Magnesium absorption in sheep infused with potassium in different parts of the digestive tract

Abstract

Two metabolism trials were conducted with 12 crossbred wether lambs, each surgically prepared with a rumen catheter, and abomasal and ileal cannulae to study the effect of K infusion in the different sites 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 of feed, feces and urine for determining mineral balance and a 6 d sampling period of feed, abomasal and ileal contents and feces for determining mineral flow and site of absorption. Chromic oxide was used as a marker.

Magnesium was absorbed primarily from the preintestinal region. Ruminal infusion of K tended to decrease preintestinal Mg absorption. Total Mg absorption was decreased ( P<. 05) by 43% when K was infused into the rumen. There was a slight absorption of Mg in the small intestine followed by a net secretion of Mg into the large intestine. Serum Mg levels tended to be depressed in the animals infused with K intraruminally.

Calcium flow into the preintestinal region was decreased ( P<. 05) by infusion of K into the rumen. Generally, a net secretion of Ca occurred in the preintestinal region and in the large intestine, with the small intestine being the major site of absorption. Only animals being infused with K in the rumen secreted Na into the preintestinal region. The large intestine was the primary site of Na absorption. Phosphorus flow into the preintestinal region was decreased (P<.05) by infusion of K into the rumen. The small intestine was the main site for P absorption. Potassium flow into both the preintestine and small intestine was increased (P<.05) by ruminal K infusion. The flow of K into the small intestine was increased by ileal K infusion. The infusion of K increased (P<.05) the absorption of K as compared to the control animals with the small intestine being the major absorptive site. The infusion of K bicarbonate into the rumen of sheep raised (P<.05) the pH of the rumen.