Help cows chill out

He says with the El Nino weather pattern bringing heatwave conditions to many parts of the country, it's important to make sure cows avoid heat stress.

AgResearch studies indicate that NZ cows can suffer heat stress when temperatures go above 23°C and humidity is high, especially when there is little or no wind.

"When cows get too hot appetite and feed intake decrease and if they can't cool down by using shade or other means, milk production is likely to decrease," says Leach.

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.

"Any activity such as walking to and from the dairy, to the water trough, or grazing, increases the risk of heat stress," he says.

"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 so are more susceptible to heat stress."

If night time temperatures are also very warm it can become even more difficult for cows to cool down without extra help through good summer management. Moving to once-a-day milking can also help and although not usually the prime reason for changing milking strategy, it may well be a contributing factor worth considering.

When hot conditions are forecast, there are some good short-term ways to reduce the risk of heat stress for cows and minimise milk production losses:

Graze cows on pasture close to the dairy so they don't have to walk as far 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 and provide supplementary feed at night so the extra heat generated by digestion occurs in the coolest part of the day

Make sure cows always have a good supply of clean drinking water; milking cows can drink over 100L of water per day in summer.

Cool cows while they wait to be milked by providing shade or using a sprinkler system in the dairy yard. 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.

Studies show that preventing heat stress is cheaper than trying to manage the consequences once cows become heat stressed.

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