Could this dog be Australia's fattest pet?

At 85kg, eight-year-old Sampson is a shocking 42kg above his normal weight.

The lardy Labrador is so unfit, staff at the Animal Aid shelter in Coldstream say it will take him at least until Christmas to shed half of his excess load.

Despite being irresistibly large and cuddly, Sampson's weighty frame carries serious health risks.

He is so overweight, the hefty hound cannot be safely exercised. Vets say his blood shot eyes are the result of fatty tissue around his head and high blood pressure.

He even has to be taken to a Melbourne shelter for a weekly weigh-in by the Animal Aid van because his porky behind cannot fit comfortably in the back seat of his foster carer's Sedan.

Vets say his unhealthy size has been caused by bad diet and excessive quantities of food. It is thought Sampson was often fed fast food, huge calorific meals and fatty treats for good behaviour.

Sampson is living with Animal Aid vet Dr Amber Lavery, who hopes to cut his weight by half before he is put up for adoption.

The World’s Fattest Pets (Pic credit: Herald Sun)

Dr Lavery told the Herald Sun: "He's the size of a small heifer.

"It's obvious to get a case of such extreme obesity, Sampson has been fed excessive quantities of the wrong types of food over a very extended period of time.

"His former owners obviously couldn't resist his big brown eyes that follow you around saying 'feed me'."

With such a keen appetite, Dr Lavery said Sampson is struggling to adjust to his new strict calorie-controlled diet of dry dog biscuits and water.

But she insists "tough love means saying 'no'."