Abstract 119

Ibrahim,-MNM; Ketelaar,-RS; Tamminga,-S; Zemmelink,-G

Department of Tropical Animal Production, Agricultural University, Wageningen, Netherlands.

Ruminant feeding systems utilizing fibrous agricultural residues - 1987. 1988, 123-126; 6 ref. Canberra, Australia; International Development Program of Australian Universities and Colleges Ltd.

A nylon bag experiment was conducted to study the effect of variety and urea treatment on the degradation of rice straw in the rumen. Five varieties of rice straw, with organic matter digestibility in vitro 35 to 55% in both the untreated and urea-treated forms, were used. Samples were incubated for 6, 12, 18, 24, 48, 72 and 240 h in the rumen of cows fed on wheat straw and hay (50:50). The degradation of DM was evaluated using a 2 fraction, exponential model with a fixed undegradable fraction and lag time. The variety of rice straw and urea treatment significantly affected the degradable fraction, undegradable fraction and the rate constant of degradation. Their effects on degradation time lag were not significant. Between varieties of untreated straw the undegradable DM fraction was 27 to 45%, and the rate of degradation (%/h) 2.07 to 2.74. Urea treatment not only increased the potentially degradable fraction, but also its rate of degradation. Nevertheless, even after treatment the differences between varieties were maintained.