Muscle Fiber Population and Biochemical Properties of Whole Body Muscles in Thoroughbred Horses

Abstract

We examine the muscle fiber population and metabolic properties of skeletal muscles from the whole body in Thoroughbred horses. Postmortem samples were taken from 46 sites in six Thoroughbred horses aged between 3 and 6 years. Fiber type population was determined on muscle fibers stained with monoclonal antibody to each myosin heavy chain isoform and metabolic enzyme activities were determined spectrophotometrically. Histochemical analysis demonstrated that most of the muscles had a high percentage of Type IIa fibers. In terms of the muscle characteristic in several parts of the horse body, the forelimb muscles had a higher percentage of Type IIa fiber and a significantly lower percentage of Type IIx fiber than the hindlimb muscles. The muscle fiber type populations in the thoracic and trunk portion were similar to those in the hindlimb portion. Biochemical analysis indicated high succinate dehydrogenase activity in respiratory-related muscle and high phosphofructokinase activity in hindlimbs. We suggested that the higher percentage of Type IIa fibers in Thoroughbred racehorses is attributed to training effects. To consider further the physiological significance of each part of the body, data for the recruitment pattern of each muscle fiber type during exercise are needed. The muscle fiber properties in this study combined with the recruitment data would provide fundamental information for physiological and pathological studies in Thoroughbred horses.

Muscular and neuromotor control and learning in the athletic horse

“…longissimus, middle gluteal and biceps femoris (Hyytiäinen et al, 2014;Kawai et al, 2009). The studies confirmed previous research findings demonstrating that the major hindlimb muscles mm.…”

“…psoas major and sacrocaudalis dorsalis lateralis, had 60-70% fast twitch fibres, while other locomotory muscles, such as mm. iliocostalis and biceps femoris, fell somewhere in between (Hyytiäinen et al, 2014;Kawai et al, 2009). There were some differences between the relative proportions of Type 2A and 2X fibres, with one study using Thoroughbreds following prolonged training and relatively deep samples of muscles (mid-section of muscle) having greater Type 2A than 2X proportions (Kawai et al, 2009 depth had greater proportions of Type 2X than 2A in their locomotory muscles, although this was more pronounced in the Quarterhorses (Hyytiäinen et al, 2014).…”

Contractile properties of muscle fibers from the deep and superficial digital flexors of horses

“…For example, the equine gluteus medius, a powerful hindlimb muscle for locomotor propulsion, has been shown to contain a relatively high percentage of fast MHC-2X fibers in addition to MHC-2A and MHC-1 fibers (36,42). Other, more specialized muscles of the distal hindlimb or forelimb, however, do not show concurrent expression of all three isoform fiber types [soleus (21,27) and interosseus (43)] and may be expected to have a primary composition of MHC-1 and MHC-2A fibers, as evidenced in the forelimb digital flexor muscles of horses in this study.…”

Regulation of an antisense RNA with the transition of neonatal to IIb myosin heavy chain during postnatal development and hypothyroidism in rat skeletal muscle

“…The IIb MHC has the fastest ATPase activity of all MHC isoforms (4). The scaling of body size to muscle speed of contraction is illustrated by the fact that IIb MHC is abundantly expressed in small mammals such as rats, mouses, guinea pigs, and rabbits (15,59), whereas it is not expressed at all in skeletal muscles of most large mammals, such as humans, baboons, horses, cows, goats, dogs, and cats (3,26,31,33,49,50,55).…”