Investigations on the in Vitro Digestibility Techniques Used Under East African Conditions

Abstract

The two-stage" in vitro" technique, proposed by Tilley and Terry (1963), was adopted with minor modifications. This method involves a 48-hour incubation of a 0.5 g. sample with strained rumen liquor and a buffer solution (McDougall, 1948) to maintain pH within the range found in the rumen. The incubation is carried out under anaerobic conditions at a temperature of 38 C. and is followed by a second 48-hour incubation with acid pepsin at the same temperature. The pepsin incubation attacks protein which is largely left untouched during the first stage. Two Zebu steers, fitted with rumen fistulae, using the method proposed by Balch and Cowrie (1962), were used as a source of rumen liquor for these investigations. The animals were restricted to stalls and fed ad lib. with freshly cut Pennisetum purpureum during periods when rumen liquor was being withdrawn. In practice they were used in turn, rumen liquor being withdrawn for a two-week period after a week in which to settle down. Food was withheld for 12 hours prior to liquor collection. This was carried out, after trials with various mechanical sucking devices, by withdrawing rumen contents by hand. Immediately after collection solid matter was removed by filtering through two layers of cheesecloth, using light suction. Carbon dioxide was bubbled through the liquor which was then placed in an incubator held at 38 C. until required. The buffer solution was warmed to 40 C. and 40 ml. dispensed into 100 ml. centrifuge tubes, containing the grass samples. 10 ml. of the rumen liquor was placed into the tubes with the aid of a Jencon's Zippette and carbon dioxide bubbled into the tubes wh