Preventing heat stress in dairy cows

Long-term forecasts predict a hot summer, making planning to avoid heat stress essential. Such stress can have severe implications for dairy cows, causing reduced feed intakes, depressed production and health issues.

Heat stress is not just caused by an increase in temperature, says ruminant nutritionist, Chris Savery of The Dairy Group. “Heat stress is triggered by a combination of temperature and humidity. When the temperature humidity index is 72 or above, then problems may arise.”

Elevated breathing rates can be an early indication of heat stress. “Walk among the herd and look at how fast individual cows are breathing,” says Mr Savery. “When more than 40% of the herd are breathing faster than normal, then you may have a problem.”

In these conditions, getting the basic things right, like air flow and water supply in buildings, are even more important.

“The first step is to improve natural air flow. Look at which areas of the building can be opened up. Taking out every other Yorkshire board and opening up the central ridge can significantly improve ventilation.

“Fans should only be installed as a last resort when building improvements can not be made.”

This is a view shared by Dick Sibley of West Ridge vets. “Before investing in high-tech systems, reduce stocking density and milk smaller groups to avoid over crowding.

“Water supply is perhaps the most important consideration but, is all too often inadequate.”

Water intakes can increase by up 10-20% in hot weather, says Diana Allen, dairy consultant. “Cows can easily drink more than 100 litres of water a day, so it is essential to make water available in the collecting yard and when cows come out of the parlour.”

High yielding cows are also more prone to suffering from heat stress. “These cows generate more heat as a result of their higher feed intake and so require more drinking water,” she says.

High temperatures can also have a knock on effect on feed intakes. “Intakes can reduce by 8-12% once temperatures go above 26C and milk production can drop by 5-20%.”

To rectify this problem, buffer feed in the early morning between 4am and 6am or late evening between 9pm and 11pm. Also, feed more frequently to prevent feed from heating up and reducing intakes further.

“Don’t forget your dry cows, particularly those close to calving,” Mrs Allen continues. “These cows will already have low dry matter intakes and rapid weight loss at this stage will lead to subsequent metabolic problems.”

During hot weather, it may also be necessary to make modifications to the ration. “Ration components will influence heat production – low quality, stemmy forages will generate more heat during fermentation, increasing a cow’s heat load. High quality forages are digested faster and will produce less heat.”

If feed intakes reduce as a result of heat stress, it may be worth enriching the diet, says Mr Savery. “The key is to make diets more energy dense, be it by using better quality forages or adding fats.”

It is also essential to ensure adequate mineral supply. “Salts can be lost via sweat, so it is essential to balance rations accordingly.”