Gunn, Hugh Michael

2018-05-14T10:13:14Z

2018-05-14T10:13:14Z

1976

(1) This study compares Greyhounds and Thoroughbreds - breeds selected for high speed running - with other breeds of their species by gross dissection, histometric and histochemical and biochemical methods, to Identify adaptations which would favour their superior athletic capacity. Skeletal muscle has been the primary tissue of interest because of its power-generating nature. (2) Carcass dissection was carried out on 44 Greyhounds from blrthweight to 37 kg, 31 other dogs from blrthweight to 47 kg, 30 Thoroughbreds from 0*69 kg to 509 kg and 33 other horses from 2*2 to 547 kg liveweight. (2a) Measurements on the humerus, radius and ulna, femur and tibia and fibula Indicated that their combined lengths were not different in Greyhounds and other dogs, but tended to be longer in adult Thoroughbreds than in adult other horses. (2b) Within limb variations in bone lengths were not apparent between breeds. However the eplpodial segment in dogs and the propodial segment in horses grows faster. (2c) There is no difference in fresh bone density between the itypes of dog and horse, but dog bones tend to be more dense than horse bones. (2d) The proportions of muscle, bone and fat relative to liveweight were compared between athletes and others in adults and during growth. In adults the most functionally significant difference is that muscle occupies a greater proportion of liveweight in athletes. Adult Greyhounds have less fat than other dogs while bone weight forms a remarkably similar proportion of liveweight in all adult dogs and horses. In athletes there is a greater growth rate of muscle which explains the difference in adult proportions. Growth changes in muscle distribution explain the greater propulsive capacity of the Greyhound spinal column and femoral region and of the Thoroughbred hindlimb. It is also compatible with the potentially higher stride frequency of the Greyhound hindlimb. (2e) Athletes tend to have heavier hearts than non-athletes at adult llveweights, despite the lower growth rate of the heart in athletes. (3) In all 33 Greyhounds from birth to 37 kg, 26 other dogs from birth to 47 kg, 34 Thoroughbreds from 11 kg to 598 kg and 34 other horses from 2*3 to 560 kg liveweight were used for histometric and biochemical assay, of samples of their m. semitendinosus, m. diaphragms and m. pectoralis transversus. Mean fibre areas were established in samples of all three muscles, and in m. semitendinosus only the transverse sectional area and total number of fibres in it were also estimated. Histochemical profiles of Individual fibres were estimated using myosin adenosine triphosphate (myosin ATPase), succinate dehydrogenase (SDHase), and glycogen phosphorylase (GPase) reactions; capillaries were also demonstrated using a modification of the myosin ATPase reaction. (3a) Athletes have more larger fibres in m. semitendinosus than non-athletes. The mean fibre area of m. dlaphragma is also larger in Greyhounds and Thoroughbreds than in their fellows but the mean fibre area of m. pectoralis transversus is similar in the two types of animal within each species. Although the mean fibre area of corresponding muscles is significantly larger in horses than in dogs the difference is not related to their liveweight difference. (3b) The major histochemical difference between fibres is their myosin ATPase activity, which differentiates them according to whether they have a high or low activity. In adult dog muscle, all fibres have a high SDHase activity and myosin ATPase low-reacting fibres have a low activity of GPase. In adult horse muscle all fibres have a high activity of GPase. In m. dlaphragma and m. pectoralis transversus all fibres also have a high SDHase activity so that only the myosin ATPase reaction differentiates fibres in these muscles, however fibres with a low activity of SDHase are present in samples of m. semitendinosus. (3c) The myosin ATPase reaction differentiates fibres at the earliest stage of growth observed. The GPase and SDHase activities gradually develop from an amorphous staining pattern in the young to the appropriate adult type. The proportional area of myosin ATPase low-reacting fibres in the three muscles studied is related to liveweight from birth to near adulthood. Thereafter the relationship is less obvious in "athletes" than "non-athletes. (3d) There is a greater proportional area of myosin ATPase high-reacting fibres in the limb muscles of both Greyhounds and Thoroughbreds and in m. diaphragma of Greyhounds. In adults this feature does not appear to be due to training as are alterations in aerobic and anaerobic capacity. This dissimilarity (in the proportions of muscles occupied by myosin ATPase high-reacting fibres) suggests that there may be differences in the nervous systems of athletes and non-athletes. (3e) It is concluded that the proportions of fibre types in muscles are related to the function of muscles and its parts. Although the proportions of fibre types in different muscles and parts of muscles and in different types of animals resemble those of adults at the earliest stages investigated, histochemical evidence has been obtained which suggests transformation of the physiological properties of fibres as a normal occurrence but to differing extents during growth of normal athletes and non-athletes. (3f) Capillary density is remarkably similar between muscles of all groups of animals at all except very early stages of growth. (4) The biochemical estimation of SDHase activity does not show a within species difference is the adult but indicates an increase in activity in both species during growth. It has also been found that there is a greater aerobic activity in m. diaphragma than in the other two muscles and a greater activity in the deep medial than in the superficial lateral region of m. semitendinosus. (5) M. longissimus is proportionally lighter in Greyhounds taken out of training than in others. Such specimens have a greater myosin ATPase high-reacting fibre area in their m. diaphragma and lesser capillary density in their m. pectoralis transversus than trained Greyhounds. (6) The crosses of Thoroughbreds with other horses, show anatomical properties more like Thoroughbreds than non-athletic horses. (7) The results are discussed in relation to stride length and frequency. It is suggested that in adult athletes enhanced stride length is favoured by longer limbs in horses, and a greater acceleration capacity in both species. A higher natural frequency of the Greyhound hindlimb, and a greater intrinsic speed of sarcomere contraction in the athletes of both species favour enhanced stride frequency. The combination of these endowments aids a greater maximum speed of running in both Greyhounds and Thoroughbreds when compared with their fellows.

http://hdl.handle.net/1842/29789

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 18

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Canine and equine skeletal muscle

A study of canine and equine skeletal muscle

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Doctoral

PhD Doctor of Philosophy