Effect of divergent selection for yearling growth rate on female reproductive performance in Angus cattle

Abstract

Beef cattle are often selected for increased growth performance. There has been some concern that selection for increased growth rate may reduce reproductive performance of females and increase the incidence of dystocia. A selection experiment was conducted where Angus cattle were selected for either high or low growth rate from birth to yearling age and a randomly bred control line was also maintained. Reproductive performance of cows following ten years of selection were evaluated. Cows from the high growth rate line had similar reproductive rates per cow joined at time of pregnancy testing (mean of 0.86), calving (mean of 0.86) and weaning (mean of 0.83) compared to the control line (means of 0.85, 0.84 and 0.78 respectively), while cows from the low growth rate line had lower reproductive rates (means of 0.77, 0.77 and 0.69 respectively) compared to the controls. Heifers from the high growth rate line were younger at puberty (mean of 324 days) than control line heifers (mean of 336 days), whereas heifers from the low growth rate line were older at puberty (mean of 355 days) than control line heifers. Among the cows that calved, there was no difference between the selection lines in the length of time from exposure to the bull to calving (means were 302, 304 and 302 days for high growth rate, control and low growth rate lines respectively), although gestation length was longer in the high growth rate line (mean of 281.5 days) compared to the control line (mean of 279.3 days), and shorter in the low growth rate line (mean of 278.1 days). There was no significant difference in the incidence of heifer dystocia between the lines (means were 0.03, 0.05 and 0.04 for high growth rate, control and low growth rate lines respectively). The results show that selection for high growth rate did not compromise reproductive performance.