We hear a lot about a horse experiencing rhabdomyolysis (tying-up) during or after exercise. However, foals are also susceptible to muscle damage. Stephanie Valberg, DVM, PhD, of the University of Minnesota, presented "A Review of the Diagnosis and Treatment of Rhabdomyolysis in Foals" at the 2002 American Association of Equine Practitioner's Convention. She began her presentation with a discussion of what a practitioner might do when presented with a possible case of tying-up.

Diagnosis

To assess the damage to the muscles, a practitioner might indicate that a serum chemistry profile is necessary, said Valberg. The activity of specific enzymes such as creatine kinase (CK), lactate dehydrogenase (LDH), and aspartate transaminase (AST) provide information about muscle damage. Serum CK values will peak about four to six hours after muscle damage, and they will return to normal between three to seven days after the muscle damage stops occurring. "Thus, high serum CK activity indicates acute muscle degeneration, and persistently elevated serum CK activity over time indicates ongoing rhabdomyolysis," she said.

Increases in LDH and AST activity can also indicate tying-up, but they can also point to liver damage. LDH peaks 12 hours after muscle damage, with values returning to normal seven to 10 days after damage. AST peaks one to two days after muscle damage and won't return to normal for five to 14 days. To rule out liver disease, a biochemistry profile will also measure glutamyl transferase (GGT) and sorbitol dehydrogenase (SDH)