22 September 2021

Our zookeepers noticed that Hugo, a 19-year-old, greater-one-horned rhino (Rhinoceros unicornis) had started bumping into logs and other structures in his paddock at our leading conservation zoo.  

An examination found that the lenses in his eyes had become cloudy, and had drastically impacted Hugo’s eyesight, so the Zoo’s vets called on the services of specialist veterinary ophthalmologist, Claudia Hartley, to perform cataract surgery - the first time the procedure had ever been performed on the species at the Zoo. 

Given an anaesthetic by dart for the op, Hugo initially laid himself down in the corner of his den on his right side - the side that vets needed access to. This meant a team of keepers and vets had to roll and move the colossal creature, who weighs over one and a-half tons, into position for the procedure.  

Senior Veterinary Officer Dr Fieke Molenaar explained: “After we administered the anaesthetic to Hugo, he fell asleep on his right-hand-side, which was the side we needed to treat, so we had to get every single keeper there to help pull him out of the corner and roll him onto his left-hand-side. After that, we had to carefully lift and position his head, which is, in itself, incredibly heavy, so that it was in the right place and angle for the microscope.” 

Keepers and vets had to be especially careful not to touch their own faces after touching Hugo, as the amount of powerful anaesthetic required to tranquilise a rhino of his size, which could have remained on his skin or in his bodily fluids, was strong enough to kill 14 people. 

Greater one-horned rhino

There are only around 3,700 Greater one-horned rhinos today. Meet Zhiwa, the 15th greater one-horned rhino to be born at the Zoo, who is helping raise awareness for her species and drive forward rhino conservation in the field. 

Dr Molenaar continued: “Hugo’s eye had to remain completely still for the microscopic incision, so several sutures, or stitches, were put into the eye tissue, to anchor it. We had to ensure that Hugo remained asleep enough throughout the procedure that he didn’t blink and break the sutures, but not so anaesthetised that his heartbeat or breathing slowed down too much.” 

Two keepers took it in turns throughout the operation to hold Hugo’s ear upright, so that the anaesthetic could be continuously administered through an IV into a blood vessel in his ear.  

After the cloudy lens had been successfully removed from his eye, keepers massaged and used ropes to shake Hugo’s enormous legs, in order to improve his circulation, so that he could stand up as soon as he came round from the anaesthesia.  

Fieke Molenaar added: “Since the operation, Hugo has recovered brilliantly, and with the lens removed, is able to see again. It’s wonderful to be part of such a life-changing operation, and even better to see Hugo back out and about, not bumping into things anymore! We’re elated about it, and I’m sure Hugo is too.” 

Best known for its own colossal beasts that graze enormous enclosures, like the Zoo’s two herds of prehistoric looking rhinoceroses, Whipsnade Zoo is home to over 9,500 amazing animals, including Amur tigers, spritely squirrel monkeys and adorable otters.

Proudly helping to protect threatened species, we've contributed to reintroductions of extinct-in-the-wild species, such as the Przewalski’s horse and the Scimitar Horned Oryx, and shares veterinary experience learned from procedures such as these with its global networks. Through their entry fee, every visitor contributes to ZSL’s worldwide conservation work for animals and their habitats.  

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