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, grass silage, and clover were measured using the mobile nylon bag method. Total tract indigestibilities measured with this method were compared with indigestible CP predicted by in vitro, 14-d ruminal incubation, and 12-h followed by 14-d ruminal incubation methods. Indigestible CP was related to chemical composition and harvest date. Ruminal disappearance of CP from nylon bags was 58, 71, and 58% for grass, grass silage, and clover, respectively. Intestinal CP disappearance was 84, 81, and 91% of escape CP, respectively. Lower ruminal disappearance was compensated by higher intestinal disappearance, resulting in a small variation in total tract indigestible CP within forage. Total tract indigestible CP was 7, 6, and 4%, respectively. Average total tract indigestible CP measured with the mobile nylon bag method (6%) was lower than 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 correlation coefficients among methods within forage. Total tract indigestible CP of grass, grass silage, and clover was related to CP content and harvest date, DM and ADIN content, and DM and CP contents, respectively.