Comparative drought resistance of Bos indicus and Bos taurus crossbred herds in central Queensland. 2. Relative mortality rates, calf birth weights, and weights and weight changes of breeding cows

Abstract

The mortality rates, weight changes and associated effects of a. draught in 1969 were observed in a herd of Shorthorn x Hereford (SH), Brahman x SH (BX) and Africander x SH (AX) crossbred cows and small herds of purebred Brahman and Africander cows at 'Belmont', Queensland. About half of the cows calved over a two month period from mid-October 1969. All the cows were weighed in February 1968, February and October 1969 and in January 1970 and the data from the crossbreds analysed by the method of least squares. The weights and weight changes of both the calving and non-calving groups followed a similar pattern though the weight changes of the non-calving group were of greater magnitude. The weights showed that the three crossbreds reached the same mature weight but at different rates. The SH cows reached mature weight least rapidly, had the highest mean weight loss during the drought and had the lowest mean gains after the season broke. Weight changes both during and after the drought were however dependent on lactational status in February 1969. The mean weight loss of cows that weaned a calf in 1969 (wet) was similar for all breeds. However, the mean loss of the dry SH cows was significantly greater than that of the dry BX and AX cows. Previously wet cows exhibited compensatory gains after calving but the gain of the wet SH cows was the lowest of the crossbred means. The mean birth weight of the SH calves was reduced below the long term mean by about 4 kg but birthweights of BX and AX calves were similar to those in other years. During the drought the purebred Brahmans lost the least and the purebred Africanders lost the most weight of all breeds. However, the nature of the data precludes any strict comparisons from being drawn. Mortality rates of breeding cows were recorded from 1960 to 1969. Rates were generally highest for the SH, particularly in the drought years of 1965 and 1969. Some reasons are advanced which may explain the differences in performance of the breed types.