Nutritional, managerial and hormonal strategies to mitigate the negative effects of heat stress on reproduction

This review aims to highlight past and recent research involving interrelationships of fertility and heat stress in dairy cattle. In addition, approaches to mitigate the negative effects of heat stress on reproduction in lactating dairy cattle will be discussed. With the continued increase in milk production per cow, sensitivity of the dairy cow to elevated climatic conditions has increased. Higher milk production associated with an increase in dry matter intake enhances metabolic heat production which aggravates thermoregulatory competence of lactating dairy cattle. A number of experiments have shown that milk production declines during summer months with a greater reduction in fertility. Intensive cooling of cattle still remains the superior strategy for improving both reproduction and milk production. Also, reducing the effects of heat stress prepartum appears to improve postpartum production performance; nonetheless, this period is often disregarded. Recent studies have evaluated both the energy demands and type of energy utilized during heat stress to support lactation. Increased demands for factors such as glucose and IGF-I during heat stress to sustain milk production may compromise early embryo development, in turn, increasing embryo loss. Recent research on manipulation of embryos in vitro with hormonal supplements has illustrated beneficial effects on fertility post transfer during summer. In addition, the use of various nutraceuticals and pharmaceuticals during summer has shown promise in negating summer fertility decline.