Veterinarni Medicina, 53, 2008 (12): 660–667 Thoroughbreds and Arabian horses (Valentine et al., 2000; McCue et al., 2006; Hunt et al., 2008).
Diagnostic criteria of PSSM are not consistent among individual authors.
Most often the diagnosis is made on the basis of amylase resistant polysaccharide presence within muscle fibres (Valberg et al., 1997; McGowan et al., 2003; Firshman et al., 2005).
Some authors also consider subsarcolemmal and intracytoplasmic accumulation of amylase sensitive glycogen to be diagnostic for PSSM (Valentine et al., 2001; Valentine and Cooper, 2005).
McCue et al. (2006) concluded that the accumulation of amylase sensitive glycogen as a diagnostic criterion might increase the sensitivity of histopathology but conversely decrease specificity of the diagnosis.
For this reason, they recommend using this criterion only for horses with clinical signs of PSSM and in the breeds that are commonly affected with PSSM.
Chronic non-specific myopathic changes including excessive fibre size variation and internal nuclei count are also found in some horses (Valentine et al., 2001; Firshman et al., 2005).
However, histopathologic finding of amylase resistant polysaccharide accumulations was described in some horses without clinical signs of myopathy (Firshman et al., 2005; Valentine and Cooper, 2005).
Recently, mutation of the GYS1 gene for glycogen synthase was identified in some horses with histhopathological features of PSSM (McCue et al., 2008).
The purposes of this study were: (1) To assess histopathological changes in muscle tissue of horses with a clinical history of ER with special reference to polysaccharide storage myopathy. (2) To compare histopathological findings in horses with and without a clinical history of ER. Original Paper ers of all horses.
On the basis of clinical history, the horses were divided into two groups: test and control group. Test group The test group consisted of 10 horses with a mean ± SD age of 6.3 ± 2.0 years.
Five horses were Quarter Horse-related breeds (three Quarter Horses, one Paint Horse, one Appaloosa), three warmbloods, one Czech Moravian Belgian draught horse (CMB) and one Thoroughbred.
Use of horses included western riding, eventing, heavy draught, flat racing and pleasure riding.
Nine of them were sampled in Brno, one in Utrecht.
All of them had had repeated episodes of ER in their history and repeatedly confirmed elevation of muscle enzyme activities and/or a positive result following an exercise test (20 min of trotting on the lunge or usual training session resulted in more than doubling of the basal creatine kinase activity four hours after exercise).
Clinical signs included stiffness and reluctance to move in all horses.
Sweating was observed in four horses, myoglobinuria in four horses, gait abnormality (short stride) in one horse and mild colic in two horses.
Stiffness lead to recumbency in one horse and the horse was euthanized.
Glutathione peroxidase (GSH-Px) activity in the whole blood was determined in all horses from the test group.
All horses had GSH-Px activity higher then the reference value (> 12 000 IU/l) that had been established previously (Ludvikova et al., 2005). Control group The control group consisted of 29 horses with a mean ± SD age of 9.0 ± 7.6 years.
Twenty-four horses were euthanized for diseases unrelated to the neuromuscular system and five were two and half year old healthy CMB horses.
None of these horses had a history or clinical signs of myopathy.
Ten horses were warmbloods, seven CMB horses, three Thoroughbreds, four Friesian horses, two Arabian horses, one Shetland pony, one Standarbred and one Hucul horse.
Nineteen of them were sampled in Brno, ten in Utrecht.
Use of horses within the control group included pleasure riding, show-jumping and dressage.
Two horses were used for heavy work 661 MATERIAL AND METHODS Horses Thirty-nine horses older then one year of age were included in the study.
Twenty-eight horses were sampled at the Equine Clinic, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic, whereas eleven horses were sampled at the Equine Clinic of the Department of Equine Sciences, Utrecht University, The Netherlands.
History connected with signs of ER and the use of horses was obtained from the own- Original Paper in the forest.
Five CMB horses were in light draught training.
Four young horses were not used for the work and kept on the pasture only.
Exercise test was not performed in the control group. Veterinarni Medicina, 53, 2008 (12): 660–667 were then wrapped in tinfoil, placed in paper boxes and kept at –80°C until processing. Staining Six-micrometer thick sections of frozen muscle were stained with haematoxylin and eosin (HE) and periodic acid-Schiff with (A-PAS) and without (PAS) amylase digestion. Muscle tissue sampling
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