Heat Stress
October 2023

November is here, and with it the long hot days of summer are close.

Cows feel the heat, just like we all do - they produce a lot of heat during the rumination and fermentation process, which is helpful during winter, but not great during the heat of summer. It has been well proven that when cows are unable to manage heat load, their feed intake and production will be significantly affected. The Dairy NZ website has some great information about heat stress and the impact on production. The combination of summer warmth and humidity in the Waikato means for our cows on average there are 70 to 80 days per year that will stress the herd enough to reduce production, with an average annual impact of 6 to 7 kg MS per cow. These numbers are for Friesians and Crossbreds – Jerseys are a little more heat tolerant.

Any shade is great, but nothing beats the shade from a leafy green tree. It has also been proven that cows will choose trees over artificial shelter - you can feel the difference yourself between a sun shelter or a tin roof versus a tree. The best advice I’ve been given about planting trees is don’t just plant a tree for a single reason. Summer shade is a great reason, but think about benefits of a deciduous tree for more winter sun, or an evergreen to give more shelter during storms. You might want to plant trees that can double as firewood species, or timber, or to attract birds and pollinators. And don’t overlook the dollars - trees can add to a farm value purely due to aesthetics.

November is a terrible time to be planting trees, but it is a great time to get some trees ordered for a planting program for next autumn or winter. It can be a bit discouraging if you want shade right now and don’t have the patience for trees to grow! Another reason to start planning as soon as possible. Poplars and eucalypts grow rapidly, and will start producing really useful amounts of shade within 3 or 4 years.

In the short term, things you can do to help a little include making sure cows have plenty of access to water around the shed, putting up artificial shelter around the shed and altering milking times to avoid the heat of the day. Sprinklers are useful, but need to soak cows to the skin to be effective - fans help assist evaporative heat loss. There is a proverb that says ‘The best time to plant a tree was 20 years ago, the second best is now’. Maybe not right this second, but start making plans and get it done!