News & Advice

Summer heat – Cow and Human Welfare

Dec 1, 2021 | Dairy, Dairy Animal Health & Welfare

Ali Cullum, Veterinarian, Anexa Vets Morrinsville

What are the sources of stress for cows during summer and what can we do about it?  

Heat, lack of shade, flies, toxins are probably our main offenders. Bos taurus cows (the type of cows we have in New Zealand) do not enjoy paddock life once ambient temperatures rise above 21oC (or 25oC for Jerseys), it is particularly stressful for them if they are expected to graze and function in areas with no shade. Farmers with shade facilities (e.g. herd home, covered feedpad, standing area under trees) report their cows will run to the facility on hot sunny days even when they are not feeding out supplement in the facility. If we do not have shade, what can we do? One instant action that does help is putting the sprinkler on in the collecting yard, the water has a cooling effect for the cows. Another consideration is to alter milking times, milk later in the evening when it is starting to cool down, or go once a day and milk in the early morning. Long term plans to plant trees to generate shade, and to look at covered standoff facilities are a good idea. 


Biting flies are a tremendous nuisance factor to cows disrupting grazing time and milking time by making them stamp, and using up energy swishing their tails and ears and shaking their heads. Ideally fly control should start in November and continue over the summer months. The idea is to start reducing the fly population before it multiplies. You can use Ripcord both on buildings and on the cows themselves. If using Ripcord on the cows, there is no milk withholding, but a 24 day meat withholding period. It acts immediately as a knockdown for flies and also has a repellent action for at least a month. On buildings it has a similar effect and helps to reduce the overall fly population. Blaze is another product that can be applied to cows and similarly reduces fly landings on the cow. It has a nil milk and 28 day meat withholding, again lasting for about a month. 


The major toxins in the summer are: 

From ryegrass endophytes which exacerbate heat stress and cause ryegrass staggers  

The fungal toxin sporidesmin which causes facial eczema.  

If you are having problems with ryegrass staggers, the first thing is to remove ryegrass from the diet of affected animals. This may be achieved through feeding supplement or crop. Anecdotally, people use several Vitamin B, seaweed based and toxin binder products in the water or supplement that help alleviate the signs of ryegrass staggers. Long term prevention is by planting animal friendly ryegrass swards. These modern grass varieties contain endophytes that do not produce tremorgen and heat stress toxins, but still repel insects. Inhibiting ingestion of sporidesmin to prevent facial eczema is a topic already covered elsewhere. 

These stresses all have an impact on cow welfare and productivity. If we can reduce them we will improve the health and production of our cows. They also have a direct and indirect impact on the humans working with and managing the cows. Biting flies are a problem for people milking the cows as well as the cows themselves. Grumpy cows who are too hot to move, or fall down on concrete are horrible to work with. Making some management changes to reduce summer cow stress also improves human welfare! 

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