Heat stress and its impact on fertility

12 September 2023 | Int. Livestockhousing Guide | JOZ BV

During the summer months, the thermometer can reach soaring temperatures. Nice for us people to get into the holiday spirit, but the cows cannot cope so well with high temperatures. At temperatures as low as 20°C, they can already suffer from so-called heat stress. And that, in turn, can have a negative impact on fertility. But why does heat affect fertility? And what measures can you take to keep the temperature in your barn from getting too high?

Heat stress and fertility
In an earlier article, we looked at improving cow health and fertility through better barn hygiene. By taking timely hygiene measures, you can lower the risk of problems such as mastitis, hoof disorders and reduced fertility. But besides barn hygiene, another factor that can affect cow fertility is heat stress.

Heat stress occurs when the cow is unable to cool down. It works as follows. Each cow has a thermoneutral zone. Within this zone, the cow does not have to waste extra energy on maintaining a constant body temperature. From 20°C, cows need extra energy to cool down and stress occurs. You notice this because they start panting, sweating, chewing less, and they want to drink a lot, for example.

If cows experience heat stress, they only want one thing: to cool down. And that can affect fertility and cow health.

What are the effects of heat stress?
If cows are unable to cool down, they eat less, are less active and produce less heat in the rumen. As a result, the cow has an energy deficit. Especially in cows reaching maturity, this can cause a very negative energy balance. This affects fertility: normally the fertilisation rate is around 90%, but heat stress can reduce it to 55%.

When cows suffer from heat stress, they have less appetite. When digesting, they produce heat and they don’t like that. Nevertheless, it is important for cows to keep eating enough. If they do not, rumen acidification may even occur. Cows stay standing longer to cool down and they ruminate less because they breathe faster due to the heat. The balance between the acid level and buffering capacity in the rumen is upset. This reduces the cow’s resistance, increasing the risk of disease.

If you want to prevent this, try to respond in time to the possible consequences of heat stress. Don’t wait for the signals, but take a proactive approach.

Make sure the barn is cool
Good ventilation can contribute to a cool barn. It keeps the humidity low, so the cows are better able to release heat. Air circulation allows the skin to cool down. Try to keep the temperature in the barn about the same as the outside temperature. The best way to do this is with a mechanical fan. If necessary, you can combine ventilation with water atomisers or sprayers.

Keep the barn clean and dry
It is important to keep the barn clean as well as cool. This requires even more attention during hot weather. This is because the heat gives bacteria a chance to grow and that can make the cows sick. If cows experience heat stress, they are also more susceptible to illnesses. To combat this, it is important to clean the barn floor regularly.

Better hygiene improves the health of your cows. And that, in turn, contributes to fertility! So, put your manure scraper or manure robot to work regularly.

Feed at cool times
In hot weather, it is important that cows continue to eat enough. So feed several times a day and at cooler times. Through smarter feeding with the Moov 2.0 feed pusher robot, you ensure your cows have access to fresh feed 24/7 and improve their energy balance. And that reduces the risk of rumen acidification.

Provide sufficient water
Like people, cows need to drink plenty of clean water in hot weather. On hot days, they need as much as 50% more. So pay close attention to this as well. Tip: the water does not have to be too cold.

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