Physiological effects of heat stress on production and reproduction

Heat stress has a significant impact on dairy cattle in the United States for a period of weeks to months each summer, depending on location. Several environmental factors contribute to heat stress, including elevated ambient temperature, radiant energy (direct and reflected sunlight), and high relative humidity, which compromise the ability of the cow to dissipate body heat. In addition, factors within the cow including level of production. feed intake, and activity contribute to heat production in the cow. When the cow is unable to dissipate sufficient heat to maintain thermal balance, her body temperature rises and heat stress occurs. The most noticeable response to heat stress is reduced milk yield, because this is measurable in both the milk tank and the milk check. Many other changes occur, including reduced feed intake, impaired reproductive performance, and often body weight loss. There are many housing, management, and nutritional modifications which one can implement to address the challenges associated with heat stress. Housing with cooling, minimizing exposure to the sun, and diet reformulation can be used to enhance milk yield and reduce intake losses. Cooling can also enhance reproductive performance of cows. An understanding of the effects of heat stress is necessary in developing an effective and economically viable system to manage cows during hot weather.