Background: Mycotoxins are naturally occurring toxic metabolites found in cereals and forage released by moulds and other fungi. In domestic farm animals, mycotoxins contribute to a spectrum of disorders. However, little is known about the impact of multiple mycotoxins in horses and there is little published data investigating mycotoxins found in forage fed to horses in the UK. Objectives: To identify the concentrations of mycotoxins found in forage fed to horses in the UK with increased liver enzyme concentrations. Study Design: Retrospective case series. Methods: Records of forage mycotoxin sampling undertaken for horses with increased liver enzymes between May 2019 – October 2021 were reviewed. The quantity and frequency of 54 mycotoxins identified were recorded. Individual mycotoxins were grouped based on their biochemical structure or fungus they are produced by. Results: Mycotoxins were detected in 50/52 (96%, CI 87-99) of forage samples; 42/52 (81%, CI 67-90) samples had two or more present. The median number of mycotoxin groups detected was three. Emerging mycotoxins were detected in 39/52 samples (75%, CI 61-86) with median concentration of 92 μg/kg [IQR 20-444] (median concentration [IQR]); fusaric acid in 25/52 samples (48%, CI 34-62), (14 [11-45]), and type B trichothecenes in 24/52 samples (46%, CI 32-61), (119 [50-1517]). One or more mycotoxin groups were detected in 14/52 samples (26%, CI 16-42) at a concentration thought to be ‘higher’ risk to animal health; 22/52 (42%, CI 29-57) samples had one or more mycotoxins groups that were detected at a concentration that was ‘medium’ or ‘higher’ risk. Main limitations: Lack of a control population and potential for case selection bias. Conclusions: Mycotoxins are frequently found in the forage eaten by horses with increased liver enzymes. The effects of mycotoxins in horses and synergistic effects of multiple mycotoxins in horses warrant further investigation.