Growth, feed intake and maternal performance of Angus heifers selected for high or low growth and milk production

Weight of calf weaned per cow that incorporates both growth and maternal component traits is an important determinant of profitability for cow-calf production systems. In New Zealand, there is little objective information available on the performance of progeny from bulls selected for either growth or maternal ability when compared under similar pastoral farming conditions. The present experiment produced 84 Angus heifers sired by Angus bulls divergently selected for high (Hi-Gr) or low (Lo-Gr) estimated breeding value (EBV) 600-day weight or high (Hi-Milk) or low (Lo-Milk) 200-day maternal EBV. Each heifer had their liveweight gain from weaning to just before first calving, herbage intake from pasture using the n-alkane method, and maternal performance (calf production after first and second parity) assessed. Liveweights of heifers born to Hi-Gr bulls were generally greater than for all other lines, while there was no difference between Lo-Gr and either of the maternal lines. There was no difference (P > 0.05) in herbage intake between the different genetic lines when measured at Days 310 (days of age from birth) and 880. At Day 400, the Lo-Milk selection line had higher (P < 0.05) intakes than the Hi-Milk, Hi-Gr and Lo-Gr lines. Calves born to the Lo-Gr heifers at the first parity were lighter while the birth weights of calves born at the second parity calving were similar for all the selection lines. Calf weaning weight was lowest (P < 0.05) after both the first and second parity weaning for the Lo-Milk sired heifers. The Lo-Milk heifers produced the least milk at Day 50 during their first lactation while the Hi-Milk heifers produced the most. This experiment confirms that for beef cattle, producers who wish to select bulls to use in their herds based on either high growth rate or high milk EBV, the resultant progeny will outperform those that are average or below average for those particular traits.