Heat stress has a huge impact on the cow’s expression of estrus. This is due to heat stress causing a decrease in the cow’s production of luteinizing hormone and estradiol. Estradiol is the hormones responsible for estrus expression. Therefore, a cow may be in estrus, but will not express it due to her body’s response to overheating. A study in Florida reported an estimate of 76 to 82% of undetected estrus events in summer months compared to 44 to 65% from October to May. Heat stress can also cause a decrease in physical activity, which further decreases estrus behavior.