Study: Omeprazole Administration May Reduce Calcium Digestibility In Horses

When Dr. Joe Pagan, owner of Kentucky Equine Research in Versailles, Ky., designs a diet for a horse, he has to determine how much of a nutrient to put in the feed to help that horse do its job — keeping in mind that every vitamin or mineral will not be completely digested and absorbed. When it came to calcium in performance horses though, Pagan and others have wondered whether ulcer medication could impact the amount of calcium those horses can absorb – and whether we should be supplementing their calcium intake.

Calcium is a mineral that must be fed in adequate amounts to a horse to build bones and keep them healthy, as well as to allow blood to clot, the heart to beat and muscles to contract. Horses eating a balanced diet generally receive enough calcium, however horses also receiving omeprazole to treat gastric ulcers may have reduced calcium availability from their diets.

Pagan designed a study to answer that question, and the results were recently published in the peer-reviewed Journal of Equine Veterinary Science.

Veterinarians estimate that between 40 and 90 percent of horses have gastric ulcers, with the condition being most prevalent among race and show horses. Excessive gastric acid production is one of the main causes of equine ulcers. Omeprazole, sold under the trade name GastroGard, is an FDA-approved proton pump inhibitor that prevents gastric acid secretion in horses, making it an effective ulcer treatment.

Humans who take a proton pump inhibitor medication have reduced digestibility of several nutrients including vitamin B12, calcium, fat, iron and protein. The effect of omeprazole on nutrient digestibility in horses was not well-studied before Pagan’s research, however.

To test whether nutrient absorption in the equine diet was affected by the use of omeprazole, Pagan, together with Dr. Laura Petroski-Rose and KER staff members Alana Manna and Ashlee Hauss, used four mature Thoroughbred geldings to evaluate the digestibility of diets that contained two different types of calcium: a feed-grade ground limestone and a marine-derived calcium source.

The study lasted for 12 weeks, divided into four 21-day periods. The horses in the study were fed timothy hay and an unfortified sweet feed, as well as a vitamin/mineral supplement and loose salt. They had unlimited access to water.

During each period, the horses were fed 18 grams of supplemental calcium from either limestone or marine-derived sources with or without omeprazole administration. The omeprazole treated horses were given a full tube of GastroGard each day during the final 14 days of the 21-day testing period. During each five-day digestibility phase at the end of each period, manure and urine was collected from each horse and analyzed to determine nutrient digestibility. Each horse had a gastroscopy performed on day 21 and blood samples were drawn.

In order for calcium to be absorbed, insoluble sources need to first be solubilized by gastric acid in the stomach before they can be absorbed from the small intestine. Pagan hypothesized that if the horse doesn’t have gastric acid (like one being treated with GastroGard), it will not be able to solubilize all of the calcium in the diet, making it unavailable for digestion and absorption.

Pagan’s nutrition company was particularly interested in this question since it recently developed a new product called Triacton that contained a marine-derived calcium source and was targeting performance horses — specifically racehorses — for its use.

“We had some nice data that showed we could promote bone density in horses returning to training with Triacton supplementation and we knew that calcium digestibility in [marine-derived calcium] was good,” said Pagan.  “However, since many racehorses are continually treated with GastroGard while in training, we wanted to determine if the digestibility of calcium from either marine sources or limestone was affected by omeprazole treatment.”

Study results showed that omeprazole treated horses had 15 to 20 percent reduced calcium digestibility.  Marine-derived calcium seemed less affected by the presence of omeprazole than calcium supplements derived from limestone. The study also looked at the digestibility of many other nutrients in the diet, including fat, protein, carbohydrates and minerals when horses were receiving omeprazole. The only nutrient they found to be affected by omeprazole administration was calcium.

What does this mean?

Trainers and managers should investigate how much calcium is actually being fed to the horse. For example, says Pagan, if the horse is being fed a commercial feed with an appropriate amount of calcium in it, but the horse isn’t getting as much feed as the label suggests, he may not be receiving sufficient calcium. If the horse is treated with omeprazole, it can exacerbate the deficiency.

Calcium is also found in adequate levels in many good quality hays, but it’s important that hay be tested to know exactly how much calcium it contains, as lower-quality hay may contain less calcium.

“The bottom line is we’ve increased the horse’s requirement for calcium by around 10 grams per day by using omeprazole,” Pagan said.

Pagan compares this additional calcium supplementation to feeding electrolytes when a horse is in intense training and sweating a lot. Replacing the electrolytes lost through sweat is necessary to maintain a healthy horse.

It’s important to add each of these factors together. If a commercial feed is not being fed per label instructions or is being cut with oats, and if the quality of hay is poor, adding in the reduction in calcium digestibility caused by omeprazole administration may indicate that a horse could benefit from calcium supplementation, Pagan said. However, if the horse is being fed an adequate diet that includes quality hay, calcium supplementation is probably not necessary.

Dr. Laurie Lawrence, a professor in the Department of Animal and Food Sciences at the University of Kentucky, concurs.

“Horses receiving 16 to 20 pounds of a mixed hay and six pounds of a commercial feed intended for performance horses are getting enough calcium to easily meet their needs without additional supplementation,” Lawrence said. “Racehorses that consume higher amounts of a commercially manufactured fortified feed are going to have calcium intakes well above the requirement.

“Dr. Pagan’s study suggested that horses given omeprazole digested and absorbed a smaller amount of calcium than untreated horses. However, [calculated nutritional] requirements already make an allowance for incomplete digestion of calcium. We know there are individual differences in nutrient digestibility among horses, so the digestibility value that is used to calculate daily calcium requirements is set fairly low. At the end of the day, I doubt that the small decrease in digestibility that was observed would put horses receiving practical diets in a deficient state.”

Pagan said that more research is needed to determine how gastric acid production changes some hormones in the horse’s body.

“One of the findings we showed was that giving omeprazole increased the concentration of gastrin in the blood,” he said.

Gastrin is a hormone that tells the horse to produce more gastric acid.

The use of omeprazole showed a very consistent increase in gastrin in horses, which is not unusual; the use of proton pump inhibitors in people does the same thing. However, gastrin may also affect the parathyroid gland, which produces parathyroid hormone (PTH) in order to maintain serum calcium concentrations. PTH also plays a role in bone remodeling, Pagan explained. PTH can stimulate bone formation when its release occurs in bursts; it can also trigger bone resorption if it’s constantly high.

“This study wasn’t conducted to determine if omeprazole affected bone metabolism, but that would be an interesting study to do,” Pagan said.

A study with that objective would be very costly and would require many more horses. Horses with and without omeprazole would need to have their PTH measured multiple times over the course of several days. The big question that study would need to answer, Pagan says, is if PTH is affected, is it chronically elevated or is it sporadically elevated? The answer to these questions would help determine if omeprazole affects the parathyroid and if it has an effect on the equine skeleton.

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