Inoculants for alfalfa silage: Effects on aerobic stability, digestibility and the growth performance of feedlot steers

Abstract

Two bacterial inoculants were applied to chopped alfalfa forage (1×10 5 cfu g −1) at the time of ensiling, and the aerobic stability and digestibility of the silages, as well as the growth performance of feedlot cattle receiving the treated silages, were compared against untreated silage. The inoculants contained a mixture of Lactobacillus plantarum and Enterococcus faecium (LP+EF) or L. plantarum alone (LP). Epiphytic populations of lactic acid-producing bacteria (LAB) prior to ensiling exceeded 2×10 8 cfu g −1. The pH of all silages declined below 4.55 and the low concentration of butyric acid and high concentration of lactic acid suggested that all silages were of good quality. Concentrations of water-soluble carbohydrates tended to be lower in inoculated than in control silage, whereas numbers of LAB tended to be higher in LP+EF-treated silage. Numbers of bacteria culturable on nutrient agar (NA) were similar among treatments. Yeasts and molds were not detected after ensiling. Inoculation of alfalfa silage with either inoculant increased ( P<0.1) DM intake by lambs in the digestibility study. Digestion of DM and OM in LP+EF silage did not differ from control silage, but they were increased ( P<0.05) in LP silage. Intake ( P<0.05) and digestion ( P<0.05) of nitrogen were greater in lambs fed LP+EF silage than in those fed the control silage. Inoculation with LP+EF increased ( P<0.05) DM intake, average daily gain (ADG) and feed efficiency of feedlot cattle as compared to control silage, whereas inoculant LP did not alter animal performance. Yeast populations were higher ( P<0.05) in LP silage after 2 days of exposure to air, but remained low (<10 2cf) in the other silages throughout the 15-day exposure period. After 13 days of aerobic exposure, bacterial populations were larger ( P<0.05) in control silage than in inoculated silages, and the increases ( P<0.05) in the pH and temperature of aerobically exposed control silage corresponded with the increase in bacterial population. Thus, it appeared that bacterial action apparently was primarily responsible for deterioration of alfalfa silage.