June may seem a long way off, but the record-breaking temperatures experienced during that month are thought to have cost UK dairy farmers more than a litre a day in lost milk production per cow.

That was the stark warning from Lallemand Animal Nutrition’s heat stress project which highlighted that average milk yield losses in June could have been up to 36.6litres per head in grazing cows, and 31.1litres for housed milkers.

The data reveals that a 200-cow housed herd could have lost 6216litres in the month, while a similarly sized grazing enterprise would have lost up to 7318 litres.

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Dr Tom Chamberlain, founder of Chalcombe Ltd, who has run the project for the last four years says the estimated milk production losses for housed herds taking part in the project ranged from 14.4 to 39.8litres per cow for the month. Losses for grazing herds were estimated to be between 19.1 and 65.6 litres per cow.

“Any reduction in milk production is a total loss; there’s no way to recoup anything as the input costs will have remained the same,” says Dr Chamberlain.

“American work suggests that milk yield losses are only about 50% of the total production losses a herd experiences after a heat wave.”

The temperatures in June, which the Met Office has confirmed as the hottest on record in the UK, are also likely to have impacted future lameness problems and herd fertility.

Excessive standing from cows trying to keep cool during the hot weather may lead to increased lameness, due to solar bruising and ulcers, that will manifest in late summer and early autumn.

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Dr Chamberlain added: “The heat may also have caused bulling signs and conception rates to fall, resulting in a drop in numbers of cows calving next March; we have previously seen a 50% fall in calving numbers from heat waves in 2022.”

He encouraged farmers to take steps to mitigate the impact of heat stress as periods of hot weather are likely to reoccur this summer.

“It was an early heat wave in June and there will probably be more to come, so farmers need to work out a heat stress management plan,” he explains.

“Cows will start to suffer when the temperature is about 19-20°C in the UK, and once they’ve been suffering for too long, they’ll start to experience problems with milk yield and fertility, as well as a deterioration in rumen health.”