Magnesium tolerance in goats fed two levels of potassium.

Magnesium tolerance tests were conducted in five female goats to determine the effect of increasing dietary potassium level from .9% (basal diet) to 4.0% (high-K diet) on an animal's capacity for disposing of an intravenous load of magnesium. Both diets contained about .07% magnesium, .91% calcium and .56% phosphorus. Following intravenous injections of magnesium acetate (.5 mEq of Mg/kg body weight), the time required for plasma magnesium concentration to decline to within 10% of the preinjection lewd averaged 239 and 176 min (P<.05) when the goats were fed the basal and high-K diet, respectively. Analysis of urine collected from two goats indicated that urinary magnesium excretion could account for all of the magnesium disappearing from plasma for 4 hr after magnesium loading when the goats were fed the basal diet but only about 80% of the magnesium when they were fed the high-K diet. It is postulated that supplementary potassium may have enhanced the disappearance of magnesium from plasma and decreased urinary magnesium excretion by increasing the cellular uptake and retention of magnesium because of increased cellular potassium levels. Regardless of diet, intravenous magnesium loading produced transitory decreases in plasma levels of calcium, potassium and phosphorus. The mechanism(s) responsible for the responses in plasma calcium, phosphorus and potassium cannot be determined from the study reported here.