Magnesium Oxide Induced Metabolic Alkalosis in Cattle

A study was designed to compare the metabolic alkalosis produced in cattle from the use of an antacid (magnesium oxide) and a saline cathartic (magnesium sulphate). Six, mature, normal cattle were treated orally with a magnesium oxide (MgO) product and one week later given a comparable cathartic dose of magnesium sulphate (MgSO₄).

The mean percent dry matter content of the cattle feces changed significantly (P<0.001) following administration of both MgO (15.6-8.1) and MgSO₄ (17.0-8.7) but there was no significant difference between treatments. The mean rumen pH values changed significantly (P<0.001) following administration of both MgO (7.-8.7) and MgSO₄ (7.3-8.3) but there was no significant difference between treatments. However, use of the MgO product caused a more severe (P<0.001) metabolic alkalosis as determined by base excess values. The base excess values remained elevated for 24 hours in the MgO treated group compared to only 12 hours after MgSO₄ administration. Following MgO administration, mean hydrogen ion concentration (pH), bicarbonate ion concentration ([HCO₃-]) and base excess were 7.44, 33.3 mmol/L and +8.0 respectively compared to 7.38, 27 mmol/L and +3.0 after MgSO₄.

Since the oral use of MgO in normal cattle causes a greater and more prolonged metabolic alkalosis compared to MgSO₄, MgO is contraindicated as a cathartic in normal cattle or in cattle with abomasal abnormalities characterized by pyloric obstruction and metabolic alkalosis.