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Absorption of Magnesium and Other Macrominerals in Sheep Infused with Potassium in Different Parts of the Digestive Tract¹

Virginia Polytechnic Institute and State University^,3, Blacksburg 24061

Abstract

Two metabolism trials were conducted with 12 crossbred wether lambs, each surgically equipped with a ruminal catheter and abomasal and ileal cannulae, to study the effect of K infusion in different sites of the digestive tract on site of absorption and flow of minerals. The treatments consisted of the infusion of 33.6, 12.0 or 12.0 g K/d as bicarbonate into either the rumen, abomasum or ileum, respectively. Each trial consisted of a minimum 5-d preliminary period, five 3-d collection periods to determine mineral balance and a 6-d sampling period to determine mineral flow and site of absorption. Chromic oxide was incorporated into the diet for use as a marker. Magnesium was absorbed primarily from the preintestinal region. Ruminal infusion of K tended to decrease preintestinal Mg absorption. Absorption of Mg in the entire tract was decreased (P<.05) 43% when K was infused into the rumen. There was a slight absorption of Mg in the small intestine, followed by a net secretion into the large intestine. Serum Mg levels tended to be depressed in lambs infused with K intraruminally. Calcium flow from the preintestinal region was decreased (P<.05) by infusion of K into the rumen. Only lambs infused with K in the rumen had a net secretion of Na into the small intestine. The large intestine was the primary site of net Na absorption for ruminal-infused lambs. Phosphorus flow from the preintestinal region was decreased (P<.05) by infusion of K into the rumen. Potassium flow from both the preintestine and small intestine was increased (P<.05) by ruminal K infusion. The infusion of K into the rumen, abomasum or ileum increased (P<.05) the total absorption of K, with the small intestine being the major absorptive site. The infusion of potassium bicarbonate into the rumen of sheep raised (P<.05) the pH of the ruminal contents 15%. Ruminal infusion of K depresses Mg absorption, while the infusion of K into the abomasum or ileum does not affect Mg absorption. Therefore, the role of K in grass tetany may be via this depression of Mg absorption.

¹ Supported in part by a grant from John Lee Pratt Animal Nutrition Program at Virginia Polytechnic Institute and State Univ., Blacksburg.

² Present address: Dept. of Anim. Sci., Texas A&M Univ., College Station.

³ Dept. of Anim. Sci.

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