Sheree Bega, The Independent Online | November 23, 2019
JOHANNESBURG: Professor Leith Meyer hopes for the day when rhino anaesthesia has become so safe that no rhino will die during immobilisation.
“This is an important goal, especially as rhino populations, unfortunately, continue to decrease,” he said.
Meyer, the director of the Centre for Veterinary Wildlife Studies, at the University of Pretoria (UP), and an associate professor in veterinary pharmacology, led award-winning research, together with SANParks and Wits University, into the role of certain immobilising drugs.
Their research found that the effects of butorphanol, an opioid, on immobilised rhinos “may be a game changer” in preventing the loss of the endangered animals, after they survive poaching attacks and other anti-poachng measures, such as dehorning and collaring.
For their work, the researchers received the 2018 Elsevier Prize, for the best article published in the journal “Veterinary Anaesthesia and Analgesia”.
“Immobilsation can be a risky exercise, with rhinos dying during these procedures in the past,” Meyer said, in a statement this week.
“Immobillisation effects are not easy to measure in rhino, so we have to develop novel ways of measuring these effects, such as adapting a human exercise physiology system, to measure the ventilation and metabolism of immobilised rhinos.”
Despite the limitations, Meyer gained insight into the physiology of an immobilised rhino.
“Typically, rhinos are immobilised using etorphine, also known as M99, an opioid that is about 4000 times more potent than morphine.”
This is usually administered in combination with a tranquilliser, which reduces induction time and opioid-associated hypertension.
But most deaths of immobilised rhinos have occurred from hypoxia – abnormally low oxygen concentrations in the blood – which is an effect of drugs such as etorphine, he explained.
Butorphanol, which is also an opioid, has been administered by vets in the past because it reverses etorphine’s effects, without reversing the immobilising effect. “This partial reveal was thought to improve the rhino’s breathing during immobilisation,” he said.
Before the study, it was believed that the deficiency of oxygen in the blood of immobilised rhinos was from the drugs depressing breathing.
But Meyer and his collaborators found that the etorphine-induced hypoxia developed from the rhino’s metabolism increasing, which was set in motion by tremors.
“The increase in metabolism is what primarily causes the hypoxia, as it burns up all the animal’s oxygen reserves. Butorphanol had been used by vets before, as it appeared to make the animals breathe better, but the research we did showed that this wasn’t necessarily the case. Butorphanol’s main beneficial effects are reducing tremors and metabolism.”
Their findings, said UP, prove incredibly important to rhino conservation. “Not only does the study confirm that butorphanol is an important drug to use during immobilisation, but also that its beneficial effects are not what they were previously thought to be. It reduces tremors, thereby reducing metabolism, to help improve the animal’s oxygen levels.
“This is a massive benefit to immobilised rhino, as it reduces the risk of anaesthetic-related deaths,” said Meyer. “The other important aspect of this study is that any future drug development needs to focus on treating the hypermetabolism caused by etorphine, not just its respiratory depressive effects.”