Cow heat stress: how is it caused by climate change?

Cow heat stress is a state that occurs when the body temperature of cattle increases and it cannot be dissipated adequately, leading to discomfort and physiological alterations. It can represent a major concern for livestock producers, as it affects negatively both the quantity and quality of production. Cow metabolism and hormonal balance are disrupted as external temperature and humidity increase, and internal body temperature starts to rise.  Heat stress has adverse effects on, reproductive performance,  health and milk production. Extreme heat events might even lead to cattle mortality.

In a climate change context where heat waves and drought will be more and more frequent, it is important to know more about the effects of heat stress and how they can be mitigated to minimize losses in their 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, northern Europe or north America.

For example, in June 2021 an exceptional heat wave hit western Canada and the north west USA, with record temperatures of up to 49°C. The effects have been destructive, on ecosystems and human activities. This event has heavily impacted the health and production of cattle in livestock farms, as reported by farmers and authorities. A series of heatwaves has similarly hit Europe and the UK this summer 2022 . Even though they were not as extreme as the 2021 event in North America, they have had negative impacts on cattle comfort and production.

The frequency of these extreme events and the evidence of their impacts on cattle is hitting livestock breeders straight in the face. However not all farmers are able to anticipate them and adopt timely measures reducing negative impacts on cattle. In northern regions, where climate is normally considered cool, the perception of risk related to heat stress is still low.

Cows in the shadow during the summer

Measuring the impact of cows heat stress on farms with Heat’Adapt :  The farm resilience score

To take actions to adapt our livestock farms to climate change, the first step is to quantify its effects by looking directly at your animals.  Heat’Adapt is a new Farmlife monitoring service to manage heat stress based on weather data and animal behavior, measured through an accelerometer sensor (AXi) on a connected collar. This service provides a heat stress forecast using the weather forecast and a mathematical model relating it with cattle heat stress. In addition, it estimates the impact of heat stress on the herd through the analysis of animal behavior during heat events compared to normal. These estimates are used to calculate your farm “resilience score”, which allows  evaluate the efficacy of the measures  putted in place to adapt to heat stress events.

The three axes of cattle welfare and health

The resilience score is calculated at the end of the season by analyzing cattle behavior over the period from April 15 to October 15. It allows farmers to benchmark their farm performance towards heat events to identify areas for improvement for next season.  A good “climate resilience score” is a good performance during heat waves, in terms of nutrition, comfort and reproduction. The accelerometer sensor (AXi) on the Farmlife connected collar can be used to measure each of these behaviors and assign them a score (ranging from from A+ to D ) in terms of their difference during heat events from an “as usual” scenario.

The global resilience score corresponds to the average along these three “axes of well being”.

  •  Nutrition: during heat events food intake and rumination time decrease as an adaptive response decreasing internal heat generation. The nutrition score is calculated by evaluating the decrease in ingestion time during heat events compared to usual.
  • Animal comfort: Signs of discomfort are identified as increased standing time or a pattern of movement different from usual, indicating restlessness. The reproduction score is calculated by evaluating the decrease in time spent lying down compared to usual.
  • Reproduction: When cows are under heat stress, reproductive efficiency declines and heat onset and pregnancy can be disrupted.  The reproduction score is calculated by comparing the number of cycles required for effective fertilization compared to usual.


Scores are assigned as follows:

  • A+ = the performance of the herd is at least 5% higher than the reference duringperiods of heat stress.
  • A = the performance of the herd is maintained compared to the reference (+/- 5%) duringperiods of heat stress.
  • B , C and D = the performance of the herd has more or less decreased compared to thereference during periods of heat stress


Livestock adaptation to climate change: how to use the resilience score

The resilience score can be used to estimate a benchmark against which farmers can assess the efficacy of adaptation measures against heat stress. As it is calculated once a year, it can be considered as an indicator of global farm performance during heat events rather than a day-to-day monitoring tool. It allows farmers to revise and ameliorate their strategy and put in place new measures that will be re-assessed year after year. It also helps planning investments on new equipment and on the adaptation of existing structures to mitigate the effect of extreme heat.

Thanks to the combination of daily indicators with a yearly resilience score, Heat’Adapt is a complete tool that can help raise the awareness on the long term effect of heat stress on cattle, and ensure livestock farm sustainability in times of climate change.

If you want to know more about Farmlife and Heat’Adapt, see here.