Effects of nutritional state on responses of Hereford steers to enforced exercise in a hot environment

Abstract

The physiological responses of two groups of steers to enforced exercise (walking) in a warm environment were studied on four consecutive days. Prior to the walking trials, the groups were fed to either lose (low plane) or gain (high plane) weight. On day 1 and the morning of day 2, the low and high plane groups were fed, respectively, on a restricted amount of oaten hay or a lucerne chaff-wheat mixture ad libitum. At the afternoon feeding and after exercise on day 2, the diets were reversed for the remainder of the study. Thus, physiological measurements on days 1 and 2 were made before, and those on days 3 and 4 after, the reversal of diets. On days 1 and 2, high plane animals exhibited a lower walking endurance and higher rectal temperatures and respiratory rates after 2 h of exercise than low plane animals. Sweating rates immediately after exercise were also greater in high plane animals, which suggests that their inferior walking ability was not due to a lower cutaneous heat loss. Between-group differences in walking ability are postulated to have resulted from differences in heat production on the two diets. On days 3 and 4, walking endurance, and rectal temperatures and respiratory rates after 2 h of exercise were similar in both groups although high plane animals recorded greater sweating rates after exercise on both days. Contrary to expectations, low plane animals showed lower physiological responses to exercise when they were fed on the lucerne chaff-wheat ration. A possible explanation is offered for these lower responses of low plane animals.