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Journal of the American Veterinary Medical Association2006; 229(7); 1134-1141; doi: 10.2460/javma.229.7.1134

Seasonal pasture myopathy in horses in the midwestern United States: 14 cases (1998-2005).

Abstract: To determine clinical signs, diagnostic findings, tissue tremetone concentrations, and clinical outcome or postmortem findings in horses evaluated for acute severe nonexertional rhabdomyolysis initially attributed to white snakeroot toxicosis. Methods: Retrospective case series. Methods: 14 horses. Methods: Records of the University of Minnesota Veterinary Medical Center or Diagnostic Laboratory were searched from 1998 to 2005. Inclusion criteria included serum creatine kinase (CK) activity > 45,000 U/L, severe nonexertional myonecrosis of proximal postural muscles at necropsy, or signs of weakness without palpably firm muscles on physical examination. Vitamin E and selenium concentrations were measured in 6 horses; tremetone concentration was measured in 7. Results: Clinical signs occurred during unfavorable weather conditions. Clinical signs of generalized weakness (n = 11 horses), muscle fasciculations (10), lethargy (6), and prolonged recumbency (4) were common. Serum CK activity ranged from 46,487 to 959,499 U/L (reference range, 82 to 449 U/L), and aspartate transaminase activity was > 1,500 U/L (reference range, 162 to 316 U/L). Two horses survived with aggressive antioxidant and fluid treatment. Postmortem examination revealed acute severe myonecrosis with lipid accumulation primarily in neck, proximal forelimb and hind limb, intercostal, and diaphragm muscles. Histopathologic signs of myocardial necrosis were detected in 7 horses. Vitamin E and selenium concentrations were within reference limits. Tremetone was not detected in liver or urine samples. Conclusions: Cases of rhabdomyolysis have been attributed to white snakeroot toxicosis; however, tremetone was not detected in any horses. Similarities exist between cases of seasonal pasture myopathy and cases of atypical myopathy in Europe.
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Publication Date: 2006-10-04 PubMed ID: 17014363DOI: 10.2460/javma.229.7.1134Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The study aimed to examine and understand the symptoms, diagnostic results, tissue tremetone concentrations, and outcomes in horses affected by an intense and nonexertional muscle breakdown disease, initially thought to be due to white snakeroot poisoning. The disease was observed during unfavorable weather conditions and displayed symptoms like generalized weakness, muscle tremors, lethargy, and an extended period of lying down. However, the study found no tremetone in the horses and observed similarities with a particular type of muscle disease in Europe.

Methods & Sample

  • Fourteen horses exhibiting the muscle disease over seven years (1998 to 2005) were included as the subjects of the study.
  • The primary criteria for inclusion were serum creatine kinase (CK) activity greater than 45,000 U/L, severe muscle necrosis in the proximal postural muscles or signs of weakness without any noticeable firmness in the muscles during the physical examination.
  • Vitamin E and selenium concentrations were measured in six of the horses, while tremetone concentration was measured in seven of the horses.

Findings

  • The disease symptoms surfaced during unfavorable weather conditions.
  • The horses showed signs of generalized weakness (11 horses), muscle spasms (10 horses), lethargy (6 horses), and prolonged lying down (4 horses).
  • The serum CK activity ranged from 46,487 to 959,499 U/L, while the standard range is 82 to 449 U/L. Aspartate transaminase activity was found to be greater than 1,500 U/L where the standard range is 162 to 316 U/L.
  • Two horses survived the disease with a rigorous antioxidant and fluid treatment.
  • Past death examination of the horses revealed severe muscle necrosis with lipid accumulation, mainly in the neck, proximal fore and hind limbs, intercostal (between the ribs) muscles, and diaphragm muscles. Damage to the heart muscle was observed in seven horses.
  • There were no abnormal readings in vitamin E and selenium concentrations, and no detection of tremetone in liver or urine samples.

Conclusion

  • The study could not confirm that white snakeroot toxicosis, associated with rhabdomyolysis, was the cause of the disease, since tremetone was not detected in the horses.
  • Interestingly, the study found similarities to cases of a specific muscle disease, known as “atypical myopathy“, found in Europe.

Cite This Article

APA
Finno CJ, Valberg SJ, Wünschmann A, Murphy MJ. (2006). Seasonal pasture myopathy in horses in the midwestern United States: 14 cases (1998-2005). J Am Vet Med Assoc, 229(7), 1134-1141. https://doi.org/10.2460/javma.229.7.1134

Publication

Journal of the American Veterinary Medical Association
ISSN: 0003-1488
NlmUniqueID: 7503067
Country: United States
Language: English
Volume: 229
Issue: 7
Pages: 1134-1141

Researcher Affiliations

Finno, Carrie J
  • Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108, USA.
Valberg, Stephanie J
    Wünschmann, Arno
      Murphy, Michael J

        MeSH Terms

        • Adenosine Triphosphatases / blood
        • Animals
        • Aspartate Aminotransferases / blood
        • Creatine Kinase / blood
        • Horse Diseases / blood
        • Horse Diseases / etiology
        • Horse Diseases / pathology
        • Horses
        • Midwestern United States
        • Muscular Diseases / blood
        • Muscular Diseases / etiology
        • Muscular Diseases / pathology
        • Muscular Diseases / veterinary
        • Poaceae / adverse effects
        • Prognosis
        • Rhabdomyolysis / blood
        • Rhabdomyolysis / etiology
        • Rhabdomyolysis / pathology
        • Rhabdomyolysis / veterinary
        • Seasons

        Citations

        This article has been cited 13 times.
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        11. Unger L, Nicholson A, Jewitt EM, Gerber V, Hegeman A, Sweetman L, Valberg S. Hypoglycin A concentrations in seeds of Acer pseudoplatanus trees growing on atypical myopathy-affected and control pastures. J Vet Intern Med 2014 Jul-Aug;28(4):1289-93.
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