Clinical Zoo: Anaesthetising an ape

General anaesthesia is undertaken every day in veterinary practice, so much so that anaesthetising dogs, cats and horses is reasonably routine. But anaesthesia of captive wildlife – even for experienced keepers – takes extensive planning, and requires a team approach to ensure the wellbeing of the patient and the safety of veterinarians, nurses and keepers.

Frala, a female western lowland gorilla, recently underwent an anaesthetic as part of a routine health check at Taronga Zoo. The experienced mother has given birth to six gorillas, including sons Fuzu and Fataki, to the Zoo’s previous silverback, Kibabu.

This is a significant contribution to the Zoo’s breeding program. It is estimated that there are only 100,000 western lowland gorillas remaining in the wild. That population remains under threat due to the increasing bush-meat trade, poaching and habitat destruction.

Frala was living off-exhibit with her two sons, as it is natural for Gorillas in the wild to move in and out of breeding groups. Meanwhile, in the main exhibit, the Zoo’s new silverback, Kibali, had been introduced to a pair of females – Mbeli and Johari.

The plan was to time a health check to immediately precede Frala’s introduction to the new breeding group.

“The Gorillas are managed under a species management plan so all breeding groups here are established according to that plan,” zoo veterinarian Frances Hulst said. “But obviously we want to ensure that all of the animals in the group get on well together. In the wild a new up-and-coming male would try to form his own breeding group by selecting females.”

At 33 years old, Frala is in her prime.

“She has successfully bred young, she knows the lay of the land,” Hulst said.

During the off-exhibit period, Frala was placed on a human oral contraceptive pill to ensure she did not become pregnant.

“It’s a reliable method of contraception if they swallow the pill,” Hulst said. Frala’s daily pill was administered in a banana.

Gorillas are gentle giants, but like any wild animal can be dangerous. At 90kg Frala can easily overpower a human, and her natural suspicion makes her a more challenging anaesthetic candidate.

“The keepers needed quite a long lead-in time to be able to get her stationed in a den area with each of her sons in a different den,” Hulst said. “The three have a very close relationship so the keepers worked very hard to ensure she could be separated comfortably to allow her induction to be done safely.”

Zoo veterinarians need to keep their options open when it comes to anaesthesia. They wanted to ensure that Frala could be induced by several routes in case one was not available. Over a period of time Frala was conditioned to accept the use of a mucosal atomiser device (MAD), as one potential option was to use medetomidine sprayed onto the oral mucosa. In addition she was trained to accept intramuscular injection.

“Our preferred method is hand injection as it is a much more controlled way to administer a drug,” Hulst said. “Oral mucosal administration has been used successfully in apes but it’s effect is less reliable as it depends on how effectively the drug is absorbed from the mucosa and whether any is swallowed.”

On the day, Frala was hand injected with a tiletamine – zolazepam combination (Zoletil) at 5mg/kg – although she pulled away at the last minute.

“She did receive enough of the dose to make her t not react badly to being darted with a supplemental dose,” Hulst said.

Once darted, it is the veterinarian’s responsibility to make sure the animal is suitably anaesthetised before others enter the den. Initially this is done by using a long pole to check reflexes. Once the veterinarian is comfortable that it is safe to enter the den, he or she does so and rechecks the reflexes. Because Frala is potentially dangerous, a net was placed over her. An intravenous catheter was placed in the superficial radial vein to provide access if required.

The Zoletil achieved a good plane of anaesthesia. Frala was placed onto a stretcher and transported in the Zoo’s van, giving oxygen via face mask.

In the hospital, Frala was intubated using a size 11 endotracheal tube and maintained on isoflurane in oxygen. Intravenous Hartmann’s was administered at 5ml/kg/hr.

A full physical examination was undertaken, along with a series of opportunistic tests including a complete blood count and biochemistry panel. Blood was also drawn for serology testing for encephalomyocarditis virus.

“We vaccinate them and monitor their titre post vaccination,” Hulst said. “It hasn’t been seen in Gorillas but it isn’t uncommon in some Zoos. Historically we have seen this in other Zoo animals but not Gorillas.”

Every five years the gorillas receive a tetanus booster vaccine.

The Zoo’s Gorillas are routinely tested for tuberculosis by both the gamma-interferon test and an intradermal skin test.

“The standard site for intradermal tuberculin skin testings on the upper eyelids in primates,” Hulst said. “The reason is that the skin is thin and unhaired and generally primates will look at you and we need to be able to see the test area to read the result.”

Avian tuberculin was administered in one upper eyelid and bovine tuberculin in the other. The eyelids are then visually inspected at 24, 48 and 72 hours.

Anti-parasitic agents are not routinely administered but faeces are monitored via faecal flotation and wet-preps regularly to detect parasites.

“We don’t see nematodes in our Gorillas,” Hulst said. “Sometimes we see low levels of protozoan organisms that don’t seem to affect the animals however we monitor these very closely.”

An ultrasound was performed to confirm that Frala was not pregnant.

Great apes are susceptible to many human infections, hence the Zoo has a strict policy that if keepers are unwell they do not work with the primates.

No abnormalities were detected during the health check, meaning that Frala could now be introduced into the breeding group. She was transported to a new den, with intravenous fluids and oxygen continuing.

“She was recovered on a thick bed of straw in a gorilla version of the human recovery position,” Hulst said.

Once in her recovery den her intravenous catheter was removed and she was extubated. The ET tube was retained for further tuberculosis testing. Hulst stayed with Frala until she was confident that the Gorilla would recover safely.

Although she woke up in a new den, it was one that Frala would recognise. Once she was completely recovered, keepers performed staged introductions.

“She was housedt at one end of the Gorilla house and the breeding group at the other, and keepers watched very carefully for signs of interest between them,” Hulst said. “They listen to vocalisations and other interactions to see if they are friendly or sexual or angry and gauge them carefully. Their ability to successfully introduce these animals is based on their huge knowledge and experience.”

Frala first met the two females, and appeared to get along very well with them. Her introduction to Kibali was also successful.

“He was very, very interested in her and she seemed very interested to meet him,” Hulst said.

Gorilla keeper Lisa Ridley said that the introductions had gone better than expected.

“We thought Frala might give Kibali a run for his money but he just strut his stuff like a typical young male,” she said. “He’s been charging at Frala and the others just to show his dominance but Frala is taking it in her stride. That’s her maturity coming through – she knows what to do.”


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