Heat Stress: Effects on Milk Production and Composition

Milking cows experience heat stress when daily average THI is 68 or greater. During heat stress, feed intake and milk synthesis decrease to sustain homeothermy. Detrimental effects of heat stress on milk production and composition of lactating dairy cows include lower percentages of both milk fat and protein, increases in SCC, serum prolactin, and decreases in milk potassium and titratable acidity. Milk coagulation properties also are affected which affects cheese-making properties. Heat stress during late gestation results in smaller calves, decreased colostrum quality and subsequent milk production of both dam and daughter.