Risk factors associated with gastric disease prevalence in extensively kept horses in Iceland evaluated four times in a calendar year.

Overview

• This study examined the prevalence and risk factors of two types of gastric diseases—Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD)—in extensively pasture-managed Icelandic horses over four different times during one year.
• The research identified key environmental, physiological, and management-related factors associated with these diseases, shedding light on potential causes beyond the typical high-starch diets or intensive exercise commonly linked to such gastric issues.

Background and Objectives

• ESGD and EGGD are two forms of gastric disease affecting horses, impacting the squamous and glandular regions of the stomach respectively.
• While typically associated with intensive management practices, such as high-starch/sugar-rich diets and heavy exercise, these diseases have also been found at high prevalence in Icelandic horses maintained extensively on pasture.
• The study aimed to determine if seasonal changes affected the prevalence of these diseases in extensively grazed Icelandic horses and to identify risk factors linked to ESGD and EGGD during four different time points (May, August, November, February) within a year.

Methods

• A prospective longitudinal cohort design was employed, involving 80 Icelandic horses aged 3 to 26 years from four different farms spread across three Icelandic regions.
• Gastroscopic examinations were conducted at four time points within one calendar year:
  • May (80 horses)
  • August (70 horses)
  • November (66 horses)
  • February (63 horses)
• Data collected included:
  • Morphometric measurements
  • Clinical assessments
  • Behavioral observations
  • Management factors related to pasture availability, supplementary feeding, and social environment
• Multivariable logistic regression analysis was performed to identify associations between risk factors and:
  • Gastroscopically significant ESGD (score ≥ 2/4)
  • Gastroscopically severe ESGD (score ≥ 3/4)
  • Gastroscopically significant EGGD (score ≥ 1/2)

Key Findings

• Prevalence:
  • ESGD prevalence ranged from 48% to 72% throughout the year.
  • EGGD prevalence ranged from 33% to 45% during the same intervals.
• Risk factors associated with ESGD (7 identified):
  • Reduction in grass availability without additional forage being provided drastically increased ESGD risk (odds ratio [OR] 10.55; 95% CI: 1.78–62.71) compared to low grass availability with supplemental forage.
  • Geographical region: Horses in the South of Iceland had a higher risk (OR 10.11; 95% CI: 2.82–36.28) compared to the North.
  • Higher Body Condition Score (BCS ≥7/9) was linked with increased ESGD risk (OR 4.44; 95% CI: 1.43–13.75) relative to BCS 6/9.
  • Additional risk factors were identified but not listed in detail in the abstract.
• Risk factors associated with EGGD (4 identified):
  • Presence of ESGD increased likelihood of EGGD (OR 3.38; 95% CI: 1.73–6.61).
  • Older age groups (>14 years) had higher risk compared to younger horses aged 3-4 years (OR 2.93; 95% CI: 1.23–6.97).
  • Dental abnormalities (dental score >0/2) were also linked with a higher risk (OR 2.30; 95% CI: 1.08–4.88), implying dental health is a factor in EGGD prevalence.
  • One other risk factor was noted but not detailed in the abstract.

Interpretation and Implications

• The study confirms moderate to high rates of ESGD and moderate rates of EGGD even in extensively managed horses that are not exposed to high-starch diets or intensive exercise.
• The reduction in available natural forage without supplementary feed was a strong risk factor for ESGD, indicating nutritional stress plays a critical role.
• Regional differences suggest environmental or pasture-related factors may influence disease risk.
• Higher body condition scores increasing ESGD risk could relate to metabolic or feeding behaviors in well-conditioned horses.
• For EGGD, the connection with older age and dental issues suggests that physiological aging and compromised dental health could impair feeding and digestive processes leading to disease.
• The presence of ESGD itself being a risk factor for EGGD demonstrates potential interrelations between types of gastric disease.
• Social factors, possibly linked to increasing herd size, may influence ESGD prevalence but require further investigation.

Limitations

• Loss of horses during the study reduced sample size in later time points (from 80 initially to 63 by February).
• The specific nutritional content of the pastures was unknown, which limits conclusions about precise dietary factors influencing disease.
• The study did not fully explore the possible impact of social dynamics or behavioral stressors, though these were suggested as potential areas for further research.

Conclusions

• The study identifies that gastric diseases in horses are multifactorial and not solely due to diet composition typical of intensive management.
• Management strategies for pasture-kept horses should consider maintaining adequate forage availability year-round and monitoring body condition and dental health to reduce gastric disease risk.
• Further research into environmental, social, and physiological factors could reveal additional modifiable elements to improve gastric health in extensively kept horses.