UTILIZATION OF RICE STRAW BY RUMINANTS AS INFLUENCED BY GRASS HAY SUPPLEMENTATION

Twenty Korean native bulls averaging 181 kg body weight were fed a fixed amount (1.5% of live weight) of concentrate and free choice roughage cubes which had four ratios of rice straw and orchard grass hay; 100:0, 85:15, 70:30 and 55:45 on a weight basis. Five bulls were assigned to each treatment and fed for 98 days in a confinement house. Nutrient digestibility and available energy content of mixed rations (40% concentrate and 60% roughage cubes) was determined in a digestion trial with twelve wethers. In vitro dry matter digestibility (IVDMD) and in situ dry matter disappearance of the roughage cubes were also determined. The ratio of grass hay to rice straw did not influence dry matter intake. Significant improvements in body weight gains and feed/gain ratios were obtained as grass hay levels increased. Average daily gain and feed/gain for each treatment was 0.83, 0.88, 0.98 and 0.99 kg; 7.63m 7.59, 6.83 and 6.41, respectively. Digestibility of the nutrients was improved with increasing levels of grass hay in the cubes. The IVDMD of roughage samples having a ritio of 100:0, 85:15, 70:30 and 55:45 between rice straw and orchard grass hay were 31.0, 37.1, 41.8 and 43.4%, respectively. Grass hay improved the IVDMD of rice straw diets in a linear manner up to 30%. In situ dry matter disappearance rate was also increased as the level of orchard grass hay increased.