Case Study: Comparative Feeding Value of Rice Straw in Growing-Finishing Diets for Calf-Fed Holstein Steers: Fibrolytic Enzyme Supplementation

One hundred twelve Holstein steers (115 ± 5 kg) were used in a 167-d performance trial. Two forage sources [rice straw vs sudangrass (SG) hay] and two levels of fibrolytic enzyme supplementation (0 vs 0.17% Yeasture®, Cenzone Tech, Inc., San Marcos, CA) were evaluated in a 2 x 2 factorial arrangement. Experimental diets (steam-flaked, corn-based) contained 15% (DM basis) forage. Forages were ground to pass through a 2.5-cm screen prior to incorporation into completely mixed diets. Fibrolytic enzyme supplementation did not affect (P> 0.20) cattle performance. Forage source did not affect (P>0.20) ADG; however, DMI tended (P=0.14) to be slightly (2%) greater for the diets containing rice straw. Dietary NEm and NEg were greater (3 and 5%, respectively; P<0.05) for the SG diets than for rice straw diets. Given that the NEm value of SG was 1.11 Mcal/kg, the replacement NEm and NEg values for ground rice straw were 0.65 and 0.16 Mcal/kg, respectively; tabular values from the NRC (1984) for NEm and NEg were 0.64 and 0.11 Mcal/kg, respectively. We concluded that ground rice straw is a highly palatable forage source and can be included as the sole roughage source in high energy, growing-finishing diets at levels of up to approximately 15% (DM) without reducing energy intake and ADG of calf-fed Holstein steers. Fibrolytic enzyme supplementation did not enhance the feeding value of either SG or rice straw under the conditions of this study.