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Nitrogen Partitioning along the Equine Digestive Tract¹

University of Maryland², College Park 20742

Abstract

Twelve adult horses were fed a corn-oats-timothy hay diet containing 2.87% nitrogen (N) for 4 wk and were then killed. Fresh digesta samples were immediately harvested from the stomach, duodenum, jejunum, ileum, cecum, large colon, small colon, rectum and feces. Total N content of the digesta (on a dry matter basis) increased from the stomach (2.74%) to the duodenum (5.58%; P<.01), decreased in the cecum (3.10%, P<.01), remained constant through the large intestine and decreased in the feces (2.10%; P<.01). High-speed centrifugation of wet digesta and low-speed centrifugation following tungstic acid treatment of wet digesta were comparable in their effectiveness in separating water soluble N-containing compounds (S-N) from insoluble N-containing compounds (P-N). The P-N was further partitioned into neutral detergent soluble (NDS-N) and neutral detergent insoluble (NDF-N) fractions. The NDF-N constituted from 6 to 17% of the total digesta N at any location along the digestive tract. The S-N constituted about 20% of the total digesta N in the stomach, increased to about 80% at mid-jejunum (P<.01), decreased to 30% in the cecum (P<.01) and increased throughout the large intestine. The calculation of cumulative apparent digestibilities indicated that total digesta N underwent net disappearance along the entire tract, except in the duodenum. Dietary NDF-N underwent net disappearance throughout the digestive tract. The NDS-N portion of the P-N disappeared in the duodenum, jejunum and small colon, but underwent net appearance in the ileum, cecum and large colon. There was a net appearance of S-N in the duodenum and net disappearances in the ileum and cecum. The shifts in N partitioning along the lower digestive tract and the decreases in N concentrations suggest that the jejunum, ileum, cecum and small colon are major sites of the net absorption of N and that much of the N absorbed in the small colon was supplied by the conversion of NDS-N to S-N.

¹ Scientific Article No. A-3261, Contribution No. 6332 of the Maryland Agr. Exp. Sta.

² Dept. of Anim. Sci.