Direct-Fed Microbials Alter Ruminal in vitro Gas Production and Fermentation with a High-Concentrate Diet

Ruminal fermentation can be altered with Direct-Fed Microbials (DFM) although these responses may depend on the length of time that DFM has been supplied. To test this hypothesis, 12 ruminally cannulated Angus steers (385 ± 35 kg) were used in a split-split plot design with dietary treatment, control or DFM, in the whole plot, treatment of the incubation media, control or DFM in the sub plot, and length of dietary treatment (14 and 28 d) in the sub-sub plot. The DFM was a mixed culture of lactate producing bacteria, primarily Lactobacillus acidophilus and Enterococcus faecium, fed at 109 cfu/day. A 90:10 concentrate to forage, corn-based diet was fed twice daily and top-dressed with DFM or its lactose carrier. Media DFM dosage (50,000 cfu) provided the same cfu per unit of dry matter as provided in the diet. Gas production decreased (P=0.02) with dietary DFM and tended (P=0.06) to decrease with media DFM. A diet by media interaction (P<0.01) was observed for gas production rate; rate was decreased by media DFM without dietary DFM but increased with media DFM with dietary DFM. Volatile Fatty Acid (VFA) concentration tended (P=0.07) to decrease with dietary DFM; however, molar proportion of acetate was increased (P=0.01). Media DFM did not alter (P ≥ 0.21) fermentation end products. Interactions between day and dietary DFM were not observed (P ≥ 0.14). Differences in gas production and fermentation end products with dietary DFM suggest that DFM altered fermentation by shifting microbial populations, while interactions between diet and media suggest that DFM also have an immediate influence on the rumen environment.