Identification of heat stress-susceptible and -tolerant phenotypes in goats in semiarid tropics

2017 
The production performance of livestock is influenced by short-term variation in weather pattern. Goat adapts to varied ecological conditions and maintains productivity; however, wide variation has been observed among individual animals in response to environmental stimuli in a population. The objective of the present study was to identify the contrasting phenotypes on the basis of the physiological response in goats during heat stress. The study utilised 138 Jamunapari and 242 Barbari goats during peak heat-stress period and 82 Jamunapari and Barbari goats under thermo-neutral conditions. The physiological response of goats to different environmental conditions was evaluated by recording various parameters such as rectal temperature (RT), respiration rate (RR) and heart rate (HR). The temperature humidity index varied from 85.36 to 89.80 and from 65.32 to 73.12 during heat-stress and thermo-neutral assessments respectively. There was direct increase in HR and RR (>25%) due to heat stress in the animals, as compared with those in thermo-neutral conditions. On the basis of the distribution of RR and HR values across the breed in the population, the individuals having a RR of ≥50 and a HR of ≥130 are recognised as heat stress-susceptible phenotypes and those having a RR of ≤30 and a HR of ≤100 are recognised as heat stress-tolerant individuals. Different biomarkers were analysed in plasma, while heat-shock proteins and leptin were analysed in tissue extracts by ELISA. C-reactive protein and HSP90 concentrations were significantly (P < 0.05) different between heat stress-susceptible and heat stress-tolerant individuals. Heat-shock proteins HSP70, HSP 90, and C-reactive protein and triiodothyronine were reliable indicators of long-term heat stress. Identification of contrasting phenotypes in regard to heat stress is necessary so as to evaluate the expression pattern at a cellular level, as well as physiological and biochemical parameters.
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