Variance components and genetic parameters of growth traits and Kleiber ratio in Muzaffarnagari sheep

- Environmental factors had significant role on pre-weaning growth traits and Kleiber ratio of sheep.
- Direct heritability estimates for all traits inflated substantially when maternal effects were ignored.
- Maternal additive effect was only important for birth weight whereas c2 effect existed from birth to weaning for all traits.
- Lower heritability estimates for all traits indicate slow genetic progress may be possible through selection.
- Both direct and c2 effects must be considered for analyzing growth traits and Kleiber ratio of sheep.

Estimates of (co)variance components and genetic parameters were obtained for birth weight (BW), weaning weight (WW), average daily weight gain from birth to weaning (ADG) and Kleiber ratio (KR) of Muzaffarnagari sheep maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 30 years (1976-2005). Records of 5835 lambs descended from 176 rams and 1703 ewes were used in the study. Analyses were carried out by restricted maximum likelihood (REML) fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Six different animal models were fitted for all traits. The best model was chosen after testing the improvement of the log-likelihood values. Direct heritability estimates were inflated substantially for all traits when maternal effects were ignored. Heritability estimates for BW, WW, ADG and KR were 0.15, 0.16, 0.15 and 0.13, respectively. Maternal genetic effects contributed only 12% of the total variance for birth weight. Estimates of fraction of variance due to maternal permanent environmental effects (c2) for BW, WW, ADG and KR accounted for 6-12% of the total phenotypic variance in this study. The estimates of the direct genetic correlation among studied traits were positive, ranging from 0.18 (BW-KR) to 0.98 (WW-ADG), whereas permanent maternal environmental correlations among traits varied from from 0.55 (BW-KR) to 0.99 (WW-ADG). The estimates of the phenotypic and environmental correlation between traits under study ranged from 0.10 to 0.99 and −0.05 to 0.99, respectively. Results suggest that maternal additive effect was only important for birth weight whereas permanent environmental maternal effects were important for other traits in our study. The moderate heritability estimates for early growth traits and Kleiber ratio of sheep in this study indicates that modest rates of genetic progress may be possible for these traits from selection under the prevailing management system.