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. In a second experiment, five treatments were applied to incubated feeds to remove bacteria fxed t o the residues and consequently to determine directly the Dg of DM and N corrected for the bacterial contamination without the need for a marker. These treatments involved chilling for 6 h at 4°C in saline

The aims of this experiment were to quantify the extent of bacterial contamination (BC) of nylon bag residues, using 15 N as a microbial marker and to establish its influence on the effective nitrogen degradability (DT N ) of 3 concentrate feeds.The N degradability of soya-bean meal (SBM), meat and bone meal (MBM) and wheat bran (WB) was measured using the nylon bag procedure (0rskov and McDonald, 1979) (99 atom% excess, 3 g/d) was infused continuously through the rumen cannula. Rumen bacterial N in the residues (as % of total residual N) was calculated from the ratio: ( 15 N atom % excess in the residue/!SN atom % excess in the bacteria) x 100. Whole rumen content was sampled in each steer 0, 3, 6 and 9 h after feeding. Liquid and solid associated bacteria (LAB and SAB) were extracted as described by LegayCarmier and Bauchart (1989 In conclusion, the BC of undegraded residues markedly affects the DT N only for fibrous concentrate feedstuffs with a rather low N content. In our experiment, the choice of reference bacterial sample only slightly influenced the results.

Faculté des Sciences Agronomiques, passage des Déportés 2, 5.030 Gembloux, BelgiumThe methodological factors studied in this experiment were the incubation time in the rumen, the site of recovery and the pore size of nylon bags. Meat and bone meal (MBM), soybean meal (SBM) and wheat bran (WB) were incubated in the rumen of 3 steers (Beckers et al, 1993