Have you ever seen a horse throw up? Probably not, since horses can't vomit. It is, along with human beings and most other creatures, part of a very limited set of animals that cannot, and this is because of their special anatomy, particularly the design of the digestive system.
The esophagus of the horse continues to the stomach at a point where a very strong band of muscle forms an incredibly powerful valve. In man, this valve serves to allow food to both be passed down and, under circumstances requiring it, back up allowing us to vomit when we want to; in the horse, it is much stronger. It only passes food in one direction: into the stomach.
This valve is very strong that it will prevent food or gas from coming back up, even under pressure. That's why horses, unlike most animals, cannot relieve themselves by vomiting if they eat something harmful or if their stomach becomes too bloated.
Another reason horses cannot vomit is because of the angle at which their esophagus meets the stomach. This angle makes it easier in humans to reverse the flow when vomiting. In a horse, this angle in fact seals off the stomach even more so when it becomes distended and quite hard for anything to move back up the esophagus.
If a horse stomach is over-filled, this can lead to a rather worse condition than vomiting: the stomach may rupture because of the way the valve and stomach wall are sealed together. This is also the reason why horses are more prone to colic or other severe gastrointestinal problems if they eat too much or ingest anything toxic.
Though this condition occurs rarely in equines, it is claimed that they do vomit, but usually only in extreme emergencies where the stomach of the horse is near or has already ruptured. If material is returning up from the stomach of the horse, it indicates a very severe emergency and most often the horse is either dead or nearly dead.
The inability to vomit is very interesting for horses. Indeed, they have formulated a highly efficient apparatus of digestion but can't be able to easily resolve gastrointestinal problems when they occur by vomiting. Hence, that makes the aspect of diet all the more important as well as looking for signs of bloating or discomfort in horses.
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