Magnesium Absorption and Secretion along the Gastrointestinal Tract of the Chicken

Abstract

Comparative-balance and isotope-dilution techniques were employed in two experiments to determine magnesium (Mg) absorption and secretion along the digestive tract of the chicken. Mature male chickens, fed semipurified diets containing 382 ppm Mg and chromic oxide (Cr₂O₃) as a marker, were each given 14 µCi ²⁸Mg by intramuscular injection. Samples were collected 24 and 48 hours after ²⁸Mg administration in experiment 1 and 48 hours after administration in experiment 2. At the end of each period the chickens were killed and plasma, intestinal mucosa, heart, liver, tibia and gastrointestinal contents were sampled for analysis. The soft tissue Mg equilibrated with plasma ²⁸Mg. However, only a small part of bone Mg was in equilibrium with the plasma Mg 48 hours postadministration. A net secretion of Mg occurred in the duodenum. However, absorption of both dietary and endogenous Mg was greatest in the duodenum and jejunum. Over 50% of the total dietary Mg absorbed during passage through the tract was absorbed in this region. Additional absorption occurred in the ileum and colon. The combined isotope-dilution and comparative-balance data showed that 72% of dietary Mg was absorbed during passage along the gastrointestinal tract, although comparative-balance data alone indicated that the chickens were essentially in Mg balance.