Direct and maternal genetic components of variance for growth traits in Nilagiri and Sandyno Sheep of South India

The Nilagiri sheep is known for its prolificacy and adaptability to high altitudes of the Nilgiri hills. This breed was crossed with exotic sheep such as Rambouillet and Merino to develop a new synthetic sheep called Sandyno at Sheep Breeding Research Station, Sandynallah (Tamil Nadu). Both these breeds have been maintained as closed flocks in this station and growth data from 1992 to 2011 were utilized to estimate direct and maternal genetic (co)variance components for various growth traits viz., weight at birth (BW), 3 (3W), 6 (6W), 9 (9W), 12 (12W) and 18 (18W) months of age. An animal model including maternal effects was used to obtain restricted maximum likelihood estimates of (co)variances. The h² values for BW, 3W, 6W, 9W, 12W and 18W were 0.140, 0.130, 0.074, 0.168, 0.129 and 0.166, respectively in Nilagiri sheep and 0.147, 0.114, 0.098, 0.141, 0.144 and 0.115 in Sandyno sheep. In Nilagiri sheep, maternal influence was significant (P<0.05) for BW, 3W, 6W and 9W and the maternal heritability values for the traits were 0.211, 0.050, 0.126 and 0.098, respectively. In Sandyno sheep, the maternal heritability values were significant (P<0.05) for BW, 3W, 6W, 9W and 18W with values of 0.285, 0.035, 0.054, 0.058 and 0.110, respectively. BW and 6W in Sandyno sheep were the only traits for which models with direct and maternal genetic correlation (σ_am) were significant (P<0.05). Genetic correlations among body weight traits were positive and moderate to high and ranged from 0.375 to 0.994 in Nilagiri and 0.553 to 0.952 in Sandyno sheep. Maternal effects were important with respect to growth traits in Nilagiri and Sandyno sheep. Moderate estimates of heritabilities and higher genetic correlations provide scope for further improvement in growth traits.