Pet euthanasia is proving a grey area for some veterinarians, with only a general code of ethics and their own judgment guiding their assessments.
While all clinics The Straits Times spoke to said they generally euthanise animals only when treatment fails to relieve their suffering, many said they accept requests to euthanise aggressive pets posing a danger to owners.
These cases are assessed on their own merit, they said.
Protocol for animal euthanasia was called into question after the recent death of seven-month-old mongrel Tammy. Its owner and a vet at The Animal Clinic deemed it to be aggressive - a claim disputed by furious animal lovers.
The clinic's managing director, Dr Lennie Lee, who has come under pressure to reveal its euthanasia protocol, told The Straits Times it will put down aggressive pets that "become a threat to the safety and lives" of humans and when behavioural therapy and treatments have not succeeded.
At the Animal Recovery Centre, an animal is put to sleep only if it has "no hope of rescue" medically. Director Jean-Paul Ly said: "Killing an animal, no matter how nicely, is still taking away a life."
Amber Vet's principal surgeon, Dr Brian Loon, noted there are often times "where the decision is grey both for the owner and veterinarian". He added that each case has to be individually assessed.
The same approach is taken at Namly Animal Clinic which has, on rare occasions, accepted requests to euthanise dogs found to be aggressive and dangerous.
One of its vets, who declined to be named, said: "If you refuse, where does the dog go? Some place them in a shelter, but would their quality of life be considered good... in a small kennel?" Dr Daniel Sing of Toa Payoh Vets added: "Once an owner is bent on it, it is difficult to persuade them otherwise."