Horses can't throw up
Q: It is a known fact that horses cannot throw up. Why?
A: The vets agree with you: horses cannot throw up.
That's what they are taught in veterinary school; that's
what the books say.
Figure: [USDA] A mare and her foal
Horses have a band of muscle around the esophagus as
it enters the stomach. This band operates in horses
much as in humans: as a one-way valve. Food freely
passes down the esophagus into the stomach as the
valve relaxes but the valve squeezes down the opening
and cuts off the passage for food going back up.
Horses, however, differ from us because their valve really works. Humans can vomit. Horses
almost physically can't because of the power of the cut-off valve muscle. Also, the esophagus
meets the stomach at an angle which enhances the cut-off function when the horse's stomach is
bloated with food or gas. Then the stomach wall pushes against the valve, closing the esophagus
even more completely from the stomach. Normally, the mechanics are such that the horse's
stomach ruptures before the valve yields.
If material does pass from stomach out the esophagus, the horse is dead or nearly so. That's why
horses can't vomit. But, sometimes they do. Rarely, to be sure.
Brent Kelley, veterinarian for a valuable mare during a difficult delivery, tells of one incident.
After the mare delivered her foal, she laid there as if dead--not even responding to her baby's
nickers. Worse: she threw up and stopped moving. Brent thought she was gone.
"But then the old girl rolled up on her sternum and called to her foal," says Kelley.
The mare lived another six years, had four more foals, and died well into her 20s...
Paper Horse equine health information
May 2, 2001