Head to your dog park, and you'll probably find yourself swimming in a sea of labrador retrievers. They've been America's favourite dog for the past 25 years, and if you've ever spent time with one, it's pretty easy to see why - labs are family friendly, just the right size and, well, adorable.
Despite the breed's out-of-control popularity, labs do have one weird problem that seems to plague them more than any other breed: weight gain. Labradors are notorious for their obsession with food, but scientists have struggled to figure out why. Now we might finally have an answer, because it looks like a very specific genetic variation could be to blame.
According to researchers from the University of Cambridge in the UK, more than a fifth of labrador retrievers carry a genetic variation that predisposes them to weight gain, reports Nicola Davis for The Guardian. This means that, despite how much owners intend to feed their dogs, some labs will always seek out more food and, therefore, gain weight faster, though overfeeding is definitely something owners should avoid.
The Cambridge team compared the DNA of 18 lean labs to 15 obese labs and searched for three specific genes that are known to cause weight gain in mice. They found that one of these genes, called POMC, was more commonly mutated in obese Labs than lean ones.
This mutation disrupts the dog's ability to sense the amount of stored fat it has and also affects the brain's reward system, Davis reports. In other words, it makes it incredibly easy for the dogs to overeat without realising it.
Taking these findings a step further, the team examined a group of 310 labs to see how the mutation directly influenced weight. After accounting for variables such as age and gender, they found that labs with one copy of the mutation were 1.9 kilograms (4.1 pounds) heavier than dogs without it.
While that doesn't seem too bad, it gets worse with every copy. For example, if a dog had two copies of the gene, this number jumped to 3.8 kilograms (8.2 pounds) heavier. "On average, the genetic mutation was associated with about a 4.5-pound weight increase in the dogs," reports Jennifer Viegas for Discovery News.
The team also offers a few ideas as to why this mutation has persisted so long. Basically, back when labs were working dogs that needed to eat heavily to perform their jobs, food-motivated dogs were in favour because they were more easily trained. This led to them being bred more and, after years of proliferation, the mutation is now widespread - despite the fact that today's labs are rarely used for work.
Also, if you're a lab owner with an animal that's constantly seeking food, it's still possible to keep them fit and healthy. "You can keep a dog with this mutation slim, but you have to be a lot more on-the-ball," one of the researchers, geneticist Eleanor Raffan, told Discovery News.
"You have to be more rigorous about portion control, and you have to be more resistant to your dog giving you the big brown eyes. If you keep a really food-motivated labrador slim, you should give yourself a pat on the back, because it's much harder for you than it is for someone with a less food-motivated dog," she adds.
The findings were published in the journal Cell Metabolism.