Influence of management systems on severity of heat stress on reproductive performance of rams in the tropics – a review

Abstract Sheep are an important source of protein for humans, and recent decades have seen a significant increase in the production of sheep-based products, thus indicating an increase in demand for this commodity. At a time when this sector is growing, sheep are exposed to various challenges. These include climate change, which can cause heat stress in sheep, including rams, which later negatively affects their growth and reproductive performance. Exposure to heat stress results in physiological and reproductive behaviour responses in rams, which could also be used to visually identify the effect of heat stress as it will affect the productivity of livestock. In addition, the year-round hot and humid climate of the tropics is expected to contribute to a higher probability of heat stress occurrences in rams reared in developing countries around the equator. Nevertheless, the adaptability of rams to heat stress varies according to their origin, whereby native breeds tend to adapt better. Despite that, native breeds still can be affected by adverse environmental conditions and rely on thermoregulation mechanisms to mitigate heat stress. This results in numerous negative physiological changes, such as sweating and increased heart rate. This review highlights the effects of heat stress on the physiology, reproductive behaviour and reproductive performance of male sheep. The review also discusses the impact of management systems on heat stress in rams, which affects sheep productivity.