Abstract
For dry, nonpregnant Holstein cows were housed in two independ-enty controlled climatic rooms, each housing 2 open-circuit respiration chambers. Two of the cows were exposed to temperatures in the order 18, 26, and 32°C and 60% RH for 2 weeks per treatment, and the other two were exposed to the same temperatures in reverse order. They were fed Italian ryegrass hay at a level corresponding to their maintenance requirements. There were no significant differences in body weight between treatments. Hay intake and block salt intake decreased at high temperatures, but water intake increased with increasing temperature. Major mineral concentrations in hay were almost adequate. There were no significant differences in Ca absorption and retention between treatments, but they tended to increase at 26°C and decrease at 32°C. Phosphorus absorption and retention decreased at 32°C. Sodium absorption and retention decreased greatly at 32°C, with especially negative retention at this temperature. The absorption and retenntion of Mg and K were not significantly different between treatment. Results suggest that the apparent absorption and retention of Ca, P, and Na in dry cows may be affected by heat stress and decrease at 32°C.
