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Hyperthermia in Cheetahs

darting dysondarting mulder

Although not many people are aware of the fact, one of the most frequent causes of deaths in cheetahs during immobilisation is hyperthermia (overheating). This phenomenon has not been studied or described much at all, but the annual health checks at AfriCat have provided Dr. Adrian Tordiffe and colleagues a unique opportunity to study and learn more about this problem - to try and understand what causes it, and to begin to develop ways of managing and preventing it.

In cheetahs who develop hyperthermia, temperatures measured shortly after darting can be over 40℃ and are sometimes still rising. If the body temperature is not brought down rapidly this can have severe consequences for the cheetah - brain damage, damage to the digestive tract and/or cardiorespiratory failure.

Hyperthermia cases we saw during AfriCat health checks seemed to be unrelated to the environmental temperatures. It was happening on cool and warm days, and at different times of day; but research done by a colleague, Prof. Leith Meyer, gave Dr. Tordiffe a clue as to what might be going on . . .


darting a cheetah

 

Darting a captive cheetah in a hold-over or catch-camp is very stressful!
Even if it’s a habituated cat, for they feel captured and cannot get away from man.
The cheetah realizes something is different and starts pacing before the vet darts and after the dart has hit, stress-levels shoot even higher before the drug takes effect - temperatures then rise fast.

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Darting the captive cheetah in a small catch-camp – this time canvas side-panels are attached to the outside preventing the cat from seeing the vet before its darted. Some cats are lying still and are relaxed before the vet gets there – however, others pace the second they are placed in a smaller enclosure, especially if they usually are housed in large areas. But once the dart hits them – they pace, run, stress - fighting the drug, until they finally fall asleep.

 

Prof. Meyer had found that impalas (another species in which hyperthermia occurs) who were stressed prior to immobilisation were at greater risk of developing the condition. Dr. Tordiffe began to look at whether the same thing was true in cheetahs. He started keeping records of the cheetahs’ stress levels immediately before they were darted - noting whether they were relaxed and lying down, pacing, or running, and giving them a stress score based on his observations. A pattern emerged. Cheetahs who scored higher on his "stress scale" were definitely more likely to have higher initial temperatures after darting.

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As soon as the cheetah is 'down' the vets moves closer, monitoring vital signs like heartbeat and temperature. The cheetah is then taken to the vehicle that will transport it to the clinic. If their temperature is 39C or higher, they are immediately soaked with cold water.

 

One of the most stressed of the cheetahs darted during the 2014 checks was a young male named Swakop. He had only recently come in to AfriCat with his sister Mundi, after the pair were found near death in the desert near Swakopmund. Swakop was very suspicious of Dr. Tordiffe - beginning to run the moment he saw the vet. His temperature had already reached 43℃ by the time we were able to measure it after darting him.

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Swakop

Dr. Tordiffe had to make a quick decision. The usual procedure for a so-called "hot cat" involves cooling them with cold water (a combination of sprayed water and wet towels) and ice packs. The cheetahs are cooled on the vehicle while they are transported to the clinic. Once at the clinic more water and ice is applied and electric fans and leaf blowers are used to cool them even further.
Dr. Tordiffe knew that, even with aggressive cooling like this, Swakop’s temperature would take a while to start coming down, and he didn’t think that with a temperature that high, they could afford the time. One of the reasons for the slow cooling is that one of the drugs used to tranquillise cheetahs (medetomidine) causes the blood vessels in the skin to close up (vasoconstriction). This actually works AGAINST cooling, as one of the body’s ways of getting rid of excess body heat is by opening up blood vessels in the skin so that the blood can be cooled as the skin is cooled. Knowing this, Dr. Tordiffe made the decision to give Swakop an antidote to the medetomidine and wake him up. This would allow Swakop’s natural cooling systems a chance to bring his temperature down. In addition to opening up the blood vessels in the skin, once awake, the cheetah is also able to properly "blow off" heat by panting - something that tranquillisation also affects.

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Swakop and the other cheetahs that overheated, were doused with cold water and given the antidote. Fortunately they recovered well, showing no lasting effects of his ordeal. Dr Tordiffe explained the whole process to the 3rd year UNAM veterinary students.

 

Swakop was doused with cold water and given the antidote. Fortunately he recovered well, showing no lasting effects of his ordeal. Unfortunately, though, the vets had been unable to give him a proper health check!

Having realized how important stress levels are, extra work has been done during subsequent health checks to try and reduce stress levels prior to darting. Canvas screens have been installed in front of the catch camps with darting "windows" to prevent the cheetahs seeing the vets. Some of the cheetahs who get stressed in the smaller "catch" camps are instead darted from a vehicle inside their larger camps. Despite these efforts, though, some of our cheetahs still get a little stressed. That means we still need to be prepared to manage hyperthermia.

The experience with Swakop got Dr. Tordiffe thinking. Once he’d worked out that the immobilization drugs were affecting the cheetah’s cooling mechanisms, he realized that there could be a way to cool a critically "hot cat" quickly, without having to reverse the immobilisation. As a result, this year the management of "hot cats" changed. Any cheetahs showing high initial temperatures were immediately rushed into the clinic. Basic cooling procedures were initiated, but, instead of spending a lot of time wetting and cooling them outside and waiting until their temperatures started dropping, they were quickly intubated, moved inside and connected to a gas anaesthetic (isofluorane) machine. They were then given the antidote to medetomidine. The response was excellent. Their temperatures came down rapidly even though they were no longer being treated with water, ice and cold air.

In total seven of the 33 cheetahs immobilised this year had initial temperatures exceeding 40C, and all of them responded very well to this new treatment.
Once again, Swakop was one of them. He is a particularly alert and feisty cat, which probably makes him more prone to becoming easily stressed by contact with strangers, and thus more prone to hyperthermia. This time, though, he didn’t manage to get out of having a thorough health check. We were pleased to find out that, aside from his "hot-blooded" tendencies, he’s in excellent shape.

 

Darting cheetah in a large enclosure where they spend most of their time, and not in a smaller, temporary ‘catch-camp’ is better, but the camp must be open - grass cut low so that you can observe the cat from afar once it lies down, and find it immediately after it has fallen asleep. This methods seems to be the best option by far.

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Picture 1: Dr Adrian Tordiffe (left) and Dr Diethardt Rodenwoldt contemplating how to tackle a complicated 'patient'. . .
Darting a free-roaming, rehabilitated cheetah in the wild seems to be the most stress-free of all methods.

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Lions however are a different challenge for you cannot just drive into their enclosure and have to either lure them close to the fence by camouflaging yourself and hiding on the back of the vehicle that feeds them daily or by medicating a piece of meat before darting them.

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