News details

May 4, 2017


Heat stress significantly affects milk components and somatic cells

Heat stress significantly affects milk components and somatic cells

Heat stress is a common and growing concern in dairy cows and beef cattle and we are now fully aware that even at low level it can significantly impact herds’ production and welfare. For several year now, Lallemand Animal Nutrition has been focusing on identifying and monitoring indicators to assess rumen efficiency on-farm and help producers manage their herd for optimal production and welfare (the REI program, see diagram). This approach has allowed gathering thousands of data from different regions and production systems which reveal the impact of heat stress beyond experimental trials, in real-life conditions.

Data obtained from dairy farms in multi continents under moderate to severe stress were compiled, indicating that during heat stress, various indicators were affected:

  • Milk fat and fat/protein ratio appears significantly lower compared to other seasons, highlighting reduced rumen efficiency (see graphs).
  • The percentage of cows in good body condition is lower.
  • The percentage of clean cows is reduced.
  • Manure screening shows reduced digestion efficiency: the occurrence of manure with more than one undigested but processed grain is increased.
  • Somatic cell count in milk is significantly increased (an indicator which is partially affected by poor rumen conditions but also impaired antioxidant status).

Aurélien Piron, comments “Our rumen audit approach which is based on objective and measurable indicators of rumen efficiency on farm is very much in line with current trends across the industry. For example a recent study from Penn State Extension1 reveals a clear correlation between heat stress level (THI), daily rumination time, and milk production: according to this study, it is estimated that for 10 points increase in THI, daily rumination could be reduced by one hour and dairy production by 2.7 Kg/day. Rumen efficiency is clearly affected by heat stress and, besides the use of heat abatement methods; we recommend to focus on ensuring optimal rumen function by adapting the ration (high quality fiber, higher energy diet, increased starch and fat, good quality forage…) and feeding strategy. In addition, we have already shown in many conditions that rumen specific live yeast Saccharomyces cerevisiae CNCM I-1077 has a positive impact on dairy and meat production performance during heat stress episodes, helping to alleviate the heat stress challenge for the rumen.”


Effect of rumen specific yeast LEVUCELL® SC on dairy and meat production under heat stress conditions: left: energy corrected milk yield in dairy cows under moderate heat stress: THI: 63-73; Fustini et al., 2013); Right: bull’s average daily weight gain under heat stress; THI 70-80 (Commercial trial, Italy, 2015).


In order to evaluate the real risks of heat stress, Lallemand Animal Nutrition has also conducted a worldwide survey at farm level under various climate conditions by recording in real-time THI variations within animals’ environments. Adding to external climate recordings, this allowed to build a world map of heat stress risks (see below), aimed at helping producers anticipate summer problems and be prepared, even in areas not primarily associated with hot climates, such as Northern and Central Europe:

World map of heat stress risk representing the amount of time spent under each stress level per 24 hours (Lallemand internal data)


1 Using rumination sensors to monitor heat stress in dairy cows, By Mathew M. Haan, Penn State Extension, Dairy Herd Management, November 02, 2016