Keeping anesthetized rhinos safe

Developing safer capture and immobilization techniques for one of the world’s most endangered animals

Leith Meyer

Professor Leith Meyer

Director: Centre for Veterinary Wildlife Research

Professor in the Department of Paraclinical Sciences
University of Pretoria

Kruger National Park on a map
Kruger National Park is set in the northeast corner of South Africa, bordering of grassland, wetland, and bush. It is home to the animal group known as the ‘Big Five’ – elephant, lion, buffalo, leopard and rhino – and for over a century, the park’s team of rangers, scientists, and veterinarians has led the way in protecting these iconic species. This is no easy job, especially when it comes to the rhino.

In 2020 alone, poachers killed over 500 rhinos across South Africa – roughly one every 22 hours. And while this is an improvement on recent years, it is far too many for the highly threatened population to sustain. There are other risks too. Many of the techniques used to protect the remaining animals, including dehorning and translocation, depend on chemical immobilization (anesthesia) using drugs that pose a risk to the animals with effects that are not perfectly understood. Professor Leith Meyer is working to change this.

Leith teaches wildlife pharmacology and medicine in the Faculty of Veterinary Science at the University of Pretoria, and is spearheading research related to wildlife capture and chemical immobilization. His goal is to improve the safety of rhinos during veterinary procedures in the field, where he works in collaboration with the Veterinary Wildlife Services team of South African National Parks, and across Africa. “We want to be able to inform people better in terms of what these drugs do, to improve the welfare of the animals and reduce the risks during anesthesia.”

Rhinos are particularly sensitive to anesthesia. They can suffer from severe cardiorespiratory depression, with respiratory rates dropping from a typical 19 breaths per minute down to as low as 3 or 4 breaths per minute. “When you look at the data of their physiology, these animals are actually sitting on a knife's edge. It's really important for us to improve how we do things during rhino anesthesia.”

On top of this, Leith is focused on finding solutions that work out in the field where vets conduct procedures with limited resources. “Using oxygen from a big cylinder is very effective in rhino, but it doesn't always help - especially when you're working from a helicopter - because you can't take that cylinder with you. When you're darting a rhino from a helicopter and you need to dehorn it or treat it, you want to make sure the animal has the best physiological response to the drugs used – you don’t have any fancy equipment to revive the animal.”

A white rhino can be up to 2m tall at the shoulder, and the average male weighs over 2 tonnes – although there are reports of the largest animals reaching 4 tonnes. Their sheer size makes any kind of intervention a difficult proposition. There is the animal’s safety to consider of course, but each procedure must be safe for people too.

Rhino with horn removed


With horn worth more than its weight in gold, poachers. Horns are made from keratin, similar to fingernails, and removing them doesn’t hurt. The horn takes around 2 years to grow back.


Drop in Kruger’s rhino
population since 2013
due to poaching 1


Rhino were poached
for their horn in South
Africa in 2020 2


Increase in rhino poaching
between 2007 - 2014 in
South Africa 1

So how exactly do you collect physiological data from rhino? Once the rhino is immobilized, Leith’s team use a PowerLab system with transducers adapted from human exercise physiology gear – mainly a gas analyzer and spirometer – to monitor the rhino’s ventilation, tidal volume, respiratory rates, and metabolism during anesthesia. Rhinos are obligate nasal breathers so all expired gases can be collected from the nostrils. In place of a face mask, Leith uses adapted equine endotracheal tubes in their nostrils to collect the expired gases, measuring airflow and also the CO2 and O2 levels each time the rhino breathes out. Calculating VO2 and VCO2 gives an indication of how much O2 the rhino is burning up, and how much CO2 they're producing. Capture drugs often make the animals hypermetabolic – Leith’s team are aiming to develop ways to reduce this elevated metabolism. To monitor blood pressure, and other variables such as blood oxygenation and pH, a catheter is inserted into an artery in the rhino’s ear.

The findings allow the capture process to be fine-tuned for the rhino, to keep them as healthy as possible. A better understanding is already paying dividends, with changes in how drugs are used during de-horning operations, where people spend up to an hour removing the horn that puts the rhino at risk from the poachers. Alongside colleagues from South Africa National Parks, Leith now helps run an advanced capture course for experienced wildlife vets from around the world, where delegates learn about the latest developments and research in the field of wildlife medicine.






Blood Oxygenation


Blood Pressure


Leith is passionate about research, although for a long time being a researcher was never the plan. “I always wanted to be a wildlife vet, but I've always had lots of questions in my head about what we are doing to the animals that we work on, and the effects of the drugs that are used. I ended up doing more research to try and better understand what happens when we do these procedures. It's always exciting. There's always something new. There's always something that we can do to help, and there's always so much that we can learn.”

Among the mentors Leith credits with inspiring him is his now research partner Dr Peter Buss, who he met when he attended a capture course just after vet school, about 20 years ago. He also credits Prof Duncan Mitchell as one of his science heroes. “He's currently one of the leading physiology researchers in the world. He's an esteemed, very well-known researcher, but he's such a down-to-earth person. We often enjoy a couple of beers together.”

For students considering a similar career? “You've got to be very dedicated. You've got to work really hard and stick to it, as the results are not instant, but very rewarding when they materialize. The outcomes, the findings, the difference that you can make globally and in the long term are really massive.”

Rhinos are a megaherbivore, and the second largest land mammal. They play an important role in shaping the grassland ecosystem – protecting them protects many other species who depend on this habitat.

Peter Buss

Dr Peter Buss

Veterinary Senior Manager

Kruger National Park

For Dr Peter Buss, a day in the field begins before dawn. He is a Veterinary Senior Manager at Kruger National Park, part of the Veterinary Wildlife Services team based just outside Skukuza camp – a village of 1200 residents known as the ‘capital city’ of the park. When they need to immobilize a rhino, it is safer for the animal to avoid the heat of the day, so the helicopter must leave at first light. It is an experience that still amazes him.

“To this day, I still find it incredible that you can take an animal like a rhino or an elephant, both huge, huge animals, and we can safely immobilize them with a very small volume of drug. We have to be able to get the drugs into a dart, which is about 3 mL. What is more incredible is when you give the antidote, literally within a minute or two, these guys are standing as if nothing ever happened to them.”

Peter has taught wildlife anesthesiology to veterinarians and veterinary students for many years, and cannot stress enough how valuable it is as a conservation technique. “Immobilizing wildlife is a fundamental tool which allows us to move animals between different national parks, to treat animals who may have been injured in a poaching incident, to de-horn animals, and to conduct disease investigations. We can also support other teams’ research projects – putting collars on animals to track them, collecting blood samples and so forth for people who need those types of resources.”

A rhino being immobilized A rhino being immobilized A rhino being immobilized

Peter collaborates with Leith on research to improve methods for immobilizing wildlife. "It’s really important to know what physiologically happens to a rhino when you immobilize it. What's actually going on with its breathing, with its heart function, with blood flow, all those things? And our ultimate question, how do we improve it? What interventions can we apply to make things safer for that rhino? And overall, how do we adjust our immobilization protocols for rhino?” While they currently focus on rhino, there are plans to work on other species, including giraffes, lions, and antelope.

Peter is positive about the future for the rhino. For all the dangers they face now – the ever-present threats of habitat loss and poaching – it’s easy to forget they are still a success story. “Rhinos are special, first of all, because they're endangered; and secondly, they're really a representation, I think, of conservation in South Africa. The success of conservation and what can be done. When you consider that people say white rhino numbers fell to fewer than 200 animals - and that was all that was remaining in the world. And we managed, through conservation efforts and the fact that we developed immobilization techniques, to increase that number to 20,000 animals. So that's a huge conservation success story. Pioneers started with this work, but how do we improve on it now, with all the challenges that we face?”

Rhino population growth

150 1929 3
Up arrow
20,000 2015 3

Continued decrease in poaching

Down arrow
6 YEARS marked in 2020 2