It is summertime, and with rising temperatures combined with high humidity, heat stress will play an important factor in all cattle operations for the next couple of months.
In addition to heat and humidity, other factors that lead to heat stress in cattle are the amount of sunlight exposure, Fescue endophyte toxicity, precipitation, wind and amount of night cooling. Hide color and breed are also factors in heat stress. Bos indicus (adapted to hotter climates) breeds tolerate more heat than Bos taurus (adapted to cooler climates) breeds, in part because Bos indicus cattle have more sweat glands, and have a slower metabolic rate than Bos taurus cattle.
The ideal temperature range or “comfort zone” for cattle is between 25 degrees F and 85 degrees F. When temperatures rise above 80 degrees F, feed intake is reduced. Compared to humans, cattle only sweat about 10 percent as much as we do. Thus they are unable to dissipate heat efficiently. In beef cattle, weight gains are greatly diminished. Dairy cattle can see huge losses in milk production as a result of decreased feed intake. In addition to eating less, cattle affected by heat stress are more susceptible to disease due to decreased immune system function; respiratory disease, postpartum infections, mastitis are common maladies seen during summer months. Reproduction also takes a serious hit during periods of heat stress. Conception rates are significantly lower, due to alterations in the uterine environment and effects on early embryonic development. Heat detection is poor, as hot cattle do not show consistent signs of heat during the day. Recovery from heat stress may take one to two months for cows to begin to cycle normally and for conception rates to increase.
So what can you do to manage heat stress? First, make sure that cattle have adequate sources of cool water. Research has shown that cattle will increase water intake when offered cool water. Secondly, alter the diet fed to cattle. Since intake decreases, change feedstuffs to increase quality so that cattle can get adequate nutrients while consuming less total pounds. Energy requirements actually increase during hot weather, as cattle require more energy to dissipate heat. If you are feeding cattle, feed smaller amounts more frequently. Feeding during cooler times of the day can increase intake dramatically. Make sure that adequate mineral is provided, as cattle respirate and perspirate more during hot weather.
Thirdly, shade and mechanical cooling with misters and fans can decrease body temperatures and increase comfort. Buildings or shades should have tall roofs and open sides to increase airflow. In dairy barns, misters should spray enough water to soak the cow’s skin, and then shut off long enough for evaporation to occur. Continual wetting will lead to high humidity, thus defeating the purpose of the sprayers. Fans can greatly enhance evaporative cooling in dairy barns or loafing sheds.
Following these suggestions can make your cattle more productive and comfortable during the summer months.
Mike Bloss, DVM, is the co-owner of Countryside Animal Clinic in Aurora, MO. He and his wife, Kirstin, operate the mixed animal practice.
