Nylon capsule method and alfalfa hay crude protein digestibility evaluation

In a trial with two dairy cows we have determined crude protein total tract digestibility (TTDPNC) by a new nylon capsule method. Nylon capsules were made of nylon cloth with 42 μm apertures. The capsule shape was lenticular, with 10 mm external diameter and 8 mm internal diameter. The capsules were loaded with two stainless steel balls of 149 mg total weight. The average weight of a sample (milled alfalfa hay) in one capsule was 12.9 mg. In each of the two periods 1260 capsules were inserted orally into each of the two cows. Mean capsule passage time (CPT) through the digestive tract was 36.1 h (s.e. 0.49). The total tract dry matter digestibility determined by the nylon capsule method (TTDMNC) was significantly (P < 0.05) influenced by the time which the capsules spent in the digestive tract. When CPT was 25.4 h, TTDMNC was 64.8%, while with CPT 50.4 h it was 70.3%. The mean value of TTDPNC was 93.8%. A similar value, 92.3%, was obtained by calculation based on the values determined by the nylon bag and the mobile bag methods. The results have shown that it is possible to use the nylon capsule method for the determination of total tract digestibility of individual feed components in cattle.