Effect of a microbial inoculant (Ecosyl ™ and/or a glycopeptide antibiotic (vancomycin) on fermentation and aerobic stability of wilted alfalfa silage

Abstract

First cutting alfalfa was wilted (420 g dry matter kg −1) and was untreated (control) or treated with a microbial inoculant (Ecosyl ™, Lactobacillus plantarum), a glycopeptide antibiotic (vancomycin, 50 or 150 ppm), or combinations of inoculant and antibiotic before ensiling. Microbial inoculation increased initial counts of lactic acid bacteria from approximately 3.5 to 4.9 log 10 cfu g −1 forage. Inoculation markedly improved fermentation as evident by lower silage pH ( P < 0.01), acetic acid ( P < 0.05) and NH 3-N ( P < 0.05) contents and greater amounts of lactic acid after 56 days of ensiling. Inoculation also caused a rapid decrease in coliform bacteria and yeasts and molds. Treatment with vancomycin resulted in an immediate decrease in coliform bacteria and a tendency for lower yeast and molds throughout ensiling. Antibiotic-treated silage also had a lower silage pH ( P < 0.01) relative to control silage in the early, but not the later stages of ensiling. Other aspects of fermentation were not consistently improved by vancomycin. Silages treated with both inoculant and antibiotic had fermentations similar to silages treated only with the inoculant. No additive effects of inoculant and antibiotic were detected. The pH of control silage and silage treated only with inoculant was stable up to 4 days of aerobic exposure. However, silage treated with inoculant plus antibiotic had a reduced aerobic stability as pH increased to above pH 6, and total yeasts and molds were more than 6.5 log 10 cfu g −1 silage after 4 days of aerobic exposure.