If your Labrador retriever seems hungry all the time, it may be because they are.
These dogs are notorious among veterinarians for their tendency to pack on the pounds. And in previous research, scientists found that one quarter of Labradors—as well as two thirds of a less common breed of dogs called flat-coated retrievers—carry a genetic mutation that is associated with obesity in other animals. And in new experiments, researchers found that dogs with this mutation both feel hungrier between meals and burn less energy than their counterparts do.
“What we see in the dogs is that they’re getting this molecular starvation signal,” says Eleanor Raffan, a veterinarian and geneticist at the University of Cambridge and a co-author of the new paper, which was published on March 6 in Science Advances. “As a result, they try to eat more and dial down their energy expenditure.”
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In the new study, Raffan and her colleagues wanted to understand how the mutation, which affects a gene called pro-opiomelanocortin (POMC), impacts the lives of dogs who carry it. So they recruited dozens of U.K.-based dog owners who were willing to take part in a series of experiments .
The first experiment, nicknamed the “sausage in a box” test, brought Labs into the lab about three hours after the dogs had eaten breakfast. Researchers showed each dog a sausage, then closed it in a plastic box with holes so the dog could smell but not eat the treat. Then they watched how the dogs interacted with the box and for how long. The researchers found that dogs with the POMC mutation were more focused on the sausage box, spending about twice as much time interacting with or manipulating it.
The researchers also had dog owners conduct an experiment at home. In this exercise, breakfast became an all-Fido-can-eat buffet in which dogs got a new can of food every 20 minutes until they stopped eating, vomited or reached the experiment’s maximum limit of 6.5 pounds of food. On average, all the dogs, whether they had normal POMC genes or not, ate about four pounds of food—“an enormous amount,” Raffan says. (Dogs with the POMC mutation ate somewhat more, though, and dogs without it were more likely to end the experiment by vomiting.) The result suggest that the mutation doesn’t make a difference in how quickly dogs feel full. The increased focus on food by the POMC-mutation group, however, suggests these dogs would continue to seek out more food if it wasn’t in front of them by, for example, begging or stealing.
The researchers also looked at the opposite side of the equation: how dogs burn energy. For this experiment, they recruited 19 flat-coated retrievers. (These dogs carry the POMC mutation more frequently than Labradors, and researchers wanted to compare dogs that didn’t have the mutation at all with dogs that had it in both copies of the gene because they expected the results would be more subtle.) The dog owners coaxed their pets into falling asleep in a chamber that measured the metabolic gases they produced, which allowed the researchers to calculate how much energy they burned while at rest. The scientists determined that dogs with the POMC mutation used less energy than their counterparts.
Taken together, the experiments show the complex way in which the mutation affects a dog’s brain and body, Raffan says: It makes them want food more without actually making them like a particular food more or need more food to feel full. Simultaneously, it makes them burn food more slowly. “They get a kind of double whammy of both eating more and burning off fewer calories, meaning that they’re predisposed to obesity from both directions,” Raffan says.
The mutation is the legacy of a now extinct breed called St. John’s water dogs, the ancestor of both Labradors and flat-coated retrievers. These dogs accompanied fishers and happily fetched fish out of the frigid waters of maritime Canada in the 16th and 17th centuries. “You can imagine that, in that context, willingness to eat anything that came your way and have a little bit of a layer of blubber under your skin to keep you warm in the sea might have actually been quite a good idea and a bit of an advantage for those dogs,” Raffan says.
But for modern pets, the mutation is more harmful because obesity can cause or exacerbate health issues ranging from breathing problems to skin disease to incontinence, Raffan says. In one survey, 11 percent of Labradors were obese, compared with 7 percent of non-Labradors. In another, 5 percent of Labradors were obese, and 36 percent were overweight.
Dogs with the mutation can stay at a healthy weight, but they need their owner’s help to do so. In particular, Raffan says that spreading out meals through the day, resisting the puppy eyes begging for human food and giving the dogs lots of exercise are key, as is giving them something to think about besides their innate hunger. “We hate being hungry. You don’t like it; I don’t like it; the dogs probably don’t like it either,” she says. “So keeping them distracted and occupied seems to be helpful.”