Prepare now to protect milk yields from heat stress this summer

Milk yields could be affected by up to 20% if UK dairy farmers aren’t fully prepared to tackle heat stress this summer.

In this month’s Nadis Disease Alert webcast, James Aitken, partner at Orchard Veterinary Group in Glastonbury, warns that even the relatively low summer temperatures experienced in the UK can result in a reduction in the feed intake of dairy cattle.

This in turn can lead to lower milk yields, reduced fertility and an increase in the risk of mastitis, he says.

“The thermal comfort zone for dairy cows is between 5C and 25C. Outside of this range, cows need to expend extra energy – either keeping cool or warm.

During hot weather, cows can increase heat dispersion by increasing blood flow to the skin and by panting and drooling.

To further reduce heat generation, fermentation in the rumen decreases and as a result the cow eats less. At 35C, dry matter intake could fall by of up to 30%.

See also: Act early to reduce dairy cow heat stress

Furthermore, drooling means much of the bicarbonate in cow saliva ends up on the floor rather than in the rumen, increasing the risk of rumen acidosis.

“This prevents efficient fermentation of fibre and means butterfats can fall dramatically. Unsurprisingly, yields can be significant reduced – by up to 20%,” he says.

Mr Aitken made a series of recommendations to tackle a fall in dry matter intake as a result of heat stress:

  • Feed proportionally more during cooler periods, for example overnight
  • Increase nutrient content of feed ration to allow for energy losses due to cooling
  • Fibre is essential to stimulate salvia, but beware poor-quality forage
  • Ensure a sufficient water supply, as cows under heat stress will consume up to 100 litres a day.

Humidity also plays a part. While typically cool, the UK has a “relatively humid environment”, he says.

Humidity can be even higher indoors, with moisture produced by the cows and poorly ventilated buildings exacerbating the problem.

“Cows will cope quite well at 30C provided the humidity is low, but at the same temperature with a 70% humidity, cows will be under severe heat stress,” he adds.

Four tips for preventing heat stress

1. Good ventilation is essential

Even modern-looking buildings may not ventilate as you would expect them to on a still day and there are often improvements you can make to ventilation in traditional buildings.

2. Beware of too many roof lights

While plenty of roof lights may make a building feel light and airy, too many will turn it into a greenhouse. Ideally roof lights should have northern aspects.

3. Fans can be helpful

Fans improve ventilation and can also be used to provide a cooling breeze.

4. Water sprays for specific situations

Spraying water over the backs of the cows is a good way to get a temporary cooling effect. But don’t forget that in turn this will increase the relative humidity indoors. So it’s often only employed in specific situations, such as in the collecting yard awaiting milk.