Effect of Magnesium Administration Route on Plasma Minerals in Holstein Calves Receiving Either Adequate or Insufficient Magnesium in Their Diets

¹ Department of Animal Science, The University of Tennessee, Knoxville 37901-1071

Rates of increase in plasma Mg following rectal or oral administration of solutions containing 30 g MgCl₂·6H₂O were compared in 10 Holstein bull calves receiving wheat straw (.07% Mg) and concentrates (.04 or .24% Mg) fed separately for ad libitum consumption. Treatments were administered in a sequence, which involved each calf with all combinations of MgCl₂·6H₂O dosing routes and dietary Mg within a 6-wk period. Plasma Mg concentration averaged 1.95 mg/dl initially but fell below 1 mg/dl within 2 wk after supplemental Mg was omitted. Maximum increases in plasma Mg concentration following oral or rectal dosing were 16 or 47% when dietary Mg was adequate and 48 or 124% when Mg was deficient. Calves fed either diet responded maximally to rectal infusion within 10 min, but plasma Mg of deficient calves increased throughout 160 min after oral dosing. Plasma Mg of deficient calves responded quicker and reached higher concentrations after rectal infusion, but the response was sustained longer after oral administration.

Key Words: magnesium • calves • hypo-magnesemia

Submitted on April 19, 1989
Accepted on July 20, 1989