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May 28, 2015

Heat stress is a reality in Europe!

May 28, 2015

Field survey across Europe reveals that heat stress is a threat from North to South and East to West: European dairy farmers could lose 3Kg of milk/cow/day (up to 5.5 kg) in the summer!

Did you know… How to evaluate heat stress?

Heat stress is linked to ambient temperature but also to relative humidity, which will amplify the impact of heat. The temperature–humidity index, or THI, is a common indicator of heat stress.

A THI of 68, which corresponds for example to 22°C for 45% of relative humidity, is the limit between cow’s comfort zone and heat stress threshold. Keep in mind that if the cow starts showing clinical signs of heat stress (panting, drooling, reduced feed intake…) it may be too late, rumen efficiency, antioxidant status and milk production are already affected (it only takes four hours under mild heat stress to reduce milk production by more than 1Kg a day!).

THI studyClick on the picture to open it in a new window.

Shall we all feel concerned about heat stress in Europe?

To answer this question, Lallemand Animal Nutrition conducted a survey to encompass different European climate types, from North to South and East to West (UK, Spain, France, Switzerland, Italy, Czech Republic and Poland). This survey monitors continuous THI (Temperature- Humidity Index, an indicator of heat stress) along the day, during the summer months of 2013 and 2014: every 30 minutes, 24 hours a day for 2-3 months.Using Burgos and Collier’s (2011) THI scale, the cumulative time spent under mid, moderate or severe heat stress conditions was calculated for each farm. The map summarizes the results of our heat stress survey and gives estimates of daily milk production loss based on the literature (Burgos & Collier, 2011).  

Lallemand-Animal-Nutrition-survey-heat-Stress-Europe-e14314235434581Click on the picture to open it in a new window.

This survey proves that heat stress is a reality in Europe and as a result, dairy farmers could experience immediate loss of milk production (70 to 550 kg milk/day for 100 cows!) as well as mid and long term health and performance issues (somatic cells count, mastitis, fertility). The implementation of practical advices and recommendations can help farmers get ready for the next summer heat.

Nutritional recommendations to prevent heat stress

 Appropriate nutritional programs are important to help limit the impact of heat stress. One of the goals is to protect rumen environment from acidosis risks and optimize rumen efficiency:

  • Feed high quality, highly digestible and palatable forage. More starch or added fat can be useful too. High quality fiber source in the diet is also essential, especially for high-producing herds receiving high starch diets. 
  • Think about LEVUCELL® SC as a valuable solution to help reduce the impact of heat stress on rumen environment, animal behavior and finally performance. Trials have shown that milk production and feed efficiency are improved (see graph). 

effect-LEVUCELL-SC-Heat-StressFigure 2: Effect of supplementation of dairy cows diet with LEVUCELL® SC

on energy corrected milk yield under moderate heat stress:

fat corrected milk yield is increased by 1.7 Kg/cow/day. (Fustini et al., 2013).


  • Take care of the mineral electrolytes balance. 
  • Increase antioxidant supply such as organic selenium (ALKOSEL®), Vitamin E, or primary antioxidant source such as MELOFEED® to help maintain the antioxidant status of the animals.


Aurelien Piron, Ruminant Technical Manager at Lallemand Animal Nutrition,

presents the results of this Heat stress survey and some tips to face summer.

To watch the video (3 minutes), click here.