Bringing a horse into work can be exciting. The possibilities seem endless—will they become your new show horse or trailblazer? Changing a horse’s environment and schedule, however, can also affect their health. So researchers set out to determine how transitioning horses from living on pasture to being housed, fed meals, and in a training program might affect rates of equine gastric ulcer syndrome (EGUS).

The team evaluated 81 Icelandic horses, with a median age of 3, from 10 farms in four regions. A gastroscopy was performed on the horses within two weeks of moving to the training establishment (before training began), and 71 horses underwent a second gastroscopy eight weeks later. Ten horses were excluded from the study after moving to a different location, going back to pasture, or starting gastric ulcer treatment. Overall, EGUS rates decreased during the study time frame, with management factors playing a key role.

“We studied the Icelandic horses since this population has not been examined before and since there were no equine gastroscopes in Iceland before,” said Nanna Luthersson, DVM, a partner at Hestedoktoren, a Danish equine veterinary clinic. “There are not many horses being examined that have not been under human-management. This was unique for these horses that have been living outside with very little or no human interference until the time they entered training.

“Other studies have not shown any significant differences in breed when looking at equine squamous gastric disease (ESGD), so we would not expect the results from this study to be different when looking at other breeds,” she added.

Luthersson and her team studied the changes that occurred when Icelandic horses went from living semi-wild on large grasslands to training.

The first two weeks of training focused on accepting the saddle, bridle, and groundwork. Then, the training increased to up to five days a week of ridden work. For consistency, one experienced clinician performed all the initial gastroscopy evaluations. On arrival, all the horses were at a healthy weight, with a median body condition score (BCS) of 6. None of the horses had a BCS lower than 5.

Ulcer Rates Before Training

The researchers assigned each horse a score of 0-4 for squamous ulcers (ulcers in the top third of the stomach) and 0-2 for glandular ulcers (ulcers in the bottom two-thirds of the stomach), with higher scores being more severe.

“Surprisingly, the prevalence was high when the horses were first brought in,” said Luthersson, noting 71.6% had squamous ulcer scores of 2 or higher, and 47% had glandular ulcer scores of 1 or higher.

Initially, when looking at equine squamous gastric disease (ESGD), 26% of the horses had Grade 2 ulcers, 40% had Grade 3 ulcers, and 6% had Grade 4 ulcers. When looking at equine glandular gastric disease (EGGD), 27% had Grade 1 ulcers, and 20% had Grade 2 ulcers.

At the second evaluation, 14% of horses had Grade 2 ESGD ulcers and 11% had Grade 3. None of the horses had Grade 4 ulcers. This was a significant reduction in the squamous ulcers without any medical treatment. When looking at EGGD at the second evaluation, results showed 32% had Grade 1 ulcers and 9% had Grade 2, which Luthersson said was not a significant change.

For ESGD, the team saw no significant differences between horses of varying sexes and ages. However, the farm and region the horses were from did make a difference.

Age, initial BCS, behavior, number of days worked per week, and performance quality appeared to play a role in EGGD prevalence.

Most of the horses (57) continued on a forage-only diet during the study, while the rest received primarily forage plus a very small amount of commercial feed (low in starch) or small amounts of soaked beet pulp. This aligns with Icelandic horses’ typical diets when stabled. The researchers said a high-forage diet might have contributed to the horses’ relatively low ulcer rate at the end of the study period.

The researchers noted that ESGD ratings decreased more in mares and stallions than in geldings. They theorized this might be because when mares and stallions come in from pasture for training, they are also being prepared for breeding and, therefore, might receive more careful management than geldings. Sex was not a factor in the EGGD ratings. Most other studies on EGUS did not show significant differences between sexes, and prior research results suggest ulcer risk might increase in geldings as they age and decrease in mares and stallions. This uncertainty might prompt a closer look at and further research into sex’s influence on the presence of ulcers.

Luthersson said she did not expect the high prevalence of EGUS at the start of the study when horses were coming in from pasture. She believes it was a consequence of the cold or harsh weather in fall, changes in the grass at the end of summer, and possibly stress from being in a large herd. However, she said she was also surprised by the reduction of ulcers in the squamous part of the stomach without any medical treatment. She said this most likely resulted from improved management, such as protection from wind, rain, and snow, and individualized feeding with a forage-based diet.

Ulcers After Training and Management

Based on their study findings, the researchers concluded that when the horses were brought in and fed multiple forage meals daily, their ESGD scores decreased. “If they received forage for a minimum of three meals per day, the chance of reducing the ESGD scores was 18 times higher, compared to getting forage only twice or once per day,” Luthersson told The Horse.

“We know that using a forage-based diet reduces the risk of ESGD, and this study clearly shows that forage needs to be fed in several meals during the day,” she continued. “From previous studies, both from my group and others, we also know that reducing the amount of starch, both per day and per meal, will reduce the risk of ESGD.”

On the other hand, no known management factors can reduce the risk of EGGD development, and the research team noted little difference in EGGD ratings.

Results were inconclusive as to whether training significantly influenced horses’ ulcer ratings or if management changes were the main factor contributing to lower overall rates. Overall, however, feeding a consistent forage-focused diet might reduce a horse’s risk of developing EGUS.

Luthersson is curious whether other factors could influence EGUS prevalence. She is currently involved in another study evaluating 80 horses that live outside year-round in Iceland. “This is to see if or how the prevalence of EGUS changes over the year,” she said. “They were scoped in May and August, and we will scope them again in November and next February.”

The study, Effect of moving from being extensively managed out in pasture into training on the incidence of equine gastric ulcer syndrome in Icelandic horses, first appeared in Sept. 2022 in the Journal of the American Veterinary Medical Association.