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). / Master of Science

Two experiments were conducted to study the effects of a high dietary potassium intake on magnesium metabolism. In experiment 1, eight 3-day balance trials were conducted with 12 crossbred wether lambs. Rations containing equal amounts of magnesium, calcium and sodium and 0.6 or 4.9% potassium were fed. Apparent absorption of magnesium was greatly depressed (P < .05) while apparent absorption of sodium and potassium were generally increased by the addition of 100 gm. of potassium bicarbonate to the ration. There was a trend for higher apparent absorption of calcium by the high-potassium fed lambs. Although blood serum calcium, sodium or potassium showed no distinct trends, there was a trend toward lowered serum magnesium levels after 14 days of potassium supplementation, which disappeared after 27 days. In experiment 2, six paired yearling wethers were fed two rations identical in ingredient composition to those used in experiment 1. All wethers received an intravenous dose of radioactive magnesium²⁸ and magnitude of fecal and urinary magnesium²⁸ excretion was determined and magnesium turnover rates calculated. The high-potassium fed wethers tended to secrete smaller amounts of magnesium²⁸ in the urine and slightly greater amounts in the feces. The high-potassium fed wethers had lower magnesium turnover rates indicating that high potassium levels interfere with magnesium absorption rather than drastically increase the excretion into the intestine. / Master of Science

M.S.

M.S.

Three experiments were conducted to study the effects of dietary potassium intake on magnesium metabolism. In experiment 1, 24 wether lambs were used in two metabolism trials to determine the minimum level of potassium that depresses magnesium absorption. Two magnesium levels (.1 and .2%) were fed with four levels of potassium (.6, 1.2, 2.4 and 4.8%) in a 2 x 4 factorial arrangement of treatments. Each trial consisted of a 10-day preliminary period followed by a 10-day collection period. Greater amounts (P<.05) of magnesium were absorbed and retained when animals were fed the high level of magnesium (.2%). Increasing the level of potassium in the diet increased (P<.05) fecal magnesium excretion. Magnesium absorption decreased linearly with increasing levels of potassium. The greatest depression in magnesium absorption occurred when the potassium level was increased from 1.2 to 2.4%. A further large decrease in absorption occurred when the potassium level was increased from 2.4 to 4.8%. Serum magnesium was depressed when higher levels of potassium were fed. Potassium absorption was not affected by level of dietary magnesium, but increased (P<.05) with increasing levels of dietary potassium. In experiment 2, two metabolism trials were conducted with 18 wether lambs, equipped with abomasal and ileal cannulae, in a 2 x 3 factorial arrangement. Two levels of magnesium (.1 and .2%) and three levels of potassium (.6, 2.4, and 4.8%) were used. Chromic oxide was used as an indicator to determine digesta flow. Each trial consisted of a 10-day preliminary period, a 7-day collection of feed, feces and urine, and a 6-day sampling of feed, abomasal and ileal fluid and feces. Magnesium was absorbed mainly prior to reaching the small intestine, followed by a low net absorption in the large intestine. Increasinq potassium level resulted in a linear decrease in magnesium absorption. Preintestinal magnesium absorption decreased (P<.05) with each increase in dietary potassium. Large amounts of magnesium flowed into the small and large intestines and was excreted in the feces when higher levels of potassium were fed. Lambs fed the high level of magnesium (.2%) absorbed larger amounts of magnesium from the stomach. Magnesium absorbed, expressed as a percent of intake, was not affected by level of magnesium. Experiment 3 consisted of three metabolism trials with six Angus x Simmental steer calves, per trial, equipped with abomasal and ileal cannulae. Steers were fed .1% magnesium and three levels of potassium, .6, 2.4 and 4.8%. Procedures were similar to those used in Experiment 2. Magnesium absorption decreased linearly (P<.05) when high levels of potassium were fed. The primary site of magnesium absorption was the preintestinal region, followed by a net secretion into the small and large intestines. Preintestinal magnesium absorption was decreased approximately 50% when steers were fed 4.8% potassium. Small amounts of magnesium tended to be secreted into the small intestine when the high level of potassium was fed. As observed in experiment 1, serum magnesium levels were depressed when increasing amounts of potassium were fed. Potassium absorption increased with increasing levels of dietary potassium. The effect of high dietary potassium on magnesium absorption was similar to those reported in experiments 1 and 2 with sheep. / Ph. D.