Labrador retrievers could make a pretty good claim for being America's dog. Last year, according to the American Kennel Club, they were the most popular purebred dogs in the country for the 25th year in a row.
There's something else very American about Labs: They have a tendency to get fat.
People whose dinners are interrupted by maniacally begging Labs know this, and so do the veterinarians who treat the diabetes and other health woes of chunky dogs. When the U.S. Association for Pet Obesity surveyed vets in 2012, they classified nearly 60 per cent of their Labrador retriever patients as overweight or obese; other large-scale studies here and in other countries have found that about half fit that description.
But it turns out that the pudgy pups, poor things, may not be able to help it. Overeating, a new study found, is very possibly in Labs' genes.
Eleanor Raffan, a veterinary surgeon and geneticist at the University of Cambridge who had studied human obesity, figured Labrador retrievers' battles with bulge might be rooted in genetics.
To find out, she and colleagues looked at three obesity-related genes in fat and slim Labs and found a variation in one, known as POMC, in 10 or 15 obese dogs, but only two of 18 lean ones. The variation - in this case, part of the gene was missing - can prevent dogs from feeling satiated after eating.
In a larger sample of 310 Labradors, the researchers found that the POMC deletion was more common among heavier dogs who, according to a survey that questioned owners about their dogs' affinity for scavenging and eating non-food items such as socks, were more "food-motivated."
When they widened the scope to a sample of 411 pet Labradors in the United States and the United Kingdom, the researchers found the POMC deletion in 23 percent of all the dogs. Of 38 other breeds tested, only flat-coated retrievers, which are related to Labs, also had the deletion.
"What we've found in the study is that there really is a hard-wired reason for some Labradors to be completely obsessed by food," Raffan said in an interview. The study was published Tuesday in the journal Cell Metabolism.
They also found something else curious: Fully three-quarters of 81 Labrador assistance dogs had the deletion. That might be an aberration, Raffan said, or it might suggest that Labs who really love food - which is used as a reward in training assistance dogs - are disproportionately chosen for the job. She said she hopes to study Labrador puppies selected as guide dogs in the United Kingdom to learn whether those with the mutation are "more likely to succeed in training."
What does this mean for you? If you're overweight, the findings add to the evidence that genes can play a role in packing on the pounds.
The same mutation in the POMC gene is also associated with obesity in people who have it, but there aren't enough of them to study, and the rats and mice typically used in research aren't of any use because their POMC is different. But it's similar in dogs, Raffan said. So scientists can now study Labradors to learn more about the function of the gene.
"That's important because the pathway that the gene acts in to switch off hunger is a potential target for therapy of obesity in humans," Raffan said.
If you're a Lab owner, well, you're just going to have to steel yourself against those big brown eyes. Or, Raffan suggested, hide food in special "feeding toys" that require dogs to work to get it out.
"The reason these dogs become overweight is largely because of the amount they eat," and not because their metabolism is different, Raffan said. "It just means that they are so much more obsessed by food. If you own one of these dogs, you are up against it if you try to keep them slim. But you can keep them slim if you pay attention."