Humans can vomit, and most of us have heard the horrible dry-heaving noise at night from our dogs right before they throw up – but what about horses… Can horses throw up?
Well, horses can’t vomit.
This is because of the way they are built. A horse’s digestive system simply does not allow it to vomit. It is a one-way system with food moving along it. The one-way contractions and sphincters in the system mean that even if pressure builds up in the stomach, you won’t see any horse vomit erupting from its mouth.
In this article, I will discuss why horses can’t vomit by looking at their anatomy and the evolutionary reason behind this unusual phenomenon.
The Science Behind The Vomiting Process
Before we can even begin to understand why horses can’t vomit, we first need to understand the whole vomiting process.
Vomiting is rather complex; it requires a whole coordinated effort from your body reflexes:
- Before throwing up, a big, deep breath occurs.
- The vocal cords close, the larynx rises up, and the soft palate closes off the airways.
- The diaphragm contracts and moves down, which releases some pressure on the oesophagus and sphincter by the stomach.
- The stomach muscle contracts in spasms, and pressure builds in the stomach.
- As the sphincter and oesophagus are relaxed, the stomach contents have a clear route up and out.
We don’t have to do any thinking when vomiting; these systems are involuntarily controlled by specific centres of your brain.
Whether human, dog, fish, or reptile, this process is pretty much the same. So, why do horses not throw up like most other animals?
Can A Horse Vomit?
As I’ve mentioned: no, horses can’t vomit. There are several reasons for this.
Horses are grazers. They constantly eat small amounts of forage for hours at a time. While their head is down, the food needs to travel up their long necks and into the digestive tract without coming back up.
To prevent food from rushing back into its mouth every time a horse dips its head, they have evolved a rather robust one-way food system.
There are three mechanisms that prevent horses from vomiting:
- Peristalsis – the rhythmic contraction of the oesophagus (food pipe) – forces food along the neck, towards the digestive system. It is a strong, one-directional system, unlike humans’ systems.
- The cardiac sphincter – the muscle at the opening of the stomach – is incredibly strong. It is essentially a one-way valve. In other animals, it can open when there is pressure from the stomach, but not in horses.
- The food pipe connects to the stomach in such a way and at such an angle, that even if there is stomach pressure, the cardiac sphincter simply closes tighter.
Their bodies don’t allow them
Horses are prey animals. They need to be quick and dash off at the first sign of a threat. It simply won’t do if they need to pause to throw up first.
When a horse runs, peristalsis, a tight sphincter at the gut, and the angle of the oesophagus connection to the stomach, all prevent horses from throwing up.
Their digestive tract simply doesn’t allow food to go in the opposite direction as intended.
Anyone who has ever tried to hug a horse probably also noticed just how bigthey are. And it is this big rib cage that also prevents vomiting. With the stomach located deep within, there are no strong abdominal muscles that can suddenly apply extreme pressure to the stomach.
Evolutionary reasons not to vomit
So why can’t horses throw up from an evolutionary perspective? Why did horses evolve like this? No one really knows, but we can do some guesswork.
Scientists suspect that the vomiting reflex evolved as a way to expel toxins. Horses are actually quite picky eaters. When they graze out at pasture, they carefully select what to nibble on. Rarely do they eat any toxic plants or substances. Because of this, it is possible they didn’t evolve the need to vomit.
Or, even if they did come into contact with toxins, the need to keep food in was greater than the need to get rid of the toxins.
Another reason is because of how fast horses run. At a full gallop, the intestines and stomach are banging against each other. In other animals this will cause vomiting – but when a horse gallops to escape predators, it simply can’t vomit in the process.
Has A Horse Ever Vomited?
So, now we know the answer to “Why don’t horses vomit?”, but has there ever been a case of a horse bringing up its lunch?
Yes, there have been… sort of.
There have been some incredibly unique cases where the food a horse swallowed came right back up again.
The first instance when this can happen is when a choking horse dislodges food stuck in the windpipe or food pipe. Technically, this is not really vomiting, but a horse choking can still be a scary sight (and sound). And for the untrained eye, it could look like vomiting.
In severe cases, a ruptured stomach could also result in the stomach contents coming out through the horse’s mouth. This is also not considered normal vomiting (as it is not a reflex), but rather a traumatic event and a medical emergency. If it looks like your horse is vomiting, keep the horse calm and contact the vet immediately.
What Does The Inability Of Horses To Vomit Mean For Horse Owners?
As a horse owner, you may be a bit concerned because your horse can’t vomit. What if some toxins enter your horse’s body and it can’t get it out? Should you always be checking your horse?
It is obvious that you shouldn’t feed your horse anything it shouldn’t eat. Horses have no way to immediately get rid of toxins, so only feed them food that is safe.
If you suspect your horse has ingested something it shouldn’t have, a trip to the vet is a must.
What is the difference between regurgitation and vomiting in horses?
Vomiting is an active reflex. It causes stomach contents to be expelled under pressure. Regurgitation is much more passive. The muscles in the oesophagus go limp, and food can flow out of the nose and mouth. If your horse is regurgitating, it could be seriously ill, and you need to contact a vet.
Do most animals vomit?
Many animals vomit. In fact, almost all vertebrates can vomit, including reptiles, birds, mammals, fish and amphibians.
Vomiting allows the body to get rid of toxins that were accidentally ingested. Or, in some cases (like birds and wild canines), food could be “vomited” up to offspring in the nest or den.
Are horses the only animals that can’t throw up?
A lot of other animals can vomit, but horses are not alone in their inability to do so. Rats, rabbits, mice, and other rodents are also unable to vomit.