Feeding Strategies to Combat Heat Stress

When the mercury's rising, feeding and best practices become crucial to keeping your cows productive

The arrival of steamy summer weather can quickly push your dairy cows out of their comfort zone. However, changing your feed management, while adopting other recommended practices, can help reduce the impact of high temperatures on your herd's milk production and comfort.

Cows are most comfortable when the ambient temperature ranges between five and 25 degrees Celsius. The air's relative humidity can also affect how warm the temperature feels, but 25 degrees is a good benchmark to keep in mind when dealing with the negative effects of heat stress.

Heat stress symptoms include elevated respiration rate, elevated rectal temperature, impaired metabolism and lowered reproductive performance. Above 25 degrees, cows will change their behaviour to reduce the effect of that stress. Cows, like all animals under heat stress, try to stabilize their body temperature within a very narrow range.

Temperature - Humidity Index Table

Temperature - Humidity Index Table

Text explanation: Temperature - Humidity Index Table

The close connection between feed intake and milk production, and the normal tendency to eat less when it is hot, is a key reason why milk production often drops in the summer. By ensuring your cows get fresh feed, you can use their natural behaviour to stimulate their appetites.

Some farms commonly feed a total mixed ration every other day. Since fermented feeds like haylage and corn silage spoil and heat quickly when it's hot outside, eliminate this practice during the summer. Mixing fresh diets daily or twice daily is important to promote feed intake.

It's also important to push feed up more frequently. This chore is still not automated on many farms and, like many seemingly small tasks, the importance of doing it frequently really can be overlooked. Many dairy farms push feed up two to four times a day to promote feed intake.

Adding two feed push-ups to your routine during hot weather will counteract some of your cows' tendencies to eat less.

Dairy cows can dramatically increase water consumption during hot weather. To ensure good water availability, check flow rate, cleanliness of troughs or bowls and accessibility by all cows, particularly timid, first-lactation cows.

Cows will also perform better when kept cooler. There are four main methods to cool them when the mercury rises: conduction, convection, radiation and evaporation. The most efficient way to improve cooling is convection-increasing the air flow over cows-and augmenting evaporative cooling by wetting the cows or the air around them. Also keep in mind, if you have overcrowding, heat dispersion through cow separation will be reduced.

Hot weather typically affects high-producing cows more than their lower producing herdmates. High-producing cows tend to have higher feed intakes and generate more metabolic heat and heat from feed digestion. This increases their stress load compared to lower producers with less feed intake.

As well, consult your copy of the Code of Practice for the Care and Handling of Dairy Cattle, published last year. The Temperature-Humidity Index chart, reproduced on page 66, shows combinations of temperature and relative humidity that exceed an index value of 72, considered the level when heat stress begins.

The code's five recommended best practices for when the Temperature-Humidity Index exceeds 72 include:

  • providing shade;
  • considering average temperature and humidity when deciding on a cooling system;
  • using evaporative cooling if temperatures are near or above normal cow temperatures for significant portions of the summer;
  • using evaporative cooling in combination with tunnel ventilation and feedline soaking for very high temperature and humidity combinations;
  • keeping milking parlours, holding pens and housing areas cool.

Adjusting for temperatures this summer can also include a discussion with your nutritionist. You want to ensure mineral levels, added buffers and non-structural carbohydrate levels, in particular, are optimal for the season.


Code of Practice for the Care and Handling of Dairy Cattle. National Farm Animal Council, 2009.

This article appeared in the Ruminations column of The Milk Producer Magazine, July 2010

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