Equine Gastric Ulcer Syndrome (EGUS) is extremely prevalent in both racing and non-racing horse populations. The exact aetiology of EGUS is unclear but many stress related risk factors have been implicated including the feeding of grain-based diets. Current treatment techniques often necessitate drug therapy which, when added to feed costs, can be expensive and may have a detrimental effect on digestion due to the mode of action of these therapies. The following experiment set out to investigate if feeding fermented, forage-based feeds (Modified Bio-Fermentation (MBF) lucerne feeds treated with Xanotyde®, registered as FiberProtect® and FiberEdge®; Fiber Fresh Feeds Ltd, Reporoa, New Zealand), could assist in the healing and prevention of ulceration. Nine adult horses with demonstrable and sustained gastric ulceration (diagnosed by gastric endoscopy), were used in a two part study. The first 42 d healing phase investigated the impact of feeding FiberProtect® (FPT) or FiberEdge® (FED) on established gastric ulcers. After 14 d on these diets 44% (4/9) of horses had no ulceration or hyperaemia (inflammation) (EGUC grade 0) and all horses were ulcer free (EGUC grade 0) at d 42. A significant (P < 0.01) relationship was determined between length of time fed and disappearance of ulcers (R2 = 0.9004; DF = 2). The prevention phase utilised the same horses, ulcer-free at d 42, and fed them a grain-based high energy racing diet alongside FPT at 40% and 60% of the total diet (DM basis). The horses were monitored for a further 28 d (d 42 – d 70), and only three showed a recurrence of ulceration throughout this period. At d 70, eight out of nine horses were ulcer free (EGUC grade 0). The findings suggest that FPT and FED can be used to heal and prevent gastric ulceration, and that FPT can be fed alongside a high grain diet to prevent recurrence of gastric ulcers.