Rice straw and concentrate were obtained from the Ruminant Metabolism Center, Tropical Feed Resources Research and Development Center (TROFREC), Khon Kaen University, Thailand. Rice straw was a single-crop variety of Oryza sativa indica. The U-cas was prepared according to Cherdthong et al. (2011a) by producing an aqueous solution of CaSO4 (23 g CaSO4 + 17 mL H2O) and dissolved with 60 g urea in the aqueous CaSO4 and then agitated the mixture at 50 °C for 10 min prior to reducing the temperature of the solution to about 25 °C. All ingredients in the feed blocks (Table 1) were mixed together and then pressed into blocks of about 10 kg by hydraulic compression for 3 min per block then left to dry under the sun for 2 to 3 days or in open room with roof.