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 (MgSO(4)). 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 MgSO(4) (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 MgSO(4) (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 MgSO(4) administration. Following MgO administration, mean hydrogen ion concentration (pH), bicarbonate ion concentration ([HCO(3)-]) 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 MgSO(4). Since the oral use of MgO in normal cattle causes a greater and more prolonged metabolic alkalosis compared to MgSO(4), MgO is contraindicated as a cathartic in normal cattle or in cattle with abomasal abnormalities characterized by pyloric obstruction and metabolic alkalosis.