Magnesium Utilization in Wethers Fed Diets with Varying Ratios of Nitrogen to Readily Fermentable Carbohydrate

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Abstract
Two experiments were conducted to study magnesium utilization in wether lambs fed diets with varying ratios of nitrogen to readily fermentable carbohydrate (N:RFC). Semipurified diets fed to the lambs contained about 4.1% nitrogen (25.6% crude protein), .08% magnesium, .4% calcium, 2.4% potassium and varied amounts of readily fermentable carbohydrate provided mainly as either starch (experiment 1) or sucrose (experiment 2). Dietary ratios of N:RFC were .2, .4, .7 and .9 in experiment 1 (five lambs/treatment), and .2 and 1.6 in experiment 2 (nine lambs/treatment). In experiment 1, ruminal fluid ammonia-nitrogen levels increased as starch intake decreased, but differences between treatments were not significant (P>.05). Apparent absorption, retention and plasma concentration of magnesium were not affected (P>.05) by decreased starch intake. In experiment 2, ruminal ammonia levels increased (P<.05) as sucrose intake decreased. Urinary excretion (P<.05) and apparent absorption (P<.1) of magnesium were higher in lambs fed supplementary sucrose than in those fed the diet without added sucrose; plasma magnesium levels were similar in both groups. Results of experiment 2 support the hypothesis that supplemental energy may enhance the availability of dietary magnesium to ruminants. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science