THERMOREGULATORY RESPONSES OF SHEEP TO STARVATION AND HEAT STRESS CONDITIONS

The present study was carried out at Sakha Animal Production Experimental Station belonging to Animal Production Research Institute. The experiment was conducted under thermoneutral conditions (TNZ) in winter (THI< 74) and during moderate heat stress (MHS, THI 74 <88) in summer season on 9 and 6 Ossimi rams, respectively. Body weight, thermoregulatory parameters and blood parameters were determined at the start of the experiment and after 48 and 96 hrs of starvation in each experiment. Ambient temperature (Ta), relative humidity (RH %) and Temperature-Humidity Index (THI) were measured simultaneously during the experiment. Under TNZ, starvation had no significant effect on rectal temperature (RT), due to a significant and insignificant reduction in heat production (HP) and evaporative cooling (minute ventilation, MV), respectively. While under MHS, starvation reduced the effect of heat stress on RT by decreasing MV and respiration rate (RR), while, HP remained almost unchanged. Under TNZ, starvation caused an insignificant and significant decrease in plasma total cholesterol (Tcho.) and total lipids (Tl), respectively. Meanwhile under MHS, starvation had no significant effect on plasma Tcho. and Tl concentrations. Before starvation, moderate heat stress caused a significant increase in RT; meanwhile, respiratory evaporation (MV) and heat production (HP) were lower than that in the TNZ. Moderate heat stress (MHS) did not affect significantly blood hematocrit (Ht) and plasma proteins (plasma total proteins (Tp), albumin (Alb) and globulin (Gl)) while it increased significantly plasma glucose concentration. It could be concluded that starved sheep can tolerate moderate heat stress by decreasing evaporative cooling; meanwhile normal fed sheep depends on heat storage to tolerate moderate heat stress.