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In our heat stress work we measure temperatures in various ways.

  • The outside sensors positioned in the grazing platform (see picture) have a while slotted cylinder for measuring shade temperature and humidity – in the same that a met office device would.
  • To get a record of how hot a grazing cow will feel in full sun we use a ‘black globe’ – see picture. This is a copper sphere 150mm in diameter, painted black and positioned in full sun. Temperatures recorded with a sensor in the center of the globe indicate how hot a black-coated cow in full sun is likely to feel.
  • In the cow sheds the sensor is covered by a white perforated hemisphere to allow air movement but no dust so these are essentially shade temperatures.

The first line graph shows the three temperatures measured at our Hampshire monitor farm over the past week. At night the outside shade and BG temperatures are the same and slightly lower than the shed temperature as the shed radiates absorbed heat and the cows warm the shed. During the day the shade temperature inside and outside the shed were very similar rising to 30’C at the start of the week and up to 32’C on Friday 9th September. The ‘black globe’ temperature rises during the day and is more volatile depending on cloud cover.  It peaked at 35’C at the start of the week rising to 40’C on 9th September before collapsing on a cloudy Sunday.


These temperatures are at, and around the cow’s body temperature and will be very uncomfortable. Providing enough shade on a commercial platform is very difficult (?impossible) so many grazing cows will have to stand in full sun in these temperatures. Understandably the cows will be miserable and feed intakes will plummet (anyone care to join them?). Is this an avoidable welfare problem?


The third bar chart shows the maximum (hourly average) temperature across nine of our monitor farms. Maxima ranged from 35’C to 42’C – very uncomfortable conditions across a wide geographical range. The maxima were reached from about noon through to 3pm building slowly to the maximum then falling off quite quickly.

Heat stress monitor in a field