Are cows still heat stressed?

This is expected during periods of hot weather, but as more recently the weather has been slightly cooler and wetter, are cows still experiencing heat stress?

Heat stress occurs when a cow’s body cannot lose heat fast enough to maintain her normal body temperature (38.6°C). The Temperature-Humidity Index (THI) is commonly used to assess heat stress risk in dairy cows. Both temperature and humidity can cause an increase in the THI index, which results in more heat stress. Therefore, the recent wet weather would still pose a risk for heat stress due to humidity. A THI of above 68 is generally considered the threshold where cows start experiencing heat stress.

Cows are particularly susceptible animals to heat stress due to their high metabolic heat production.

Rumen fermentation and milk synthesis are processes which produce a lot of energy in the form of heat. This means it is more difficult for dairy cows to lose heat during periods of hot weather. In particular, housed cows will struggle during hot or humid weather, especially if sheds are overcrowded or poorly ventilated.

It is important to look out for the key signs of heat stress, and remain diligent, even during our current wetter spell when initially, we may not expect heat stress in cows. Common signs of heat stress are panting, reduced feed intake, decreased milk production, decreased rumination and less time spent lying down (cows stand to try to lose heat). In severe cases, heat stress can lead to poor fertility, a compromised immune system and even death.

To reduce the risk of heat stress during hot and humid weather, there are a number of measures we can take.

Provide adequate drinking water

At least 15% of the herd should be able to drink at the same time, so allow for adequate trough space. Also, check refresh rates and watch cows in the afternoon when water points are under pressure. Ordinarily, lactating cows drink over 100 litres of water per cow per day, so this will be increased greatly during warm periods. Provide clean, fresh water to encourage intakes and maintain health and production.

Apply careful herd management

Tightly stocked sheds can have poor airflow, especially during humid spells. Reduce stocking density where possible. Open vents or shed sides to improve ventilation and if using fans, make sure they are carefully placed. Make sure plenty of shade is available for grazing cows.

Diet Management

Mix rations just before feeding out, so feed is always fresh. Adjust volumes if required and clear away refusals. Consider adding AcidBuf to the diet to encourage optimal rumen function and reduce the risk of acidosis due to heat stress. Dry matter intake is reduced during periods of heat stress, and cows ruminate less, therefore less saliva is produced for buffering, and cows may experience acidosis. Maintain the cow’s energy and nutrient intake through ensuring optimal nutrient density of the ration and make it as palatable as possible.

In conclusion, yes, cows could still be experiencing heat stress in our current humid conditions. Heat stress due to humidity poses a serious challenge to cow health and production that requires proactive management. For more information on how to prevent heat stress in your herd, or on AcidBuf rumen buffer, please contact Trident MicroNutri on 02894 473478 or visit

www.tridentmicronutri.com.