An obese eight-year-old black Labrador has lost nearly half a stone in weight by running on an underwater treadmill at a fat dog boot camp in Dawlish.
Prince attends the rehab centre during the week where he is placed on a diet which includes fasting one day a week.
Other techniques veterinary clinic Linhay uses to rehabilitate pets include Pilates and trampolining.
Meanwhile an RSPCA spokeswoman warned pet owners that overfeeding an animal is just as cruel as under-feeding them.
Health risks
"Owners should not give in to puppy-dog eyes, but should remember they have a duty of care to their pets to keep them healthy," said the spokeswoman.
Prince became overweight when his owners moved away to Kuwait for two years and left him with family members who fed him an inappropriate diet.
Linhay vet Kate Rew said owners should not feel guilty but should give their pets a new lease of life by exercising and putting them on a diet.
"Prince loves being here, he is already starting to show signs of being a Labrador again as he's chasing pheasants and he can run a lot further.
"His owner says Prince loves coming back after the weekends," she said.
In the two weeks of his new regime, Prince's weight dropped from 11st 8lb (75 kg) to 11st 2lb (71.5 kg). His target weight is 5st 5lb (35kg).
As Prince is morbidly overweight, he has had to have surgery for ligament disease in his knees which he developed due to his weight. He now has acupuncture to control the pain and to enable him to exercise.
Other health problems Prince has include poor cardiovascular fitness and the inability to control his body temperature.
Meanwhile, Shamrock, a Rottweiler from Plymouth, is to be crowned Hill's Pet Slimmer of the Year for the south west on Tuesday.
He shed 40kg in puppy weight by swimming 10,000m in the family pool.
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