REPRODUCTIVE-PERFORMANCE OF SHORTHORN AND BRAHMAN CROSSBRED COWS IN THE DRY TROPICS OF NORTH QUEENSLAND

A study was made (1 970 to 1973) of the reproductive performance of Shorthorn and Brahman crossbred cows grazing pasture in the dry tropics of north Queensland. Breed had a variable effect on the conception rates of lactating cows, with Brahman crossbreds having significantly higher (P < 0.05) conception rates in the first year. The two breeds had similar conception rates in the following year. In the third year, overall conception rates of both breeds were reduced due to a prolonged dry season, with Shorthorn cows having significantly higher (P < 0.01) conception rates than Brahman cows. However, during this dry period, twice as many Shorthorn cows required survival feeding as did Brahman cows. Calving rates followed conception rates closely, prenatal loss in each breed being low. In all years, Shorthorns had significantly earlier (P < 0.05) calving dates than Brahmans. The interval from calving to first recorded ovarian activity was significantly longer (P < 0.05) in Brahman cross than in Shorthorn cows in only one of the three years. There was no significant difference between breeds for the interval from first recorded ovarian activity to conception, but this interval decreased with increasing age of the cow. Breed had a variable effect on gestation length. Brahman cows were generally heavier each year in April and in better condition throughout the experimental period than Shorthorn cows. © 1979 ASEG.