Serving the Farming Industry across the Midlands for 35 Years
Dairy farmers are being urged to keep heat stress front of mind following two extreme heatwaves this summer.

• Cows struggle in hot conditions

• Lower performance and fertility

• Feed during cooler temperatures

Dairy farmers are being urged to keep heat stress front of mind following two extreme heatwaves this summer.

Met Office predictions suggest extreme weather events are likely to become the norm. This summer saw a record-breaking 40.3°C heatwave in July – followed by a 35°C heatwave three weeks later in August.

The UK is experiencing more frequent heat waves each summer, with temperatures reaching the highs of 30°C in the day, say meteorologists, while evening in-shed temperatures are staying above 20°C. 

Wynnstay dairy specialist Beth Parry says this means a change of tack when it comes to ventilation and minimising heat stress in dairy herds. “High temperatures will see cows struggle and performance and fertility may be affected,” she warns.

Conception rates, days open and anestrus, will all be impacted when the 24-hour daily average THI (temperature humidity index) is 65 or more. This is easily achieved when the temperature hits 21°C at 60% humidity.

“This can affect not only cows being served on the day, but also those served up to three weeks ago, and those to be served in the next three weeks.”


While farmers can look to invest in ventilation systems and fans within the shed for long-term solutions, Mrs Parry says there are a few management techniques which can help more immediately.

“Cows suffering from heat stress often see a drop in milk production and quality which is linked to the cow’s innate instinct to utilise her glucose reserves to reduce her core body temperature through panting, saliva and sweating,” she explains.

“This results in excreting vital electrolytes required for health. These reserves would otherwise be partitioned for maintenance, production and fertility.”

Mrs Parry recommends offering a buffer feed during the cooler morning and evening periods to help to alleviate the problem. But higher fibre buffers such as hay or older silage take longer to digest, and the cow will produce more heat as a result.

Better forage

“Supplementing higher-quality forage with a molasses product will help to improve fibre digestibility and stimulate dry matter intakes. This will benefit milk quality and butterfat levels.

“Molasses has also been shown to produce a greater amount of butyrate in the rumen, the volatile fatty acid responsible for gut tissue growth, thus promoting a healthier and more efficient rumen.”

Molasses-based products are naturally high in potassium, helping to replace electrolytes lost in the greatest amounts through the increased sweat and saliva production of heat-stressed cows, says Mrs Parry.

“Research has shown that supplementation with potassium can counter some of the yield losses experienced through heat stress, particularly if a sodium source, such as rock salt is also provided.”

Stay vigilant for signs of stress

Monitoring water intake and manure consistency can help identify whether livestock are heat stressed.

“Like humans, cows increase their water intake in the heat, drinking 90-150 litres on a normal day, so we need to offer plentiful, clean water. Outdoors, check any natural sources as the lack of rainfall is impacting water levels,” says Mrs Parry.

“Also watch out for manure consistency,” she adds.

“Decreased gut motility and rumen fermentation occurs when the cow is experiencing heat stress, leading to loose muck and lost nutrients. Reformulating the ration can help achieve optimum nutrition potential during phases when dry matter intake drops.

“Alongside this, we want to reduce cow standing time. Consider making milking groups smaller throughout the summer, so less time in the collecting yard. This can help cow flow in the parlour, and competition to feed and water troughs in the shed.

“Managing extreme heat isn’t going away, so ensure it stays top of your priority list and use the cooler winter months to plan ahead for prevention next year.”