SOURCES OF VARIATION IN REPRODUCTION PERFORMANCE IN SELECTED HERDS OF BEEF CATTLE IN NORTH-EASTERN AUSTRALIA

This paper contains observations of several sources of variation in reproductive performance on 13 herds of beef cattle in north‐eastern Australia. Nearly 15,000 cows were examined, man, on more than one occasion. Variation between herds in pregnancy rate in June or September 1964, was 44 to 75 per cent. Lactating heifers had lower pregnancy rates than lactating cows, which in turn had lower rates than non‐lactating animals. Within classes, cows in poor body condition had lower fertility than those in forward‐store or fat condition. Losses of calves between pregnancy tests and branding ranged from 6 to 40 per cent in a sample of herds. In herds where year‐to‐year data were avail‐able, the majority of cattle had one calf every two years, or two calves every three years. In one herd, cows that calved before February reared more calves than those that calved later. The main conclusion was that improved nutrition of lactating heifers and cows would be expected to increase pregnancy rates substantially. Copyright © 1969, Wiley Blackwell. All rights reserved