Impacts of heat stress and its mitigation by capsaicin in health status and digestive enzymes in house sparrows (Passer domesticus)

Heatwaves and warm spells occurring worldwide as a result of climate change disrupt the homeostasis of animals, leading to heat stress. Consequently, animals must respond to these alterations in order to ensure their survival. The response involves several physiological changes, such as releasing of glucocorticoids and catecholamines, to restore homeostasis. Due to the lack of knowledge on this subject in wild birds, the objective of the present work was to study the effect of heat stress on body condition and digestive system in house sparrows (Passer domesticus). In addition, since capsaicin is used as additive in poultry to mitigate heat stress and it is a common additive in seeds for house birdfeeders to prevent squirrels from eating their food, the second objective of this study was a possible role of capsaicin as a dietary additive in mitigating heat stress and to check the effect of capsaicin in digestive system. In this work, we measured heterophil/lymphocytes ratio (H/L ratio) as a proxy of stress; body mass, hematocrit, uric acid and digestive enzymes (intestinal and pancreatic) under stress conditions at 32 ± 2 °C and under normal conditions at 22 ± 2 °C. In addition, we evaluated the effect of capsaicin in both situations (heat stress at 32 °C and normal condition 22 °C). We found an increase of H/L ratio under heat stress, and decrease of H/L ratio with capsaicin on animals exposed to heat stress. Although a loss of intestinal mass was observed in animals exposed at 32 °C, digestive enzyme activity does not change under heat stress or under capsaicin administration. Improving knowledge in this field is relevant at the level of animal nutrition and veterinary medicine, while also bearing relevance for wild birds, where it becomes crucial to explore potential mitigation strategies for future global warming scenarios.