Movement and absorption of major minerals and water in ovine gastrointestinal tract.

Movement of calcium, chloride, magnesium, potassium, sodium, and water in the intestine of sheep was determined with cerium-141 as an unabsorbed reference substance. Net secretion of phosphorus and sodium, but not of potassium and calcium, was observed to the rumen. Water disappeared from the omasum and was secreted in the abomasum. Chloride secretion occurred in the omasum and more in the abomasum. Extensive secretion in the duodenum increased flows of sodium and potassium 8 to 9 times; of calcium, chloride, and phosphorus 3 to 6 times; of magnesium 1.3 times; and of water 12 times. Reabsorption was rapid in the small intestine, the major site of disappearance of all ions. Rates of disappearance decreased with increasing distance from the pylorus. Little further net disappearance of calcium, phosphorus, magnesium, or potassium was found in the large intestine, whereas water, sodium, and chloride disappearance continued. Overall absorption of sodium, potassium, and chloride was approximately 90%, of phosphorus 63%, of calcium 38%, and of magnesium 71%. This study highlights the importance of endogenous secretions in mineral absorption in the sheep.