Temperature and humidity monitors installed in cow sheds this summer have recorded heat stress conditions in all regions, including Scotland, in the first three weeks of June.

The monitors, installed by Cargill, have recorded levels of 57 or above, a figure that can affect cow fertility, according to Donald Macleod, the company's ruminant adviser in Scotland

“Relative humidity in the UK is normally about 60%, so when temperatures in our cow sheds – or outdoors – exceed 14°C, we get a THI reading of 57. If the daily average THI is above 57 then oestrus activity can decline with a knock-on effect on insemination rates.

“When temperatures exceed 22°C, the THI increases to 65, and conception rates can be seen to drop. We recorded average daily temperatures of this level or above on two days in early June in Scotland.”

Cargill has installed a network of 30 data loggers in cow sheds across the UK, including on dairy units in south-west Scotland. Data is recorded every 15 minutes and relayed from each monitor to a website every hour, 24 hours a day.

Mr Macleod added: “This data is freely available. We are encouraging farmers and advisers to use the information so they can gauge conditions on their units, and take the necessary actions to mitigate heat stress in their cows.

“The data has also shown us the maximum daily temperatures recorded on farm, which can flag up extremes when heat stress may be more acute. We recorded THIs in Scotland of 67 and above on 10 of the days from June 1 to June 20. Temperatures on these days will have been above 22°C and at a level where cow behaviour, as well as fertility, can be affected.

“At these temperatures and THIs it would not be unusual to find cows spending more time standing in cooler areas rather than lying in cubicles, more time visiting the water trough, and make fewer visits to automated milking facilities. These all have an impact on overall performance and productivity.”

Fertility is the first ‘casualty’ of heat stress, and at relatively cooler summer temperatures. The effects of this are not seen immediately on many units and farmers might not link a drop in oestrus or conception rates with increased temperatures.

“Heat stress is certainly not confined to warmer parts of the UK. It can have a real impact on the performance of all dairy units, and particularly high production units. Cows producing 45 litres of milk a day will produce 26% more body heat than those producing 32 litres a day.”

While heat stress can affect grazing cows too, the THI in buildings will typically be between two and four points higher than outdoors, depending on building design.

Improving the building environment with ventilation and fans, and ensuring fresh feed is put out more frequently in warmer periods will help to reduce the impact of elevated temperatures and potential heat stress in cows.

However, diets can reduce the impact of heat stress on cows.

Mr Macleod added: “I’ve seen the use of buffers with specialised cooling ingredients, like Equaliser CoolCow, help to mitigate the effects of heat stress. The buffer element helps to maintain a good rumen environment, and the cooling elements can reduce the cow’s internal temperature and keep her hydrated at a cellular level so she can better manage the metabolic challenges that heat stress brings.”

Cargill’s THI website is updated directly from the network of loggers and can be accessed in real-time on https://weatherdatauk.provimi.eu/