Managing heat stress

Trees can provide valuable shade and shelter for livestock. Well-placed trees can reduce temperatures under the canopy by up to 10°C during summer, and providing shade does not necessarily reduce grazing time. When planning shade trees:

• Plant on northern and western paddock boundaries to provide afternoon shade.
• Provide enough shade for the herd. Up to 5 m² per cow is recommended to minimise competition, soil compaction and pasture damage.
• Consider the mature size of trees and their winter shadows. A 20 m tree can cast a 40-50 m shadow in winter, so avoid planting too close to buildings, laneways and yards.
• Use paddock edges, corners, steep areas and riparian strips where appropriate.
• Shade near waterways can also support water quality and provide habitat for native fish and insect communities.

Choosing trees

When selecting shade trees, look for species that are fast growing, tall, broad-crowned, wind-firm and have strong branches. Broad canopies generally provide more shade than narrow trees of the same height.

Fast growing species such as poplars, willows and some eucalypts are commonly used to establish shade quickly. Longer-lived species such as oaks, tōtara, pūriri and other native trees can provide shade and shelter for decades.

Many farmers combine fast growing and long-lived species. The faster-growing trees provide shade sooner and can be removed later, before they become a risk from falling branches.

The best choice will depend on your site, planting design and the other benefits you want from the trees.

Where natural shade is limited, shade cloth structures, covered yards, feed pads and stand-off areas can provide protection from direct sunlight.

Good airflow is important. Shade without ventilation can create hot conditions underneath the structure, reducing its effectiveness. When planning artificial shade:

• Provide enough shaded space for all cows to access at the same time.
• Ensure structures are high enough to allow good airflow.
• Consider how shade moves throughout the day and position structures to provide protection during the hottest periods.
• Combine shade with good water access and, where appropriate, sprinklers, misters or fans.

Shade cloth can be a lower-cost option than a solid roof while allowing greater airflow. Shade cloth should block at least 50% of solar radiation.

When used well, sprinklers can help cows stay cooler for 2-6 hours after wetting. To get the best results:

• Wet the dairy yard before cows arrive to reduce heat from the concrete surface.
• Aim to wet all cows within the first 10 minutes of arriving at the dairy.
• If water conservation is important, use sprinklers on an intermittent cycle, for example, three minutes on every 15 minutes.
• Use large droplets that reach the skin and run down the cow's side. Water that sits only on the coat provides less cooling.
• Position sprinklers about 2 m above cows to reduce the risk of wetting udders or getting water into ears.
• Use fans where possible to increase airflow and improve evaporation.
• After a warm night, consider using sprinklers during morning milking to reduce carry-over heat load, particularly where shade is limited during the day.

Centre pivots and travelling irrigators may also provide incidental cooling where system design and water availability allow.

Misters cool the air around cows by releasing a fine spray of water. DairyNZ's 2025/26 summer trial found that cows exposed to misters had lower breathing rates in the yard than cows receiving no cooling, indicating they can help reduce heat stress during high-risk periods before milking.

Misters generally use less water than sprinklers but rely on good airflow to work effectively. Combining misters with fans can improve their performance.

• Wetting concrete yards before bringing cows in.
• Using paddocks closer to the dairy for afternoon milkings to reduce walking distances.
• Moving cows calmly and avoiding unnecessary pressure when walking them to the dairy.
• Allowing more yard space per cow at milking.
• Reducing the time cows spend in unshaded yards by milking earlier in the morning and later in the afternoon.
• Considering once-a-day milking during periods of extreme heat.

• Offering more of the daily feed allocation during the cooler parts of the day, such as early morning, evening or overnight.
• Maintaining feed quality and energy density to help offset reduced appetite.
• Using highly digestible feeds where appropriate, as lower-quality feeds generally produce more heat during digestion.
• Working with your nutritionist to review energy, fibre and supplementation requirements during hot weather.
• Avoiding sudden diet changes, which can increase the risk of digestive upset in heat-stressed cows.
• Providing additional sodium, potassium and magnesium where appropriate to help replace electrolytes lost through sweat and urine.