Friday, June 6, 2008

Ulcers in Horses

Ulcers: Why horses are so vulnerable, and what we can do about it


In the last few years, we have learned that an alarming number of horses suffer from stomach ulcers, a problem the scientific community refers to as Equine Gastric Ulcer Syndrome (EGUS) because of its complex nature. Estimates are that ulcers are present in 25-50% of foals, 60% of show horses, and over 90% of racehorses. With so many horses suffering, one might wonder why we were not aware of this problem before. The answer lies partly in how difficult it used to be to diagnose EGUS, which has only recently become easier due to the development of appropriate endoscopic equipment. Another part of the problem is that many horses with EGUS show little in the way of symptoms, and what they do show can easily be attributed to any number of causes. Symptoms may include poor appetite, poor body condition, diarrhea, a change in attitude, mild or recurrent colic, mild anemia, and a decrease in performance. Foals may also exhibit symptoms of teeth grinding, frequently lying on their back, poor nursing, and excessive salivation.

While the reports on the high incidence of EGUS are certainly worrisome, Western horse owners have taken some comfort from a much-quoted study (Bertone et al., 2000) which showed that high-level Western performance horses had a lower rate of ulcers than other elite level horses, at “only” 40%. One speculation was that the lower incidence might be related to breed, as the horses in most previous ulcer studies of high level performance horses had been thoroughbreds or standardbreds. Stock horse owners might therefore have concluded that our tough, cool-headed cow horses were simply better equipped to handle the stresses of travel and competition than their more high-strung cousins.

However, new evidence suggests that it was probably the high alfalfa diet of the horses in the Bertone study that was responsible for the lower incidence of EGUS – not their cow horse heritage. A group of researchers at Texas A&M recently conducted a study to test the effect of different sources of roughage on EGUS. Team member Dr. Pete G. Gibbs, Professor and Extension Horse Specialist in the Department of Animal Science, reports that “There was a significant reduction in ulcer severity scores in horses fed the alfalfa hay diet compared to grass hay. Even after a 21-day turn out period in a pasture, which is commonly suggested for horses affected by EGUS, the ulcer severity score was significantly lower in horses fed alfalfa hay compared to horses on grass hay diets.” Asked why this is the case, Gibbs says, “Alfalfa may be having a buffering effect because of the calcium and/or the protein, not necessarily just amounts of each, but the comparative quality of each nutrient. Future studies are needed to better pinpoint all of that.”

Unfortunately, this means that Western performance horses not on high alfalfa diets may be more at risk than the Bertone study suggested. Add to this the fact that another recent study found a shockingly high rate of ulcers in broodmares on pasture – a group that experts had put at very low risk for ulcers – and it becomes clear that it is in the interest of all horse owners to do everything we can to prevent our horses from developing gastric ulcers.


WHY HORSES GET ULCERS SO EASILY

The stomach of the horse secretes hydrochloric acid on a continual basis, regardless of the presence or absence of food. This makes sense in an animal designed to take in small amounts of food almost non-stop throughout the day and night. But when horses are subjected to the unnatural conditions and activities imposed on them by domestication, this constant secretion of acid leaves them highly vulnerable to ulcers. The lower part of the horse’s stomach, called the glandular region, is less prone to ulceration due to a protective coating which usually keeps it from being damaged by acid. However, the upper portion of the stomach, called the squamous or non-glandular mucosa, does not have as much protection from acid, and this is where we find the vast majority of ulcers in horses, especially in adult horses.

CAUSES OF EGUS

EGUS can be caused by a number of different factors alone or in combination, but the widespread practice of feeding horses relatively large but infrequent meals (2-3 times daily) is one of the most common causes, as the acidity of the stomach increases rapidly after only a few hours without food. Fasting a horse is so likely to cause ulcers, in fact, that it is the method most often used by scientists to induce ulcers for research purposes. Anything that prevents a horse from eating for more than 6-8 hours at a time – infrequent feedings, trailering, stress, illness, or herd dynamics – may lead to ulcers.

Diets high in concentrates are also a culprit. Concentrates are rich in fermentable carbohydrates, which produce volatile fatty acids as they break down, and these can cause cell damage, inflammation, and ulceration in the squamous mucosa. Concentrates also require much less “chew time” than hay, which means the horse produces less saliva to eat them. Since saliva contains bicarbonates, which act as a natural buffer against hydrochloric acid, less saliva means higher acid concentrations in the stomach.

Another important factor in EGUS is the intensity of training, as there is a direct correlation between intense exercise and the incidence and severity of ulcers. The jury is still out on exactly why this happens, but there is evidence that exercise increases the acidity of the stomach, and that it increases abdominal pressure, which may allow acid from the lower part of the stomach to reflux into the more vulnerable upper portion. There are likely other factors, as well, but it has been established that the harder and more often a horse is worked, the more likely it is to have severe ulcers.

Experts also agree that trailering, keeping horses in stalls, and the use of non-steroidal anti-inflammatory drugs such as “bute” (phenylbutazone) can be factors in the development of EGUS. However, when it comes to the less tangible factor of psychological stress, opinions differ wildly. While there is anecdotal evidence suggesting that psychological stress can play a role in the development of EGUS, and many articles and advertisements state that it does, there is little in the way of hard science to support this view. This may be due to the fact that it is extremely difficult to design a scientifically sound study around something as unquantifiable as a horse’s feelings. As Michael J. Murray, DVM, MS, Dipl. ACVIM, one of the world’s leading authorities on the formation and treatment of equine ulcers explains, “We really can’t say in many cases what the precise mechanism is that is causing the ulcers. We just know that in conditions which we can imagine are stressful, based on what we do know about horses, we see ulcers occur frequently. The question is, what is the link between what may be stressful and the development of an ulcer? In many cases, I suspect that it involves interruption of feeding behaviors, as we know that the horse’s stomach becomes highly acidic within minutes of ceasing eating.”

Nonetheless, even if we assume that psychological stress is a factor in the formation of ulcers, we cannot extrapolate that a horse whose temperament makes it more prone to appear “stressed out” is necessarily at higher risk for ulcers than individuals that seem more laid-back. Says Murray, “There is no correlation between what we might call high-strung or nervous horses and the incidence of ulcers. Both the high-strung ones and the apparently calm ones are equally at risk in stressful situations.”

One thing we know not to be a factor in EGUS is Helicobacter pylori bacteria, which is the main cause of ulcers in humans. Researchers have investigated this avenue, but have no evidence of any bacterial involvement in EGUS.

TREATMENT AND PREVENTION

There are a variety of treatments available to help alleviate symptoms and heal ulcers in horses. The Government of Ontario website (http://www.omafra.gov.on.ca/english/livestock/horses/facts/info_gastric.htm) lists the following:

Antacids (aluminum and magnesium hydroxide) will reduce the acidity of the stomach for a short period but must be given every two hours to be effective.

Histamine-receptor antagonists. Cimetidine (Tagamet) and ranitidine (Xantac) are commonly used in the horse and are considered very effective in the prevention and treatment of ulcers. They reduce both basal gastric acid production and induced acid production (e.g., from food) by competitively inhibiting histamine at the H2 receptors of the parietal cells (4).

Omeprazole (Gastrogard, Pepsid) is the most potent anti-ulcer medication currently available. As a proton pump inhibitor, it inhibits gastric acid secretion by interfering with hydrogen ions in the final stage of acid secretion. This medication is given by mouth once daily and, therefore, owner compliance is improved. The raw chemical of omeprazole is available from compounding pharmacies. This type of product is less expensive than the commercial preparations. However, studies have shown that generic, compounded medications may be less effective. There is no quality control for compounded products. Therefore, the amount of active ingredient available in the compounded product may be very variable.

Sucralfate (Carafate) is another type of medication that is useful in treating stomach ulcers, especially in foals. After ingestion, sucralfate reacts with hydrochloric acid in the stomach to form a paste-like complex that will bind to the proteinaceous exudates that are generally found at ulcer sites. This insoluble complex forms a barrier at the site and prevents the ulcer from further damage caused by pepsin, acid and bile (4). Sucralfate will remain adherent to the ulcer crater for more than six hours (1). Because it requires an acidic environment to be effective, sucralfate should be administered at least ½ hour prior to cimetidine or antacids.

There are also a number of herbal or naturopathic products promoted for the treatment and prevention of ulcers, but there is currently no clinical evidence to support their claims. One trial showed a very modest reduction in the severity of ulcers with the use of an herbal product, but the reduction was not enough to be considered a successful treatment.

Most veterinarians consider omeprazole (Gastrogard) to be the most effective treatment by far, the main drawback being the price. Omeprazole can also be used as a preventative measure if horses are going to be put into stressful situations such as those encountered during the show season.

Before spending a fortune on medications, however, it is worth considering the words of Madalyn Ward, DVM, of Austin, Texas, who says, “Conventional treatment for gastric ulcers involves neutralizing the normal stomach acid or blocking its production. However, the problem is not an excess production of acid. Horses produce a small amount of acid continually because they are designed to eat continually. So, blocking acid production is a Band-Aid solution when what we really need to do is reevaluate management.”

With that in mind, the first thing to consider is your feeding program. If you only feed twice a day, try breaking that up into four feedings spaced as evenly as possible over 24 hours. If your schedule doesn’t allow for that, you may want to look at some of the automatic feeders now available. Another very effective option is to look into "slow feeding" -- using a small-mesh hay net or one of a number of commercially available feeders that slow the horse's intake of hay. Such slow feeders have proven to reduce the incidence and severity of ulcers in racehorses and could do the same for yours. A great website to learn more about slow feeding is: http://paddockparadise.wetpaint.com , where you will find comparisons of a number of slow feeders, plus discussions about how to build your own if you are a DIY type.

You may also want to take a close look at what you are feeding, and the quantities. Most adult horses do not require large quantities of grain, and more and more equine nutritionists are suggesting that we should avoid feeding grain altogether. Consult a nutritionist or your veterinarian if you want to consider other sources of calories that may be a healthier alternative for your horse.

As the new research shows, increasing your horse’s intake of alfalfa might also be beneficial in the prevention and treatment of EGUS. However, as certain medical conditions such as Equine Rhabdomyolysis Syndrome (“tying up”) and insulin resistance can make it difficult for some horses to tolerate alfalfa in even small amounts, you should consult your veterinarian before adding/increasing alfalfa if your horse has any known medical condition.

Giving horses access to pasture has long been thought to help lower the incidence of ulcers and to help horses with ulcers heal, but this may not always be the case. The Texas A&M team were surprised to find the horses in their study did not show improvement in their ulcer scores when turned out to pasture. In fact, says Dr. Gibbs, “During the turnout time on pasture, horses that had been on alfalfa hay actually experienced increased ulcer scores after leaving alfalfa and moving to a grass grazing situation.”

Equally surprising are the results of a recent UC Davis study which looked at 62 broodmares on irrigated grass pasture and found that 66.6% of the pregnant mares and 75.9% of the non-pregnant mares had ulcers. Researchers do not yet know why the horses in these pasture situations had such problems with EGUS, but some experts speculate that herd dynamics may be a factor. Therefore, if you are going to turn your horses out in groups on pasture, it is worth paying attention to how your horses get along with each other, and trying to assure that they are kept with or near horses they like, as they may be much more sensitive to upsets in their social situation than we realize.

Overall, the best thing you can do to help prevent and treat EGUS is to give your horse as natural and as stress-free an environment as possible. And, when circumstances are such that your horse will be subjected to stress, try to minimize the stress by maintaining your feeding schedule and even bringing along a horse buddy to a show if possible. Be aware of the often subtle symptoms of EGUS, and talk to your veterinarian about medical strategies if you’re doing all you can but still have concerns.