Renal efficiency underlies adaptive heterothermy of heat-stressed hypohydrated goats

We investigated the thermotolerance of the F1 progeny (Black Bedouin × Damascus crossbreed) to summer conditions alongside that of two pure breeds. Male goats (n = 7 per breed) were used to conduct a summertime 28-day trial along with hypohydration. The animals were fitted with miniscule thermologgers, intraperitoneally and subcutaneously, to measure core (T_c) and peripheral (T_p) body temperatures (BT), respectively. All goats were kept under shaded housing for a 7-day basal period before being switched to unshaded pens for the next 21 days. During the first 14 days, animals had free access to water. However, during the third 7-day period, access to water was time-restricted (4 h/day). Finally, it was restricted to 40% of the third week's average daily intake over the last 7 days. Exposure to the unshaded conditions resulted in pronounced heat stress in all animals, as reflected by 0.42 and 1.44 °C rises for T_c and T_p, respectively. The F1 goats displayed a clear heterothermic adaptive response, especially after the water restriction bouts' initiation. Interestingly, the F1 goats displayed higher ratios of renal relative medullary thickness (77.7, 73.3, and 72.6 ± 1.1%) along with higher circulating concentrations of antidiuretic hormone (44.6, 31.6, and 11.6 ± 3.7 ng/mL), respectively, which suggested an improved water metabolism.