Risk factors for stomach ulcers in Icelandic horses explored

Being stabled and exercised does not automatically mean a higher incidence of gastric ulcers in Icelandic horses, a study has shown.

Equine gastric ulcer syndrome, or EGUS, is the overriding term for the erosive and ulcerative lesions of the equine stomach, terminal oesophagus and proximal duodenum, which can harm welfare and performance.

The disordered physiological processes involved in the development of these lesions, the risk factors and their response to treatment primarily depend on the location of the ulcers.

Currently, the term Equine Squamous Gastric Disease (ESGD) is used to describe ulcers in the upper non-acid-producing squamous mucosa of the stomach, while the term Equine Glandular Gastric Disease is used for those found in the lower acid-producing glandular part.

Depending on the method, scoring system and the grades included, gastric ulcers can be present in around 90% of actively training and exercising horses, and in up to 80% of pleasure riding animals.

Nanna Luthersson and her fellow researchers, writing in the journal Animals, said horses being housed and managed more intensively have been considered to be more at risk of gastric ulcers.

However, a recent study investigating the incidence of gastric ulcers in Iceland-based Icelandic horses showed a comparatively high incidence of lesions, in both regions of the stomach, in animals coming from pasture.

This high incidence was identified by performing a gastroscopy on the horses within two weeks of coming into training for the first time from pasture.

A significant improvement was found in horses with lesions in the squamous (non-glandular) region after eight weeks, especially for those being provided with more than three meals of forage each day.

The authors suggested that local farm management was likely to be a significant contributor to the likelihood of the ESGD score reducing. None of the management factors evaluated (which included the number of riders/week and the number of people feeding the horses) affected the incidence of EGGD despite a relatively high proportion of the horses having glandular ulcers upon arrival.

However, analysis failed to identify any management-related risk factors responsible for either EGGD reduction or increase over the eight weeks of being at the training establishment with very light training.

The study had only evaluated naïve horses coming from pasture into light training for the first time for eight weeks, during which time they were fed very little complementary feed.

In the latest study, researchers from Denmark and Britain set out to assess the prevalence and risk factors for EGUS in Icelandic horses at various stages of training.

Their work centered on 211 adult horses, aged 3 to 20, recruited from four different regions of Iceland. All were described by their owners as riding horses.

The researchers included those who had been in training for a longer period and/or had undertaken repeated bouts of training and were potentially being fed higher intakes of complementary feed and exercised more intensively.

They found a low prevalence (around 27%) of gastroscopically significant squamous ulcers in Icelandic horses being kept in training establishments and fed low starch and low sugar diets.

Body condition score, cresty neck score, stable/turnout behaviour, exercise intensity/frequency and age were not significantly associated with ulcer scores, but the region of Iceland where the horses were being kept did have an influence.

Horses from the southern region were more likely to have gastroscopically severe ESGD ulcers than those from the Reykjavik region. Those from the south were, however, less likely to have gastroscopically significant EGGD than those from the west.

Sex also had an influence. Geldings were more likely to have gastroscopically significant ESGD than both mares and stallions, and more EGGD than stallions.

Having come off the pasture into training for four weeks or less was a significant risk factor for significant and severe ESGD compared to five weeks or more.

Being stabled, but spending more than two hours a day out in the paddock, compared with less than two hours of paddock time or full-time turnout, was protective for gastroscopically significant ESGD, as was being fed complementary feed low in non-structural carbohydrates.

This suggests that, potentially, some access to areas where the horses can move freely, potentially interact directly with other horses, and have access to forage may be beneficial; whereas permanent maintenance outside may be detrimental.

“Being stabled for part of the day may also provide benefits, such as protection from adverse environmental conditions, individual feeding and access to forage without disturbance,” they said.

Being at a training establishment for more than four weeks may have proved protective for significant or severe ESGD, but not EGGD.

Animals who showed clinical signs often associated with gastric ulcers were at increased risk of having significant or severe lesions.

The study also highlighted the relatively high prevalence of ulcers in the glandular region (affecting around 46% of the horses) but did not identify any risk factors for such ulcers that could easily be modified.

“This study confirms the findings of the initial study on naïve horses entering training for the first time, according to which being stabled and exercised does not automatically mean a high ulcer incidence.

“It also suggests that being extensively grazed at least during the autumn/winter increases the risk of gastroscopically significant and severe ESGD.”

It also confirms the relatively low prevalence of ESGD in Icelandic horses being kept in training establishments in Iceland when fed diets low in non-structural carbohydrates, but highlights the high prevalence of EGGD.

“Importantly, as with other studies, no modifiable risk factors were identified for EGGD other than perhaps moving region.

“Whether sex is a direct risk factor for EGUS, or is associated with other indirect management factors, needs to be evaluated further.”

The study team comprised Nanna Luthersson, with Hestedoktoren Animal Hospital in Denmark; Úndína Ýr Þorgrímsdóttir, with Dyrlæge ehf; Patricia Harris, with the Equine Studies Group, part of the Waltham Petcare Science Institute in England; Tim Parkin, with the University of Bristol; Charlotte Hopster-Iversen, with the University of Copenhagen; and Euan Bennet, with the University of Glasgow in Scotland.

Luthersson, N.; Þorgrímsdóttir, Ú.Ý.; Harris, P.A.; Parkin, T.; Hopster-Iversen, C.; Bennet, E.D. Risk Factors for Equine Gastric Ulcer Syndrome Incidence in Adult Icelandic Riding Horses. Animals 2023, 13, 3512. https://doi.org/10.3390/ani13223512

The study, published under a Creative Commons License, can be read here.