The current El Nino heatwave conditions have the potential to cause heat stress and health issues for cows, warns DairyNZ.

As temperature and humidity levels rise this summer, farmers should take steps to ensure stock stay cool and where necessary put in place a plan help prevent facial eczema, says animal welfare team manager Chris Leach.

Providing shade is one way of keeping cows cool this summer. File photo.

'These conditions also encourage facial eczema, so farmers are reminded to monitor spore levels in your area, talk to your vet and put in place a prevention plan to suit your farm situation.

'When it comes to high temperatures this summer, put simply a cool cow is a happy cow,” says Chris.

'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.”

Studies indicate that New Zealand cows can suffer heat stress when temperatures go above 23°C and humidity is high, especially with little or no wind.

They also show that proactive prevention of heat stress is 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 Chris.

'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.

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

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 iron roofing can also dramatically improve the milking environment for cows and milkers alike.

'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 Chris.

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 to:

• 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 facilities

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

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

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