Heat Stress from Calving to Mating: Mechanisms and Impact on Cattle Fertility.

Animal production is a core sector to solve the increasing food demand worldwide, with productivity severely affected by climate change. Experts are predicting huge global productive losses in animal-derived products. Moreover, productive loss affects the economy, and the US dairy industry has reported losses of 1.5 billion dollars annually due to climate change. Beef and dairy production are based on cow reproduction and fertility is a key indicator of productivity. However, under heat stress (HS), several physiological modifications decrease cows' fertility. Lower levels of estradiol, progesterone, and epidermal growth factor lead to undetectable ovulations, an inability to maintain the embryo and the pregnancy, or increased cortisol levels, inducing immunosuppression and, consequently, puerperal diseases delaying new pregnancies. The welfare of cows under HS, especially those raised on pasture, is a huge concern. Considering the impact of ambient-temperature-induced HS, developing strategies to improve fertility-namely through the selection of thermotolerant breeds allied to environmental management measures-can improve cattle production efficiency and reduce resource use, thereby reducing the carbon footprint. This review focuses on the effects of HS on female fertility, from parturition until the new conception, and on the role of heat shock proteins during this period.