Mixed Ensiling Increases Degradation Without Altering Attached Microbiota Through In Situ Ruminal Incubation...

Mixed silage can disrupt the girder structure of rape straw, and thus facilitate ruminal degradation. Further investigation is warranted to validate this observation in vivo. The objective of this study was to investigate the degradation kinetics and bacterial colonization of mixed silage during digestion using an in situ ruminal incubation technique. The experiment comprised two treatments: a mixture of rape straw and corn silage (control), and a mixed silage treatment of rape straw and whole crop corn (mixed silage). Three ruminally cannulated Holstein bulls were employed. Substrates were incubated for varying durations (4, 12, 24, 48, 72, 96, 120 and 216 h) to assess substrate degradation kinetics. Bacterial colonization were analyzed after 4- and 48-h incubation time. Mixed ensiling disrupted the fiber structure of rape straw, and thus had lower fiber content compared to the control, as NDF and ADF content ‌decreased by 55 g/kg (678 vs. 623 g/kg) and 27 g/kg (440 vs. 413 g/kg), respectively. Compared to the control group, ruminal DM disappearance of mixed silage significantly (p ≤ 0.05) increased from 315 to 366 g/kg (+16.2%) at an incubation time of 4 h, 552 to 638 g/kg (+15.6%) at 120 h, and 563 to 651 g/kg (+15.6%) at 216 h. Similarly, compared to the control group, NDF disappearance of mixed silage significantly (p ≤ 0.05) rose from 112 to 201 g/kg (+79.5%) at 4 h, 405 to 517 g/kg (+27.7%) at 120 h, and 429 to 532 g/kg (+24.0%) at 216 h. Compared to the control group, soluble and washout nutrient fractions (a) of DM or NDF fraction in mixed silage significantly (p ≤ 0.05) rose from 289 to 340 g/kg (+17.6%), potentially degradable fractions (b) of NDF increased from 310 to 370 g/kg (+19.4%), and the undegraded fraction of NDF (μNDF) decreased from 582 to 471 g/kg (-19.1%). Incubation time, apart from in the mixed ensiling treatment, altered the bacterial community. The study highlights that higher total potentially degradable fractions account for enhanced ruminal substrate degradation of mixed silage.