The use of ¹⁵N for the determination of in sacco bacterial contamination of 3 concentrate feeds and N degradability of feeds in the rumen

Abstract

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.