THE EFFECT OF ORAL MAGNESIUM SUPPLEMENTAT ION ADMINISTERED AS MGO ANDMGSO4 IN COWS WITH FASTING-INDUCED HYPOMAGNESEMIA

The effects of magnesium (Mg) supplementation as magnesium oxide (MgO) or magnesium sulphate (MgSO4) on Mg concentrations in plasma and urin e was determined and compared in cows with fasting induced hypomagnesa emia. 6 cows were submitted to 3 successive treatments. After an adapt ation period, cows were not fed for 3 days; food was delivered on the fourth day. Two groups were supplemented orally with either an equival ent of 30 g/day of Mg as MgO (55 g/day) or MgSO4 (334 g/day) for 4 day s. The other group was considered control. Blood and urine samples wer e obtained at 8 and 16 hours during the experimental period. Plasma ma gnesium (Mg-p), urinary magnesium (Mg-u), creatinine corrected urinary magnesium concentration (CUM) and urinary magnesium fractional cleara nce ratio (FCR) were measured. Mg-p decreased to hypomagnesaemic value s during the fasting period, recovering faster (p < 0.05) in the suppl emented groups. Mg-u, CUM and FCR values decreased during fasting, but there were considerable differences between cows. Animals recovered f aster during the feeding period in the supplemented groups, especially in the group supplemented with MgSO4. But with the exception of the F CR values observed between control and MgSO4 groups (p < 0.05), the di fferences between groups were not significant (p > 0.05). The results suggest that oral supplementation with 30 g/d of Mg salts either as ox ide or sulphate are effective in correcting fasting induced hypomagnes aemia in cows; MgSO4 showing the fastest response.