Two horses (
a 7-year-old Groninger warmblood gelding and a six-month-old Trakehner mare) with pathologically confirmed
rhabdomyolysis were diagnosed as suffering from
multiple acyl-CoA dehydrogenase deficiency (MADD). This disorder has not been recognised in animals before. Clinical signs of both horses were a stiff, insecure gait,
myoglobinuria, and finally recumbency. Urine, plasma, and muscle tissues were investigated. Analysis of plasma showed
hyperglycemia, lactic acidemia, increased activity of muscle
enzymes (ASAT, LDH, CK), and impaired kidney function (increased
urea and
creatinine). The most remarkable findings of organic
acids in urine of both horses were increased
lactic acid,
ethylmalonic acid (EMA), 2-methylsuccinic
acid, butyrylglycine (iso)valerylglycine, and
hexanoylglycine. EMA was also increased in plasma of both animals. Furthermore, the profile of acylcarnitines in plasma from both animals showed a substantial elevation of C4-, C5-, C6-, C8-, and C5-DC-carnitine. Concentrations of acylcarnitines in urine of both animals revealed increased excretions of C2-, C3-, C4-, C5-, C6-, C5-OH-, C8-, C10:1-, C10-, and C5-DC-carnitine. In addition, concentrations of free
carnitine were also increased. Quantitative biochemical measurement of
enzyme activities in muscle tissue showed deficiencies of
short-chain acyl-CoA dehydrogenase (SCAD),
medium-chain acyl-CoA dehydrogenase (MCAD), and
isovaleryl-CoA dehydrogenase (IVD) also indicating MADD. Histology revealed extensive
rhabdomyolysis with microvesicular
lipidosis predominantly in type 1 muscle fibers and mitochondrial damage. However, the ETF and ETF-QO activities were within normal limits indicating the metabolic disorder to be acquired rather than inherited. To our knowledge, these are the first cases of biochemical MADD reported in equine medicine.