Effect of Varying Dietary Protein-Magnesium Ratios on Nitrogen Utilization and Magnesium Retention in Growing Rats

Abstract

To test the effect of different dietary protein-magnesium ratios on nitrogen and magnesium utilization, male weanling rats were fed diets with 12 or 36% casein and with 0.01, 0.05 or 0.1% magnesium for 5 weeks. Signs of magnesium deficiency developed in rats fed the 0.01% magnesium diets. Food efficiency and net nitrogen utilization were specifically affected by magnesium intake on the high protein diets; the 0.05% magnesium level was apparently not adequate for optimum growth and protein utilization. Other criteria which changed with magnesium intake were plasma proteins and plasma and liver ribonuclease. Total carcass and plasma magnesium concentrations on 0.01% magnesium intakes were slightly lower in animals fed the high protein diet. Magnesium retention and utilization were more efficient, however, with the 36% than the 12% casein diet at all levels of magnesium intake. This latter finding conflicts with previous reports in the literature. Possible reasons for the discrepancy are discussed.