Magnesium metabolism in sheep fed different levels of soluble carbohydrate and potassium

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1982
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Virginia Polytechnic Institute and State University
Abstract

Two metabolism trials were conducted with 12 wethers surgically equipped with abomasal and ileal cannulae. A 2 x 2 factorial arrangement was used with diets containing 3 and 23% soluble carbohydrate and .6 and 4% potassium, dry basis. Each trial consisted of a 10-d preliminary period followed by a 7-d collection of feed, feces and urine and a 6-d sampling of feed, abomasal and ileal contents and feces. Chromic oxide was used as an indicator to measure the flow of minerals along digestive tract. The pH of the rumen and ileal fluid was decreased (P<.05) by high levels of soluble carbohydrate. Increased dietary potassium increased (P<.05) ruminal pH. Magnesium absorption and retention were not affected by the level of dietary soluble carbohydrate. High potassium levels decreased (P<.05) magnesium absorption, expressed a g/d or percent of intake. The primary site of magnesium absorption in all animals was the preintestinal region. A net secretion of magnesium into the small intestine was followed by a small net absorption in the large intestine. High levels of dietary potassium tended to depress preintestinal magnesium absorption and increase flow through the small and large intestine. Soluble carbohydrate level had no effect on potassium absorption or retention. Increased potassium intake increased (P<.05) apparent absorption, retention and urinary excretion of potassium. In animals fed the low potassium diet, potassium was absorbed primarily in the small intestine, but at the high level the stomach was also important. The addition of soluble carbohydrate had no consistent effects on calcium and phosphorus balance and absorption. Sodium absorption in the small intestine was increased (P<.05) by the high level of soluble carbohydrate. Increased dietary potassium increased sodium availability and urinary excretion (P<.05). Calcium was absorbed primarily in the preintestinal region. Sodium and phosphorus were secreted into the preintestial region and absorbed from the large and small intestine, respectively. Serum magnesium and calcium levels wei:e not. affected by soluble carbohydrate level, but tended to be depressed at the high potassium level. Bigb dietary potassium increased serum potassium level (P<.05), whereas high soluble carbohydrate intake decreased the level (P<. 05).

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