With hot summer weather ahead, dairy producers are reminded of the importance of managing dairy cattle to minimize the negative impacts of heat stress that may inhibit immune function, impacting their health and productivity.

“Heat stress is a health and economic issue in every dairy-producing area of the world,” said Dr. Robert Collier, professor at the University of Arizona Agricultural Research Center.  “Production, reproduction and animal health are all impaired by hyperthermia. During heat stress, respiration rates and body temperature increase, while feed intake, milk yield and reproduction decrease.”

Speaking at a pre-conference symposium at the 25th Annual Florida Ruminant Nutrition Symposium in Gainesville, Fla., Collier said heat-stressed dairy cows may experience increased levels of the stress hormone, cortisol, which can weaken their natural immune system and make them more susceptible to disease and infection. “High somatic cell counts and a high incidence of clinical mastitis are associated with the hot summer months,” he said. 

He noted that decreased milk production is linked in part with reduced feed intake, as well as metabolic changes, during extremely hot, humid weather. “In heat-stressed dairy animals, an increased metabolic rate causes a reduction in the metabolizable energy that is available for milk production,” he explained.

Collier also summarized results of a recent heat stress research project at the University of Arizona, which involved feeding a proprietary immune-boosting nutritional supplement* to Holstein cows housed in controlled environments. Use of the product resulted in greater dry matter intake, reduced respiration rates and lower rectal temperatures during heat stress, compared to control cows. They also had lower somatic cell counts after heat stress during the recovery period. 

In addition to supporting immune function, dairy experts recommend diet modifications for managing heat stress, such as adding supplemental sources of fat or utilizing lower-fiber feedstuffs to help reduce the heat of digestion. They also encourage producers to provide an adequate source of cool, fresh water, adequate shade, air movement and sprinklers, to promote cow comfort and help animals better tolerate a hot environment.

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• OmniGen-AF®, from Prince Agri Products.