In Vitro Inoculum Enriched with Particle-Associated Microorganisms for Determining Rates of Fiber Digestion and Protein Degradation

In trial 1, rates of neutral detergent fiber digestion were measured on alfalfa hay with conventional inoculum prepared with strained ruminal fluid or inoculum also enriched with particle-associated microorganisms. Microorganisms from particles were obtained by washing the particle residue four times with nutrient-buffer. During the first 24 h, rates of neutral detergent fiber digestion from the enriched inoculum were approximately doubled. However, by 48 h differences in extent of neutral detergent fiber digestion were small. With the enriched inoculum but not the conventional inoculum, there was a linear increase of rate of neutral detergent fiber digestion with graded application of a mixture containing potassium carbonate, which enhanced field drying of hay. In trial 2, two additional inocula were prepared from whole contents of rumen that were either blended or had been chilled at 4°C. Digestion of neutral detergent fiber was not increased by chilling, and blending tended to lower digestion. In trial 3, seven inocula were evaluated in a protein degradation study. Three inocula enriched with particle-associated organisms yielded degradation rates of casein that were more than twice those with the conventional inoculum (.17/h versus .39/h). Inocula prepared from blended whole contents of rumen (with or without chilling) or from addition of Tween 80 before chilling did not increase rates of protein degradation. Inoculum enriched with particle-associated organisms can be used routinely to obtain improved estimates of in vitro rates of fiber digestion and protein degradation.