Significant milk yield losses as a result of heat stress on UK dairy cattle could amount to tens of thousands of pounds in both housed and grazing systems, if the results of a study conducted last summer are anything to go by.

According to Dr Tom Chamberlain, founder of Chalcombe who was working in partnership with Lallemand Animal Nutrition, on the ongoing project, dairy cattle were impacted by heat stress on more than a third of the days during a six-month study in the summer of 2021.

“Milk yield losses due to heat stress averaged 128 litres per cow over the summer period in housed situations, ranging from 84 to 191 litres,” Dr Chamberlain said.

“Potential losses were even higher in grazing situations at an average of 284 litres per cow. They ranged from 171 to 445 litres but actual losses would depend on the amount of shade available.”

Producers’ financial losses as a result of heat stress can amount to more than £20,000, on average, per 200 grazing cows and more than £10,000 on average per 200 housed cattle; these losses equate to the full sales value of the milk as no costs, such as concentrates fed, can be recovered.

The study was run across eight farms outdoors and six farms indoors, none of which had fans or misting systems in their buildings.

“Temperature and humidity are measured at pasture and inside the shed for the study. The data is then converted into a temperature index also used in Australia and the US.

“However for farmers in everyday situations, there are simple things they can do to monitor whether their cows are experiencing heat stress,” he said.

“Generally, our cows start to suffer when the temperature goes above 20 degrees and producers can monitor cows panting to check if they reach over 60 breaths per minute which suggests that they’re suffering from heat stress. Cow behaviour is also a good indicator, such as when cows are standing more or clustering in the shade.”

To help mitigate heat stress, producers should provide cows with as much access to shade as possible and ample cool water, as water intakes rise markedly during heat stress, says Lientjie Colahan, Lallemand sales and technical support.

Read more: Heat stress in Scottish dairy herds hits fertility

“It’s also important to review their ration and consider supporting the rumen with feed additives,” she said.

“When animals are suffering with heat stress their rumen is not working as efficiently as usual so, feeding a rumen specific live yeast such as Levucell SC can help to improve rumen function which, in turn, will help support cow health and performance.

“Another impact of heat stress is cows suffering from a sodium deficiency. A side effect of this is reduced feed and water intakes, which can negatively impact mineral balance and milk performance. To help mitigate this, producers should provide cows with free access to salt licks around the feeding area,” she adds.

The study will be running again this year, on 20 sites across 10 farms over a wider geographical area of England. To support all dairy farmers, the results from the Lallemand sponsored farms will be reported in real time here: https://bit.ly/3sMo25X