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While summer in the south west means lots of visits to the beach, it also means lots of hot cows (and hot farmers and hot vets).

As well as the heat from the sun and surrounds, cows have an increased challenge in that their rumen is a massive fermentation vat that also produces heat.

Heat stress can reduce a cow’s milk production, fertility, and compromise their immune system. High producing dairy cows, and those with greater areas of black on their coats, are at greater risk of heat stress.

Keeping cows cool The Vet Group


How do cows keep cool?

Like most mammals, cows need to maintain a core body temperature between 38.6°C and 39.3°C to remain healthy. Cows try to reduce their body temperature in several ways.

1) They reduce exposure to heat by seeking shade and/or changing their orientation to the sun throughout the day.

2) They increase heat loss by:

  • Increasing water intake. They can drink up to 200-250 litres/cow/day in hot weather – double their normal intake. The cooler the water the more heat cows can lose.
  • Increasing time spent standing to increase exposure to air.
  • Looking for areas with greater air movement (so long as it’s a cool breeze and not a hot wind!)
  • Standing in water if able to, such as in dams or in troughs
  • Increasing their respiratory rate
  • Sweating

3) Cows also decrease their heat production by reducing movement where possible and reducing their dry matter intake (particularly of fibre). This way their rumens don’t ferment as much and produce less heat.

Cows can handle high ambient temperatures during the day if they’re able to lose that heat at night. If night time ambient temperatures remain high, especially if the relative humidity is also high and wind speeds are low, there is no time for them to recover. This was the case several summers ago when some farmers lost a considerable number of cows due to the heat: these cows were unable to cope with a high number of consecutive 30+ degree days with hot nights.


Signs of heat stress in cows

Signs that the herd is hot include crowding over water troughs, splashing their bodies with water, agitation, restlessness and bunching to seek shade from other cattle. If seven or more cows have respiratory rates greater than 80 breaths per minute, they are feeling the heat, if respiratory rates are greater than 100 breaths per minute, immediate action should be taken to reduce heat stress.

An individual cow that is really suffering with the heat will have open-mouth and laboured breathing. They will be excessively salivating and be weak and not wanting to move. These animals should be treated urgently: sprayed with cool water, administered cool water orally, and provided with fanning and shade if possible.

Keeping cows cool on hot days: as much shade and water as you can provide!

  • Change milking times to cooler parts of the day and spray cows with cool water at milking.
  • Aim to feed out hay/silage cows by 9am on heat wave days, or after the evening milking. Have the paddock or feed-out area ready as soon as cows leave the dairy and ensure that every cow has adequate access.
  • In milking cows, around 30% of daily water consumption occurs just after milking , so water should be easily accessible as soon as cows leave the dairy.
  • Place the herd in paddocks with shade and easily accessible water, ideally located in a position such that cows do not have to cross areas of hot sun to get a drink.
  • Ideal water sources would be shaded troughs, with large volume, adequate access and good flow rates (a cow can drink 20 litres of water per minute).
  • Check the herd as well as heifer and calf groups during the day to ensure water is available. We have seen cases where cows have broken their water troughs and then gone without water.
  • Minimise other husbandry procedures – if unavoidable, start earlier (as vets we’re more than happy to do this too)
  • Don’t forget yourself and your staff. Plan to have iced water available to drink, ensure everyone is wearing heats and keeping out of the sun where ever possible. And stock up on icy poles in the freezer!

Dairy Australia’s Cool Cows website has advice on planning your farm’s water supply as well as other tips for preventing and dealing with heat stress: www.coolcows.com.au