Veterinary scientists seem to have unraveled a mystery about why certain dogs simply can’t ever get enough to eat. In research out this week, they found evidence that a common mutation in Labrador retrievers causes them to experience greater hunger than usual while also reducing their metabolic rate, both of which make the dogs predisposed to obesity. The findings might help better understand and treat obesity in both dogs and their owners.
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Labradors are one of the most popular dog breeds in the world, treasured for their playful energy and their adeptness as a working dog (they’re often used as service dogs). But while labs do live relatively long lives—about 13 years on average—they’re also known to have a ravenous appetite and accordingly high rates of obesity.
Labs aren’t alone in their plight: Much like humans, dogs in general are experiencing higher rates of obesity. University of Cambridge scientist Eleanor Raffan has been working to unpack the genetics of obesity and metabolic disease in dogs. Her team has especially focused on the Labrador retriever, given its reputation for obesity, and its close relative the flat-coated retriever.
In 2016, they published a study finding a clear link between obesity in these breeds and a mutation in a gene responsible for the protein pro-opiomelanocortin, or POMC. This alteration seems to delete some of the POMC gene in affected dogs. They also found that a quarter of Labrador retrievers and two-thirds of flat-coated retrievers appear to have this mutation. In their newest research, published Wednesday in the journal Science Advances, the team says they’ve figured out how these POMC mutations physically help cause obese retrievers.
The researchers conducted various experiments with 87 adult pet labs. The dogs ranged in size from a healthy weight to a bit overweight, and some of them carried the POMC mutation. One of these experiments (which can be seen in the video above) had the dogs eat their normal-sized breakfast, then led them to a transparent plastic box with a sausage inside. The box had holes so the dogs could both see and smell the tempting treat.
Compared to dogs without the mutation, the POMC labs tried harder in their fruitless quest for sausage. However, another experiment—which involved giving the labs as many cans of food as they wanted every 20 minutes until they stopped eating—showed that there was no significant difference in how much either group of dogs could eat before feeling full. And a third experiment found that the POMC dogs had a lower resting metabolic rate than other labs, burning around 25% fewer calories.
Put it all together, Raffan said, and the results suggest that this mutation creates a “double whammy” in affected dogs. Not only do these dogs want to eat more than others (without actually having larger stomachs to fill), they also burn off less of the calories they end up consuming, which then makes them more likely to become obese.
“Practically, this means that owners of dogs with the mutation need to work particularly hard to keep them slim,” she told Gizmodo in an email. “It is possible, but requires owners to pay attention to what they feed and closing off opportunities for dogs to steal or scavenge extra food.”
As for how this happens on a biological level: The loss of the POMC gene in these dogs appears to prevent the production of two other hormones in their brain, beta-melanocyte stimulating hormone (β-MSH) and beta-endorphin.
Humans also produce these hormones, and there are known genetic disorders tied to a dysfunctional POMC mutation that greatly raise a person’s risk of obesity, as well as recently developed drugs that try to counteract the effects of this mutation. Normally, we’d be able to study the POMC gene more closely using lab mice, but their version appears to work differently than the one in dogs and humans. So the knowledge we gain from studying POMC-deficient Labrador dogs might help us better illuminate these genetic drivers of obesity in humans.
“Learning more about the biology of the pathway is important so we can understand how it works in humans too,” Raffan said.
POMC isn’t the only gene suspected to make labs obesity-prone, though. So Raffan and her team are already studying what other genes might be involved.
