Fernando Diaz
Thermostasis is the process by which cows attempt to keep their body temperature constant in spite of changes in environmental temperatures. Heat stress occurs when the cow is incapable of dissipating enough heat to maintain its core body temperature below 101.3°F. This increase in body temperature results from the combination of heat from the environment and that produced internally during rumen fermentation and nutrient metabolism.
In addition, heat stress leads to an increase in respiratory frequency (panting) in an attempt to increase heat dissipation. This increase in physical activity is the reason why cows in hot environments produce more heat than in cold environments.
Internal heat production increases at higher feed intakes and milk production, which is why high producing cows are more sensitive to heat stress than lower-producing cows. One mechanism the organism has to reduce heat production is to reduce intake and thus less heat needs to be dissipated.
Knapp and Grummer (1991) reported that when a cow’s body temperature increased from 101.3° to 104°F, dry matter intakes decreased from 45 to 31 pounds. Berman (2005) showed cows started to suffer from heat stress at temperatures 9°F cooler when production increased from 77 to 99 pounds per day.
Continue reading this article published in eXtension.
