06/02/2026
Have We Accidentally Bred Horses More Susceptible to Ulcers?
When people think about equine gastric ulcers, the conversation usually focuses on management:
diet, turnout, feeding frequency, stress, travel, confinement, and training intensity.
And rightly so. These factors absolutely matter.
But research showing gastric lesions even in pre-weaning foals raises an interesting question:
Could some horses be inherently more susceptible to ulcers than others?
One study found that prior to weaning, 21% of foals already had gastric ulcers. Following weaning, lesion prevalence increased dramatically to 98%.
Weaning itself is clearly a major physiological stressor. But the pre-weaning numbers are particularly interesting because these foals were still nursing, living socially, and had not yet experienced separation from the mare.
So why were ulcers already present?
The answer is likely complex.
Ulcer development probably involves an interaction between:
* management
* stress physiology
* temperament
* nervous system sensitivity
* feeding behavior
* microbiome health
* inflammation
* genetics
* and individual resilience
Some horses naturally appear more stress-reactive, vigilant, sensitive, or sympathetic-driven than others. These same horses may also show tendencies toward:
* chronic muscle tension
* anxiety
* difficulty maintaining weight
* stereotypic behaviors
* body tension
* or recurrent digestive issues
Selective breeding has already shaped many traits in modern horses:
speed, athleticism, responsiveness, sensitivity, flexibility, reactivity, and even connective tissue characteristics.
So it may be worth asking whether some physiological traits associated with performance and sensitivity could also indirectly influence ulcer susceptibility.
That does not mean ulcers are “genetic” in a simple sense.
And it certainly does not mean management is unimportant.
Ulcers are probably best understood as a multifactorial condition where biology and environment constantly interact.
Wild horses likely experience ulcers too. Life in the wild includes predators, drought, injury, competition, and environmental stress.
But horses also evolved under conditions of:
* near-constant forage intake
* continuous movement
* stable social structures
* and freedom to regulate behavior naturally
Modern horses may experience fewer survival threats overall, but often face a very different kind of stress:
confinement, intermittent feeding, transport, social disruption, training pressure, and chronic low-grade sympathetic activation.
Perhaps the better question is not:
“Do humans cause ulcers?”
But rather:
“How do genetics, nervous system regulation, evolution, and modern management interact to influence which horses become ulcer-prone?”
In case you think foals are too young to develop digestive issues:
“Prior to weaning, 21% of foals had gastric ulcers, with 9% glandular and 7% squamous lesions. Following weaning, 98% of foals had gastric lesions with 97% squamous and 59% glandular. Severity of lesions was more pronounced after weaning.”
— Nancy S. Loving, DVM
Even young horses who have “never had a stressful day in their life” can develop ulcers.
Talk with your veterinarian about ways to help support your foals gut health during the weaning process.
https://equimanagement.com/articles/blood-sucrose-as-a-diagnostic-tool-for-foal-gastric-ulcer-syndrome
https://koperequine.com/groundbreaking-study-links-gut-bacteria-in-foals-to-long-term-health-performance/
https://koperequine.com/a-guide-to-understanding-biotics-prebiotics-probiotics-and-postbiotics/
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