By Kathleen Shore,

Ruminant Nutritionist, New-Life Mills


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When temperatures are high, cows are no longer able to lose heat by emitting it to their surroundings (radiation), passing it to the ground (conduction) or passing it to the air (convection). The only way for them to dissipate their heat load is by evaporation: breathing and sweating. However, when humidity increases, evaporation decreases because the air is already saturated with moisture. – cows are affected much more quickly than humans because cows are only able to sweat a tenth of what humans are able to sweat.

        • Cows are actively seeking shade
        • A body temperature over 39.3⁰C (102.7⁰F)
        • An increased respiration rate, above 60 breaths per minute
        • Severe heat stress will generate a rate of up to 140 breaths per minute (BPM)
        • Panting and increased saliva production
        • Increased standing time

Heat stress in your dairy cow can result in a decreased intake of feed – directly impacting milk production.  Heat stress will also increase the risk of illness and can contribute to reproductive issues or low birth weights.  Rumen Acidosis and high somatic cell counts can be  caused directly by heat stress.  Be informed and on the watch for heat stress in your dairy herd to mainitain production and promote a healthier herd.


Nutritional Solutions

        • High moisture forages improve intake – fermented feeds have lower pH so mold and yeast growth is slower in the ration
        • and heating is reduced
        • Add water when the DM of the diet is >60% to bring it down to 50% – water conditions the ration, reduces the dust and increases its acceptability
        • High quality fibre to decrease heat of fermentation (Aim for at least 22% DM effective NDF)
        • Maintain high concentrations of starch and sugars in the diet
        • Cereal grains that contain starch with slower degradation rates such as corn are a better option than those with faster degradation rates (barley, wheat)
        • Feed forages with higher sugar/starch content
        • 1-2 % rumen-protected fat supplementation to increase energy density of the diet
        • 1-3% yeast to improve feed efficiency and milk yield
        • Sodium bicarbonate to lower body temperature and assist rumen in buffering
        • Heat stressed cows lose lots of minerals – increase the concentration of sodium, potassium and magnesium
        • Organic minerals in particular Zinc have been shown to improve functionality of the gut
        • Try to keep the DM of the diet around 50% to increase consumption and reduce dust
        • Avoid feed shortages: refusals should be between 0.5 and 5%


Barn Management to Reduce Heat Stress

        • Provide ample shade and water
        • Remember to cool your dry cows, she is that much hotter as she approaches calving and much more susceptible
        • Keep the water troughs in the shade and CLEAN them frequently use fans to circulate the air – high volume
        • low speed (HVLS) fans are just as effective as low volume high speed (LVHS) fans, but use 86% less energy
        • Use sprinklers to cool the air down (1-2 minute cycles every 15 minutes)
        • Feed at cooler times of the day (before 6 am and after 9 pm)
        • Mix feed in smaller, more frequent batches to discourage secondary fermentation


Contact a Dairy Specialist for more information