24 Sept 2021
Ben Sykes
Job Title
Image © Valeri Vatel / Adobe Stock
Equine gastric ulcer syndrome (EGUS) is a common disease of the athletic horse – with prevalence rates for equine squamous gastric disease (ESGD) as high as 90% to 100% in Thoroughbred racehorses and approximately 50% to 60% across a range of performance horse types for equine glandular gastric disease (EGGD; Sykes et al, 2015a).
Because it is so common, and because many horses can have severe gastroscopic lesions without overt clinical signs, it is often dismissed as a cause of poor performance.
The purpose of this article is to review the evidence that exists for ESGD and EGGD as a cause of poor performance to challenge this assertion. The article also reviews updates in the management of EGGD.
Indirect effects associated with EGUS – particularly changes in eating behaviour – that occur outside of the performance period can have indirect effects on performance.
This can occur over the short term (such as in sport horses competing in multi-day events wherein the primary problems are the potential for decreased feed intake to reduce the stimulus for water intake, or decreased performance over the course of an event due to decreasing energy levels) or long term (such as in racehorses where decreased intake over time impacts on the horse’s ability to recover and maintain its bodyweight between competitions).
Being a “picky eater” (Vatistas et al, 1999) and failing to maintain body condition (Lester et al, 2008) have both been associated with increasing ESGD score, supporting the link between ESGD and indirect effects on performance.
The effects of EGGD on appetite or body condition score are less apparent, with one study (Sykes et al, 2019) failing to demonstrate any association in racehorses.
In the author’s experience, ESGD is more commonly associated with appetite changes than EGGD, where changes in appetite are uncommon.
Direct impacts of EGUS occur at the time of performance and may be related to physiological changes associated with ulceration or behavioural changes, such as a decreased willingness to work.
Directs effects on performance have been demonstrated for both ESGD and EGGD.
In racehorses, performing below trainer expectation has been demonstrated for both ESGD (Vatistas et al, 1999; Jonsson and Egenvall, 2006; Lester et al, 2008) and EGGD (Sykes et al, 2019). Effects on performance are less clearly evident in sports horses, but in one study showjumpers with EGGD were less likely to compete at international level than horses without disease (Pedersen et al, 2018).
Collectively these findings, although limited, provide a moderate body of evidence supporting the potential role of EGUS in poor performance, even in the absence of other overt clinical signs.
As such, the author’s opinion is that EGUS should be considered alongside a range of other differentials – such as orthopaedic or airway disease – in assessing non-specific poor performance.
The release of the results of a study at BEVA Congress (subsequently published in 2019) supporting the use of misoprostol over the combination of omeprazole-sucralfate (Varley et al, 2019) resulted in a shift away from acid suppression as the primary means of treatment at that time.
The findings of that study were consistent with early studies that demonstrated the response of EGGD to monotherapy with oral omeprazole was poor in a racehorse population, with a healing rate of approximately 25% observed following a four‑week treatment period observed across a range of studies (Sykes et al, 2014a; 2014b; 2015b).
Importantly, administration of oral omeprazole in Varley et al (2019) was not adjusted to accommodate the impact of diet on drug absorption, a factor now well documented to decrease both bioavailability (Daurio et al, 1999; Sykes et al, 2017a) and the intra-day duration of acid suppression observed in the ventral stomach following oral administration (Sykes et al, 2017b).
This may have inadvertently disadvantaged the omeprazole-sucralfate combination in this study, and the reported response rate may not truly reflect the expected response rates for EGGD when best practice guidelines for optimising oral omeprazole’s efficacy (Sykes, 2019) are followed.
The potential impact of this was demonstrated by a recent conference abstract in which the response in sports horses to monotherapy with oral omeprazole appeared to be better, with the reported response rate of EGGD greater than 50% (Kranenburg et al, 2020), although the specifics of omeprazole administration with regards to feeding are not yet clear in that study.
A study with a more potent form of acid suppression – namely systemic administration of an IM formulation of long-acting omeprazole – yielded higher EGGD response rates with acid suppression monotherapy than that reported for oral formulations (Sykes et al, 2017c).
In the author’s opinion, this supports continuation of a “no-acid, no-ulcer” approach for front-line treatment of EGGD, with a focus on optimisation of acid suppression.
Conflicting evidence exists between the work of Varley et al (2019), who reported a 20% success rate with the combination of oral omeprazole and sucralfate, an earlier abstract presentation that reported a 62.5% success rate (Hepburn and Proudman, 2014) and a recent abstract presentation in which a 79% success rate was reported (Kranenburg et al, 2020).
Regardless, the most recent abstract demonstrated a clear benefit of the addition of sucralfate over omeprazole monotherapy alone, with an approximate 25% difference in response rate observed between the two groups.
Accordingly, the author now routinely uses sucralfate in the front‑line management of EGGD regardless of the concurrent primary medication (in other words, alongside acid suppression or misoprostol).
The use of misoprostol as a primary treatment for EGGD is supported by the work of Varley et al (2019), wherein a 72% response rate was observed. A recent abstract reported a lower response rate of 58% (Pickles et al, 2020).
Although initially thought to be an effective acid suppressor, the same abstract reported more than 40% of horses treated with misoprostol developed ESGD lesions during treatment (Pickles et al, 2020). As such, when used, misoprostol is reserved for cases with only EGGD.
Recent pharmacokinetic studies have demonstrated a short half-life and limited persistence of misoprostol in circulation (Lopp et al, 2019; Martin et al, 2019).
Considering this, the author now recommends administration three times daily when misoprostol is used.
Considering the above, the author’s approach to the treatment of EGGD is to focus on optimising acid suppression alongside the concurrent use of sucralfate.
Misoprostol is reserved for management of refractory cases and given three times daily alongside sucralfate when used.
