Summer heat stress is big challenge for dairy cows

• Cows suffer during heatwaves

• Study aims to raise awareness

• Focus is on water and nutrition

Heat stress is becoming a costly problem on UK dairy farms with some businesses losing up to £90,000 due to their cattle overheating, according to results from an ongoing study.

The study, which is entering its fourth year, aims to raise awareness of heat stress and assess how big a problem it is on UK dairy farms.

Findings from last year’s study were published at the Society of Feed Technologists ruminant conference in Coventry. Tom Chamberlain, founder of Chalcombe dairy consultants, is conducting the research in partnership with Lallemand Animal Nutrition.

“The study took place across nine farms in England and we continuously measured the temperature and humidity inside and outside the sheds, with the results streamed in real-time,” said Dr Chamberlain.

“The results show there were four heatwaves inside the sheds starting from early May until the middle of September, with the cows experiencing heat stress for 99 days, or 57% of the six-month trial period.”

Grazing animals

Data from cows grazed outdoors found they experienced heat stress for 37 days, or 22% of the trial period, with the heat stress season running from the middle of June until the middle of September.

“Predicted milk yield losses averaged 138 litres per cow for housed cattle, ranging from 100 to 187 litres, while grazing cattle experienced an average loss of 129 litres per cow, ranging from 79 to 169 litres,” added Dr Chamberlain.

“The average financial loss incurred was £128 per cow, ranging from £96 to £180 a cow, with herd losses ranging from £24,000 to £90,000.”

He said the study results show heat stress is a growing problem for both housed and grazed dairy cows, and it should be considered in herd management plans.

Milk yield

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

Dairy farmers can mitigate the impact of heat stress by focusing on water, the cows’ environment, and nutrition.

He said: “Farmers should open up sheds as much as possible, install fans and misting systems to keep cows cool, and ensure a good supply of clean and cool drinking water that’s less than 20°C.

“They can also improve rumen health by feeding fresh rations more frequently, using high-quality forage, and including a rumen-specific live yeast, such as Levucell SC, in the ration.”

The heat stress trial will be expanded for 2023 to comprise 12 farms across the UK – ranging from dairy units near Edinburgh in Scotland to Southampton in the south of England, including a holding in Northern Ireland.