Raising and tending to dairy cattle is filled with challenges. Ensuring they are properly fed with the right nutritional balance, treated well and provided with creature comforts, and housed appropriately for the conditions all require a balancing act to meet the needs of your dairy cattle. When any one of these factors is compromised, the health and consequently the milk production of your cattle can be likewise compromised.

Preventing heat stress in dairy cattle is important to ensure they are as healthy as they can be and optimally productive. Any insult to your dairy cattle’s health will diminish their milk production and be bad for both you and them. Appropriate housing can save you both time and money.

We discussed some of the basics of heat stress before, but we revisit and expand on those topics here because heat stress is an important contributor to health problems in dairy cattle and doing everything you can to mitigate it will improve your dairy cattle’s health and your bottom line.

What is heat stress?

Heat stress is a medical condition experienced by animals that is caused by excessive hot or humid conditions. This condition affects many aspects of an animal’s well-being, but most importantly, it can cause them significant distress, illness, or even death if not properly dealt with. Heat stress happens when the animal is unable to cope with the ambient conditions and their central body temperature increases. When this happens, the animal’s organs and the cells that make them up may be injured or even die.

The reasons an animal is unable to cope with excessive heat are multiple and some of them are determined by their living conditions and others are determined by their species’ particular disposition. Whatever the cause, the end result is the animal is unable to appropriately deal with the increased temperature or humidity. This results in their distress because their body’s temperature is too high for it to function as it should. An organ and the cells that make it up are meant to function in a narrow range of temperature that is ideally suited for their biological purpose, so an increase in the animal’s body temperature means that the temperature is no longer in the ideal range for the organ to function.

Dairy cattle are particularly sensitive to temperature changes as they have a limited ability to regulate their inner temperature. Dairy cattle can be kept in conditions between -15C to 25C and still be productive and manage their temperature safely. When the temperature exceeds this range, or if it’s particularly humid, they begin to experience discomfort and this is already considered to be heat stress. As the temperature or humidity rises, this discomfort can progress to more serious health issues such as neurological symptoms or even organ failure.

It’s important to understand what heat stress is, how to spot it, and the steps you can take to prevent it in your animals so they don’t suffer needlessly.

What do dairy cattle need?

Understanding what dairy cattle need to survive and thrive starts with understanding them as animals. Like any living animal, dairy cattle need food, water, and shelter, but it’s not quite that simple. They specifically need the right food that provides them the necessary nutritional balance, they need the right amount of water to drink, and they need to have shelter that controls the ambient temperature so they can regulate their body temperature and comfort themselves.

As for their normal food intake, dairy cattle consume from 50 to 55 kilograms of wet feed per day, or 22 to 25 kilograms of dry matter. The volume of food they need to consume increases substantially when they are producing milk as they lose nutrients through their milk which need to be replenished. A dairy cow should have a proper balance of dry weight material, fats, and protein as a part of a balanced and optimal diet. They also require multiple vitamins and mineral nutrients to perform normal metabolic functions, for their cells to function appropriately, and to replace their losses from effluent and dairy production. These include a combination of calcium, phosphorus, sodium, potassium, chloride, magnesium, sulphur, selenium, copper, and Vitamins A, D, E, K, and B vitamins, as well as trace minerals like cobalt, selenium, copper, iron, manganese, iodine, and zinc. A normal diet can provide most of these nutrients, but calcium, phosphorus, magnesium, and sodium may need to be supplemented at certain times throughout the cow’s life to ensure their metabolic needs are met.

While the right food in the right amounts is an essential component to meeting the needs of your dairy cattle, even more important is their water consumption. Water makes up a majority of the bodies of all living things, so it’s only expected that it is also a necessity in their diets. Dairy cattle need a regular, ample water supply so their bodies can function normally and they can produce the milk that we harvest from them. When dairy cattle don’t have enough water to drink, their milk production will suffer in addition to their general health. In order to ensure they have the supply they need, dairy cows should have access to a water source that can provide them at least 15L per minute.

What causes heat stress?

The possibility of your dairy cattle suffering from heat stress is not strictly limited to the prevailing temperature. Understanding the ambient temperature in a sheltered space, the relative humidity, the air flow, and the animal’s intake, and outputs are all factors that can contribute to them developing heat stress.

Remember, a useful guide to use in assessing an animal’s living conditions is the Temperature Humidity Index (THI). This index simplifies environmental conditions to a single number, whereby the animal will be the most comfortable and least likely to suffer from heat stress when the THI is below 72 and becomes critical at 99. We discussed this in more detail in our first post.

Temperatures vary widely by the season, by your geography, the time of day, the available shelter, and the presence or absence of any precipitation. In New Zealand, summer temperatures throughout the country can reach levels that might cause heat stress in your dairy cattle, so it’s important to be on the lookout for any signs and take steps to prevent it before it becomes a problem.

How does heat stress affect dairy cattle?

Dairy cattle are a hardy bunch, but there are a number of things that can affect their health, and consequently their milk output. Productive dairy cattle are healthy, well-fed, well-housed, and can provide a steady supply of milk for several years. Any circumstances that affect a cow’s health, nutrition, or shelter will therefore negatively impact their milk production.

Heat stress is a serious cause of lost productivity and health concerns in dairy cattle. While heat stress has an impact on your dairy cattle’s health, it can be prevented with appropriate shelter, air flow, and access to water. When the temperature or THI do rise, by housing your dairy cattle in a more comfortable setting, you won’t need to worry about the more serious consequences of heat stress.

Cows are homeothermic animals that need to maintain their temperature between 38.3 C and 39.3 C. They do so by balancing their metabolism, blood flow, intake, output, and breathing with their surrounding environment, whether hot or cold. When it’s cold (-15C), they’ll increase their intake and reduce their milk production, while hot weather (25C) causes them to both increase heat dispersion strategies and reduce their heat production.

How do dairy cattle regulate their heat?

So when the temperature or humidity or both rise, dairy cattle turn to their innate defences to avoid the strains of heat stress. They will increase their breathing and drooling, as well as the blood flow to their skin to improve heat dispersion. But they also reduce their activity level to reduce heat production, and in turn reduce their feeding. What they do eat, they become more selective about tending to eat less roughage.

When these mechanisms aren’t effective, your cow will experience heat stress, causing her to reduce her feed intake even more and subsequently her milk production. Cows that produce high yields also have increased metabolic rates and increased heat production. This is another factor to consider in providing appropriate shelter for high-yield cattle.

Cattle are best able to adapt to temperature changes that happen gradually. Sudden changes in temperature put the animals at risk without appropriate shelter. As conditions normalise, they are more capable of managing higher temperatures so long as they have access to food and water.

How to prevent heat stress

While you can’t change the weather, there are a number of mitigation strategies that can ensure the effects of heat stress on your herd are limited. A few of the most effective include:


With lactating cows requiring around 100L of water on an average day, you’ll need to ensure they have easy access to hydration on a hot one. Adjust the flow rates of your troughs to guarantee they’re never empty, and consider installing troughs in races so that cows can rehydrate immediately after milking.

Herd management

Decrease both the distance and the speed of the walk to the dairy, and cut back the time that animals spend in unshaded fields and yards. Keep a close eye on your herd, and act quickly if you see an animal with symptoms – isolate it, and provide it with shade, moving air and water. Avoid the heat of the day when milking.

Shade and cooling

Retaining trees in grazing paddocks is essential, although with each cow requiring around 5m² of shade, ensuring you have enough coverage can be a challenge. A more effective solution is to invest in a purpose-built shaded area, like a SmartShelters livestock shelter.

Heat stress is a particular concern for calves as heat stress will increase the rate of dehydration and lower the immune system. Both factors will lead to their energy being used to drive off heat vs. growing into strong and healthy animals. Our calf rearing shelters are a popular choice.

Fabric covered, perfectly ventilated and providing shade while making the most of natural light, a SmartShelters livestock shelter offers your animals a cool oasis in the heat of summer. With spans of up to 50m, these shelters can cover the biggest herds, while being incredibly quick and easy to construct.

Heat stress is a real concern for any New Zealand dairy farmer looking to maximise the productivity of their herd, and with temperatures set to rise into the future, the importance of heat stress management will only increase.

To discuss a truly smart livestock shelter solution, chat to our friendly team today!