Abstract 116

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

Department of Tropical Animal Production, Agricultural University, PO Box 338, 6700 AH Wageningen, Netherlands.

Animal-Feed-Science-and-Technology. 1989, 24: 1-2, 83-95; 33 ref.

The degradation characteristics of 5 varieties of rice straw (in vitro organic matter digestibility (IVOMD) ranging from 35 to 55%), untreated or urea-treated, were studied using the nylon bag procedure. Bag incubations up to 10 days were performed in the rumen of cows given a diet of 50% wheat straw and 50% hay. The degradation characteristics for organic matter (OM) and cell wall components were evaluated using a two fraction model with a fixed undegradable fraction and lag time. The variety of rice straw and urea treatment affected (P < 0.001) the potentially degradable fraction (D), undegradable fraction and the rate constant of degradation of all components studied. Their effects on degradation time-lag were not significant. Between varieties, the undegradable OM fraction ranged from 27 to 50%, and the rate of degradation from 2.15 to 2.91%/h. Urea treatment increased the potentially degradable fraction and its rate of degradation. Nevertheless, even after treatment the differences between varieties were maintained. With the low quality straw (IVOMD 35%), treatment released more OM and fibre for degradation, but its use even as a maintenance diet is doubtful. The maximum benefit of urea treatment was obtained with the medium quality straw (IVOMD 48%), where the D fraction and its rate of degradation were similar to a good quality straw after treatment. With good quality straws (IVOMD 55%), the benefits achieved with urea treatment may be similar to that obtainable with nitrogen supplementation. Around 50-60% of the N in straws was released after 10 days of incubation in the rumen. Although up to 13% of the N added by urea treatment was insoluble in water, the amounts of N remaining in the rumen-incubated residues were similar for untreated and treated straws.