TOBY the collie is more used to eating lamb chops than rounding up sheep.
At 6st 6lb, he weighs as much as the average 12-year-old boy.
But all that is about to change when Toby battles to shed the pounds in a weight-loss challenge with the country's tubbiest animals.
He is one of 21 dogs, cats and rabbits from across the country selected to take part in Pet Fit Club – a national pet slimming competition run by veterinary charity PDSA.
Owner Michelle Brown, 35, said: "Toby's weight problems have gotten worse since I had children, as he follows them round eating any crumbs and leftovers like a Hoover.
"Over the past 12 months, other people have started have commented on how big he's got, so we knew something had to be done.
"We've had Toby for ten years, since he was eight weeks old. He is a big softie and wouldn't hurt a fly."
The collie-cross weighs two-thirds more than a healthy dog of his type.
He was entered into the six-month diet and fitness challenge after being rated morbidly obese by PDSA vets.
They put him straight on a weight-loss programme.
The collie is now given a special diet food, which can be eaten straight out of the can or baked into biscuits.
"He's on tinned food that looks like gravy," said Michelle.
"Apparently I can bake it and make him little biscuits as well. He likes it.
"I have to walk him little and often. I take him down to West Park and let him off the lead just to have a bit of exercise."
The vets said Toby's weight could be a major risk if nothing is done about it.
Overweight dogs are more susceptible to illness and chronic health problems.
"Toby is morbidly obese, which can have very serious consequences for his health and life expectancy," said head nurse Helen Darnell, who will be monitoring Toby's weight loss.
"Overweight pets are less mobile, less willing to play and more likely to develop a number of serious health conditions. The good news is it's never too late to make a positive change and improve a pet's lifestyle.
"We're confident Toby will have a slim-line figure and new lease of life by the end of the competition."
Research from the annual PDSA Animal Wellbeing Report has found more than 18 million pets are being fed inappropriate high calorie diets.
Coupled with little or no exercise, it means their life spans can be cut short by conditions like diabetes.
Visit www.pdsa.org.uk/pet fitclub to sponsor Toby's weight loss challenge and monitor his progress.
