It is showering and cool as I write this column, but as all Southwest Missouri natives know, we are only “two weeks away from a drought." It is summertime, and with rising temperatures combined with rising humidity, heat stress will play an important factor in all cattle operations for the next couple of months. I would like to give an overview of heat stress and some recommendations for control of this profit robber.
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.
The ideal temperature range or “comfort zone” for cattle is between 25 F and 85 F. When temperatures rise above 80 F, feed intake is reduced by as much as 8 to 12 percent. 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, 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? There are many things you can do to relieve your cattle. 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 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. For those beef herds on pastures, trees provide the best shade option, but timbers need to be open to allow airflow. Low brush and limbs obstruct air and make the timber areas less appealing as a place to cool off on a hot day. Portable shades are an option where tree space is limited. Move shades regularly to keep standing areas cleaner.
Mike Bloss, DVM, owns Countryside Animal Clinic with his wife, Kirstin Bloss, DVM, in Aurora, Mo.
