Studies of magnesium metabolism in cattle : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury

Abstract

To investigate production responses to Mg supplementation, 38 Friesian cows (third-calvers) in mid-lactation were allocated to control and treated groups in equal numbers. The cows grazed ryegrass/white clover pastures and those in the treated group were drenched at the dose rate of 10 g Mg/cow/day. This was supplied through 180 mls of Causmag solution (MgO). The overall mean herbage Mg level recorded was 2.7 ± 0.09 g Mg kg⁻¹ DM (2.2 - 3.1 g kg⁻¹ DM⁻¹). Overall mean serum Mg concentration was 21.1 ± 0.10 mg Mg 1itre⁻¹ (20.7 - 21.6 mg Mg 1itre⁻¹) and 21.2 + 0.23 mg Mg litre⁻¹ (20.4 - 22.1 mg Mg litre⁻¹) for the control and treated groups respective1y.

Production responses to Mg supplementation were not significant, nor did Mg supplementation significantly increase serum Mg concentration.

In a second experiment, four 4-month-old steers were supplemented with four levels of Mg (0 (control), 3.5, 6.5 and 10 g Mg), according to their position in a 4 x 4 Latin Square design over a 4-week period. This was in addition to the Mg provided by the ryegrass/white clover diet (2.5 g Mg kg⁻¹ DM⁻¹).

Magnesium supplementation was associated with trend for increase in serum Mg concentration to a peak at 16.00 h with lowest values at 20.00 h. Mg supplementation did not have any significant effect on overall mean serum Mg, Ca and inorganic P concentrations.