Dose-dependent effects of magnesium supplementation on serum and intracellular magnesium concentrations in healthy horses

Abstract

For magnesium supplementation in horses, dosages for MgO, MgCO3, and MgSO₄ were described previously. However, for magnesium as magnesiumaspartate-hydrochloride (MAH) dose-dependent effects on the magnesium levels have not yet been determined in horses. Therefore, the magnesium concentrations in blood lymphocytes, serum, urine and the fractional magnesium excretion in the urine were measured in five healthy adult horses before and after oral supplementation with 15, 30 and 60 mg/kg bodyweight (BW) magnesium as MAH respectively for seven days. There was no wash-out period in between experimental periods. In erythrocytes, the intracellular baseline magnesium concentration and the intracellular magnesium concentration after one week of supplementation with 60 mg/kg BW magnesium were determined. All horses were exclusively fed with hay of which the magnesium concentration was measured each week. All horses were clinically examined daily, including signs of colic and soft feces. There were no significant changes in the magnesium concentration in the diet. Signs of colic, soft feces or other side effects were not observed. The serum magnesium concentration after supplementation with 60 mg/kg BW magnesium as MAH was significantly higher than the baseline and exceeded the reference range in four of five horses. After 15 and 30 mg/ kg BW magnesium as MAH, the serum magnesium concentration showed a significant increase over time. Neither a significant increase of the intracellular magnesium concentration nor significant changes in urine magnesium concentration or fractional excretion were observed. In erythrocytes, a trend for higher magnesium concentrations was found after supplementation with 60 mg/kg BW magnesium as MAH. For short-term supplementation in cases of increased magnesium requirements, these dosages seem effective and the dosages of 15 mg/kg BW and 30 mg/kg BW safe to use. For supplementation with 60 mg/kg magnesium as MAH, veterinary supervision and monitoring of the serum magnesium concentration is recommended.