Changes in plasma, red blood cell and cerebrospinal fluid mineral concentrations in calves during magnesium depletion followed by repletion with rectally infused magnesium chloride.

Hypomagnesemic and normomagnesemic calves were infused rectally with MgCl2 X 6H2O to determine effects on magnesium (Mg), calcium (Ca) and potassium (K) concentrations in plasma, red blood cells (RBC) and cerebrospinal fluid (CSF). Sixteen Holstein bull calves were fed one of four semipurified diets containing low or adequate Mg and normal or excess K in a 2 X 2 factorial arrangement. When CSF Mg concentration began to decrease in calves fed low Mg diets, each calf was given a rectal infusion of 50 ml of 30% MgCl2 X 6H2O solution while under general anesthesia. Blood and CSF were then sampled periodically for 3 hours and plasma, RBC and CSF were analyzed for Mg, Ca and K concentration. Plasma Mg increased (P less than 0.001) within 5 minutes after rectal infusion in all calves regardless of diet. An increase (P less than 0.01) in CSF Mg was also observed within 30 minutes in hypomagnesemic calves with CSF Mg levels less than 1.8 mg/dl. Rectal infusions had no effect on K in plasma, Ca or K in CSF, Mg, Ca or K in RBC, or packed cell volume but plasma Ca had increased (P less than 0.05) within 120 minutes in calves fed low Mg and high K and within 60 minutes in those fed adequate Mg, normal K diets.