Rumen ammonia concentrations, and non-ammonia nitrogen passage to and apparent absorption from the small intestine of sheep ingesting subtropical, temperate, and tannin-containing forages

Non-ammonia nitrogen (NAN) passage to the small intestine and disappearance of NAN in that organ have been studied in multi-cannulated sheep on pasture or fed indoors. Forages under investigation included a number of subtropical grasses, foggages and hay, temperate grasses, lucerne (Medicago sativa), triticale (Triticale X Secale), oven-dried ryegrass (Lolium multiflorum), and the tannin-containing forages sainfoin (Onobrychis viciifolia) and sheeps' burnet (Sanguisorba minor). Digesta flow was measured with reference to Yb-acetate and Cr-EDTA as particulate and fluid markers, respectively. Rumen ammonia concentrations were exponentially associated with the nitrogen (N) content of the forage, with concentrations increasing progressively above 2.5% N in the forage dry matter. Ruminal fermentation of tannin-containing forages resulted in much lower ammonia concentrations than ruminal fermentation of forages without tannins. NAN passage to the small intestine as a proportion of N intake was significantly (P";;; 0.05) different between forage classes: 0.97:!: 0.09 for subtropical forages, 0.75:!: 0.09 for temperate grasses plus lucerne and triticale, and 1.12:!: 0.08 for tannin-containing forages and dried grass. NAN passage as a proportion of N intake declined with increasing N intake in all non-tannin forages, the decline being especially severe in forages with high total (above 3%) and/ or high soluble N. NAN disappearance in the small intestine as a proportion of NAN entering that organ differed significantly (P";;; 0.01) between tannin-containing forages and subtropical foggages and hay on the one hand (0.64 :!: 0.06), and all other forages on the other hand (0.76 :!: 0.02). NAN disappearance as a proportion of N intake increased in the order: temperate grasses plus lucerne and triticale, subtropical foggages and hay, subtropical grasses, tannin-containing forages, and dried grass.