Certain retriever breeds have excess hunger and a lower resting metabolic rate because of a genetic mutation, a recent study published in Science Advances found. Labrador retrievers are notorious for being highly food-motivated and eating everything in sight, and these findings could explain why. The results also shed light on the increased prevalence of obesity in retrievers.
Background
The leptin-melanocortin pathway plays a central role in mammalian food intake. During a meal, circulating hormones, such as leptin and insulin, are released by adipocytes and pancreatic beta cells. The hormones cross the blood-brain barrier to bind to receptors on the surface of pro-opiomelanocortin (POMC) neurons to promote activation of alpha- and beta-melanocyte-stimulating hormones, which send signals to the body to decrease food intake and increase energy expenditure. These neurons are inactivated by nutritional deficiency.
Researchers had found in a previous study that a mutation in POMC significantly affected body weight and adiposity in Labrador and flat-coated retrievers. In the recent study, scientists evaluated affected dogs to understand how the mutation affects energy homeostasis. The POMC mutation is found in 12% of Labradors and 60% of flat-coated retrievers, so this factor is important to research.
Canine participants
Participating study dogs were companion animals kept as pets in the United Kingdom. Eligible dogs were genotyped for the POMC mutation using a TaqMan assay. A veterinary professional or trained researcher measured the dogs’ weight and adiposity using calibrated weight scales and a standard body conditioning score (BCS). Two hundred and twenty-one dogs met the inclusion criteria. Before the testing, dogs were gradually introduced to a standard diet over 7 to 10 days and they ate this food exclusively for 48 hours before beginning the study.
Experiments
Researchers conducted three experiments to evaluate the affected dog’s food response.
The researchers also measured energy expenditure and blood pressure in POMC mutated and non-mutated flat coated retrievers, which have a higher POMC mutation incidence than Labradors.
Results
Dogs with the POMC mutation spent more time interacting with the sausage box than the non-mutated dogs, suggesting they were more hungry. These findings are consistent with humans with the POMC mutation, who report feeling extreme hunger.
When offered a new can of food every 20 minutes, dogs in both groups ate about four pounds of food, which is about twice their total daily energy requirement, and the non-mutated dogs were more likely to vomit or regurgitate. These findings suggest that the POMC mutation doesn’t affect satiety, but may allow dogs to better tolerate a large meal.
All dogs presented with food mixed with lime juice took fewer bites and paused between bites, compared with their response to palatable food, but the POMC-mutated dogs ate the food more quickly. These findings suggest the mutation has no effect on aversive response.
POMC mutated dogs had a significantly lower (i.e., approximately 25%) resting metabolic rate and lower resting systolic blood pressure measurements than non-mutated dogs.
This study shows that Labradors and flat-coated retrievers are more hungry and burn fewer calories, putting them at high risk for weight gain and obesity. To maintain a healthy body weight, owners must restrict food intake to below the recommended amounts for non-mutated dogs, which can be challenging. Genetic testing on susceptible breeds may help educate your clients about obesity’s harmful effects, so you can work with together to keep their retriever slim and healthy.
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