Electromyographic changes of motor unit activity in horses with induced hypocalcemia and hypomagnesemia.
OBJECTIVE
To determine whether electromyographic abnormalities are evident in skeletal muscles in horses with induced hypocalcemia and hypomagnesemia.


METHODS
7 healthy adult Dutch Warmblood horses.


METHODS
Electromyographic examination was performed in the lateral vastus, triceps, and subclavian muscles before and after IV infusion of EDTA. An initial dose (mean +/- SD, 564+/-48 ml) of a 10% solution of sodium EDTA was administered IV during a period of 21+/-73 minutes to establish a blood concentration of ionized calcium of approximately 0.5 mmol/L. Average rate of EDTA infusion to maintain ionized calcium at this concentration was 6.6 ml/min.


RESULTS
Mean blood concentrations of ionized calcium and magnesium were 1.39+/-0.06 and 0.84+/-0.09 mM, respectively before EDTA infusion; after EDTA infusion, concentrations were 0.48+/-0.05 and 0.44+/-0.20 mM, respectively. This state induced positive waves; fibrillation potentials; doublets, triplets, and multiplets; complex repetitive discharges; and neuromyotonia. Analysis of motor unit action potentials (MUAP) after EDTA infusion revealed an increase in prevalence of polyphasic and complex MUAP in all muscles.


CONCLUSIONS
None of the horses had classical signs of hypocalcemia and hypomagnesemia. In contrast, all horses had spontaneous activity in the measured muscles indicative of nerve hyperirritability. Calcium and magnesium deficits appear to have consequences, which may be subclinical, affecting functions of the neuromuscular system. This is of interest for equestrian sports in which hypocalcemia and hypomagnesemia are expected, such as during endurance rides.
Wijnberg
Inge D
ID
Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
van der Kolk
Johannes H
JH
Franssen
Hessel
H
Breukink
Henk J
HJ
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D002614:Chelating Agents; D004492:Edetic Acid; D004576:Electromyography / Q000662:veterinary; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses; D006996:Hypocalcemia / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D008345:Manganese / Q000097:blood*; D009043:Motor Activity / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*
D002614:Chelating Agents; D008345:Manganese; D004492:Edetic Acid