Abstract
The experiment was carried out to study the digestibility of nutrients in the neutralized urea-treated rice straw when it was fed singly or in combination with concentrates. A total of 8 crossbred Holstein steers were randomly allocated in a $4{\times}4$ Latin square design consisted of 4 treatments, in which the neutralized straw/concentrates ratio on DM basis varied as 100/0, 90/10, 80/20 and 70/30. The results indicated that the digestibility of DM, ether extract and NFE, and TDN and DE of the diets tended to increase with an increase in the level of concentrates. Regression analysis showed that the values of intercepts should be used for estimating DM digestibility, TDN and DE of neutralized straw, when it was fed with concentrates. Digestibilities of crude fiber, NDF and ADF tended to be higher when it was fed singly than when fed with concentrates. Digestibilities of organic matter and CP were not so much changed with the increasing level of concentrates. Although the animals singly fed the neutralized straw showed positive body weight gain and N-balance, it should be necessary to supplement the concentrates to get more body weight gain and N-balance in the crossbred Holstein steers.