ARS | Publication request: Microbial inoculant effects on silage and in vitro ruminal fermentation, and microbial biomass estimation for alfalfa, bmr corn, and corn silages

Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2010
Publication Date: January 3, 2011
Citation: Contreras-Govea, F.E., Muck, R.E., Mertens, D.R., Weimer, P.J. 2011. Microbial inoculant effects on silage and in vitro ruminal fermentation, and microbial biomass estimation for alfalfa, bmr corn, and corn silages. Animal Feed Science and Technology. 163:2-10.

Interpretive Summary: Lactic acid bacteria (commonly called inoculants) are often added to crops going into silos, helping guarantee a good fermentation and preservation in the silo. Frequently, this addition of bacteria at ensiling appears to increase the amount of milk produced by cows fed these inoculated silages, but we do not understand why. We ensiled alfalfa and corn with and without one of four different inoculants. We then measured how well these silages were digested when placed in fluid taken from the main stomach, the rumen, of several cows. Interestingly, when the silages produced by three of the four inoculants were digested in rumen fluid, more rumen bacteria were produced than those produced from untreated silage. This increase in rumen bacteria could potentially explain the increase in milk production from inoculated silage because rumen bacteria are an excellent source of protein for the cow and the milk she produces. These results provide dairy farmers some confidence that some inoculants can improve milk production. Also, this work suggests that inoculant manufacturers may be able to screen for new inoculants that will improve cow performance using digestion techniques that use rumen fluid.

Technical Abstract: Third cut alfalfa, brown mid-rib (bmr) corn, and corn were chopped and inoculated with one of four different strains of lactic acid bacteria (LAB). Uninoculated silage was the control treatment. For each crop, four mini-silos 1-L glass jars were ensiled per treatment. All silos were fermented for 60 days at room temperature (22°C). Silos were opened and analyzed for fermentation products, fiber constituents and nitrogen fractions. A fraction of wet silage was ground with a Robot Coupe blender for 30 s. In vitro gas production was measured in 160 ml sealed serum vials at 3, 6, 9, 24, and 48 h using the wet-ground silage. At 9 and 48 h rumen fluid was analyzed for volatile fatty acids (VFA) and microbial biomass yield (MBY). In all three trials, the four inoculants produced only minor changes in pH and fermentation products. The most consistent effect in silage characteristics across the trials was a reduction in soluble nonprotein nitrogen (NPN) by some inoculants. At 9 h incubation, in vitro gas production and VFA did not differ between control and inoculated silages, but MBY did. Among crops, alfalfa and corn silage produced greater MBY than bmr corn silage. Among treatments, three of the inoculated silage treatments produced more MBY than control. At 48 h, in vitro acetate concentration was lower in one inoculated treatment than control. Alfalfa silage produced higher MBY than corn and bmr silage. Similar to 9 h, three of the inoculated treatments produced greater MBY than control, and inoculant by crop interaction was not statistically significant. These results suggest that some silage inoculants are capable of altering rumen fermentation even in cases where effects on silage fermentation are small and that this effect may be linked to better preservation of crop protein during ensiling.