Labradors are more prone to obesity because we've trained them with food for years

'It’s not unusual to train with food – very many animals are trained with food, including our own children sometimes'

Labrador retrievers may need a bit more exercise to control their runaway appetite (Rex)

Labrador retrievers may be prone to obesity because they have been trained by humans using food as a reward, according to new genetic research.

The dogs – favoured particularly as guide dogs for blind people – were found to often have a mutated gene which interferes with the process that turns off feelings of hunger after a meal.

Labrador retrievers are descended from the St John’s water dog, which were originally trained by fishermen to help them in the freezing waters on Canada’s eastern coast.

The theory is that over the last 100 to 200 years humans have selected dogs with the obesity-linked mutation because they were easier to train as they wanted the treat given as a reward more than other animals.

Lead researcher Dr Eleanor Raffan, a veterinary surgeon and geneticist at Cambridge Univeristy, said their research provided a genetic reason for the dogs' appetites and associated weight problems.

“We’ve found something in about a quarter of pet Labradors that fits with a hard-wired biological reason for the food-obsessed behaviour reported by owners,” she said.

“There are plenty of food-motivated dogs ... who don’t have the mutation, but there’s still quite a striking effect.”

The proportion of dogs with the mutation increased from about 23 per cent to 76 per cent among Labrador retrievers that were being used to help people.

“It was surprising. It’s possible that these dogs are more food-motivated and therefore more likely to be selected for assistance-dog breeding programs, which historically train using food rewards,” Dr Raffan said.

The study, which was reported in the journal, Cell Metabolism, was the first to describe a gene associated with canine obesity.

Fellow researcher Dr Giles Yeo, also a Cambridge University geneticist, told The Independent that the human trainers had simply been choosing the most “trainable dogs”.

“Because they train with food that’s why that specific mutation got entrenched within that class of dog,” he said.

“It’s not unusual to train with food – very many animals are trained with food, including our own children sometimes.

“Clearly children get treats and there’s nothing wrong with giving children treats as long as the treat doesn’t become the norm.”

The propensity towards obesity appeared to have evolved as an “unintended consequence” of their training programme, Dr Yeo said.

And he praised trainers for turning Labradors into the “Navy Seals of dogs”, aka the guide dog.

“You never hear of a Labrador dragging a blind person into the road because they were chasing a chicken,” Dr Yeo said.

“These dogs are being bred to serve humans and they do it very well because they are very well trained.”

Rachel Moxon, canine research associate for the charity Guide Dogs, said the welfare of all their dogs was "absolutely paramount".

"The fact that Labradors are more motivated by food than some other breeds makes them ideal to train as guide dogs because they respond well to positive reward training and develop a really strong bond with their owner," she said.

"But we work closely with all our guide dog owners to make sure our dogs maintain a healthy weight.

“These measures have been shown to be effective, because while some dogs are more likely to be overweight than others, obesity levels among guide dogs are no higher than in the wider dog population.

"Regardless of genetics, all dogs need a healthy, controlled diet and plenty of exercise."