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OSU Extension

College of Food, Agricultural, and Environmental Sciences

July 28, 2016 - 6:53am -- lewandowski.11@...

          The forecast is calling for hot weather.  Dairy cows begin to experience heat stress when the temperature-humidity index exceeds 68 so this current spell of hot weather can definitely have a negative impact on milk production, reproductive performance and immune function.   Many of these negative impacts can be explained by changes in cow behavior when they experience heat stress.  These changes include more time standing, decreased dry matter intake, and an increased maintenance energy requirement.

          Generally dairy farmers minimize heat stress by providing fans and water misting systems in barns and milking holding areas.  Providing ample cool, clean water is vitally important to minimize heat stress.  Water consumption by dairy cattle will increase 29% with an increase in air temperature from 64 to 86 degrees F.  Another strategy to reduce heat stress for dairy cattle is to modify the ration.  An excellent article in the dairy section of the eXtension web site entitled “Dairy Feeding and Management Considerations during Heat Stress” provides some good information about ration modifications during periods of high temperatures.  I will summarize some of the main points:

  • Maintain effective fiber intake: This is best done by feeding high quality forages that will increase the energy content of the diet while maintaining adequate rumination without excessive heat of fermentation.
  • Add fat to the diet: This is expected to decrease heat production during feed digestion while increasing available energy.
  • Add yeast cultures:  Yeast cultures have been shown to improve fiber digestion and to stabilize the rumen environment.
  • Modify the mineral content of the ration: Sweat from heat stressed cows contains high amounts of potassium and sodium that need to be replaced.  According to the eXtension article, “To achieve these increased concentrations of potassium and sodium and maintain adequate dietary cation-anion difference (DCAD), additional amounts of sodium bicarbonate, potassium carbonate, or both may need to be added to the diet. In addition, higher amounts of potassium reduce the absorption of magnesium, thus increasing the requirements for magnesium.” 

          The entire article can be read on-line at: or you can contact the Wayne County Extension office at 330-264-8722 and I can provide you with a copy of the article.