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Heat stress on cows this summer

With several very warm days, what’s the risk of heat stress occurring on our cows.



Heat stress in cows is a big challenge globally. This is because cows are quite sensitive to extremes of temperature. It is simple because as ruminants they generate a lot of heat through fermentation in their rumens anyway.

They prefer cooler climate temperatures with an optimal range from 0-15 degrees Celsius. So in some countries that experience temperatures regularly over 35 degrees Celsius, farmers have to work very hard to keep cows cool.

They do this by providing shade, using sprinklers and fans indoors.

We in Ireland are lucky that our temperate outdoor summer grazing should make for happy cows.

Symptoms of heat stress

Cows suffering from heat stress experience an increase in core temperature. Feed intakes drop and respiration rate increases. They do this to expel the excess heat and this can be seen as panting and later on open-mouth breathing. In extreme cases, this can cause anaphylaxis fluid in the lungs, with collapse and even death

With most heat stress it is the reduced feed intakes, stress impacting immunity that can affect welfare and cow performance.

We must be mindful however during warm weather in Ireland to monitor feed intakes during very warm periods over the summer months.

Rising temperatures

As regards predicting the weather this summer. It looks like it could be dry and hot. This may be the future for our summers with the changes from global warming hard to ignore.

So is this affecting our cows?

I spent half an hour today watching some cows at lunchtime. It hit 27 degrees and cows were happy but a lot of them were not grazing. Mid-day is a pretty inactive time anyway with many cows lying and ruminating. One notable thing was water drinkers were experiencing very high traffic. I think we are still at a level that cows aren’t unduly stressed. However, this is dependent on a couple of very important things we must remember to get right.

  • Most importantly we must provide plenty of clean available water. It should be the first job every day with cows in paddocks to check water flow rates and drinkers are full. Remember as dry matter intake may be reduced and with the dry matter now high in the grass. Cows will need to drink more water, so check those troughs every day.
  • On very warm days where shade is available cows will lie in it. This brings the challenge of fly control also.
  • Avoid movement or highly stressful events in very high temperatures at midday. Where buffer feeding cows do it in the cooler temperatures in the early morning and late evening.
  • Where cows are in covered collecting yards for long periods we must be mindful of airflow and heat. There may be a time in the future where we see fans in place in our covered collecting yards.

I think when temperatures stay below 30 degrees Celsius with plenty of clean water available Irish cows will be ok. However, this warm weather brings bigger challenges with poor grass growth rates and feed availability. Many farms are now beginning to supplement more and buffer cows. So here is hoping we will see some rain over the coming weeks.

Happy safe farming

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