Study tracks gastric disease risk in Iceland’s pasture-managed horses: full analysis

A new study in Equine Veterinary Journal suggests gastric disease in horses may be less tied to intensive management than many clinicians assume. In a year-long prospective cohort study of extensively pasture-managed Icelandic horses in Iceland, researchers found that both equine squamous gastric disease and equine glandular gastric disease were common at every timepoint measured, with significant ESGD affecting 48% to 72% of horses and significant EGGD affecting 33% to 45%. The paper was published online ahead of print on September 1, 2025. (pubmed.ncbi.nlm.nih.gov)

The work builds on earlier Icelandic horse research from some of the same investigators, which had already raised questions about standard assumptions around equine gastric ulcer syndrome. In that prior work, horses entering training showed unexpectedly high ulcer prevalence before substantial ridden work began, and squamous lesions decreased after management changes without medical treatment, while glandular lesions changed less. Researchers and trade coverage at the time pointed to possible roles for weather, pasture changes, herd stress, and forage-based feeding patterns. (pmc.ncbi.nlm.nih.gov)

In the new study, the team gastroscoped 80 horses ages 3 to 26 years from four farms in three Icelandic regions in May, August, November, and the following February, with sample size tapering modestly over time. Their multivariable analysis identified seven risk factors associated with significant ESGD and four associated with significant EGGD. Among the most striking findings, horses facing reduced grass availability without additional forage had markedly higher odds of ESGD than horses on low grass with forage provided. Region also mattered, suggesting local environmental or management effects. For EGGD, older age, dental abnormalities, and concurrent ESGD were associated with higher odds. The authors concluded that moderate EGGD prevalence can persist even in horses that are not intensively exercised, and that moderate to high ESGD prevalence can occur without high-starch feeding. (pubmed.ncbi.nlm.nih.gov)

That matters because conventional risk narratives often focus on racehorses, show horses, stall confinement, and concentrate-heavy diets. Those factors remain important, but this paper points to a broader and more nuanced picture. Earlier work in Icelandic riding horses found that "farm" accounted for a substantial share of ESGD-related variance, implying that local management conditions can shape risk in ways not fully captured by standard variables. The authors of that earlier study also noted that no clear modifiable management factor had emerged for EGGD, underscoring how much remains unresolved about glandular disease pathophysiology. (pmc.ncbi.nlm.nih.gov)

Outside commentary broadly aligns with that interpretation. In coverage of related Icelandic horse research, lead investigator Nanna Luthersson said the group was surprised by the high ulcer prevalence in horses arriving from pasture and by the reduction in squamous lesions without medical treatment. She suggested harsh weather, late-season grass changes, and stress in large herds as possible contributors, while also noting that a high-forage diet may have helped explain lower ulcer rates later in the training period. Those comments don't directly validate the new paper's causal conclusions, but they do help frame why a seasonal, pasture-based study in Iceland is clinically interesting. (thehorse.com)

Why it matters: For veterinary professionals, this study is a reminder not to over-rely on management stereotypes when considering gastric disease risk. Horses in extensive systems, including those not in hard work and not receiving starch-heavy rations, may still warrant diagnostic consideration if they present with poor body condition, vague performance concerns, behavioral changes, or recurrent abdominal discomfort. The findings also elevate practical herd-level questions: whether forage supplementation during low-grass periods can blunt ESGD risk, whether routine dental assessment could help identify horses at higher EGGD risk, and whether regional or social-management factors deserve more scrutiny in preventive planning. Existing consensus guidance also emphasizes that clinical signs are often nonspecific, so gastroscopy remains central when confirmation is needed. (pubmed.ncbi.nlm.nih.gov)

The study has limits that matter in practice. It involved 80 horses from four farms, all in Iceland and all of one breed, so generalizability should be cautious. Even so, the signal is strong enough to challenge a simplistic equation of "pasture-kept" with "low gastric disease risk." For clinicians, the most useful takeaway may be less about breed-specific biology and more about management continuity: when pasture quality declines, the absence of supplemental forage may be a bigger red flag than the label attached to the production system. (pubmed.ncbi.nlm.nih.gov)

What to watch: The next step is intervention research, especially studies testing whether targeted forage supplementation during seasonal pasture decline, along with closer monitoring of older horses and those with dental abnormalities, can reduce ESGD or EGGD prevalence in extensive equine systems. (pubmed.ncbi.nlm.nih.gov)