NITROGEN-METABOLISM OF SHEEP AND GOATS CONSUMING ACACIA-BREVISPICA AND SESBANIA-SESBAN

We described the effects of two East African browses, Acacia brevispic a and Sesbania sesban, on nitrogen metabolism of sheep and goats. The A. brevispica had a substantial amount of proanthocyanidins (condensed tannins); S. sesban did not. The browses were fed at three levels in combination with vetch (Vicia dasycarpa) and teff straw (Eragrostis ab yssinica). Fecal N, N balance, and plasma urea N (PUN) were estimated with intact animals. Ruminal ammonia (RuA) and VFA concentrations were estimated with ruminally fistulated animals. Urinary N loss, PUN, RuA , and VFA concentrations were higher for S. sesban diets than for A. b revispica diets. Fecal N was highest with diets including A. brevispic a due to high levels of fecal neutral-detergent insoluble N. Nitrogen retention was highest for diets including S. sesban. Nitrogen retentio n was adequate for A. brevispica diets because low urinary N compensat ed for high fecal N. Four hypotheses describe possible effects of tann ins on N metabolism: 1) escape of protein from the rumen to the lower tract; 2) increased microbial yield; 3) increase in N-containing endog enous products; and 4) protein made indigestible in tannin-protein com plexes. The effect of tannins in A. brevispica on N metabolism can bes t be described by the formation of indigestible tannin-protein complex es, although increased production of endogenous products is also possi ble.