Heat Stress in Dairy Cows

Heat Stress in Dairy Cows
By Ali Cullum, Veterinarian, Anexa Vets Morrinsville

Cows have a much lower comfort zone for heat than we do: they like between 4 and 20oC. Personally, coming from the Northern Hemisphere, I find temperatures of 15-20oC perfect, but most New Zealanders prefer temperatures around 22oC if the air conditioning settings in our buildings are anything to go by! Cows find the current ambient daytime temperatures of 24 – 30oC way too hot! They have a fermenting vat inside them (rumen) which makes them extra hot to start with!

What can we do to help our cows, and how do we know how distressed they are?

Friesians and Crossbreds find temperatures over 21oC too hot whilst Jerseys (coming from a warmer area of the world) don’t suffer heat stress until around 25oC. Humidity will increase this effect, especially if it is over 70% - which is often the case in the Waikato.

On hot days, if cows are seeking shade, bunching up in mobs and mouth breathing, they are probably suffering from heat stress. We can help them by providing shade (trees, covered stand-off areas), by giving them plenty of freshwater to drink, and by using a sprinkler in the collecting yard. We can also consider adjusting our milking times to avoid yarding and walking during the hottest part of the day. Feeding supplement at night or in the early morning means they do not suffer excess heat from digestion in the hotter part of the day. Milking once a day also enables a reduced movement of cows on hot afternoons.

Sprinklers cool the cows but are only effective if the humid atmosphere is moved away. Therefore, if there is no active breeze, an industrial fan will be required to generate air movement. Otherwise, the cows just get hot and steamy!

If you want to look at how hot your cows might be getting, DairyNZ have some excellent resources on their website. This link https://www.dairynz.co.nz/animal/cow-health/heat-stress/ has a table which shows how many hours cows spend being too hot between December and February.

Remember, cool cows are happy, and are able to eat more, and to produce more milk.

Autumn Calvers

Late gestation cows also suffer from heat stress- which reduces colostrum quality and increases the risk of diseases around calving time as well as going on to reduce production in early lactation. So please use shady paddocks for them too!



Date Added: Tuesday, 9th February 2021


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