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Be watchful for animals overheating

Animal Health: Do your best to prevent it, and be prepared to provide relief on hot days

Risk for hyperthermia increases as temperatures reach 30 C for too long a period.

Every year during the first few hot days of summer we hear many warnings regarding leaving pets or even children unattended in vehicles as the temperature inside closed vehicles on warm days can rise to more than 50 C. We often don’t realize how susceptible livestock are to the same condition.

Many farmers and veterinarians have been fooled by symptoms resembling toxemia or pneumonia which are actually symptoms related to overheating — technically known as hyperthermia. The early-August hot spell was evidence that temperatures can get well over 35 C. It is very important to recognize and then treat heat stress, but more importantly simple steps can be taken to prevent it. Not surprisingly, solid- or mainly black-coloured cattle are much more susceptible to heat stress. And if the predictions of global warming are correct we may be in store for warmer days in subsequent years.

We used to see very little hyperthermia but with the development of more open (treeless) pastures, more cases are seen, especially with people now birthing cattle later in the year towards summer. More exotic livestock such as elk, deer and bison calve late spring but with no access to shade their offspring are also susceptible.

There is definitely a higher susceptibility in newborn animals up to three weeks of age. A combination of small body size, no fat for insulation and always taking in hot milk as the main diet all contribute to a much higher susceptibility in young animals. Younger animals such as yearling bison don’t shed out as quickly as mature animals in the spring and this thick hair cover doesn’t allow the body heat to dissipate. The pregnant females need to dissipate heat and the birthing process in itself produces extra heat from physical exertion. Downer animals need to be provided with shade as they are unable to move into shaded areas.

Hot for too long

Hyperthermia results from a combination of too high an ambient temperature over too long a period. Risk increases as temperatures reach 30 C and above, and also if it continues for several or more consecutive days. Combine that with the absence of shade, no breeze, a heavy hair or wool cover, solid dark hair colour, physical exertion or high humidity and clinical cases will develop. Physical activity such as processing, loading, or overcrowding during transport, for example, can also cause hyperthermia.

Overly fat animals such as finished feedlot cattle have a hard time dissipating heat (reverse insulation). If you do need to transport during very hot weather it is imperative to keep the truck or trailer moving to provide airflow and if you do stop, park in the shade. All livestock also need more room if transporting during extremely hot weather. Make sure the trailers have open areas for air movement and load up just before you are ready to go. Other activities such as processing cattle or moving cattle should be halted when ambient temperature is too high. Another option is to plan to process cattle very early in the morning to get the task done by noon.

With overheating you first see an increase in body temperature. It is not uncommon to see body temp rise to 42 C and higher. Respiratory rate will also increase but the breaths will be quite shallow, and the tongue is often out. Those signs or symptoms are often confused with pneumonia or some other respiratory insult. Animals will appear very depressed and lethargic and young ones often will not want to nurse. Often they will want to lay down a lot, and this can be followed by an inability to rise. Stress will often cause diarrhea and can even lead to a coma from depression of respiration.


Treatment involves getting the internal body temperature back down by cooling. Depending on the severity, measures to cool livestock include using fans, placing in cool buildings or shade, spraying with water and in severe cases cold water enemas are given. Spraying with water is the easiest with no handling necessary and once the animal is wet remember that evaporation is also a cooling process.

If you see cattle at pasture crowding against shaded areas and if most are dark coloured this is a good indication hyperthermia may be close at hand. The simple treatment of a garden hose of hand sprayer may avert a disaster. A simple rule is if you are extremely hot and unable to do much think about the cattle as they may be in the same boat. I haven’t even mentioned the impact on conception rates or early embryonic death of fetuses that may be the result of hyperthermia as well. As producers we are always watching the weather for rain, hail etc. so extremely hot temperatures is what we also need to be aware of.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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