Role of plant bioactive compounds in improving ruminant resilience to heat stress challenge

This review presents the reader with a comprehensive overview of the impact of phytogenic compounds on the productivity and health of lactating cows and growing ruminants, including calves and sheep, during heat stress challenge. Exposure to heat stress may result in reduced feed intake, compromised immune function, oxidative stress and productivity losses. The positive impacts of phytogenic compounds on the health and productivity of farm animals is well established, and recent evidence suggests that they may serve as an effective nutritional strategy to mitigate the adverse effects of heat stress on animals. More information is available on lactating cows than calves, particularly during the pre-weaning period. Although their specific mode of action is not clearly understood, some phytogenic compounds stimulate feed consumption in animals experiencing heat stress, which is associated with improved productivity (milk production or growth) compared with non-supplemented animals. Phytogenics may also play a role in improving immune and endocrine function, and alleviate hyperthermia-induced oxidative stress. Certain phytogenics (e.g. capsaicin) may regulate body temperature by expanding the blood vessels in the skin and facilitating heat exchange in heat-loaded animals. Phytogenic compounds may play a regulatory role in insulin secretion and sensitivity, promoting energy partitioning for productive purposes and increasing the resilience of animals to heat stress challenges. Still, it is a largely unexplored research area. Additional research is required at varying degrees of heat stress intensity and duration to confirm the potential effects of phytogenic compounds and expand upon these encouraging findings.