Reducing heat stress as temperatures rise

As temperature and humidity levels rise this summer, farmers should take steps to ensure stock stay cool and, where necessary, have a plan to prevent facial eczema.

“Hot, humid conditions also encourage facial eczema, so remember to monitor spore levels in your area, talk to your vet and put a prevention plan in place to suit your farm situation,” says DairyNZ animal welfare developer Jacqueline McGowan.

“In high temperatures this summer, a cool cow is a happy cow. When cows get too hot and if they can’t cool down by shade or other means, their appetite and feed intake decrease and milk production is likely to suffer.”

Prevention better than cure
Studies indicate that NZ cows can suffer heat stress and milk production starts to decline when temperatures go above 21°C and at more than 75% humidity, especially with little or no wind.

Proactive prevention of heat stress is also shown to be more cost-effective than trying to manage the consequences once cows become heat stressed.

Normal respiration rates vary from 15-25 breaths per minute. A rate of more than 30 breaths per minute indicates that cows are heat stressed. Really hot cows will start to pant and breathe through an open mouth, with the tongue hanging out.

“All activity such as walking to the water trough, walking to and from the dairy – and even just grazing as normal – will contribute to increasing the risk of heat stress,” says McGowan.

“Digesting food and producing milk also generates heat in dairy cows and on hot days this can overload their system. High-producing animals tend to eat more and are therefore more susceptible to heat stress.”

If night-time temperatures are also very warm, it can be even more difficult for cows to cool down, without extra help.

Ways to get cool

Moving to once-a-day milking can help and, while heat stress is not usually the main reason for changing milking strategy, it is worth considering.

Alternatively, ensure morning milking is completed before the day warms up, and delay letting the cows go for evening milking until as late as possible. Milking during a cool evening is more enjoyable for people too.

Make sure troughs never run low during the day. If the system can’t supply water quick enough, consider providing additional temporary troughs during hot periods.

Another way to cool cows is providing shade or using a sprinkler system in the dairy yard, while the cows wait to be milked. Wetting the skin is one of the most effective ways to cool a cow, however high humidity can make sprinklers less effective on a hot concrete surface.

So turn the water on half an hour before milking to cool the yard, using sprinklers that give a large droplet size and, if possible, use fans to create air movement when there is little or no wind.

Periodically wetting the roof to reduce radiated heat from hot steel roofing can also improve the milking environment for cows and milkers.

“Although installing sprinklers or shade structures can be costly, they will reduce the impact of high heat on cow comfort and milk production, especially in hotter parts of the country,” says McGowan.

How to get cool cows

When hot conditions are forecast, some short-term solutions to reduce heat stress for cows and minimise milk production losses are:

• Graze cows close to the dairy to reduce walking distance for milking and let them move at their own pace

• Milk cows later in the afternoon/early evening when the temperature has dropped

• Use paddocks with shade or provide cows with access to well-ventilated, shaded housing

• Provide supplementary feed at night, so the extra heat generated by digestion occurs at the coolest time of day

• As always, make sure cows have good clean drinking water. Milking cows can drink over 100L of water per day in summer

• Provide shade or use a sprinkler system in the dairy yard, while the cows wait to be milked.

*Look out for this article and other interesting on-farm management stories in Getting the Basics Right 2018 issue arriving in your mail boxes soon.