“As I write this it feels like the recent heat wave has eased – but the forthcoming forecast is not much cooler.  Given this is June we can be certain this will not be the last heat wave. Generally speaking, the previous weekend was the hottest part of the week with heat loads easing as the week went on. Most farm buildings were in the top of the ‘moderate’ heat stress category with predicted milk losses averaging 1.5 l/cow/day across all the farms. Sheds in all regions suffered heat stress last week but the precise farm location and shed design had a big influence.

Looking at the grazing situation most farms had more heat stress outside than inside; pastures were in the top of the ‘moderate’ heat stress category or up into the ‘high’ band with predicted milk losses averaging 2.2 l/cow/day across all the farms. Again, all regions suffered heat stress last week with a clear geographical pattern of being more severe in the South and inland.

The hottest period in most sheds is 10:00am to 4:00pm so try and minimise animal handling in these periods and expect reduced feed intake during the day.  Shade is a vital component of any housing so make sure collecting yards and other holding facilities are shaded – even with a simple, temporary screen.  Buildings with high eaves and open sides may also benefit from shades on the side-walls.

You can see from graphs below that the daily average index figures shown here hide a very big daily range.  Temperatures in the full sun can be over 38’C from 11:00am through to 4:00pm on a typical sunny afternoon. These are very hot and unpleasant conditions to be out in the full sun especially for a milking cow with a high rate of work (metabolic load). Shade provision is a first step but natural shade is not available in many grazing paddocks.


Several farms are considering installing fans. Some suppliers are saying they can supply within a few weeks.  The aim of such fans is to create a good air flow to cool the cows. Fans should be directed slightly down to make sure the moving air gets down into the cows.”


You can see real-time data (recorded every 20 minutes) for the East Lothian farm and the other UK/Ire monitor farms at https://connect.lallemandanimalnutrition.com/en/united-kingdom-ireland/heat-stress-in-dairy-cows/ and also some more detailed info on Tom Chamberlain’s website at www.dchs.info.

Csaba Adamik, Regional Business Manager, Scotland, Lallemand Animal Nutrition UK Limited