Now is a good time for producers to assess their heat stress management programs as heat stress can impose a significant financial and welfare cost to a business.
Heat stress has been shown to decrease milk yield by 10 to 25 per cent, feed intake by 10 to 20 per cent, decrease six-week and 100-day in-calf rates, drop natural and artificial insemination conception rates, and increase the risk of clinical mastitis in higher yielding cows.
To manage the impact of heat stress the following actions can be taken when a high heat day is expected:
- Use low-stress stock handling techniques; this helps reduce physical body heat.
- Delay afternoon milking until 5pm.
- Wet the dairy yard for an hour before cows arrive.
- Use yard sprinklers as they encourage heat loss and are an effective method of cooling herds of cows quickly by: aiming for a moderate to large water droplet from the sprinkler; using an on/off cycle, sprinkling cows for one to three minutes every 15 minutes; and bringing the milking herd back to the dairy yard around midday if you don’t have a shade shed and using the sprinkler system to cool cows.
- Instal a large water trough on the exit side of the dairy; during hot weather a cow can drink 200 to 250 litres/day.
- Place fans above sprinklers and tilting them down 20-30° so they blow air between and underneath cows to enhance whole-body cooling.
- Provide cows with the highest quality pasture available to graze overnight when they are cooler.
Importantly, if animals are heat-affected and show no signs of improvement, contact your local veterinarian for assistance.
In the long-term the following actions can be considered to manage heat stress to benefit the enterprise and ensure the welfare of cattle:
- Review or undertake a whole farm plan including: the placement of shade structures; and tree plantings on northern and western edges of pastures (trees can reduce the radiant heat load by 50 per cent or more).
- Fence-off tree lines to protect tree roots and reduce the chance of cows lying down in mud and dung.
- Install a shade cloth over the dairy yard; this could be permanent or retractable. Modelling has shown when shade is provided there are 53 per cent fewer moderate and 86 per cent fewer severe heat stress events. Shade, sprinklers and air movement enables faster milk let-down and more incentive for the herd to walk to the dairy.
- If you have a permanent feed-out pad, consider installing a shade structure over it.
- Assess the impact of withholding insemination during hot weather on herd profitability.
For further information, see Dairy Australia’s Feeding Cool Cows Research fact sheets at: https://www.dairyaustralia.com.au/resource-repository/2023/08/11/feeding-cool-cows-research-fact-sheets
By Richard Smith
Agriculture Victoria dairy extension officer, Tatura