A comparative study of the performance of dairy cows during summer and winter in a subtropical climate

Abstract

Two groups of acclimatized Australian Illawarra Shorthorn cows, one of which calved in May and the other in November, were studied for 196 days at Biloela, central Queensland. They were individually stall-fed a similar quantity of feed of known composition and, though not given access to pasture, were exposed to normal climatic conditions. Although the May group produced significantly more milk (4 per cent fat corrected milk (F.C.M.)) during the first two months, the difference in total production was not significant. The May group were, on average, heavier initially, and after adjustment for this by covariance analysis differences in production of 4 per cent F.C.M. between groups during the first two months were eliminated. Elevations in rectal temperature, respiratory rate, and water intake during summer were comparatively small. During a particularly hot period there was a significant regression of relative humidity on rectal temperature and respiratory rate and dry bulb temperature on respiratory rate. The combined effect of dry bulb temperature and relative humidity on both rectal temperature and respiratory rate was also significant. The indications from this experiment are that, if fed adequately, acclimatized European-type cattle produce equally well during summer and winter in a subtropical environment.