Model comparisons for estimation of genetic parameters of pre-weaning daily weight gains in Muzaffarnagari sheep

Variance components and genetic parameters were obtained for pre-weaning average daily body weight gains of Muzaffarnagari sheep maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 17 years (1976-1983 and 1996-2004). In this study, the pre-weaning average daily gains (ADG) was considered in six successive 15 day periods starting at birth and up to 90 days (ADG1-6). Records of 2930 lambs descended from 78 rams and 977 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 for comparisons of models in this study. The best model was chosen after testing the improvement of the log-likelihood values. Direct heritability estimates were inflated for all traits when maternal effects were ignored. Direct heritabilities estimates ranged from 0.01 to 0.26 for pre-weaning average daily weight gains in this study. The permanent maternal environmental (c2) effects on average daily weight gains during birth to 15 days (ADG1), 15-30 days (ADG2) and 30-45 days (ADG3) accounted for 5-17% of the total phenotypic variance in this breed. The very low to moderate heritability estimates of pre-weaning daily weight gains in this study indicates that only slow genetic progress may be possible for these traits from selection under the prevailing management system. Results suggest that direct and permanent environmental maternal effects were important for this trait; however, maternal additive effects had no impact on this trait.