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Effect of High Ambient Temperature and Low Humidity on Nutrient Utilization and on Some Physiological Responses in Awasi Sheep Fed Different Levels of Roughage^{1, 2,}

American University of Beirut³, Lebanon

Abstract

Two experiments were conducted in a climatic chamber with eight Awasi wethers fed four different isonitrogenous rations to study the effect of high ambient temperature with low humidity on nutrient utilization, and on some physiological reactions in sheep as influenced by the level of dietary fiber. Rations 1, 2 and 3 contained ground alfalfa hay and a concentrate mixture in the ratios of 25:75, 50:50 and 75:25. Ration 4 also contained 75% ground hay but had tallow incorporated in it in order to make it isocaloric to ration 1. Four trials (periods of environments) were conducted in experiment 1, while experiment 2 consisted of two trials. Each trial lasted for about 4 weeks. During trials 2 and 3 of experiment 1, the daily temperature of the chamber was gradually raised from 20C at 7 am to 27C at 2 pm followed by a slow decline through the night to normalcy (20C); while the temperature rose, the relative humidity fell from 66 to 39% with temperature rise. In experiment 2, the chamber temperature was increased daily in trial 1 from 21C at 7 am to 33C at 2 pm with a simultaneous drop of relative humidity from 69 to 33%; trial 2 was under normal conditions. The results of the first experiment indicated that the environmental stress did not have any effect on intake and digestibility of feed nutrients, body temperature, heart rate, total serum protein and its protein fractions, R.B.C. count, hematocrit and hemoglobin values and mean corpuscular volume in all sheep fed different rations; however, W.B.C. count, respiration rate and blood glucose concentration, increased significantly. Prolonging the stress for 2 months did not have any further effect. In experiment 2, a significant depression of feed intake and an increased digestibility of crude fiber were observed as a result of the heat stress along with other changes already noticed in expt. 1.

¹ Journal No. 425 of the Faculty of Agricultural Sciences, A.U.B.

² The assistance of Messrs. S. Shamoun, M. Alulu and T. M. Khan in the animal care and data collection and of Mrs. Sagherian in the hematological work is acknowledged with thanks.

³ Department of Animal Science.

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