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There is a lot that can go wrong inside a horse’s abdomen. When something does go wrong, and we start seeing symptoms, we refer to it as “colic”. If you’ve worked around horses for long enough, you’ve seen the signs – inappetence, pawing at the ground, lifting the upper lip, rolling… it can be pretty scary. Colic just means “abdominal pain”, however most often we use it to refer to a problem with the gastrointestinal tract. The horse’s intestinal tract, like ours, is made up of the stomach, small intestine, and large intestine. In this blog post, we are going to discuss a specific disorder that affects the small intestine – “anterior enteritis”. This is a complex disorder, which can be confusing – we’ll try our best to keep things as simple and clear as possible, and try to make sense of this dangerous disease.

Anterior enteritis goes by many names, including duodenitis-proximal jejunitis, proximal enteritis, gastroduodenitisjejunitis, and proximal duodenitis- jejunitis. (Whew!) To help make sense of that, remember that the small intestine is made up of the duodenum, the jejunum and the ileum… and “-itis” means inflammation. Whatever terms we use, it means that the small intestine is inflamed and not happy. The cause is not always known, but bacterial overgrowth, viruses or parasites may be to blame. In general, studies have failed to show a root cause – each case can have a different reason for developing inflammation. That can make it very difficult to figure out how to prevent it. Regardless of cause, however, the effects of this disease can be devastating.

To understand what happens in this disease, you first must understand the normal function of the small intestine. The small intestine is about 80 feet of a narrow, flexible tube which connects the stomach to the cecum (the first part of the large intestine, where fermentation begins). The small intestine is responsible for absorption of nutrients, including proteins, simple carbohydrates, fats and vitamins. To do this, the inside of the small intestine is covered in lots of projections (called “villi”) which increase the surface area. When the small intestine becomes inflamed, absorption stops. Instead, fluid starts entering the small intestine, sometimes at an alarming rate. Like an 80 foot long water balloon, the small intestine becomes distended with fluid. The significant distension inhibits contractions which would normally cause the fluid to enter the large intestine; instead, fluid backs up into the stomach. Since horses cannot vomit, fluid entering the stomach has nowhere else to go. If a tube is not placed by a veterinarian, the stomach can actually rupture.

Horses with anterior enteritis typically present as moderate to severe colics. They are quite uncomfortable and may or may not have a fever. Their heart rate tends to be elevated (>60 bpm) and a rectal exam can reveal distended loops of small intestine. One of the most significant findings is the amount of gastric reflux (fluid build-up in the stomach) obtained when a naso-gastric tube is passed, due to the reasons mentioned above. It is not uncommon to obtain 10-20 L of fluid off of a horse’s stomach that is suffering from this disease. As we said, if the fluid is not removed, the stomach could rupture – which, as you can imagine, is usually fatal. Oftentimes, the heart rate will decrease after removal of the fluid, indicating that the gastric distension is a significant source of pain. In this disease process, the nasogastric tube generally must be left in place as fluid will continue to accumulate in the stomach and must be regularly removed.

Since a horse with anterior enteritis is dumping so much fluid into the small intestine and stomach, they can become dehydrated very quickly. These fluids have to be replaced via intravenous fluids. Other treatments include anti-inflammatory medication (usually Banamine) and anti-endotoxic drugs such as polymyxin B. Motility agents such as lidocaine or metoclopramide are also employed many times to counteract the effects of distended intestine. Antibiotics are not always necessary, however if the cause of the disease is suspected to be bacterial, or secondary bacterial infections are found, then they may be added.

If all we had to worry about with anterior enteritis was fluid removal from the stomach, and intravenous fluid replacement to maintain hydration, we would still have a lot on our hands. Unfortunately, that’s not all we have to worry about. When the gut becomes compromised, bacteria and toxins are free to enter the bloodstream and basically run amok among the horse’s internal organ systems. These elements can cause many complications alongside the already difficult to treat enteritis. One of the more common sequelae of anterior enteritis is laminitis. Horses are very prone to developing laminitis in this disease process and steps such as icing the feet should be maintained as a preventative measure as soon as possible. Other complications include aspiration pneumonia, septic peritonitis, esophageal ulceration and perforation, and as already mentioned, gastric rupture.

As we said, this can be a devastating disease. If treatment is instituted early, complications may be limited. The best possible care for a horse suffering from anterior enteritis is at a 24-hour equine hospital, as treatment must be around the clock if the patient is to have the best chance for survival. With the highest level of care, the survival rate is around 60-80%. We have a chance of treating this on the farm, but the survival rate is not likely to be as high. In the case of all emergencies, it’s a good idea to make the decision regarding whether or not referral to a hospital is an option BEFORE it occurs. When emotions are running high, this decision can be exceedingly difficult.

As with any type of colic, please call your veterinarian as soon as possible to have them evaluated when you first start seeing signs. The sooner appropriate care is begun, the better chance your horse will have of coming through without complications. We never mind chatting about clinical signs – so if you have any concerns that what you’re seeing is colic, just call.