Heat stress affects heifers and growth rate

Cooling cows is well known to have an economic return, but there are advantages to keeping heifers comfortable too.

The early warm temperatures this spring can serve as a reminder to be prepared for higher summer temperatures that are sure to arrive. Last summer’s extreme heat tested humans, cows and calves. We often prepare for cooling cows with additional fans, misting, etc. But calves can feel the heat too. According to several studies, calves have a “thermal neutral zone” which is from about 60-75 degrees F in still air. The thermal neutral zone is the temperature range in which the calf does not need to expend extra energy to either keep warm or to stay cool. The range varies due to age, feed intake, body fat levels and hair coat thickness. The strain of maintaining normal body functions in very cool or hot weather decreases the calf’s growth rate and your bottom line. It’s important to keep calves comfortable outside of those temperatures. Also remember that heat and humidity can combine to cause even more stress than is reflected on the thermometer.

Below is a list of visible signs of heat stress in calves that are important warning signs to recognize:

  • Reduced movement
  • Faster breathing rates
  • Open-mouthed panting
  • Decreased feed intake
  • Increased water consumption

What can you do to decrease heat stress? In hot summer months, move hutches into the shade or cover them with shade cloth. Supply unlimited amounts of cool, fresh water to avoid dehydration. A heat-stressed calf can drink up to six gallons of water daily. Fill and/or change the water in calf buckets at least three times per day. Calves may wait to eat until the cooler evening hours so make sure they have plenty of water for overnight. Prop a back edge of the calf hutch up six-eight inches to increase air flow. Don’t handle or vaccinate calves except in the cool early morning hours.

Addressing heat stress in calves makes good economic sense. Heat stressed calves may grow more slowly, reach maturity later and be delayed in entering the milking herd. Worse yet, you might even lose valuable heifer calves.

Lastly, what about heifers ready to calve for the first time? Research has shown that decreasing heat stress in dry cows results in increased calf size as well as improved colostrum quality. So pre-calving heifers should not be exposed to extreme heat either.

Minimizing heat stress on calves and heifers can definitely increase their growth rate and even improve their chances of entering the milking herd on schedule.

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