During times of heat stress feed intake is reduce by 8-12 percent or more. This reduction in feed intake reduces volatile fatty acid production in the rumen resulting in decreased production. Heat Stress and Ration Balancing Cattle will automatically reduce their feed intake during hot weather. Typically, early lactation cows are most swiftly and severely affected. This decreased forage intake alters the composition of the rumen and leads to acidosis and reduced fat content of milk.
Forage generates more heat than a grain ration, thereby contributing to reduced intake.
One way to correct this problem is to feed your high quality forage during the summer, thus requiring less intake to maintain a balanced ration. If cows reduce their intake during heat stress, more nutrients need to be packed into a smaller volume of feed. Remember that a cow's energy requirement for lactation is unchanged and her energy needs to remain cool actually increase. Therefore, maintaining adequate nutrient intake becomes critical to avoid undue milk production loss. Optional methods to increase dietary nutrient density include feeding high quality forage, feeding more grain, and use of supplemental fats.