Ronéus M
Department of Medicine and Surgery, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala.
Equine Vet J. 1993 Mar;25(2):143-6. doi: 10.1111/j.2042-3306.1993.tb02925.x.
Biopsy samples were taken from the middle gluteal muscle in 107 health Standardbred horses. The horses were separated according to sex and divided into 4 age groups (1, 2, 3 and 4-6 years). The proportion of Type I fibres increased with age (from 16 to 20%), irrespective of sex. The proportions of Type IIA and IIB fibres varied with age and differed between stallions and mares. Type IIA fibres increased in mares from 37 to 47% and in stallions from 40 to 48% and Type IIB fibres decreased from 49 to 34% in mares, and from 43 to 30% in stallions. Mares and stallions did not differ in enzyme activities, which changed with age. The activity of citrate synthase increased from 30 to 62 mmol/kg/min and that of lactate dehydrogenase decreased from 1,930 to 1,565 mmol/kg/min. The relative area of each fibre type was measured in biopsy samples from 7 mares and 7 stallions aged 1 year and 7 mares and 11 stallions aged 4-6 years. The relative areas of Type IIA and IIB fibres changed with age and differed between sexes. The relative area of Type IIA fibres increased in mares from 30 to 35% and in stallions from 33 to 47% and that of Type IIB fibres decreased in mares from 63 to 54% and in stallions from 55 to 38% between the ages of 1 and 4-6 years.(ABSTRACT TRUNCATED AT 250 WORDS)
