What worked on dairy units to combat this year’s heatwaves?

“Soakers”, space, diet and shade have been effective tactics in reducing heat stress in dairy cows this year – Britain’s hottest on record, with five official heatwaves logged since May.

See also: Heat-stress strategies for grazing cows tested in NZ herds

The big win for Charlotte Fowler’s dairy farm clients has been operating soakers in collecting yards. However, she says there is still some confusion about the difference between soakers and sprinklers.

Charlotte, a vet with Homefield Farm Vets at Milborne St Andrew, Dorset, explains that sprinklers create a mist, and unless also using high-volume fans, they don’t cool cows, but instead create extra humidity.

By contrast, soakers make the cow very wet and can keep her cool for two to six hours, she says.

“The size of the water droplets needs to feel like rain, so it soaks the skin. You can blow air across the cows [as well] to increase evaporation. Soaking at milking twice a day is long enough to cool cows sufficiently,” she adds.

Window of opportunity

Adult cows are normally very good at dissipating heat by standing more, eating less and producing less milk, says Charlotte. This means they can cope with a wide range in ambient temperature, from 5C to 25C, provided they are not super high-yielding, or stressed (although high humidity levels influence this too).

“At 31 litres/day, a cow produces 48% more heat than a dry cow; more milk means more heat is produced by the cow’s metabolism,” she says.

In fact, for every extra 10kg of milk produced, each day the upper temperature limit drops by 5C. Effectively, the higher-yielding cow becomes heat stressed at lower temperatures.

Yet milk yield only falls 24-48 hours after a cow’s body temperature stays high over a 24-hour period. If she can be cooled at some point during that period, it prevents milk drop.

As parlours and collecting yards can start to feel hot once it hits 20C for cows giving 25 litres/day, Charlotte thinks this is the time to turn soakers on.

Grazing at night

Another technique she saw to cool cows at milking was to halve the number standing in the collecting yard, thereby increasing the amount of space around each cow. In addition, clients with cows at grass in summer changed their grazing patterns. Cows were housed in shady buildings during the day, then turned out at 9-10pm.

“Voluntary intakes are higher when cows are cool, so by grazing at night you aim for cows to eat 60% of their ration at night,” she says.

Because of the drought, many herds were also having to buffer feed. To avoid overloading the cow with heat from fermenting fibre, feeding times were altered to avoid the heat of the day. Rations were reformulated to increase the energy density, helping to minimise milk loss to 1-2 litres/day.

“But it needs to be done carefully, working with your nutritionist: you don’t want to cause acidosis,” she adds.

© Tim Scrivener

Youngstock and dry cows

While Charlotte didn’t see any radical switches in milking times, other jobs, such as TB testing, were pushed into cooler early morning slots.

Calves also benefitted from being fed more milk from their daily allowance in the morning, with a smaller portion in the afternoon when temperatures had built up.

But heat stress isn’t just about protecting performance in lactating cows. Next year, she hopes that dry cows and youngstock won’t be forgotten.

Poor transition during periods of heat stress can see cows calve in “without much milk”, she points out. As heifers with poor feed intakes on hot days don’t grow so well and heat stress affects the quality of their oocysts, both can delay age at first calving.

Plan ahead to reduce heat stress

Learning from this year’s heatwaves to plan for those forecast in 2027, Charlotte says it’s important for every farm to find practical, cost-effective options to reduce heat stress.

She suggests planning with the whole farm team (including vet and nutritionist) to explore what the business can afford to spend money on.

Capital investment in infrastructure must include budgets for running costs as well – such as electricity for fans, or water for soaking systems.

One client, she says, was able to buy a strip of soakers online for about £20 (she thinks originally intended for garden use).

Yet running costs could be high on account of the cost and volumes of water involved, leading some dairy farms to look at water recovery systems to reduce long-term costs.

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