Natural high ambient temperature-induced respiratory hypocapnia without activation of the hypothalamic-pituitary-adrenal axis in lactating goats.

The natural HTa (ΔTa; 5-8°C) in this study activated evaporative heat dissipation and was high enough to induce respiratory hypocapnia. Importantly, this ΔTa did not activate the HPA axis but was correlated with a change in antioxidant defense. Therefore, under natural HTa in tropical conditions, respiratory hypocapnia is the first line of physiological response in goats within a specific range of natural ΔTa (5-8°C).