Recognize, prevent heat stress in dairy cattle

Dairy cow.
(Farm and Dairy file photo)

We’re coming up on some of the hottest months of the year. It’s time to get familiar with the signs of heat stress and how you can keep your dairy herd healthy and happy.

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1What is it?
According to an article by University of Tennessee Extension Dairy Specialist Peter Krawczel, in the most basic sense, heat stress occurs when a cow must change her behavior and physiology to cope with environmental conditions.

2Signs and symptoms
Here are some key signs to watch for in cattle affected by heat stress:

  • Increased respiration rates.
  • Increased rectal temperatures.
  • Decreased dry matter intake.
  • Decreased rumination.
  • Decreased milk production.
  • Increased somatic cell count.

Less visible effects include:

  • Increases in mastitis and other diseases.
  • Increases in mastitis and other diseases.
  • Impaired rumen function
  • Decreased immune function.
  • Increased maintenance costs.

3Behavioral changes
Here are some key behavioral changes to watch for in cattle affected by heat stress:

  • Increased standing time.
  • Crowding around water sources and increased intake.
  • Crowding around shaded areas or cooler areas of the barn.

Cows will increase their water intake up to 50 percent in response to heat stress. Having clean, cool water is a must. Provide at least two inches of linear water space per cow and locate water troughs every 50 feet within a barn or close to shade in a pasture.

Water in troughs should be at least three inches deep and the refill rate of water troughs should be between three to four and a half gallons per minute. Water should also be provided when exiting the milking parlor.

Another critical factor in controlling heat stress is proper air flow. Fans should be installed 12 feet above the cows and angled at 20 degrees. Fans should move roughly 500 cubic feet of air per cow per minute and should move air at a speed of 2.5 to 5.5 miles per cow.

Fans should be included in the holding area as this can be one of the most stressful places for the cow. Water in holding areas can also help with heat stress, but adding water in humid or poorly ventilated holding pens or barns can make the situation worse — water can actually hold the heat in the cow if it does not evaporate off the cow.

A covered feeding area keeps cows comfortable when they are eating. It also keeps feed dry. Some producers may install sprinkler systems, spraying away from the feed and onto the cows. Fans are then used to dissipate the heat from the cow by evaporative cooling of the water on the animal. Water should avoid the cow’s udder, and a cow’s feet should have limited exposure to water.

When in the pasture for long periods of time, cows should have access to clean, cool water and some shade. Consider portable or permanent shade stations to provide relief. If mud holes become a problem where cows congregate, consider moving the shade structure or fencing off muddy areas until that area has dried.

7Increase ration density
Cows decrease in milk production during hot weather because they eat less. Increasing the energy density of the diet can compensate for the decrease in dry matter intake.

High-quality forages such as summer annuals or high-quality perennials should be available. Silage, pasture, and hay are acceptable.

Do not overfeed highly degradable protein (65 percent or greater degradable crude protein in the rumen) because this also increases the heat increment and requires more heat to be dissipated from the animal.

Sources: University of Tennessee Extensions: Tips for Recognizing and Managing Heat Stress in Dairy Cattle; Heat Stress in Dairy Cattle.

(Farm and Dairy is featuring a series of “101” columns throughout the year to help young and beginning farmers master farm living. From finances to management to machinery repair and animal care, farmers do it all.)

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  1. That’s a good idea to make sure that the cows will have plenty of water to drink. I would think that would be a good way to make sure that the beat doesn’t dehydrate them. I’ll have to remember that as well as potentially getting a soaker or something for them if I decide to get some cows.


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