Effect of different level of urea addition for rice straw fermentation application: in vitro evaluation

Rice straw is an agricultural by-product that generally used as a roughage. The fermentation process could increase the nutrient availability of rice straw. Urea addition in the fermentation process is expected to increase the digestibility. The current study aimed to evaluate the nutrient content and in vitro digestibility of fermented rice straw by different levels of urea addition. Microstar LA2 was used for the fermentation process in rice straw by 21 days. Completely randomized design with four treatments and five replications was applied in the current study. The treatments were K (fermented rice straw without urea addition), U1 (fermented rice straw with 0.15% urea addition), U2 (fermented rice straw with 0.3% urea addition) and U3 (fermented rice straw with 0.45% urea addition). The observed parameters were the nutrient content, in vitro gas production, in vitro true digestibility (IVTD) and rumen fermentation product. The results showed that there was no significant difference in ether extract (EE), neutral detergent fiber (NDF) and acid detergent fiber (ADF) for all treatments. However, adding urea on the rice straw fermentation process could increase total gas production after 24h time of incubation (P<0.05). Adding 0.15% urea could increase gas production caused by fermentation of the insoluble fraction (GPNSF) by 31.62% (P<0.05). There was no significant difference between U1, U2, and U3 on GPNSF variables. Adding a minimum 0.15% urea on the rice straw fermentation process also could increase metabolizable energy (ME), organic matter digestibility (OMD), microbial protein (MP) and single-chain fatty acid (SCFA) production. It could be concluded that adding 0.15% urea on the fermentation process is enough to increase the nutrient availability and in vitro digestibility of rice straw.