The word "horse" conjures up images of graceful, powerful animals roaming across miles of rolling hills, periodically stopping to graze on lush, green grass. In reality, such scenes are rare; these days, many horses live without grazing at all.

Equine nutritionist and veterinarian Susan Garlinghouse, DVM, MSc, of Wellington, Colo., says the reasons behind the non-grazing trend are largely circumstantial. "The limitation, in most cases, is not that a horse is unable to graze, but usually that safe pasture is not available, either because of more horses living in urban situations, or because what turnout is available has unsafe fencing or social structure," she says. "For example, turning out stallions together or into a group of mares with foals may not be possible. In desert areas, grass is not easily grown and maintained, so turnout provides exercise opportunities only."

Urban sprawl has contributed to a lack of suitable pasture. "More and more horses are reared and maintained around urban areas," says Paul Siciliano, PhD, a nutritionist and associate professor in the Department of Animal Sciences at Colorado State University. "Here in Colorado, there are certainly a number of three- and five-acre horse operations, but there is no water that goes with it. When you live somewhere where there is 14 inches of rain annually, there’s not a lot of available pasture."

These circumstances aside, there are many conditions that keep horses from grazing normally. "Some horses have restrictions that render them physically unable to graze, such as those with chronically malformed dental occlusions as a result of congenital defects (including) parrot mouth or monkey mouth, or severe injury," Garlinghouse says. These afflictions differ from those associated with horses which have not received regular dental treatment