Learn more about gastric ulcers
How does the horses's stomach work?
It is important to remember that horses are herbivores, meaning that they are true vegetarians. Consequently, the anatomy and physiology of their gastrointestinal system is much different from ours. It is also important to remember that horses have very small stomachs when you consider their size - only approximately 4 gallons at holding capacity. This, again, reflects the way that they would eat in the wild - very frequent small meals, so that the stomach is never stretched to full capacity. To start with, the horse's stomach is made up of two different parts. The primary difference between these two parts is that they have different types of cells lining them. Epithelium is a general term for the covering of any surface of the body, and it consists of many cells tightly joined to each other. The first type of epithelium encountered in the stomach is stratified squamous epithelium, after which a glandular epithelium is found. A distinct margin, called the margo plicatus, separates the two. Insert figure 1 - stomach anatomy The glandular epithelium, as its name suggests, contains many glands that produce gastric secretions. The squamous epithelium contains no glands, and merely serves to contain food, without aiding in any chemical digestion. The purpose of the stomach is to help in the long process of digesting food. In order to do this, the stomach must not only mix food, but produce secretions that help to break down food. Two digestive factors, hydrochloric acid (gastric acid) and pepsin, are produced in the glandular portion of the stomach. Both hydrochloric acid and pepsin begin the digestive process in the stomach before food reaches the small intestine. The glandular portion of the stomach also secretes factors that help to protect the stomach. One of these, a mucus-bicarbonate layer serves to protect the stomach lining both by preventing acid from physical contact with the stomach surface, and by buffering gastric acid at the level of the stomach lining .
This mucous-bicarbonate layer protects only the glandular portion of the stomach, and not the squamous portion. Other protective factors include prostaglandin E, which causes increased blood flow in the stomach lining, increased secretion of the mucus-bicarbonate layer, and also causes decreases in hydrochloric acid production various growth factors. Unlike humans, horses produce gastric acid continually, regardless of whether they are eating regularly. If horses do not eat, then their stomachs become more and more acidic because acid production cannot be 'turned-off'. The squamous portion of the stomach is at the greatest risk from increased acid production, because it does not benefit from all the protective factors that the glandular portion of the stomach enjoys.
What causes gastric ulceration in horses?
Gastric ulceration in horses occurs when acid production overwhelms the protective factors. Although there is a clearly established bacterial cause of gastric ulceration in humans, we haven't been able to find a similar connection in horses. Rather, it seems that any situation that can allow acid to overwhelm the stomach's protective mechanicsms, such as infrequent, low-roughage feeding that leaves the stomach empty the majority of the time, can provide a window of opportunity for gastric acid to erode the stomach lining. With sport horses, intensive training, tends to go hand-in-hand with infrequent turnout and low-roughage, high-concentrate feeding. If we add to this chronic use of NSAIDs (non-steroidal anti-inflammatory drugs), we have a recipe for ulcer disaster!
What are NSAIDS and how do they cause gastric ulceration?
Common NSAIDs include phenylbutazone ('bute') and flunixin meglumine (Banamine™). They act by interrupting the production of prostaglandins, which are a diverse family of molecules with extremely diverse effects. The most familiar action of NSAIDs is that by blocking the production of prostaglandins, they help to decrease fevers, aches, and pains. One particular prostaglandin, called PgE2, plays an important role in preventing gastric ulceration. PgE2 does this by decreasing gastric acid production as well as by increasing blood flow to the gastric epithelium. Unfortunately, the NSAIDs that we commonly use to decrease fevers, aches, and pains also blocks normal blood flow to the stomach.. The results are multiple - the horse's stomach becomes more acidic, and this contributes to the development of gastric ulceration. Normal blood flow is necessary to healing, and so disruption of normal blood flow leads to a double whammy - not only does the horse develop gastric ulcers, but he also can't heal them very well. It's a vicious cycle.
What happens during the gastroscopic examination?
If, after extensive examination, we decide that the medical history and physical examination findings are very suggestive of gastric ulceration, the definitive way to diagnose gastric ulceration is with a very long endoscope, known as a gastroscope. This allows us to place a camera inside the horse's stomach, and thus get a close-up view of the stomach lining. The type of endoscope that is commonly used to look at a horse's upper airways simply won't do - it isn't long enough. In order to visualize the adult horses stomach, an endoscope that is at least 220 cm long is necessary. That translates to 6.9 feet! In order to obtain a good view of the stomach, it is important for the stomach to be empty. That's why we'll usually ask you to keep your horse from eating for 18-24 hours before the gastroscopic examination. Your horse will still be able to drink during this time.
In order to do a gastroscopic examination, we must pass the scope through the nostrils, into the pharynx(area just before the esophagus, or swallowing tube), and then into the esophagus, and, finally, into the stomach. Although gastroscopy isn't painful to the horse, most horses do resent anything being passed through the nostrils. The anxiety can be diminished considerably by giving the horse a tranquilizer - usually xylazine or a combination of xylazine and another drug. Long 'scopes' with the ability to see all the way into the stomach are extremely expensive, and we'd rather keep your horse from chewing on it in case it doubles up and goes back into the mouth (yes, this has happened!). For this reason, usually a short plastic tube (similar to, but much shorter than the tube that is used for deworming your horse), is first passed through the horse's nose and into the esophagus, and then the scope is passed through that shorter tube.
- Gastroscopy itself doesn't take very long - only approximately 15-20 minutes. Because the stomach is a collapsible organ, it must often be pumped up with air during the examination so that every bit of the surface can be seen.
- Typical findings include areas of the stomach that are eroded, thinning, bleeding, or have abnormal amounts of scar tissue. Insert figures 3 (gastric ulcers at post mortem) and 4 (gastric ulcers seen with a gastroscope)
- After the gastroscopic examination is finished, all the air will be let out of your horse's stomach to avoid colic. Then, your horse will still be kept off any food until he seems to have fully woken from the tranquilizer.
How do we treat gastric ulcers?
The goal of treatment is to decrease the level of acidity in the stomach in order to allow the horse's natural healing processes to mend the ulcers. There are several ways to achieve this goal: all of them center around addressing the situation that allowed your horse to develop gastric ulceration in the first place. The way that you and your veterinarian choose to treat gastric ulceration will usually depend on your schedule as well as your ability to change your horse's environment.
Most horses do require some drug therapy in order to successfully treat gastric ulcers. Drugs designed to treat gastric ulcers may 1) decrease the amount of acid produced by the stomach, 2) physically coat the stomach to prevent the acid from wreaking havoc, or 3) buffer the acid in the stomach.
Drugs that decrease the amount of acid produced by the stomach:
- H-2 blockers:
These drugs block histamine, one of the factors that stimulates acid production. They reduce the signals to the acid-producing cells, so that they slow down their rate of acid production. Drugs that fall into this category include cimetidine, ranitidine, and famotidine. All of these are available as over-the-counter drugs for humans, albeit in much smaller concentrations than are suitable for a horse! Most of them must be given three times a day for them to work properly.
- Proton pump inhibitors:
Proton, or hydrogen pumps, are the mechanism by which acid is actually produced by the cells. Acidity is merely a reflection of the amount of hydrogen ions, or protons that are in a fluid. If you prevent the pumps from working, then the acid level will decrease dramatically. Gastroguard® is a proton pump inhibitor that is now on the market for horses. One of the nice features of this drug is that it is only given once a day.
Drugs that block acid:
The most commonly used drug that blocks acid from getting access to the stomach lining is sucralfate. Sucralfate, however, is best for helping to heal ulcers in the glandular mucosa, and most adult horses have ulcers in the squamous mucosa. For this reason, it is not suitable for use on its own in treating gastric ulcers in adult horses.
Drugs that buffer acid:
Antacids are commonly used in humans, and some veterinarians advocate using them in horses. Antacids can buffer an adult horse's stomach, however, the effect lasts for less than an hour, and very large volumes (over 1/3rd of a pint) must be used.
Feeding and environmental changes:
It is difficult to impossible to fully heal gastric ulcers using drugs alone. The most important thing we can do to heal ulcers is to recognize that horses need to live like horses! In the wild, horses do not have two, or three, or even ten meals a day - they eat small amounts of roughage all the time. If we fed horses the way they are meant to be fed, we probably wouldn't ever have to treat ulcers. The drugs may vastly improve the clinical signs, but many veterinarians report that the ulcers themselves still persist. In order to have full resolution of the gastric ulcers, it is important to give the horse as much 'down time' as possible. In the best of all possible worlds, this would mean pasture turnout for 24 hours a day. Your horse should also be given free choice hay, so that he always has something in his stomach. If possible, grain should be avoided. If your horse needs the extra calories, they can be supplemented with many small meals and the addition of high calorie vegetable oil to his food.
It is important to remember that although your horse's signs may abate within the first week of treatment, the ulcers do not heal without at least three weeks of drug therapy and changes in environment and feeding. It is very important to follow your veterinarians recommendations for the frequency and length of treatment, as well. For instance, your horse may feel a lot better after he is given a low dose of cimetidine twice a day, instead of the recommended high dose three times a day. However, at the end of three weeks, your horse will likely still have gastric ulcers.
If it is at all possible, you should have a re-check gastroscopy performed 3-4 weeks after you start treatment. In this way, you will have hard evidence of how well the ulcers are healing. You will be able to make a more intelligent and informed decision about how long, if at all, you should continue treatment.