Effectiveness of selection for growth rate in Zebu × British crossbred cattle. II.* Post-weaning growth and genetic estimates

Abstract

The response to one generation of selection for weight per day of age at 18 months (W/A_f), in Africander cross (AX) and Brahman cross (BX) cattle, was evaluated in the female offspring of the up and down selected parents. The high W/A< line gained significantly more than the low line over a year from weaning. The advantage of the high W/A line occurred during flush nutritional periods.

The realized heritability (h²) of W/A_f at 18 months was 0.52, while the estimates of h² from mid-parental means computed within sires was higher. Heritability estimates for birth weight (W_b), weaning weight per day of age (W/A_w), pre-weaning average daily gain (G_bw) and total average daily gain from birth to final weight (G_t) were all high, while the estimate for post-weaning average daily gain from weaning to final weight (G_pw) was low.

The correlated responses of all the traits were high. The genetic correlations estimated from the response and the parent-offspring regressions were all positive and high. Birth weight was the most highly correlated with Gt. All phenotypic correlations were positive but lower than the genetic correlations, the correlation between G_bw and G_pw being the lowest. Environmental correlations between birth weight and pre-weaning traits were essentially zero, and between birth weight and post-weaning traits and G_t, negative.

Weight per day of age at 18 months appeared to be the most efficient and practical single trait to select beef cattle for increased growth rate.