Unlike humans, however, horse owners often don't see the dangers of an overweight horse, said Philip Johnson, a veterinary medicine professor at the University of Missouri-Columbia.
To make matters worse, not only do owners often overfeed their horses, but what is fed them is frequently genetically altered grass meant for food animals.
"The paradigm is that we feed horses the same grasses we are feeding food animals," Johnson said. "The genetically designed grass we feed horses was designed to fatten food animals quicker."
The genetics of horses, as in many species, allows for the extra storing of fat in preparation for winter, when there is typically less food available. In nature, horses would eat less in the winter and lose the weight by spring, noted Johnson. Under human care, horses are fed generously year round and never lose the extra weight.
"Horses need to be exercised daily in meaningful ways," said Johnson. "It's not enough to ride your horse twice a week for 20 minutes."