Abstract
Three experiments were conducted to examine the effects of the conditions of moisture level and temperature for urea or urea plus urease treatment on the degradability of rice (Oryza sativa L.) straw in polyester bags incubated in the rumens of sheep, and to compare urea with ammonia treatment (Expt. 1), to measure the rate of urea breakdown under some ensiling conditions (Expt. 2), and to compare in more detail the effects of urea and ammonia treatment on the degradability and composition of straw (Expt. 3). Degradability was most improved when the straw was ensiled with urea at 300 g kg^<-1> of moisture level and 40℃, the effect being almost equal to that of ammonia. The addition of urease produced little further improvement. When usea was ensiled with straw at 300 g kg^<-1> of moisture level, its hydrolysis with time followed a quadratic relationship with a maximum close to Day 21 by which time 96 and 98% of urea added had hydrolysed at either room temperature or 40℃, respectively. The maximum potential degradability of straw treated with urea at 300 g kg^<-1> of moisture level increased to 704 and 749 g kg^<-1> DM, at room temperature and 40℃ respectively, compared to 649 g kg^<-1> DM for untreated controls. Similarly, rates of degradation increased to 5.6 and 6.7 %/h compared to 5.2 %/h for controls. Urea treatment produced the effects similar to those of ammonia treatment. It is concluded that urea can be an effective source of ammonia for straw treatment under optimum ensiling condition.
