The seven dogs and one cat, who are all more than 30 percent overweight and weigh a combined total of 421 lbs, were picked by veterinary charity PDSA who are running the slimming contest.
The animals, who need to lose a total of 163 lbs to reach their ideal weight, will be put on specially tailored diet and exercise programs.
The pet who achieves the biggest percentage weight loss and best follows their new regime will be crowned champion, winning their owner a pet-friendly holiday.
PDSA statistics show around 30 percent of Britain's dogs are overweight or obese, amounting to around 1.95 million fat dogs.
"Alongside their daily portions of pet food, owners often show their affection by giving unhealthy human treats such as cheese, buttered toast and biscuits. They don't realize they are actually killing their pets with kindness," said Sean Wensley, a veterinary surgeon at PDSA.