Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 19 PLASMA MAGNESIUM LEVELS IN SHEEP IN RESPONSE TO MAGNESIUM OXIDE OR AN AMINO-ACID MAGNESIUM CHELATE INCLUDED IN THE RATION R. R. CARTERA, D. P. M' GEEA and D. L. GRIFFINB *Bayer Australia Ltd., P.O.Box 903, Pymble, N.S.W. 2073. *Dept of Veterinary Pathology, University of Sydney, N.S.W. 2006. Hypomagnesaemia or low blood magnesium (Mg) concentration, and subsequent effects on the cerebrospinal fluid Mg level, initiate grass tetany in ruminants. Dietary Mg level and the efficiency of Mg absorption are believed to be the major determinants of blood Mg concentration. Consequently, control strategies are based on Mg supplementation. This preliminary experiment was conducted in sheep to determine the plasma concentration of Mg in response to the consumption of diets containing either MgO or an amino-acid Mg chelate (Albion Labs., U.S.A.). Twenty-four Merino wethers of mean liveweight 57.4 & 10 kg were individually offered a control ration ad Zibitum containing 0.18% Mg from MgO for 28 days. The basal diet consisted of 70% cracked corn, 20% cottonseed hulls, 10% soybean meal, 0.7% limestone, 0.1% dicalcium phosphate plus a trace mineral-vitamin premix. On day 28 of the control period jugular blood was collected from each sheep by venipuncture into heparinized vacutainers. Sheep were then allocated in a randomized block design to 1 of 4 treatment rations: no supplemental Mg source (A); 0.18% Mg from MgO (B); 0.18% Mg from an amino-acid chelate (C); 0.36% Mg from MgO (D). Jugular blood was collected as before on day 7 and 14 of the treatment period. Plasma Mg concentrations were determined by the Calmagite method. Table 1. Mean (k s.e.) plasma Mg concentration (mmol/L) in sheep fed a ration containing MgO or an amino-acid Mg chelate The change in plasma Mg concentration from the control diet to the treatment diets for each treatment was analysed using a l-tailed paired t-test. Whilst plasma Mg concentrations remained in the normal range, only the change in concentration for treatment C was significantly different from zero. These preliminary results suggest that the bioavailability of Mg from the amino-acid chelate is better than than from MgO. However, a Mg balance study is required to confirm this in hypomagnesaemic animals. 391
