Polysaccharide storage myopathy in Cob Normand draft horses.

The research investigated polysaccharide storage myopathy, a muscular disorder, in Cob Normand horses, indicating that 38% showed signs of the disease. It provided subjective facts around the muscle fiber sizes in affected and healthy horses, and differentiated between two groups based on the amount of fibers containing aggregates.

Research Context and Methodology

• The article revolves around research conducted on Cob Normand horses — a breed of draft horses — being studied for Polysaccharide storage myopathy (PSSM), a genetic disease that affects their muscles.
• Gluteus medius muscle samples were taken from 53 Cob Normand horses to evaluate at a histological level. The research study largely focused on observing for the presence of amylase-resistant material in the muscle cells (myocytes) — an indicator of PSSM.

Findings and Observations

• The research found that 38% of the horses (that totals to twenty horses) exhibited amylase-resistant material in their myocytes, indicative of PSSM.
• It was also noticed that the diameter of affected type II muscle fibers in horses showing disease symptoms was larger (67.7 microm) compared to those in healthy horses (57.3 microm).
• The horses were divided into two groups — the first group, consisting of 14 horses (equating to 26% of total horses sampled), exhibited a low percentage of fibers with aggregate formation, without any significant myopathy.
• The second group was comprised of 6 horses (11%) which displayed a high percentage of fibers with aggregates evidenced in their biopsy but also showing chronic myopathic changes.
• In re-examination of 4 of the horses, an increase in the number of aggregate-containing fibers was found, but only in horses from the first group.
• In a single horse that was necropsied—the process of examining a body after death — aggregates were noticed in an array of muscles, which even included the smooth muscles (non-striated involuntary muscles).
• On an ultrastructural level, granular material interspersed with filamentous material was discovered.

Conclusion

• The study conclusively points to the incidence of PSSM in substantial numbers of Cob Normand horses, and provides clues into the disorder’s manifestation at a histology and ultrastructural level.