# Impact of Low-Starch Dietary Modifications on Faecal Microbiota Composition and Gastric Disease Scores in Performance Horses

## TL;DR

Switching to a low-starch diet improved stomach health in showjumping horses without medication, though gut bacteria diversity remained unchanged.

## Contribution

This study provides evidence that low-starch diets can heal gastric ulcers in performance horses without relying on medication.

## Key findings

- Switching to a low-starch diet reduced the severity and frequency of gastric ulcers in elite showjumping horses.
- The Firmicute to Bacteroidota ratio in the gut decreased, which is associated with improved gut health.
- Faecal microbiota diversity was not significantly altered by the diet change.

## Abstract

Gastric ulcers are a common problem in performance horses and can affect their health, behaviour, and welfare. Ulcers are often linked to feeding practices involving high levels of starch and sugar and not enough fibre. Unfortunately, not all horses respond well to medication, so feed-based approaches to managing gastric ulcers alongside veterinary treatment are highly desirable. We examined how switching from a high- to low-starch diet affected gastric ulcers and the gut microbiome in elite showjumping horses. Over a 12 week period, we observed improvements in stomach health, with fewer and less severe ulcers following the diet change. Although we found no overall changes in gut bacteria communities, the balance between two major groups of bacteria shifted in a manner previously linked to improved gut health. These findings suggest that diet changes alone, without the use of anti-ulcer drugs, may improve gastric ulcer healing in performance horses.

Equine gastric disease (EGD) is a common condition in performance horses (Equus caballus), potentially compromising behaviour, performance, and welfare. EGD is often attributed to high-starch, high-sugar feeds and limited forage. Evidence for diet-induced changes on digestive microbiota is lacking. Nine elite showjumping horses were housed at the same performance yard with standardised diet and management throughout the study. Horses were transitioned from a high-sugar and -starch (31%) feed to a low-starch and -sugar (16.5%) concentrate feed. Gastroscopies, blood, and faecal samples were taken pre- and 12 weeks post-diet change. Squamous and glandular ulceration was blindly graded a posteriori using 0–4 scores and faecal microbiota profiled using 16S rRNA gene amplicon sequencing. Total (t(1,8) = −6.17, p < 0.001; Pre: 4 [0–5], Post: 1 [0–2]), squamous (t(1,8) = −5.32, p < 0.001; Pre: 1 [0–3], Post: 0 [0–1]), and glandular (t(1,8) = −2.53, p = 0.04; Pre: 2.5 [0–4], Post: 0 [0–2]) disease improved following the introduction of a low-starch diet. Diet change did not impact microbiota communities (PERMANOVA: F(1,16) = 1.37, p = 0.15, r2 = 0.08), but Firmicute to Bacteroidota (F/B) ratio reduced (t(1,8) = −3.13, p = 0.01; Pre: 2.07 ± 0.21 vs. Post: 1.29 ± 0.14). Lower F/B ratios were associated with reduced total EGD scores (ChiSq(1,17) = 3.83, p = 0.05). Low-starch diets did not influence faecal microbiota diversity but aided gastric disease healing and reduced F/B ratios in elite showjumpers during a competition season without medication.