Physiological Effects of Feeding High Levels of Magnesium to Sheep

Abstract

The effects of feeding high levels of Mg to sheep on animal health, nutrient digestibility, metabolism of macro-minerals, blood and tissue mineral concentrations and hematological and histological tissue changes were evaluated. Six lambs were allotted to each of four diets supplemented with MgO to attain .2, .6, 1.2 or 2.4% Mg. Total fecal and urinary collections were made for the initial 20 d and last 10 d of a 50 d study. Diarrhea was noted in lambs fed the two highest Mg levels. Apparent digestibility of DM, ADF and CP decreased linearly (P < .01) with increasing Mg levels. Dietary Mg levels did not affect (P > .05) rectal temperature, respiration rate or pulse rate. Apparent absorption and retention of Mg (g/d) were lowest in lambs fed 2.4% Mg until 15 d on trial, after which values increased linearly (P < .01) with dietary Mg. Phosphorus absorption and retention decreased linearly (P < .01) with increasing Mg levels. Increasing dietary Mg resulted in a linear increase (P < .01) in serum Mg and variable increases (P <.05) in erythrocyte Mg. Serum Ca was decreased linearly (P < .05) and quadratically (P < .05) by added Mg during the d 1 to 30 and 40 to 50 periods, respectively. Serum inorganic P was elevated consistently in lambs fed 2.4% Mg. A linear response to increasing dietary Mg (P < .05) occurred in the Mg content of liver, kidney, rib bone and femur bone. Dietary Mg did not alter (P > .05) other criteria. Dietary Mg as low as .6% depressed nutrient utilization; at 2.4%, Mg affected Mg levels in selected tissues.