Cows can become affected by heat stress when temperatures reach just 20C. This can lead to reduced milk yields as a result of depression on food intakes.
Just recently the temperatures in the UK have been far above the 20C marker. This combined with 83% humidity gave a stress risk of around 70%. The cows at grass are at a particularly high risk.
Dairy farmers must act promptly to treat the first signs of any heat stress, this is because the rumen can take a long time to adjust, and it can still affect cows a long time after the temperatures have cooled. By adding rumen buffers and yeasts to the diet it can help offset acidosis risk and promote better intakes. If your cows are suffering heat stress they should also be fed less forage.