Microbial inoculation of a grass-dominant pasture improves rumen function in vitro

Introduction Interventions applied to pastures that modify nutritional attributes of the pasture may increase ruminant productivity and reduce the environmental footprint of production. We evaluated bovine in vitro fermentation responses to a microbial inoculant applied to a mixed-sward pasture, along with nutritional attributes of the treated pasture. Methods A 4.2 ha heterogeneous pasture sward was randomly assigned to either a single intervention (inoculant) area or a control (no inoculant) area. Graze2Rumen ® (Agrovive Biologicals) inoculant was applied to the intervention area. The pastures were potentially non-equivalent across the field. A fermentation study with a single-factor design was then performed using two treatment groups. Inoculated and control pastures were chopped daily and fed to five fistulated Holstein cows per treatment group for 35 days. At weekly intervals for five weeks, a rumen sample was collected from each cow, and the following in vitro measures were determined: apparent digested organic matter (aOMD), hydrogen, carbon dioxide, methane, ammonia, total gas, apparent partitioning factor (aPF), microbial biomass production (aMBP), and pH after 24 hours of fermentation. Pasture samples were collected weekly for wet chemistry analysis from one week before (-7 days) to two weeks after the fermentation study (49 days). Results and discussion Pasture samples obtained from potentially non-equivalent pastures, one inoculated and one untreated, showed that the inoculated pasture had a higher neutral detergent fiber content than the control for weeks 5, 6, and 8, and differences in phosphorus, potassium, and starch or resistant sugar content were associated with inoculation. An increase in aMBP of fermented rumen fluid was a key indicator of the potential for increased milk, wool, or meat production resulting from inoculation. This finding is consistent with approximately an 8.7% reduction in methane production and an 11.1% improvement in organic matter digestibility with inoculation. Similarly, a 15% improvement in the apparent partitioning factor with inoculation indicates the potential for increased feed intake if these results are reflected in vivo . These early results indicate the potential for aerial application of a microbial inoculation to affect pasture characteristics and possibly provide a scalable intervention to improve production and reduce the environmental footprint of ruminant production.