Electromyographic changes of motor unit activity in horses with induced hypocalcemia and hypomagnesemia.

The research article is about a study that tested the impact of induced hypocalcemia and hypomagnesemia on horse skeletal muscles, finding that such conditions can trigger nerve hyperirritability even if the horses do not display classical signs of these conditions.

Research Methods

• The researchers examined seven healthy adult Dutch Warmblood horses in this study.
• Measurements of electromyographic activity were taken from three muscles – the lateral vastus, triceps, and subclavian – both before and after the horses were given an intravenous infusion of sodium EDTA.
• To initiate the condition of hypocalcemia (low calcium levels in blood), the horses received an average initial dose of 564+/-48 ml of a 10% solution of sodium EDTA over approximately 21+/-73 minutes. The goal was to establish a blood concentration of ionized calcium of about 0.5 mmol/L.
• The researchers then maintained this level of ionized calcium by continuing the infusion of EDTA at a rate of about 6.6 ml per minute.

Research Results

• Prior to the infusion of EDTA, the average blood concentrations of ionized calcium and magnesium were recorded as 1.39+/-0.06 mM and 0.84+/-0.09 mM, respectively.
• After the infusion, these concentrations dropped substantially, with calcium at 0.48+/-0.05mM and magnesium at 0.44+/-0.2mM.
• By triggering lowered levels of calcium and magnesium – conditions known as hypocalcemia and hypomagnesemia – the researchers detected various abnormal muscle activities. These included positive waves, fibrillation potentials, doublets, triplets, multiplets, complex repetitive discharges, and neuromyotonia.
• They also observed an increase in the occurrence of polyphasic and complex motor unit action potentials (MUAP) in all muscles after the EDTA infusion.

Conclusions

• Despite the horses not presenting any classical signs of hypocalcemia and hypomagnesemia, such as muscle twitching, seizures, or cardiac arrhythmias, they all displayed spontaneous muscle activity indicating nerve hyperirritability.
• This suggested that deficits in calcium and magnesium can have consequences, potentially at a subclinical level, on the functioning of the neuromuscular system.
• The researchers highlighted the potential relevance of this discovery to equestrian sports, particularly endurance riding, where horses are expected to encounter situations that may lead to hypocalcemia and hypomagnesemia.