Total carnitine content of the middle gluteal muscle of Thoroughbred horses: normal values, variability and effect of acute exercise

There was no detectable loss of total carnitine associated with intense exercise from the middle gluteal muscle of Thoroughbred horses. Measurements made on a single biopsy obtained during the course of a normal training and exercise programme may, therefore, be considered representative of the normal content at rest. The variability in total carnitine content within the normal muscle biopsy area amounted to 13.2 per cent of the normal mean content. Approximately 50 per cent of this variability could be attributed to covariation with citrate synthase, to which it was highly significantly correlated. The muscle carnitine content of yearling Thoroughbred horses ranged from 10.5 to 18.8 mmol/kg dry muscle (dm); the ranges in untrained, lightly trained and fully trained two-year-olds were 18.5 to 34.7, 14.1 to 24.2 and 22.9 to 26.9 mmol/kg dm, respectively. In horses aged over three years total carnitine ranged from 21.3 to 35.5 mmol/kg dm. A trend toward higher contents of total carnitine with age and training appeared to be largely a consequence of underlying changes in mitochondria density as indicated by differences in levels of citrate synthase activity. There was a marked difference in ratios of total carnitine to citrate synthase activity between training yards, reflecting possible differences in management regimens and/or bloodstock selection.