Why a Horse Can’t Vomit
In most mammals, vomiting is a coordinated reflex: the stomach and abdominal muscles contract while a muscular valve at the junction of the esophagus and stomach opens, allowing stomach contents to travel back up. In horses, that route is unusually difficult to open in reverse. The esophagus enters the stomach at a sharp angle, and a powerful ring of muscle at the junction—the lower esophageal sphincter—keeps the opening tightly closed.
A One-Way Passage With Consequences
The arrangement helps keep food and stomach acid from flowing back into the esophagus. But it also means a horse generally cannot bring swallowed material back up by vomiting, even when its stomach is painfully overfull. The esophagus itself also moves food toward the stomach through coordinated muscular waves, rather than serving as an easy route in the opposite direction.
This is one reason digestive trouble can become serious quickly in horses. Their stomachs do not stretch much, and they cannot relieve pressure by vomiting. If gas or feed builds up, the discomfort may develop into colic—a broad term for abdominal pain in horses. A horse that appears to be trying to vomit may instead be showing signs of a dangerous digestive problem, so the behavior warrants prompt attention rather than being treated as an ordinary reflex.
