Genetic parameters of body weights at different ages in Sahiwal heifers

The data on body weights of 780 Sahiwal animals from birth to first calving for a period of 47 years (1961- 2007) were adjusted for significant non-genetic factors (season and period) using least squares analysis and the adjusted records were used for subsequent analysis. The season of birth had no significant effect on birth weight, body weights at 24 months age, 30 months age and weight at first calving. Body weight at 12 months of age was significantly influenced (P £ 0.05) by season of birth and the effect of season was highly significant (P £ 0.01) on 6 and 18 months body weights. The period of birth had highly significant (P £ 0.01) influence on all body weights from birth to first calving. The least squares analysis of variance showed the highly significant (P £ 0.01) regression of body weights at 6, 12, 18, 24 and 30 months of age and weight at first calving on birth weight in Sahiwal cattle. The heritability estimates were: 0.13 ± 0.06, 0.15 ± 0.09, 0.13 ± 0.08, 0.11 ± 0.08, 0.27 ± 0.11, 0.31 ± 0.12 and 0.19 ± 0.10 for body weights at birth, 6, 12, 18, 24, 30 and at first calving. The heritability estimate of birth weight was moderate and significant for Sahiwal calves. The estimates of heritability of body weights at six, twelve and eighteen months were not significantly different from zero as standard errors were higher. However, the heritability estimates of twenty four and thirty months body weights were higher and significant in Sahiwal heifers. The estimates of genetic correlations of 6 months body weight with 12 months body weight, 24 months body weight with 30 months body weight and body weight at first calving and 30 months body weight with body weight at first calving were higher in magnitude. Most of the body weight traits showed highly significant (P £ 0.01) phenotypic correlation amongst themselves. However, non-significant phenotypic correlations were observed in case of birth weight with six months body weight and weight at first calving.