Sheep were supplemented with increased Na and K levels. Increasing K and Na intake reduced Mg absorption and increased the percentage of Mg excreted in feces. Poe et al., 1985. JAS

Six Angus × Simmental steers, surgically equipped with abomasal and ileal cannulae, were used during three metabolism trials. The primary site of Mg absorption was the preintestinal region followed by a net secretion into the small intestine. Preintestinal Mg absorption was decreased 39% when 4.8% K was fed. Greene et al., 1983 JAS.

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. Feeding dolomitic limestone depressed (P<.01) the digestibility of the carbohydrate fractions and energy of the ration. Gerken et al., 1967. JAS.

Three experiments were conducted with eight gestating Angus cows to study  As calculated from regression equations obtained at each stage of gestation for the effect of dietary magnesium on serum magnesium, 8.5, 7.0, and 9.0 g of dietary magnesium would be required per day to maintain serum magnesium levels of 2.0 mg per 100 ml at 155, 200, and 255 days gestation, respectively. O Kelley et al., 1973. JAS

Sixty dry, nonpregnant, mature cows of five breeds (Angus, A; Brahman, B; Hereford, He; Holstein, Ho and Jersey, J) and their F, crosses (AB, AHe, AHo, AJ, BHe, BHo, BJ, HeHo, HeJ and HoJ, reciprocal crosses pooled). Predicted true digestibility of Mg was higher (P<.05) for B, BHo, A and HeHo than He, HeJ, BHe, J and Ho. The estimated endogenous excretion of Mg ranged from 1.8 to 10.5 g/d. Holstein-Jersey and HeHo had a larger (P<.05) quantity of estimated endogenous Mg excreted than AB, He, Ho, HeJ and BHe. Differences observed between breeds of cattle for grass tetany may be partially related to these changes in Mg digestibility. Greene et al., 1986. JAS

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