DETERMINATION OF THE RUMINAL ESCAPE VALUE AND DUODENAL AMINO-ACID FLOW OF RAPESEED MEAL

A 4 x 4 Latin square metabolism trial was conducted to evaluate protei n escape potential, duodenal amino acid (AA) flows, and ruminal digest ion effects of rapeseed meal (RSM) when fed with non-endophyte-infecte d tall fescue (Festuca arundinacea) hay. Four Holstein steers (average BW = 400 +/- 6.5 kg), each equipped with ruminal and duodenal cannula s, were fed twice daily at 0700 and 1900. Protein supplements compared with RSM, soybean meal (SBM), blood meal (BM), and a negative control based on urea (U). Diets were formulated to contain 14% CP. Rapeseed meal-supplemented steers had lower (P < .01) ruminal NDF and OM digest ibilities than steers fed SBM. Based on in situ data, the lower NDF, D M, and OM digestibilities that occurred when RSM was fed than when SBM and BM were fed were possibly due to the reduced digestibility of the hulls in the RSM. Ruminal pH was not different (P > .05) among treatm ents. Blood meal supplementation decreased (P < .01) ruminal and total tract CP digestibilities compared to all other supplements. Ruminal l iquid and particulate passage rates were not changed (P > .05) by supp lement source. Urea supplementation resulted in the highest (P < .01) ruminal ammonia concentration, whereas BM supplementation resulted in the lowest ruminal ammonia concentration (P < .01). Blood meal resulte d in greater (P < .01) dietary protein flow to the duodenum than the o ther treatments. However, microbial efficiencies, as well as microbial DM and protein flows to the duodenum were not different (P > .05) amo ng treatments. Rapeseed meal supplementation resulted in higher (P < . 01) duodenal flows of cystine, methionine, arginine, and isoleucine th an did SBM. Total AA flow to the duodenum was highest (P < .01) for BM (675 g/d) and lowest for U (438 g/d). Rapeseed meal resulted in great er (P < .01) total AA flow than did SBM (511 vs 439 g/d). The ruminal escape value of rapeseed meal was greater than that of SBM but less th an BM. Rapeseed meal supplementation is one way to increase duodenal f low of sulfur AA for ruminants.