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When I was recently feeding our horses, I remembered learning that horses can’t vomit, but I never understood why they couldn’t. So I decided to do some research to find out why horses can’t throw up.
Horses can’t vomit because they have a strong lower esophageal sphincter that acts as a one-way valve, preventing food from coming up. Food and water pass through the sphincter and into the stomach, but the contents can’t travel in the reverse direction because of the valve’s strength.
Many horse owners know horses can’t vomit but don’t know why. There is a lot to learn about a horses’ digestion system and what prevents them from throwing up.
Why Can’t a Horse Vomit?
The most widely accepted reason horses can’t vomit is due to the strength of their lower esophageal sphincter. Humans, horses, and many other animals have a lower esophageal sphincter (LES).
The horse’s lower esophageal plays a vital role in the horse’s digestive system. It attaches to the stomach at a low angle, and the muscle around it gives food its final push into a horse’s belly and closes tightly.
The sphincter muscles do much of the same in humans; it helps food make its way to the stomach and closes as well. But the sphincter in humans works as a one-way pressure valve.
In other words, food travels through the valve and into the stomach, just like it does with a horse. But what makes us different is when pressure builds in our gut, the LES is forced open, and our stomach contents to pass back into the esophagus and out of our mouths, we vomit.
The LES of a horse remains shut even under pressure, making it truly a one-way valve. The lower esophageal sphincter doesn’t allow material to flow back into and out of their mouth.
Once the muscular sphincter shuts, it’s almost impossible to open with internal stomach pressure. So if you see a horse that seems to be vomiting, it is in severe distress and likely has burst its esophagus or stomach.
Besides the strength of the sphincter, other factors help keep the valve closed. The location of where it joins the stomach is at an angle that presses it closed when distended with gas.
As we all know, our stomach muscles contract when we vomit; for a horse, this action’s almost impossible. Because their abdominal muscles are located inside its rib cage, making it extremely difficult for them to contract and assist the vomiting process.
It’s also believed horses don’t have a vomiting reflex. But, with all that said, what we do know is that the lower esophageal sphincter doesn’t allow a horses’ stomach content to pass back into the esophagus, a horse can’t vomit.
Does vomiting serve a purpose?
As nasty as vomiting is, it does serve a purpose. In humans and many animals, vomiting is a protection system; it rids the stomach of possible food-related intolerances, such as poisons, bacteria, and viral infections.
Animals use the senses of taste and smell to identify spoiled and infected food. These senses aren’t always perfect in discerning the differences between good and spoiled food, and vomiting is a defensive mechanism to rid the body of infected material from the stomach.
Nausea and vomiting, as protective systems, cannot afford to make mistakes, and thus by necessity, must have a low threshold for activation. (Click on the link to read more about why vomiting is important.)
Vomiting isn’t always a defensive mechanism in animals. Some animals bring food back out of their stomachs regurgitate food to chew the cud, and some swallow food in large chunks, then vomit it up later to feed their offspring.
There are a few reasons horses survive without throwing up: They are very picky eater and aren’t likely to ingest poisons; they graze and only consume small amounts at a time, and their tiny stomachs process food quickly.
The inability to vomit helped horses survive.
Horses survived thousands of years as prey animals on this planet thanks to evolution. They’ve adapted coats that protect them from extreme weather, and have learned to signal warning signs through their herds.
And evolution played a role as well in a horse’s inability to vomit. A key to horses’ survival is their ability to avoid predators with their quickness and speed.
When horses run, their intestines hammer on their stomach, causing pressure to build-up in the organ. If their sphincter valve opened under pressure, horses would vomit every time they ran, and eventually, the predator would catch his prey.
So it’s apparent that it was more important for horses’ survival to escape predators than keep food down. Horses are at risk of sustaining severe digestive disorders because they don’t vomit.
When I was recently feeding our horses, I took my eyes off one of the grandchildren, and he filled a bucket with sweet feed. The horse was eating as fast as he could.
Horses that overeat grain risk significant complications to their intestinal health, causing abdominal pain, colic, and diarrhea. Horses may even develop laminitis, which typically doesn’t present symptoms until a few days later.
Our horse didn’t consume enough grain to cause a problem, sever issues arise when a feed door is left open, and a horse or horses eat for an extended time.
But in the past, I’ve owned horses that developed colic. This condition doesn’t happen in most animals because they can vomit and release pressure in their stomachs.
If you suspect your horse is colicky, you should keep him on his feet and try to lead him around; this may help relieve some intestinal pressure. It’s also critical to contact your vet right away.
You should also notify your horse care professional when horses eat too much high-starch grain. Addressing these problems quickly is of utmost importance to prevent or lessen the severity of the damage.
Numerous things cause colic, and some are not related to a horse’s failure to throw up, but many instances are.
What happens if a horse throws up?
If a horse throws up, it’s in critical condition and could die. You need to contact a vet immediately to seek help. When horses vomit, it’s typically caused by an organ bursting in their digestive system.
The most likely scenario is a ruptured stomach caused by extreme pressure that has no way out. The horse’s lower esophageal valve is powerful and withstands a lot of pressure.
When pressure builds in the stomach, it has to go somewhere, or it increases so high that it will bust the animal’s gut or esophagus and escape. If this happens, it may look like vomit escaping, but it’s not, it’s a much more critical episode.
Most horses die when they vomit. However, there are reported instances of horses that threw up and survived, but this is rare.
What other animals can’t throw up
Most mammals can throw up, with the exception being horses, rabbits and rodents such as mice, squirrels and guinea pigs. The primary reason poisons work so well mice is because of they lack the ability to vomit.
Most other vertebrates, including fish, reptiles, birds, can vomit. But there are a few other animal species that don’t throw up, most notably frogs and rabbits.
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