Abstract
Effects of low dietary Mg with low or high Ca and K and sudden Ca loss, on Ca kinetics and Mg balance in sheep were studied. Six sheep were randomly assigned to one of two dietary treatments to provide (g d−1) either low levels of Ca (3.9), K (8.4) and Mg (2.3) or high levels of Ca (6.4) and K (30.6), and low levels of Mg (2.1). Lactational Ca loss was simulated via continuous iv infusion of ethylene glycol-bis (β-amino ethyl ether) N, N, N1, N1-tetraacetic acid (EGTA). In a control period sheep were not infused. Kinetics of Ca absorption and metabolism were determined using a radio-dilution technique and the Simulation, Analysis and Modeling program. Diets containing high Ca and K and low Mg reduced apparent Mg absorption and Mg balance compared to diets containing low Ca, K, and Mg. Confronted with a simulated lactational Ca loss, bone Ca resorption failed to increase when diets contained high Ca and K levels, whereas Ca absorption failed to increase when diets contained low Ca and K levels. Calcium balance was negative, and size of the exchangeable Ca pool was smaller in EGTA-infused sheep fed a low Ca, K, and Mg diet compared to a high Ca, K and low Mg diet. Key words: Calcium, magnesium, potassium, metabolism, kinetics, sheep, SAAM
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