July 2, 2007
Editor's note: Dr. Chebel is no longer with the School of Veterinary Medicine.
Last summer’s extreme heat wave was blamed for the deaths of about 25,000 cattle in California, according to Doctor Ricardo Chebel, veterinary medicine extension specialist at the UC Veterinary Medicine Teaching and Research Center in Tulare. "The heat wave started affecting the entire U.S. on July 15, with almost all states reaching temperatures above 90 ºF July 17," he said. "One of the biggest problems observed was the high overnight temperatures, which did not allow cows to cool down before facing the hottest part of the following day." The ideal ambient temperature for cows is between 41 and 77 ºF. Once the ambient temperature reaches 95 ºF and the relative humidity reaches 75 percent, cows are already under severe heat stress.
Unlike humans, cattle have only a small number of sweat glands. Cattle dissipate heat primarily through breathing. That is why many times during the summer months cows' tongues may be hanging out of their mouths. This is an attempt to increase the volume of air that passes through the airways, maximizing the exchange of heat with the environment, Chebel said. If the environment around cows is very hot, the animals will be ineffective in dissipating heat.
There are a variety of ways to cool cows down.
* Soak cows from the hair to the skin and use fans to circulate the air around them. Without air circulation wetting the cows down creates a more humid environment in which it will be more difficult to dissipate heat. "By wetting the cows down and creating air circulation around them, we are "sweating" for them," Chebel said.
* Try to minimize the time cows spend in the holding area of the milk barn. Because that is an area commonly overcrowded, it is usually hotter and more humid.
* Overcrowding in any area of the dairy should be avoided because it increases ambient temperature and humidity and reduces the air circulation, making dissipation of heat more difficult.
* Providing shade to animals is critical. Direct sunlight is a contributor to heat stress.
* Drinking water is one way cattle try to cool down. High-producing dairy cows may drink 50 percent more water when the temperature-humidity index is greater than 80. Water should be fresh, clean and free of contaminants. The ideal water temperature for cattle consumption is between 70° and 86°F.