Is it too late in the summer to combat heat stress?


We discuss the negative impact heat stress can have on cows fertility rates and how it's never too late to do something about it...


Is it too late in the summer to combat heat stress?

With the continued warm and humid weather, even with intermitten downpours of rain, heat stress will still be a problem across UK herds for the next few weeks. In a previous article we referenced the resultant impact on fertility levels, with estimates showing that a swing in temperatures, from 14⁰C to 22⁰C at a relative humidity of 60%, can cause 20% of cows in an all year round calving herd to slip a cycle.  Indeed there are other problems resulting from heat stress including reduces intakes and milk yield however, it's fertility that is affected first.

So is it too late to do anything about it?

Farms are already starting to see lower Pd rates in June and July resulting from the warmer weather seen in May and June. As the weather continues on a humid stretch this week, concerns about fertility will remain. THI monitors have been installed on farms across the UK and many have seen levels above 57 even when temperatures seemed lower before last week's hot spell which saw levels of 68 plus.

Heat stress in dairy cows is recognised as impacting production (yield and milk quality) when the average daily THI exceeds 68. Further research has shown the impact on fertility traits to start from as low as daily average THI of 57 (oestrus activity reduces) with impacts on conception rates observed from a daily average THI of 65.

And remember the important numbers for THI:

  • THI 57 – oestrus activity reduces
  • THI 65 – conception rate reduces
  • THI 68 – milk protein yield reduces
  • THI 70 – milk urea nitrogen (MUN) increases
  • THI 75 – up to 43% of cows may slip a fertility cycle through reduced oestrus activity and reduced conception rates




Equaliser® CoolCow is a unique blend of internal cooling elements (including an osmolyte), buffering agents, alkalising ingredients and flavouring that provide nutritional support and help maintain production performance throughout the summer.

Fed at 100 grams/cow/day would support oestrus activity even when seeing these levels and as we move into this week we will be seeing a lot more THI 65+ and THI 68+ in late afternoon when heat has built for the day so ensuring plentiful access to good, clean water and regular feed push ups is more important. 

Including Equaliser Cool Cow into their daily ration will help to start recovery and:-

  • Support rumen function and intakes
  • Support milk yields and components
  • Help maintain fertility
  • Help regulate core body temperature
  • Restore electrolyte balance
  • Protect herd profits from poor summer fertility


Cow Comfort

Other things that can be done to mitigiate this warmer, humid weather include:

  • Make sure all your water troughs are really clean.
    High yielding cows need 150+litres a cow/day, with milk constituting 85% water. One without other = less milk. 
  • Fans and sprinklers can help reduce temperatures in the shed
  • Reduce stocking densities where possible
  • Ensure feed is regularly pushed up 

If you'd like any further information on the effects of heat stress, please contact your Ruminant Specialist or call the office on 015242 63139.


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