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How to manage heat stress in your dairy herd

Seasonal challenge Seasonal challenge3-6-2020

With the weather beginning to heat up again, it’s time to be mindful of how rising temperatures affect cow performance.

By putting measures in place now to help cows manage summer weather, will help to mitigate negative effects on herd health and performance from heat stress.

Rising temperatures

Dairy cow at water

The ideal ambient temperature for cows is 5-25°C, depending on size and breed, but it’s important to remember that humidity levels exasperate the effects of even small increases in temperature.

Exposure to temperatures above this will cause heat stress and trigger self-regulating behaviours like panting, drooling and increased blood flow. Doing this uses up the cow’s energy sources, diverting what is normally used to power milk production, resulting in lower yields.

Signs of heat stress include cows becoming lethargic or inactive, reduced feed intakes and standing with heads bowed. Evidence of reduced rumen function, such as loose dung and poor rumen fill, may also be seen.

Knock on effects

Not only does heat stress affect milk production, it has also been found to negative affect fertility and embryo development. According to one study in the Journal of Dairy Science cows subjected to heat stress were 63% less likely to get pregnant compared to cows who were not.

Additionally, early growing embryos are likely to die within the first three days of fertilisation from prolonged periods of heat stress. Heat detection also becomes more difficult due to lack of activity or movement by cows and heifers.

Combating heat stress

Keeping cows fed well, hydrated and in well ventilated housing is essential to overcoming the above consequences of hot weather.

Encourage higher intakes by feeding 60-70% of your herd’s diet between 8pm and 8am, the coolest part of the day. Increasing the energy density of the diet by providing additional concentrate will mitigate drops in intake and help to maintain milk quality. High quality forages will also reduce the amount of heat produced during digestion compared to low quality, stemmy forage. It is essential to ensure that any changes made to the diet do not create an imbalance in the diet – otherwise your herd could develop digestive disorders like acidosis.

Adequate provision of clean, fresh water at all times is absolutely essential to keeping cows hydrated during hot weather and will reduce the risk of acidosis and maintaining feed utilisation. During times of heat stress, cows can drink an extra 100 litres of water per day so be sure to monitor water levels regularly.

Good ventilation in cow housing will keep fresh air coming in and move stale air out, keeping the temperature inside cooler. Research from the United States that air flow as low as 10 kph reduces respiration rates in heat stressed cows by up to 50%! If your cows are normally in paddocks during summer months, consider bringing them inside during the hottest part of the day and ensure that they have access to shade and plenty of water in paddocks.

The most effective way to do this is to install an open or protected ridge in the roof of housing and increase the volume of air inlets. This will bring in more fresh air from beside the building and push old air up and out. Fans are also effective ways of keeping air moving within buildings, especially in high traffic areas like collecting yards.

For more information

For more details about dealing with heat stress, please contact your local Account Manager or contact our specialist dairy team here.