Effect of mechanical processing of corn silage on in vitro ruminai fermentation, and in situ bacterial colonization and dry matter degradation

Abstract

Rumen fermentation and bacterial colonization of mechanically processed corn silage were evaluated in a series of in vitro and in situ experiments using ruminally cannulated cows. Data from rumen-simulated continuous culture (Rusitec) showed that total VFA concentration was increased (P < 0.001) by feeding processed corn silage, while pH was reduced (P < 0.001) and ammonia nitrogen remained unchanged (P > 0.05). Mechanical processing enhanced the in situ rate and extent of dry matter disappearance for corn stems and kernels, respectively (P < 0.05). It also enhanced in situ, the initial attachment of rumen bacteria responsible for corn digestion, as monitored by real-time PCR. The 16S rDNA copy numbers of amylolytic and lipolytic bacteria, such as Succinivibrio dextrinosolvens, Ruminobacter amylophilus and Anaerovibrio lipolytica, attached to corn kernels were increased for processed corn silage (P < 0.05), in particular at 2 h after the start of incubation. In addition, com stemattached cellulolytic and hemicellulolytic bacteria, such as Fibrobacter succinogenes, ruminococci and Eubacterium ruminantium, increased in 16S rDNA copy numbers for processed com silage (P < 0.05). This was observed for the initial incubation period from 10 min to 2 h. These results demonstrate more rapid attachment and heavier colonization of rumen bacteria to the processed compared with the unprocessed silage, which facilitates ruminai digestion and fermentation.