Direct and maternal components of variance for relative growth rate in Nilagiri and Sandyno sheep

A study was conducted to estimate genetic parameters of relative growth rate (RGR) and explore the possibility of its use as a selection criterion in Nilagiri and Sandyno sheep. RGR for the pre-weaning (birth to 3 months, n=6504) and post-weaning (3–6, 6–9, 9–12 and 3–12 months, n=4309, 3267, 2978 and 3257, respectively) periods were studied. The maximum RGR was noticed for the pre-weaning period and least during the latest age interval from 9 to 12 months. The ability of the trait to adjust for body size was evident from the effects of litter size, breed and age of dam on the trait. An animal model, including maternal effects was used to obtain REML estimates of (co)variances. Maternal genetic effects and inbreeding were not significant for RGR at any of the age intervals. Moderate estimates of heritability were obtained for pre-weaning RGR, with values of 0.126 and 0.103 for Nilagiri and Sandyno sheep, respectively. Among the post-weaning RGR, the age interval 3–6 months showed moderate value (0.140) in Nilagiri sheep. Post-weaning RGR for other intervals in Nilagiri and all intervals in Sandyno sheep showed negligible to low heritability estimates. The genetic correlations between pre-weaning RGR and body weight traits were high and positive in Nilagiri sheep. The estimates for the breed were found to decrease with age. Moderate heritability for pre-weaning RGR and high genetic correlation of the trait with other body weight traits provide scope for indirect selection using the trait in Nilagiri sheep. The result of the study supports the fact that RGR is able to adjust growth curve in such a way as to improve growth without affecting mature body size.