Effects of once-yearly weaning on some aspects of herd productivity in an extensive herd in the semi-arid tropics of northern Australia

Abstract

Cow reproductive rates, mortalities and liveweights, and steer growth rates from a herd of 500 Bos indicus - Bos taurus cross cows and their progeny were recorded over a period of 4 years from June 1981. The cattle grazed native pastures and were not supplemented. Cows which had a calf of more than 100 kg in June were allocated to 2 treatments: weaned and unweaned. Where the calf weighed less than this amount, cows were allocated to a separate 'young calf group. In the year following branding, weaning increased (P<0.05) conception rate from 73.9 to 93.8% and reduced (P<0.05) cow mortality rate from 14.1 to 4.5%, relative to the unweaned group. On average, weaned cows conceived 3 months earlier (P<0.05) than the other 2 groups, in November, and 27% of weaned cows subsequently calved out of season the following year, compared to 4% of the other groups. This affected subsequent weaning management by increasing the number of calves too young to wean in June. Weaned steers grew at a reduced (P<0.05) rate during the first year post-weaning. Despite compensatory gain in the next 2 years, they were still 26 kg lighter (P<0.05) than their unweaned counterparts at 3.5 years of age.