Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/30/2007
Publication Date: 11/1/2007
Citation: Muck, R.E., Filya, I., Contreras-Govea, F.B. 2007. Inoculant effects on alfalfa silage: in vitro gas and volatile fatty acid production. Journal of Dairy Science. 90(11):5115-5125. Interpretive Summary: The application of lactic acid bacteria to crops when stored in silos is a common practice in the U.S. These bacteria help guarantee the crop (and the resulting silage) will be preserved well in the silo, but they also can have a positive effect on the cow that we do not understand. We performed two trials where we stored (ensiled) alfalfa in laboratory silos with a wide range of commercial lactic acid bacteria (8 commercial products and 6 individual bacterial strains). This report details what happened to the silages when placed in digestive fluid taken from several cows' stomachs, which should help us understand how cows might respond to the different silages. One of the common products of digestion is gas: carbon dioxide and methane, two greenhouse gases. Surprisingly, when the silages treated with lactic acid bacteria were digested, they produced less gas than the untreated silages especially early in the digestion process. These results suggest that these treated silages are being digested differently by the cow in a way that may reduce greenhouse gases and improve the nutritional value of the silage to the cow. If confirmed by additional studies, these additives could prove to be beneficial to the cow, the farmer's bottom line and the environment.
Technical Abstract: Alfalfa silages from two similar trials, 15 treatments with an untreated control and 14 lactic acid bacterial inoculants, were analyzed for in vitro ruminal gas production. First cut (477 g DM/kg) and second cut (393 g DM/kg) alfalfa had been ensiled in glass jars for a minimum of 30 days at room temperature (~22 C). A portion of the silages at opening were wet ground with a mixer. A subsample was analyzed fresh for in vitro ruminal gas production while the remainder was frozen and analyzed in duplicate in separate in vitro runs. In vitro gas production was measured in 160 ml sealed serum vials manually using a pressure gauge at 3, 6, 9, 24, 48 and 96 h. At 96 h, the rumen fluid was analyzed for pH and volatile fatty acids. In the two trials, the untreated control produced either the highest or one of the highest levels of gas production per unit DM incubated whether silage fermentation was affected substantially by inoculation with lactic acid bacteria or not. Furthermore, the fraction of total gas production at 3, 6 and 9 h was highest for the control in the first cut where the inoculants produced the largest effects on silage fermentation. In the second cut, two of 14 inoculated treatments produced faster fractional rates of gas production than the control, but most inoculated treatments again had slower fractional rates in the first 9 h. The in vitro fermentation of the control silages had one of the highest acetate:propionate ratios in both trials even though the control silage was highest in lactic acid in one trial and lowest in the other. Overall, it appears that inoculation of crops at ensiling is affecting in vitro rumen fermentation even in absence of large effects during silage fermentation.