EFFECTS OF CANOLA-MEAL TREATED WITH ACETIC-ACID ON RUMEN DEGRADATION AND INTESTINAL DIGESTIBILITY IN LACTATING DAIRY-COWS

Five midlactation lactating Holstein cows (628 +/- 42 kg) fitted with large rumen cannulas and T-type cannulas in the proximal duodenum were used in a 4 x 4 Latin square experiment to determine the effects of a cetic acid treatment of canola meal on rumen degradation of its protei n, rumen fermentation, and postruminal digestion. Canola meal was mixe d with 3% (vol/wt) acetic acid in a mixer, followed by drying at 105-d egrees-C. Acetic acid treatment of canola meal reduced is in situ rume n DM and CP degradability by up to 17.0 or 28.6 percentage units, resp ectively, dependent upon the assumed rumen turnover rate. Cows were fe d TMR twice daily containing 60% concentrate, 8% alfalfa silage, and 3 2% whole crop oat silage on a DM basis. Treated canola meal replaced u ntreated canola meal in the concentrate at 0, 33, 67, and 100%. Each e xperimental period was 21 d. Average concentration of rumen acetate an d isobutyrate increased linearly, but rumen pH, NH3 N, lactic acid, an d VFA concentrations, other than acetate and isobutyrate, were not aff ected by inclusion of treated canola meal. Treatment of canola meal wi th acetic acid was effective in increasing escape from the rumen of po struminally digestible canola meal protein.