INTESTINAL DIGESTIBILITY IN DAIRY-COWS OF PROTEIN FROM GRASS AND CLOVER MEASURED WITH MOBILE NYLON BAG AND OTHER METHODS

Ruminal, intestinal, and total tract digestibilities of CP in grass, g rass silage, and clover were measured using the mobile nylon bag metho d. Total tract indigestibilities measured with this method were compar ed with indigestible CP predicted by in vitro, 14-d ruminal incubation , and 12-h followed by 14-d ruminal incubation methods. Indigestible C P was related to chemical composition and harvest date. Ruminal disapp earance of CP from nylon bags was 58, 71, and 58% for grass, grass sil age, and clover, respectively. Intestinal CP disappearance was 84, 81, and 91% of escape CP, respectively. Lower ruminal disappearance was c ompensated by higher intestinal disappearance, resulting in a small va riation in total tract indigestible CP within forage. Total tract indi gestible CP was 7, 6, and 4%, respectively. Average total tract indige stible CP measured with the mobile nylon bag method (6%) was lower tha n that estimated by the in vitro (13%), 14-d ruminal incubation (14%), or 12-h ruminal incubation followed by 14-d ruminal incubation (11%) methods. All methods ranked forages similarly, resulting in high corre lation coefficients among methods within forage. Total tract indigesti ble CP of grass, grass silage, and clover was related to CP content an d harvest date, DM and ADIN content, and DM and CP contents, respectiv ely.