After a special diet of tinned prunes and oranges failed to work, Paignton Zoo say drastic action is now being taken.
They're now adding droppings from the other gorillas to their eldest gorilla in what's being dubbed 'poo-shakes'.
The process, which in the past has been used to help save endangered species, aims to transfer the micro-organisms he's lacking.
Pertinax, a 36-year-old Western lowland gorilla ,weighs-in at a healthy 200 kilos which is achieved on a vegetable diet.
He is effectively retired and living separately from the zoo’s three boisterous youngsters Kiondo, Kivu and N’Dowe.
One of his keepers, Gemma, says: "He's always had a problem with constipation. He eats the same diet as the others and lives in the same environment, but they poo normally and he doesn't."
Zoo research officer Dr Holly Farmer explains the aim of a faecal transplant: "Sharing a healthy animal’s gut flora through a faecal transplant can improve physical health and an animal’s temperament.
"We hope that micro-organisms from the stomach of a healthy gorilla will help sort out Pertinax’s issues.”
"Transfaunation is a technique commonly used to treat indigestion in dairy cattle. It involves transferring a range of micro-organisms including bacteria, protozoa, fungi and archaea from the rumen (first stomach) of a healthy animal to that of a sick one.
"Meanwhile, scientists are looking at how faecal transplants might help save the koala from extinction by changing its bacterial flora and extending the range of foods different groups are able to digest.
"In addition, vets prescribe faecal transplants for domestic pets with a variety of intestinal problems.
"Poo from all three of the other gorillas - Kiondo, Kivu and N’Dowe - was used.
"Keeper Anne Lunt mixed it with warm water, apple and blackcurrant squash and honey to make the unappealing cocktail - and was both pleased and amazed by Pertinax’s response: “He drank three or four paper cups – he seemed to like it!”
"Results can be achieved with one dose, though sometimes more are required. After a few days, keepers noted very promising improvements.
They will continue to monitor Pertinax closely, but the technique does seem to be working."