Ogunade, I.M., Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, United States
Kim, D.H., Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, United States, Division of Applied Life Science (BK21Plus, Institute of Agriculture and Life Science), Gyeongsang National University, Jinju, South Korea
Jiang, Y., Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, United States
Weinberg, Z.G., Department of Food Safety and Quality, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Jeong, K.C., Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, United States
Adesogan, A.T., Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, United States

This study was conducted to examine if adding microbial inoculants or propionic acid to alfalfa silages contaminated with Escherichia coli O157:H7 would inhibit the growth of the pathogen during or after ensiling. Alfalfa forage was harvested at the early bloom stage, wilted to a dry matter concentration of 54%, chopped to 19-mm lengths, and ensiled after treatment with one of the following: (1) distilled water (control); (2) 1 × 105 cfu/g of E. coli O157:H7 (EC); (3) EC and 1 × 106 cfu/g of Lactobacillus plantarum (EC+LP); (4) EC and 1 × 106 cfu/g of Lactobacillus buchneri (EC+LB); and (5) EC and 2.2 g/kg of propionic acid (EC+PA). Each treatment was ensiled in quadruplicate in laboratory silos for 0, 3, 7, 16, and 100 d and analyzed for EC counts, pH, and organic acids. In addition, samples from d 100 were analyzed for chemical composition, ammonia-N, counts of yeasts and molds, and aerobic stability. Escherichia coli O157:H7 was detected in all silages until d 7, but by d 16 it was not detected in those treated with EC+LB and EC+LP, though it was still detected in EC and EC+PA silages. However, by d 100, the pathogen was not detected in any silage. The rate of pH decrease to 5.0 was fastest for the EC+LP silage (7 d), followed by the EC+LB silage (16 d). Nevertheless, all silages had attained a pH of or less than 5.0 by d 100. The rapid decrease in pH in EC+LP and EC+LB silages was observed due to higher lactate and acetate concentrations, respectively, relative to the other silages during the early fermentation phase (d 3-16). Propionic acid was only detected in the EC+PA silage. Yeast counts were lowest in EC+LB and EC+PA silages. Subsamples of all d-100 silages were reinoculated with 1 × 105 cfu/g of EC immediately after silo opening. When the pathogen was subsequently enumerated after 168 h of aerobic exposure, it was not detected in silages treated with EC+PA, EC+LB, or EC+LP, which all had pH values less than 5.0. Whereas the EC silage had a pH value of 5.4 and 2.3 log cfu/g of the pathogen. Certain bacterial inoculants can hasten the inhibition of E. coli O157:H7 during ensiling, such as propionic acid, and they can also prevent its growth on silage contaminated with the pathogen after ensiling. © 2016 American Dairy Science Association.