Biological and Mathematical Analysis of Desert Sheep and Goats Responses To Natural Heat Stress, in Egypt

The study aimed to assess the physiological responses of the desert Barki sheep and goats to natural heat stress, under the hot-dry conditions of the Coastal Zone of Western Desert, Egypt. Fifty nine Barki ewes and twenty five Barki does, at non reproductive status, were exposed to natural heat stress (NHS) under direct solar radiation within the period from 12:00 to14:00 for 3 successive days in summer of 2009 (July and August). Meteorological and biological parameters were recorded pre- and directly post-exposure to NHS. To assess individual physiological responses of desert Barki sheep and goats to natural heat stresses the variability in individual responses of the main five physiological parameters rectal temperature (RT), respiration rate (RR), tidal volume (TV), minute ventilation (MV) and metabolic rate (MR) as well as their normality were statistically tested. The possibility of developing animal heat tolerance index to natural heat stress based on the changes in these physiological parameters was evaluated. Results indicated that all physiological parameters studied were significantly affected by NHS, in terms of change between post and pre exposure values. The minute ventilation volume (MV) increased in sheep, while decreased in goats, reflecting specie differences in respiratory response to NHS. Increase shallow panting and decreasing metabolic rate seems to be the primary mechanisms for goats to tolerate NHS. Meanwhile, sheep depend more on respiratory heat loss where respiration rate (RR) was almost tripled in response to NHS in sheep with high significant increase in MV reflecting higher gas exchange than in goats. Based on the changes in RR, RT, TV, MV and MR an animal heat tolerance index (AHTI) was developed to assess individual animal response to NHS. Evaluation of AHTI indicated that although RR followed by RT were the two main physiological parameters contributing to the AHTI depth of respiration (TV) and MR must be included to identify heat tolerant from heat susceptible animals.