Comparative mortality rates of Bos indicus and Bos taurus cattle in central Queensland

Abstract

A study was made over several years of lifetime mortality rates of both purebred Bos taurus and Bos indicus breeds and of several generations of crosses between the breeds. Of 4,678 calves born during the period, 4.7 per cent died at or within one week of birth. A further 2.3 per cent of those remaining died before weaning and a further 1.1 per cent died from weaning to 15 months. Sixteen of 22 calves born as twins were perinatal mortalities. Perinatal losses were highest in purebred Zebus (Africander and Brahman) and in first generation Brahman crossbred (BX) calves. Africander crossbreds (AX) generally had the lowest mortality rates of all crossbreds at each stage of the life cycle. Perinatal mortalities were however high in both F1 AX and F1 BX calves born to primiparous purebred British (Hereford and Shorthorn) heifers. Over all crossbred generations, perinatal mortalities were highest in calves from 3-year-old heifers and decreased with age of dam. More males (4.7 per cent) than females (2.9 per cent) died at or near birth. Mortalities in F1 BX males (10.3 per cent) were the highest of all groups. Relatively high or low birth weight was associated with high perinatal mortalities in the crossbreeds. Losses of stock after weaning were generally higher in the British breed-types than in the Zebu breed-types with the greatest differences in adult mortality rates. Annual mortality rates of breeding cows of each breed were studied over a similar period. 9,537 cow years were involved in the study. Mortality rates of both purebred and crossbred British cows were higher than for purebred and crossbred Zebu cows. One contributing cause was the difference in numbers of cows of each breed that died while calving. In all, 1.4 per cent of British crossbred calvings resulted in the death of the cow compared with 0.6 and 0.3 per cent for comparable AX and BX cows. Losses were negligible in purebred Zebus. Mortality rates in adults generally increased slowly with age and were highest in 8 - 10-year-old cows.