Recognising and preventing heat stress in dairy cattle

Heat stress can affect feed intake, fertility, body condition and milk production. One of the biggest challenges is that cows often eat less during hot weather, making it harder to meet their energy requirements and maintain performance. So it’s vital for your dairy business that you know how to manage it.

What is heat stress?

Heat stress occurs when cows become too hot and cannot cool down sufficiently. Like most mammals, it’s vital that a cow’s core body temperature is kept somewhere between 38.5oC and 39.3oC. To maintain that balance during the warmer temperatures of summer, cows need to lose as much of the additional heat as possible.

Even relatively short periods of hot weather can place cows under heat stress, particularly when overnight temperatures remain high, and cows are unable to cool down effectively. And the risk is particularly potent around calving time and among cattle who are ill or have a history of pneumonia. Cattle that are young, old or have dark hair are also more susceptible to heat stress.

What are the signs of heat stress?

As with most illnesses, changes in behaviour act as an early warning sign for the onset of heat stress. Initial symptoms include increased rate of breathing, followed by open-mouth breathing and drooling. As heat stress develops and becomes more severe, cattle will tremble and lose coordination.

Stage 1: elevated breathing rate, restlessness, reluctance to lie down.

Stage 2: elevated breathing rate, restlessness, slight drooling, reluctance to lie down.

Stage 3: elevated breathing rate, restlessness, excessive drooling or foaming at the mouth, reluctance to lie down.

Stage 4: elevated breathing rate, open mouth breathing, possible drooling, reluctance to lie down.

Stage 5: elevated breathing, restlessness, open mouth breathing with tongue protruding, possible drooling, reluctance to lie down.

Stage 6: breathing rate is decreased but more laboured, open mouth with tongue protruding, little or no drooling, isolation from the herd.

It’s vital to keep a close eye on your cattle during prolonged high temperatures. Heat stress can come on fast and quickly develop to heatstroke, which is a medical emergency. Essentially, a cow with heat stress will maintain control of normal bodily functions e.g. drinking, standing and so on, and their condition can be reversed if they are able to cool sufficiently. A cow with heatstroke meanwhile, cannot stand and may be unresponsive. The key to survival is early intervention. But as always, prevention is better than cure.

7 steps for preventing heat stress in dairy cattle

There are several measures that will help to protect your herd from heat stress. Some are easy to implement, and others will require a little more thought. The most important thing is that you do something to make sure you are prepared. Prolonged periods of hot weather can affect feed intake and herd performance, so having a plan in place can make a real difference. Here are seven tips.

1. Provide lots of clean drinking water

Just like you need to glug more of the wet stuff on a hot day, cows do too. Add water troughs across your site, particularly in shaded areas as well as at parlour exits, as cows will have one serious thirst after milking. If possible, make sure metal troughs are shielded from the sun so the water stays nice and cool. Provide additional tank capacity as water intake increases and check your water sources frequently for cleanliness.

2. Feed your cattle when it’s cooler

Eating is heating. The act of digestion creates bodily heat, which peaks a few hours after food is consumed. That’s why it’s best to make sure feeding time in indoor systems is in the late afternoon or early evening. That way, the ambient temperature will have cooled by the time the heat produced by digestion reaches its peak. If your cattle are used to being fed several times per day, make sure the largest part of the ration is fed in the evening. And if your cattle are on pasture? Note that they will graze much better during the early morning and the evening when temperatures are cooler.

3. Choose your ingredients carefully

Certain foods will exacerbate the heat that’s produced from digestion, and others will have the opposite effect. High-fibre forages will require much more chewing and work to break down for digestion than low-fibre supplements and generate greater heat per unit of energy.

One of the biggest nutritional challenges during hot weather is maintaining energy intake when cows are eating less.

Rumen-protected fats, such as Megalac, provide a concentrated source of energy without generating large amounts of heat during digestion.

Because they are not fermented in the rumen, they are often described as a ‘cool’ source of energy. This allows farmers and nutritionists to increase the energy density of the diet and help support milk production when dry matter intake falls.

And the fact that Megalac is gentle on the rumen has additional health benefits too. Reduced DM intake and increased drooling, typical during the early stages of heat stress, reduce the availability of saliva, which disrupts the pH of the rumen and can lead to acidosis. You can find out more about how Megalac helps to protect against heat stress in this short leaflet (pdf).

4. Milking in the morning and evening

You don’t want your cows traipsing to and fro during the hottest part of the day. Nor do you want them bunched together in confined spaces when the sun is beating down. Move milking to the early morning and late afternoon or early evening, when the temperatures are cooler.

5. Improve the airflow in housing

Cows lose heat through evaporative cooling: respiration (breathing) and sweating. But all that moisture needs somewhere to go because humid housing can quickly cause problems. Removing the roof ridge, ask a professional, is a low-cost way to reduce humidity and encourage moisture to escape.

6. Mist/sprinkle with caution

Misting only works if there is air movement at cow level along with decent outlets, which often isn’t the case in high-eave buildings. Without a means for moisture to escape, you are simply raising the humidity of your housing, leading to damp and increasing the risk of disease and mastitis. Misters and sprinklers are fine to use if you have adequate air circulation in your housing, though make sure you have a backup plan if your power or water systems fail.

7.Maximise the use of outdoor shade

If your herd is at pasture, try to maximise the use of paddocks with hedges and trees that provide shade. However, beware that having your entire herd huddled together under the shade of one solitary tree is often worse than providing no shade at all. On scorching days, it may be better to keep your herd in well-ventilated housing and let them out for grazing in the evening.

Share your experiences

Do you have any cattle cooling tips of your own? How do you manage the summer heat on your dairy farm? Share your thoughts and get some insight of your own with our farming communities on Instagram, Facebook and LinkedIn.