Even moderately warm temperatures can cause heat stress in cattle. This results in depressed feed intakes, lower milk yields, reduced fertility and increased risk of mastitis. 

Historically, ambient temperatures in UK summer milk production would not have been considered as a limiting factor. However, according to a report by Ian Ohnstad from The Dairy Group, there is increasing evidence that even the relatively low temperatures experienced during the UK summer can have these effects.

Dairy cows are homoeothermic animals and need to maintain a constant body temperature of around 38.8°C +/- 0.5°C.

Animals exhibiting signs of heat stress will become lethargic and inactive and will often stand with heads bowed. They will often pant in an attempt to increase heat loss. Perversely, cows suffering heat stress will often move closer together and stand in tightly packed groups. Respiration rates will also increase as cows attempt to increase their heat dispersion.

A summary of the advice in Ian Ohnstad’s report is as follows:

Increase nutrient concentration. Whenever feed intake decreases due to heat stress, nutrient concentration should increase to maintain adequate intake of all required nutrients. Increasing the energy density might entail the use of greater amounts of concentrate and/or by-products. Increasing the energy density of the diet, using high quality forages and feeding more concentrates should help the animal maintain her energy requirements even though she consumes less dry matter. However, care should be taken to balance diets properly in order to avoid digestive disorders such as acidosis and displaced abomasums.

Change feeding times. Changing feeding times can also be helpful. Feeding 60% of the summer ration between 8.00pm and 8.00am will assist intakes.

Provision of water is critical. Cows are unlikely to walk more than 250 metres to drink so it is essential that all fields and buildings are adequately supplied. As temperatures rise, cows will drink more. In hot weather, water intakes can increase by 10 - 20%

Consider shade, ventilation, and cooling. Common areas where cows congregate that will benefit from a reduction in heat exposure are holding areas, feed areas and loafing areas. The installation of fans, combined with spraying water onto cows can dramatically reduce the effects of heat stress. Also consider roof insulation and the effects of roof lighting on building heat.