Taurine content and distribution in equine skeletal muscle

Taurine (TAU) is found in large but variable amounts in the skeletal muscles of many species. It has been reported that slow twitch muscles in the rat exhibit higher TAU levels than fast twitch muscles. Variation in muscle taurine content may be attributable to differences in the fibre type composition of different muscles. TAU content (mmol kg-1 dry muscle) and percentage type-1, type-2A, and type-2B fibre section area (f.s.a.) were measured in muscle samples taken from up to six sites in the middle gluteal muscle of four horses and one pony at post mortem and in biopsy samples taken from twenty Thoroughbred horses in race training. TAU was positively correlated to type-1 f.s.a. (r = 0.94, p < 0.001) in both post mortem samples and biopsies from horses in race-training. Multiple linear regression analysis was used to estimate the TAU content of individual fibre types when present at 100%. TAU is almost exclusively localized in type-1 fibres. The TAU content of type-1 and type-2A fibres was estimated to be 45.4 mmol kg-1 d.m. and 4.5 mmol kg-1 d.m. respectively in the post mortem horses, and 32.4 mmol kg-1 d.m. and 7.9 mmol kg-1 d.m. respectively in the horses in training. TAU was estimated to be absent from type-2B fibres in both horse groups.