Availability and Utilization of Magnesium from Dolomitic Limestone and Magnesium Oxide in Steers

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Abstract
Three metabolism trials were conducted with six yearling steers to study the utilization of supplemental magnesium by beef steers when supplied as dolomitic limestone and magnesium oxide. The basal ration supplied 4.85 gm. of magnesium per day. Total magnesium intakes were 14.4 and 13.5 gm. for the rations supplemented with dolomitic limestone and magnesium oxide, respectively. Magnesium absorption, expressed as percentage of dietary magnesium was 53, 27 and 52% for the basal, dolomitic limestone and magnesium oxide rations, respectively. The availability of supplemental magnesium, calculated by difference, was much higher (P<.01) for magnesium oxide than for dolomitic limestone. There was a significant difference (P<.01) in the change in blood serum magnesium values between steers fed dolomitic limestone and those fed magnesium oxide; values were higher for the magnesium oxide supplemented steers. Calcium absorption and retention were lower when dolomitic limestone was fed, and blood serum calcium values tended to be lower compared to the other two rations. Phosphorus absorption and retention, and blood serum inorganic phosphorus were similar between rations. Feeding dolomitic limestone depressed (P<.01) the digestibility of the carbohydrate fractions and energy of the ration.