Cows on hot day where heat stress is always a risk

Heat stress in cows

Moderate to high environmental temperatures and high humidity have the potential to significantly impact the productivity, health and fertility of dairy cows. This page is intended to provide a better understanding of the challenge of controlling heat stress for dairy farmers. Always consult your own veterinary surgeon for diagnosis and advice.

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What is heat stress?

Heat stress in cows is caused by a a moderate to high temperature in combination with high humidity. At temperatures above 22ºC cows are unable to dissipate their body heat effectively. This results in reduced feed intake, reduced milk production, decreased immunity and poor fertility. Heat stress can occur both indoors and outdoors. How do you support your cows during and after periods of heat stress? OmniGen can help you.

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Symptoms heat stress

Easy to recognise warning signs include groups of cows panting, standing in the shade or collecting around drinking troughs.

Nico Bons 2 - Door Lianna Kolf

Nico Bons, Top breeder and owner Of Bons Holstein, 
The Netherlands

“Since introducing OmniGen into their diet, my cows have been much better able to deal with heat stress. Even during extended periods of excessively hot weather they eat more and there has been a noticeable decrease in cases of illness, vet costs and vet visits.”

Read the full story here Read the complete article here


Causes of heat stress in cows

The effects of hot, humid weather can be exacerbated by poor ventilation in cattle sheds, a lack of shade in grazing pastures and insufficient access to fresh water.

The Temperature Humidity Index (THI) accounts for the combined effects of temperature and humidity and is a useful and easy way of assessing the risk of heat stress.

The table below illustrates the impact of temperature and humidity on the severity of heat stress.

Table that illustrates the impact of temperature and humidity on the severity of heat stress

Source: National Animal Diseases Information Services

Consequences of heat stress in cows

The performance of cows suffering from heat stress can be significantly impacted: they will consume less (in particular less roughage) and as a result, the rumen will function less efficiently to the point that rumen acidosis may occur. Heat stress can also have a negative impact on the cows’ immune systems.

In a hot and humid cattle shed, the number of bacteria increases and therefore so does the risk of infection. This in turn results in an increased risk of diseases such as mastitis and hoof problems. Cow fertility can also suffer due to heat stress.


Heat stress prevention

You cannot do much about the weather, but you can certainly take measures to improve the living environment for your cows.

  • Make sure cows have free access to plenty of fresh, clean drinking water. Bear in mind that cows can drink more water in a shorter amount of time when the water is 20ºC compared to when the water is cold.
  • Ensure cattle sheds are well-ventilated: prevent excessive direct sunlight and use fans to increase airflow.
  • For grazing herds, bring the cows and feed them inside during the hottest part of the day, or keep them inside during the day and let them outside at night.
  • Keep the cubicles clean and dry to prevent mastitis.
  • Ensure grazing cows have access to shade.
  • Lower the temperature in cattle sheds by installing fans and/or sprinklers.
  • Modify your herd’s feeding regime by feed your cows more often, during cooler parts of the day. Adjust your herd’s diet in consultation with your nutritionist.

heat stress checklist

OmniGen and heat stress

OmniGen can help to alleviate the effects of heat stress by supporting the immune system of dairy cows. Research has shown lower body temperatures and respiration rates in heat stressed cows fed OmniGen, and higher feed intake and milk production. When you start feeding OmniGen  to your cows on time and at the right moment, they may be better able to deal with and recover faster from heat stress.


Get an immunity assessment for your herd

If you’d like to find out more about how we could help you to optimise your herd’s performance, please submit your telephone number to request a callback. We’ll call you within three working days to set a date for a telephone or face-to-face meeting to discuss the following:


Current situation analysis

We’ll work with you to understand your herd’s current status and to identify areas for improvement.


Designing a plan of action

We’ll recommend where improvements can be made and how our products can unlock your herd’s full potential.



We’ll carry out a detailed review to make sure the changes we’ve put in place are working effectively and, where necessary, provide additional support and advice to enable your herd to continue to improve.

Arrange your immunity assessment Get an immunity assessment