, sex, birth type and age of doe. In addition, random effects included direct additive genetic effects of autosomal chromosomes, direct additive genetic effects of sex-linked, maternal genetic effects, maternal permanent environmental effects and residual effects. (Co)variance components and genetic parameters were estimated using six different single-trait analysis via Average Information algorithm of Restricted Maximum Likelihood method using WOMBAT software. Akaike’s Information Criterion (AIC) test was applied to select the most apropariate model for each trait.

The most suitable model for KR1, KR2, KR3 and KR4 traits were the sixth, first, fourth and first models, respectively. Based on the best models, the estimated direct autosomal heritabilities were 0.410, 0.019, 0.172 and 0.020 for KR1, KR2, KR3 and KR4, respectively. The estimated sex-linked direct heritabilities were 0.008, 0.021, 0.049 and 0.023 for KR1, KR2, KR3 and KR4, respectively. The maternal heritability for KR1 and KR3 were 0.106 and 0.057, respectively. The maternal permanent environmental effect of 0.064 was estimatedfor KR1. The autosomal, sex-chromosome and phenotypic correlations between traits were ranged from -0.518 to 0.901, -0.943 to 0.652 and -0.001 to 0.312, respectively.

The results of this study showed that a considerable ratio of the phenotypic variance is explained by sex-linked chromosome effects. Therefore, including the sex-linked chromosome effect in the model may lead to a more precise estimates of direct autosomal heritability.