Effects of Heat Stress on Nutritional Requirements of Lactating Dairy Cattle

Heat stress negatively impacts a variety of dairy parameters including milk yield and reproduction and therefore is a significant financial burden (~$900 million/year in the USA; St. Pierre et al., 2003) in many dairy-producing areas of the world. Advances in management (i.e. cooling systems) and nutritional strategies have alleviated some of the negative impact of thermal stress on dairy cattle, but production continues to decrease during the summer. Accurately identifying heat-stressed cows and understanding the biological mechanism(s) by which thermal stress reduces milk synthesis and reproductive indices is critical for developing novel approaches (i.e. genetic, managerial and nutritional) to maintain production or minimize the reduction in dairy cow productivity during stressful summer months.