Why Rats Can't Vomit

No one enjoys vomiting and there's actually one animal species that never has to deal with this unpleasant symptom. The rat! The rat is one of the few animal species that lacks the ability to vomit.

There are several reasons why the rat is unable to vomit. In humans, vomiting requires the action of the abdominal muscles and the diaphragm to put pressure on the stomach to expel its contents. It also requires contraction of the muscles of the esophagus to open the junction that lies between the stomach and the esophagus. The rat's diaphragmatic muscles are unable to coordinate as a unit to produce the contractions of the diaphragm required to put pressure on the stomach for food expulsion. Plus, the barrier that lies between the stomach and esophagus in the rat is so strong that the esophagus can't generate the strength to overcome it. Rats also lack a "vomiting center" in the brain which humans have. The vomiting center serves to connect and coordinate the nerves and muscles involved in the process of vomiting. This coordinated system is lacking in the rat.

Since vomiting serves the protective mechanism of ridding the body of toxic substances, what's a rat to do? Because of the limitation of being unable to vomit, the rat has developed super efficient food avoidance behaviors to avoid ingesting a potentially toxic substance. The have a very acute sense of taste and smell which allows them to sense foods that might be harmful to them using these senses. They have a tendency to eat small amounts of a food initially and it they experience any symptoms of illness, they'll avoid that food in the future. Another strategy they use is eating clay and other non-food items which helps to bind some of the toxins in the foods they eat so they can't exert their harmful effects.

Interesting enough, not only can rats not vomit, they also can't burp or expel entrapped air for the same reasons listed above.Fortunately, because of their acute sense of taste and smell and their ability to ingest non-food items to bind toxins, they've been able to function normally despite their inability to vomit.

Is the rat the only mammal that's unable to vomit? There are a few other mammals that lack this ability, most of them in the rodent family. These include the house mouse, guinea pig, and rabbit. These would make great house pets if you don't want to deal with the presence of vomit on your brand new carpeting!