Co)variance components for growth traits in the Nguni cattle breed

Production records for birth weight (BW), weaning weight (WW), yearling weight (YW) and eighteenmonth weight (EW) of Nguni herds participating in the National Beef Cattle Improvement Scheme from 1960 to 2001 were analysed. The dataset consisted of 26677 BW, 23723 WW, 10256 YW and 7260 EW records. Direct heritability estimates for BW, WW, YW and EW obtained by single trait analyses were 0.26, 0.17, 0.13 and 0.13, respectively. Maternal heritability estimates were the same (0.10) for BW, YW and EW but slightly higher for WW (0.11). Direct genetic correlations (multivariate analyses) among the four growth traits were moderate to high (0.50 to 0.95) while the maternal genetic correlation between BW and WW (bivariate analyses) were moderate (0.49). It was concluded that selection on WW alone would be undesirable as all other weights may increase. Breeding values for production traits should be seen in conjunction with one another to prevent undesirable correlated responses.