This summer has just started but it has already been marked by some extreme heat episodes in central Europe. During the second and third week of June a heatwave has hit France, Spain, Germany, and the southern UK. This heat episode has occurred unusually early in the season, ahead of the summer solstice. Drought is also striking, with heavy consequences for agriculture in southern European countries. In Italy, lack of moisture and high temperatures are putting harvests in jeopardy.

However, extreme heat does not only affect crops. It also impacts on animal welfare and dairy cattle production.  In a climate change context where heat waves and drought will be more and more frequent, it is important for farmers to know how heat is affecting their livestock, and what the consequences might be for his dairy farm. This might be true even for regions where heat stress was not considered as an issue until a few decades ago, such as the UK or northern Europe.


The Temperature Humidity index

The Temperature Humidity Index (THI) quantifies the intensity of weather stressors and helps stockbreeders monitor heat stress. It considers the combined effects of excessive heat temperature and relative humidity on cow health. The index is expressed as a score.  Dairy cows begin to show signs of heat stress at a THI of 68 or more.

THI index température humidité
Temperature Humidity Index (THI)


An increase in THI above 70-75 which corresponds to temperature of above 25°C and RH of 50%  or more, results in a significant decrease in the pregnancy rate of cattle. This decrease can be as important as 50%  compared to optimal climate conditions.against cow heat stress


Cows heat stress symptoms

Animals exhibiting heat stress symptoms will be seen standing rather than lying down. They will pant and sweat and will often move closer together and stand in tightly packed groups. When stress is intense cows will become restless. They might keep their mouth open and breathe with tongue protruding, possibly drooling,

The physiological responses to heat stress include:

  • Panting: respiration rates increase up to the stage of panting. This thermoregulation mechanism involves an increase in evaporative cooling, but it might also lead to an increase in blood pH.
  • Sweating:  also to lose heat through evaporative cooling.
  • Vasodilation: higher blood flow toward the cow’s skin favors the dissipation of body heat.
  • Increased salivation:  for wetting the animal’s body.

Effect of heat stress on cow milk production

Traite de vache, production de lait

Heat stress can represent a major concern for dairy producers, as it affects negatively both the quantity and quality of production. High temperature and humidity result in a loss of appetite as an adaptive response that decreases rumination time. In lactating cows, feed intake begins to decline at air temperatures of 25–26 °C. In effect, rumination is a process generating metabolic heat, whose decrease reduces body temperature, allowing cows to adapt to higher ambient temperatures. However, as lower amounts of food are ingested milk production also declines. This effect is particularly evident in high yield breeds such as the Holstein, where heat stress can result in yield reduction of 10 – 40%.

In addition to quantity, quality is also impacted. Many studies highlight decreased fat and protein contents in milk from heat stressed cows. Heat stress can increase the somatic cell content, which is an indicator of a degradation in milk quality. In addition, altered levels of prolactin, thyroid hormones, glucocorticoid, growth hormone, estrogen, progesterone and oxytocin might be observed, with further effects on the milk production and quality.

Effect of heat stress on cows reproduction system and fertility rate

When cows are under heat stress, reproductive efficiency declines. Heat stress results in reduced duration and intensity of estrus, altered follicular development and less efficient sperm.

In addition, even when fertilization takes place, heat stress can result in abnormal embryonic development.

These effects are likely multifactorial and connected to hormonal alterations taking place in the body of cows. As a result, during the hot season conception rate in dairy cows decreases worldwide. The Temperature – Humidity index is a useful indicator to evaluate the link between weather and conception rate.

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Providing cow comfort and preserving production: Solutions

Given the adverse effects of excessive heat, it is important to put in place protective measures for the dairy herd. Different practices can help cows cope with high temperatures:

Increase available water.

Cows need to increase water intake during times of heat stress to dissipate heat through respiration and by sweating. According to US veterinarians water consumption might increase by as much as 50% in high temperature periods. If sufficient water is not available, cows might divert water normally destined for milk production for transpiration and heat dissipation.

Improve forage quality and change feeding timing.

During severe heat stress, total feed intake and milk production may decrease by more than 25%. Changing feeding time to make it correspond to cooler moments during the day (such as in the evening), and switch to a better forage quality might help cows to cope with heat stress.

Provide shade.

Providing shade is essential in order to reduce heat stress. Shade can reduce heat loads on cattle by up to 30%. Natural shade provided by trees is ideal but is difficult to provide in many situations. Providing artificial in the form of  permanent or portable structures can represent a valid alternative to trees. Particular attention should be payed also when designing livestock buildings. In order to avoid excessive temperature roof windows should be avoided and the building should feature ventilation openings. Alternatively, ventilation fans could be installed to grant fresh air during warm spells.

Keep a special eye on herd health status.

During times of high stress the herd needs extra monitoring to be ready if any health trouble arises. Already vulnerable cows might suffer more during heat spells and require special care. Monitoring tools have been developed to keep an eye on the herd at all times. One of them is Farmlife, a tool by ITK for monitoring livestock health and reproduction.

Heat’Adapt and Farmlife

Heat’Adapt is a new service of Farmlife against heat stress. It calculates the THI in real time and for the next 5 days, based on the weather forecast.  This service is combined with the Feed’Live and Time’Live services in FarmLife and provides insights on how the herd is coping. After the summer, the overall resilience of the farm is scored, based on heat stress impacts which are measured on herd behavior, pregnancy rate and milk production and considering the specific level of exposure. Embedded in this new service there is an innovative warranty to mitigate the economic loss in case of exceptionally hot summers.

Heat’Adapt service in Farmlife : THI dynamics are displayed in graphs

Heat’Adapt goes beyond simple alert service.

It offers an all-round assistance service that help farmers anticipate, monitor, mitigate heat stress. It does not only warn farmers about the level of heat stress affecting their cattle, but allows to develop resilience and adopt, over time, the right measures to protect cattle and milk production during heat waves.

Farmlife is a comprehensive solution that uses real time data from a sensor installed in a collar worn by cows.  These are combined and analysed with artificial intelligence to provide a holistic view of cow health status, reproductive functions and the risk of heat stress.

Farmlife offers 6 services in one :

  1. Feed’live, to monitor ingestion and rumination
  2. Heat’live, to monitor heat onset
  3. Vel’live, to know when calving is imminent
  4. Time’live, to monitor cow health and be aware of discomfort and disease symptoms
  5. Grass’live, to monitor and quantify the time cows spend grazing in outside pastures
  6. Heat ‘dapt, to forecast heat stress risk, monitor the efficiency of adaptive measures against heat stress, and improve farm resilience against heat waves

The integration of information on feeding, movement, reproduction and heat stress effectively allows to have a complete picture of cow’s health in real time at all times, making Farmlife a holistic animal care tool.

Stockbreeders can compare individual behaviours to the behaviour of the herd and spot cases that need particular attention. Once the problem is identified they can easily check the effectiveness of their measures, to decide whether they should be followed or not.