Interrelationships of Heat Stress and Reproduction in Lactating Dairy Cows

Efficient reproductive performance of lactating dairy cattle in tropical/subtropical and arid environments throughout the world is impacted by a multiplicity of factors such as: the physical environment, socialeconomic status of producers, available nutrients, adaptability and genetic composition of cattle, intensive or extensive management systems, and available reproductive technology. Seasonal summer reductions in reproductive performance of lactating cows has been well-documented and is associated with decreased thermoregulatory competence of lactating dairy cows, partially due to intensive genetic selection for high milk production (AlKatanani et al., 1999). With higher production, the associated increase in dietary dry matter intake (DMI) enhances heat increment, which when coupled with increases in metabolic heat production to produce milk, aggravates thermal balance during the stressful summer period.