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Dairy & Ruminant

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Animal Health

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Livestock Production
Monday, June 25, 2007 5:11:17 PM
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Heat stress in dairy cows: implications and nutritional management

Lallemand Animal Nutrition


Dairy cows are very sensitive to heat stress, which has a significant economic impact for the farmer: not only loss of productivity and milk quality (increased somatic cells count), but also health related problems.


The farmer is usually aware of some essential herd management practices necessary in this critical period, however, some nutritional solutions may not be known. In particular, probiotics, which, by improving rumen conditions and functions affected by the stress factors, can help preserve cows' digestive health, milk productivity and overall animal health status.


During heat stress periods, the oxidative balance is also affected and it is very important to increase the anti-oxidant intake in order to preserve the cows' reproductive health and immunity, preventing mastitis.


The severity of heat stress is correlated to both ambient temperature and humidity level, with the bovine thermal comfort zone between ¡��C13 deg C and +25 deg C. Within this temperature range, animal comfort is optimal, with a body temperature between 38.4ºC and 39.1ºC (Lefebvre and Plamondon, 2003). Above 25 deg C, and even 20 deg C according to some authors, the cow suffers from heat stress: its health status and zootechnical performance are affected.


Severe heat stress can induce financial losses of up to EUR422/cow (St-Pierre et al. 2003).


Bovines have two main ways of maintaining their thermal balance and regulating their body temperature under high heat conditions. They rely essentially on both:

    • Favoring heat dispersion, in particular through evaporation, by increasing subcutaneous blood flow, panting, drooling and other ways.
    • Limiting heat production by reducing all activity and changing feeding pattern.  

In periods of heat stress, the risks of acidosis are also increased.


To prevent the effects of heat stress, keeping cows comfortable and as cool as possible are key. 


In order to limit the physiological risks linked to heat stress, and in particular rumen acidosis, the ration can be adjusted: high energy, more palatable diets, with high quality, highly palatable forages. The ration can also be secured with ruminant specific live yeast to prevent acidosis.


Finally, anti-oxidants intake should be increased.


Ruminant specific live yeast Saccharomyces cerevisiae CNCM I- 1077 , or Levucell SC, is a particular yeast strain deposited at Pasteur Institute, that has been selected and its effects in ruminants validated by internationally renowned research centres. Over 40 scientific papers have been published on the subject.


Three main mechanisms have been identified to explain its effects on ruminants' performance and health:

    • Improved rumen pH: reduced acidosis risk
    • Improved fibre digestion and nitrogen utilisation: increased feed efficacy
    • Rumen microflora stabilisation 

Heat stress generally increases production of free radicals, leading to oxidative stress. In dairy cows, oxidative stress has a negative impact on immune and reproductive functions.


The glutathione peroxydases family of anti-oxidative enzymes, containing selenium incorporated within an amino acid (organic form), plays a major role in maintaining the anti-oxidative balance, protecting the cells from damage.


Alkosel R397 is an organic selenium-enriched yeast product (strain Saccharomyces cerevisiae NCYC R397). Based on selenium anti-oxidative activity, Alkosel R397 is able to improve immune and reproductive functions, which are deeply affected by heat stress.


For more of the article, please click here.


Article made possible through the contribution of Lallemand Animal Nutrition.

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