In view of the heatwave, dairy producers are being warned to take steps to reduce the impact of heat stress which can cause a major decline in cow performance.

Signs of heat stress include cows flicking water over their backs, loose muck, cows lying against walls and a reluctance to come to the feed area where it is usually hotter.

Tom Chanter, InTouch feeding specialist, said: “Cows are most comfortable at an ambient temperature of just 4°C and therefore the heat is causing major issues, with many producers noting a marked drop in milk quality.

“This is due to an increased level of nutrients being used to simply keep the body cool, in combination with a change in behaviour which can result in reduced daily feed intakes.

“A reduction in milk quality is a widely observed outcome and if feed intakes are inhibited, milk yield will also drop off.”

While achieving good ventilation in sheds should be a top priority, Mr Chanter says the addition of a live yeast into the diet at maintenance level, can also help to ‘settle’ cows and maintain performance during the summer.

Live yeast supports rumen stability and digestion, increasing utilisation of available nutrients, which is particularly important if cows are not achieving expected daily intakes.

“An additional benefit is that it also scavenges oxygen. Oxygen in the rumen generates heat and therefore by reducing the level, there’s less internal heat for the cow to expel, lowering the energy required for maintenance.”

Mr Chanter added that its inclusion in diets can also help mitigate the risk of acidosis.

“Cows with heat stress can be predisposed to developing acidosis, particularly if feed intakes are down, as this can cause the diet to become unbalanced, risking acid loading."

John Lawrence of Mole Valley Farmers says that providing speciality feed supplements can boost immune function and help cows cope better during the periods of heat stress currently being seen in the UK.

He said: “Heat stress is not just about temperature - it’s a combination of temperature and humidity which is used to produce a Temperature Humidity Index (THI). If you look at the THI from Hereford to Devon and Dorset, all areas are showing a THI of 72 or higher which is likely to cause heat stress.”