As a breed, Labrador Retrievers often have serious food-related issues — a behavioural quirk that often leads to over-eating and canine obesity. Researchers have finally figured out why, and the answer could influence the way we treat human obesity. Many years ago, I had a friend who owned a Labrador Retriever. This dog was constantly begging for scraps and doing its darnedest to sneak a quick meal. Once, I lobbed a morsel of food across the room to my friend, and his dog made an incredible leap for a timely mid-air chomp.
At the time, I ascribed this over-the-top food-seeking behaviour to this one dog, but dog experts have long observed that Labrador Retrievers always seem to be interested in food. In an effort to learn why, veterinary surgeon and geneticist Eleanor Raffan from the University of Cambridge conducted a genetic study of the breed. "Whenever there's something more common in one breed than another, we think genetics are involved," she said in a statement. Those results now appear in Cell Metabolism.
Image: E. Raffan et al., 2016/Cell Metabolism
For the first part of the study, Raffan and her colleagues analysed the genetic profiles of 15 obese and 18 lean Labrador Retrievers. Of the three obesity-related genes analysed, one particular gene — the POMC gene — stood out.
This particular gene appeared to be a bit messed up among the obese Labradors, such that they are unable to produce special appetite suppressing neuropeptides. These small protein-like molecules are involved in switching off feelings of hunger after eating a meal. So these dogs are always hungry, even after gobbling down a bowl full of kibble. This mutation was absent from other breeds (except the related Flat-Coated Retriever).
Raffan's team also looked at a larger sample of 310 Labradors, and they noticed a significant number of canine behaviours associated with the impaired POMC gene. Not all Labradors with the DNA variation were fat, but the mutation was definitely associated with higher weight. And dogs with the impaired gene exhibited more food motivated behaviours, such as begging more frequently, paying more attention during meal time and scavenging for scraps more often. On average, the POMC deletion was associated with a 2kg weight increase.
"We've found something in about a quarter of pet Labradors that fits with a hardwired biological reason for the food-obsessed behaviour reported by owners," said Raffan. "There are plenty of food-motivated dogs in the cohort who don't have the mutation, but there's still quite a striking effect."
Only about one in four Labradors have this mutation (same for the Flat-Coated Retriever), so other factors may be involved. However, the mutation was found to occur in about three out of every four assistance dogs. It's possible that these dogs are more likely to be selected for assistance-dog breeding programs, because their insatiable desire for food makes them more trainable.
There could be potential therapeutic implications for human obesity. The canine POMC gene works similarly in humans, unlike the way it functions in rats and mice. "Further research in these obese Labradors may not only help the well-being of companion animals, but also carry important lessons for human health," said Stephen O'Rahilly, a senior author on the study.
Raffan said that it's still possible to own a dog with this mutation and keep them slim. She advises owners to be more rigorous about portion control, and to resist their "big brown eyes" when they plead for food.
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