Beef 911: Hyperthermia (overheating) in farm animals

Calving during hot weather with no shade is a recipe for trouble

Every year during the first few hot days of summer we hear media warnings about leaving pets unattended in closed vehicles, where temperatures can rise to over 50 C. We often don’t realize how susceptible livestock are to the same condition.

Many a farmer or veterinarian has been fooled by symptoms resembling a toxemia or pneumonia. It is very important to recognize it and then treat, but more importantly, simple steps that can be taken to prevent it.

We used to see very little hyperthermia, but with the advent of more open pastures and especially with people now birthing out cattle and camelids towards summer, more cases are seen. Elk and deer naturally calve late spring, but with no access to shade, their offspring are also susceptible.

There is definitely a higher susceptibility in the newborn to three weeks of age. A combination of small body size, no fat for insulation and hot milk as the main diet all contribute to a much higher susceptibility in young animals.

Black colouring on cattle exacerbates the problem with the dark colour really heating up in the sun. 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.

Springtime shearing

This is why camelids (llamas and alpacas) should be shorn every spring. 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.

Hyperthermia results from a combination of too high an ambient temperature for too long a period of time. That in combination with the absence of shade, no breeze and a heavy hair or wool cover and clinical cases will develop. Physical activity such as processing, loading, or overcrowding during transport can cause the body temperature to also rise, resulting in hyperthermia.

Keep moving

If you do need to transport during very hot weather it is imperative to keep moving, stop as little as possible, and if you do stop, park in the shade. 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 endurance rides for horses should be halted when ambient temperature is too high — or start early in the morning to get the task done by noon.

When overheating, the body’s response is to have the blood vessels open up and allow heat loss. With young animals, especially if they are somewhat dehydrated from scours, this ability to expand the blood vessels is lost. So they are many more times susceptible to overheating.

With overheating you first see an increase in temperature. Not uncommon to see body temp. rise to 42 C and higher. Respiratory rate will also increase but the breathing will be quite shallow. It is often confused with pneumonia. Animals will appear very depressed and lethargic and young ones often will not want to nurse. They initially will want to lay down lots 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 using fans, placing in cool buildings, spraying with water and in severe cases cold-water enemas all contribute to bringing body temperature down. Spraying with water is the easiest. As well, evaporation is a cooling process, so this secondarily cools the animal down. This is why high humidity is worse for hyperthermia, as evaporation from sweating horses for example, doesn’t happen. Give fluids if necessary to keep hydration up.

I often cover with antibiotics as the heat stress and cooling with water may lead to a susceptibility of contracting pneumonia or scours — but discuss this with your veterinarian.

If animals are down and unable to rise products given such as selenium and vitamin E (antioxidants) minimize muscle damage. The recovery period may be long in these instances.

I believe the critical temperature is in the 28 to 29 C mark, especially if temperatures this high and above continue for more than one day in a row. Obviously how low the temperature drops to at night will have a great influence. As mentioned, the trend towards later calving has them giving birth when even in Canada temperatures can get quite hot. As a preventive, try to calve in pastures with some bush or shaded areas. Missing the odd calving will be a small sacrifice compared to preventing cases of hyperthermia when the temperature gets too hot. The newborns should be the ones in the pastures with the most shade. Watch the weather channel and if they are predicting high temperatures, be proactive and move the livestock ahead of time. Even open-faced sheds or porosity fences provide some relief from the sun. If all these proactive things are done, you hopefully will never need to deal with hyperthermia.

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