Intake and Utilization of Nutrients in Sheep Fed Different Levels of Roughage under Heat Stress

Abstract

Three trials were conducted with eight Awasi wethers fed four different isonitrogenous rations, to study the effect of heat stress on nutrient utilization and related body functions in sheep as influenced by the level of dietary fiber. Rations 1, 2 and 3 contained barley hay and a concentrate mixture, respectively, in the ratios of 25:75, 50:50 and 75:25. Ration 4 also contained 75% hay and was supplemented with tallow to make it isocaloric to ration 1. Each trial lasted for 4 weeks. In trial 2, the experimental chamber simulated a hot and humid day in which the temperature was approximately 10C higher at the peak hour (12 noon) than the ambient temperature of 22C in trials 1 and 3, with a sharp rise from 7 am and a gradual fall during the night. Relative humidity also increased from 65% in trials 1 and 3 to 88% in trial 2. The high ambient temperature and humidity decreased feed intake (P<.01) and increased water consumption (P<.01) and urine volume (P<.05). The heat stress also lowered the digestibility of dry matter, crude protein, ether extract and energy but did not affect the digestibility of crude fiber and NFE of rations. The digestibility depressions were most severe at the 75% roughage level and the addition of fat seemed to alleviate the depression. The metabolizable energy of rations was also depressed when the animals were exposed to high temperature, and the effect was maximum in the 75% roughage ration. Neither ration composition nor ambient temperature had any effect on nitrogen utilization. Respiration rate, heart beat and rectal temperature increased significantly during the high temperature trial and the effect was highest in the 75% roughage fed group. Intrathoracic and subcutaneous temperatures of lambs tended to be higher with 75% roughage than with 25% of roughage ration and this trend was intensified at high ambient temperature. Serum protein fractions did not show any change (P>.05), while blood glucose concentration increased significantly (P<.05) as a result of heat stress in all groups.