Physiological and genetic adaptation of desert sheep and goats to heat stress in the arid areas of Egypt

Abstract

Abstract The study was carried out to investigate physiological and genetic adaptation of desert Barki sheep and goats to heat stress at the hot dry areas of Egypt. Two hundreds and ninety one mature ewes, and 166 mature does were involved in the study, over the period from 2008-2012. The animals were exposed to: zero stress (at Rest), summer heat stress (SHS); and physical exercise under heat stress (EHS, simulating summer grazing on poor pasture). Physiological parameters (thermal, respiratory and metabolic) were measured on the animals at Rest, and post exposure to heat stress. The animals utilized basically respiratory mechanism to maintain their homoeothermic, and tolerate heat stress. Accelerating panting, seems to be the main mechanism of desert sheep to tolerate SHS; however, with the extra energy required for physical exercise (EHS), they turn to deep breathing. Shallow rapid panting and decreased metabolic rate, were the main mechanisms of desert goats to tolerate heat stressors. Desert goats showed generally, better tolerance to heat stressors than desert sheep. Both Barki sheep and goats showed detectable individual variations in their response to heat stress. No single physiological parameter was reliable enough to identify high or low tolerant animals to heat stress. Animal heat tolerant index was developed, based on changes in RT, RR, GV and MR; the index was successful in identifying HT animals, and to a reasonable extend LT ones. Relative quantitative analysis of 6 gene, involved in multiple pathways for wide variety of biochemical process include thermo-tolerance melanogenesis; showed variations in the level of gene expression between low tolerant (LT) and high tolerant (HT) animals. High tolerant animals showed, generally, higher gene expression than LT ones. Gene expression of number of genes, can be utilized for early identification of HT sheep and goats for breeding purposes.