PSXII-24 Effects of a phytogenic mixture with or without direct-fed microbials on ruminal fermentation in an artificial rumen system (Rusitec).

Abstract Naturally occurring plant secondary compounds (NOPSC) and direct-fed microbials (DFM) are potential alternatives to in-feed antibiotics. However, information about the efficacy of combinations of NOPSC and DFM in modulating rumen fermentation is lacking. An experiment using an artificial rumen (Rusitec) was conducted to assess the effect of NOPSC with or without DFM on ruminal digestion, microbial protein synthesis and microbial populations. The artificial rumen was fed a dairy TMR alone (C) or supplemented with a mixture of NOPSC containing essential oils, tannins, and flavonoids (T1), a combination of T1 and a 4-species mixture of Bacillus spp. (T2), or with monensin (M). The experiment was conducted twice, over 19 d, with 4 replicate fermenters per treatment. Data were subjected to analysis of variance using the MIXED procedure of SAS with treatments as main effects and differences assessed using the LSMEANS procedure of SAS with the PDIFF option. Supplementation of T1 and T2 increased (P< 0.01) neutral detergent fibre (NDF) disappearance, decreased (P< 0.05) ruminal ammonia concentration but had no effects on DM disappearance or production of volatile fatty acids, total gas or total microbial protein. Compared to C, T2 increased (P< 0.05) rumen particle-associated microbial protein synthesis, but a similar response was not observed for T1. Neither T1 nor T2 affected the daily output of 16S rRNA gene copies of Fibrobacter succinogenes, Prevotella bryantii, Ruminobacter amylophilus, Ruminococcus albus, Ruminococcus flavefaciens, Selenomonas ruminantium, Streptococcus bovis or total methanogens from the Rusitec fermentation system. In contrast, M decreased (P< 0.01-0.001) most of fermentation parameters measured and daily outputs of F. succinogenes, P. bryantii, R. albus, R. flavefaciens and total methanogens but increased (P< 0.01) that of S. ruminantium and R. amylophilus. Combination of NOPSC and Bacillus species as defined in this study and applied in appropriate dosage has potential to improve rumen fermentation by increasing NDF digestion and feed particle related microbial protein synthesis.