Intestinal nitrogen degradation of hay and grass silage estimated by the mobile bag technique

Four ruminal and duodenally cannulated heifers about 550 kg were used to study the intestinal N degradation of hay and grass silage. The animals were fed at maintenance hay or grass silage, without or with barley (0.70 X DM intake) in a 2 X 2 factorial design in 4 X 4 Latin square with periods of 21 days. Intestinal degradation was measured by the mobile bag method, containing 800 mg of hay or freeze-dried grass silage or their rumen-incubated residues. 31.0-38.4 percent of original hay and grass silage dry matter (DM), and 9.6-13.7 percent of DM of their rumen-incubated residues disappeared from the bags during the intestinal exposure. Except for bound nitrogen in acid detergent fibre (ADF-N) the N disappearance values (53.4-83.1 percent) were high compared to respective DM values. The disappearance of DM, organic matter (OM), neutral detergent fibre N (NDF-N) and ADF-N, but not total N or amino acid N (AA-N) was different (P 0.05) between hay and grass silage. Except for NDF-N, the intestinal degradation of these variates was altered (P 0.05), usually reduced, by the pre-incubation in the rumen, but not by the barley supplementation of the diets. Microbial nitrogen attached to the rumen-incubated roughages disturbed the intestinal N degradation measurements. Markedly greater NDF-N disappearance compared to DM, however, indicated a high N decomposing capacity in the ruminant intestine. It was concluded that the mobile bag technique is a suitable tool in comparing the relative intestinal N degradability among similar type of feeds.