Urea-ammonia treatment of rice straw to improve its nutritive value for ruminants

Abstract

Three experiments were conducted to evaluate the effectiveness of urea as a source of ammonia in an ‘ensiling’ process for improving the nutritive value of chopped rice straw. In Experiment 1 rice straw treated with six levels of urea was ensiled in sealed polythene bags for periods varying from 1 to 6 weeks. In vitro digestibility increased significantly with increasing level of urea but ensiling beyond 3–4 weeks had no further effect. The optimum level of treatment appeared to be around 4% urea with an ensiling period of 3–4 weeks. In Experiment 2 two levels of urea (4% and 8%) were used to ensile rice straw for 4 weeks. These two treatments were compared with a control treatment having 4% urea sprinkled over the straw prior to feeding, using growing sheep fed ad libitum on straw with 100 g concentrate mixture per animal per day. The ensiling process had a significant effect on digestibility. Doubling the quantity of urea had no effect on digestibility but voluntary dry matter (DM) intake increased by 25%. In Experiment 3 the loss of urea as ammonia, on exposure of ensiled straw to the atmosphere, was estimated as 25% over a period of 2h. It is concluded that rice straw can be successfully upgraded in feeding value by urea-ensiling for 3–4 weeks. More research is, however, required before the method is extended to the farmer.