Cow comfort measures, such as misters and fans, can be effective steps to help protect dairy cows from heat stress. Producers, however, should not overlook the importance of feed management and nutritional strategies to help offset the effects of heat stress not only on milk production, but also cow health.

Kirk david
Director, Dairy Technical Services, North America / Phibro Animal Health Corporation

Dairy cows are subjected to heat stress during some parts of the year, which may affect herd health and profitability. During heat stress, respiration rate and body temperature increase, while feed intake, milk yield and reproduction decrease. It is estimated that losses related to heat stress cost the dairy industry up to $1.5 billion annually.

Heat stress in dairy cows has been defined as the point at which rectal temperature exceeds 101.3ºF, with breaths exceeding 60 per minute. Dry matter intake is reduced, and the cow’s mechanisms to digest and utilize nutrients are altered. Conversely, as the cow’s heat load is reduced, nutrients are “freed up” to be utilized for more productive tasks, such as milk production, reproduction and immune function.

Without heat abatement measures, heat stress can cause a significant increase in blood concentration of the stress hormone, cortisol. This can severely weaken dairy cows’ immune systems, making them more susceptible to costly diseases such as metritis and mastitis, as well as increase somatic cell counts. High-producing cows are particularly at risk, as they generate more heat.

While steps to improve the animals’ physical environment can help alleviate heat stress, their health may still be compromised. Changing diets and feeding strategies can further help the dairy cow cope with hot temperatures. However, when considering new or novel nutritional strategies to support normal health and immune status during heat stress, it is a good idea to ask for a review of supporting research before making a final decision.


Nutritional recommendations

Steps dairy producers can take to manage heat stress include:

  • Use high-quality forages, and increase the energy density of the diet to reduce gut fill.
  • Consider the addition of high-fat feeds, bypass fats or lower fiber feedstuffs.
  • Alter feeding times to allow more feed intake at night, when it is cool.
  • Utilize total mixed rations to reduce feed sorting by cattle.
  • Ensure an adequate source of cool, fresh water. As temperatures rise into the mid-90s, dairy cows will increase their water intake by as much as 50 percent.
  • Consider adding a nutritional supplement to help support normal immune function.

Heat stress research

Results of a study conducted at the University of Arizona demonstrated that animals receiving a proprietary nutritional product had significantly greater dry matter intake, reduced respiration rates and lower rectal temperatures during heat stress, and lower somatic cell counts after heat stress during the recovery period, compared with non-supplemented cows.

In a Texas study, cows receiving the same nutritional supplement averaged 2.8 pounds more milk per day than the control group during a 15-week trial period, from July through October, and five more pounds of milk during the final seven weeks of the study. Both cow groups were housed in a freestall barn equipped with fans and sprinklers.

Heat stress is a risk facing every dairy-producing region of the U.S. Using proven nutrition and heat abatement strategies gives dairy producers the best line of defense against heat stress, resulting in improved herd health and productivity. PD

References omitted but are available upon request. Click here to email an editor.

David Kirk, Ph.D., PAS, is a dairy technology manager with Phibro Animal Health Corp. and has 25 years of experience as a dairy nutritionist in the feed industry.

David Kirk
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  • Dairy Technology Manager
  • Phibro Animal Health Corp.
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