Got a fat pony that won’t lose weight? Give him some slack—it might not be entirely his fault. According to new study results, some horse and pony breeds just tend to hold on to their weight better than others, despite diets and exercise. But don’t give up on your weight loss regimen, the researchers say, as a fat horse is still at increased risk for serious disease. These scientists are helping lead the way toward a better understanding of how to manage weight in various breeds.

“Ponies and certain horse breeds (such as some Andalusians, Morgans, and Warmbloods) are known for their tendency to put on body fat quite readily (compared to Thoroughbreds and Standardbreds),” said Simon Bailey, BVMS, PhD, FHEA, Dipl. ECVPT, MRCVS, associate professor in preclinical veterinary sciences at the Faculty of Veterinary Science at the University of Melbourne, in Australia.

Bailey and his fellow researchers allowed ponies, Standardbreds, and Andalusian crosses to gain weight before putting them on controlled diets and exercise programs to help them lose weight. They found that the Standardbreds lost weight quickly just by switching to a hay-only diet, but many of the ponies and Andalusian crosses retained their weight, despite a restricted diet and daily light exercise.

The team is also evaluating how and where fat is deposited on the horses’ bodies as they gain weight, and how various hormones are affected and potentially play a role in both weight gain and loss in the different breeds