Comparative evaluation of different animal models for genetic analysis of body weight traits in an organized Corriedale sheep population

Abstract

The present study aimed to evaluate different animal models for their appropriateness to best fit the body weight data of Corriedale lambs at different ages and reared under temperate conditions. Data used in this study consisted of 24,907 body weight records on a total of 6162 lambs of Corriedale sheep population. The data pertained to body weight traits at different ages i.e., at birth (BW), weaning (WW), six months (SW), nine months (NW) and yearling age (YW). The (co)variance components of five traits were estimated using univariate analysis based on restricted maximum likelihood (REML) algorithm in WOMBAT program. Six different univariate animal models, with or without maternal genetic effect, maternal permanent environment effect and covariance between additive genetic and maternal genetic effects, were fitted on the body weight data of the Corriedale sheep population. All univariate animal models incorporated season (winter, spring) and period of lambing (8 periods, each of 5-year duration), and sex of lamb (male, female) as fixed effects. AIC, Log-likelihood and likelihood ratio test results were used to evaluate the best fit models for body weights at different ages. Model I, incorporating additive genetic effect of the individual as random effect, showed the minimum AIC estimate for BW. Model III showed the minimum AIC values for all other traits under consideration i.e., WW, SW, NW and YW. The direct additive genetic heritability for birth weight was 0.025 under the best fit model i.e., model I. The direct heritability estimates for WW, SW, NW and YW were 0.151, 0.216, 0.103 and 0.132, respectively under the best-fit models. Maternal genetic heritability ranged from 0.043 to 0.087 for different body weights, except BW for which model I was the best-fit. Most of the covariance and correlation estimates between direct additive genetic and maternal genetic effects were negative. Low estimates of heritability found in best-fit models in this research are suggestive of the less appropriateness of applying individual selection for this population as it may only result in slow progress for body weight traits in Corriedale sheep. Environmental factors played a significant role in generating the variation in body weight traits in Corriedale sheep.