EPIPHYTIC LACTIC-ACID BACTERIA SUCCESSION DURING THE PRE-ENSILING AND ENSILING PERIODS OF ALFALFA AND MAIZE

Epiphytic lactic acid bacteria (LAB) succession during the pre-ensiling and ensiling periods were studied in 1989 for two cuttings of alfalfa (Medicago sativa L.), each harvested at three stages of maturity, and three whole-plant maize (Zea mays L.) hybrids. Twenty-three species and 306 strains were found. Epiphytic LAB counts were low and variable on the standing crops, particularly on alfalfa. Wilting increased LAB numbers slightly for alfalfa, but the chopping process increased the counts dramatically. Population shifts in LAB also took place during the pre-ensiling period. Lactobacillus plantarum, Pediococcus pentosaceus, Enterococcus faecium, and Ent. faecalis were predominant on both standing crops. Lactobacillus brevis dominated alfalfa at the second cutting, 10% bloom, but Lact. viridescens was predominant after chopping. The changes in LAB caused by wilting or chopping were reflected mainly in proportional changes of Lact. plantarum, Ped. pentosaceus, Ent. faecium and Ent. faecalis. Once the crops were ensiled, total LAB counts increased rapidly, reached a maximum within 1 d, and then declined after 7 d of fermentation. Enterococcus species decreased sharply or disappeared entirely after the early stages of the ensiling period, and the species most involved in microbial succession through day 7 were Lact. plantarum and Ped. pentosaceus. After 7 d, more species, e.g. Lact. homohiochii, Lact. brevis and Lact. gasseri, joined the succession and became prevalent, depending on the crop. Only two of the six alfalfa silages were well preserved, whereas all three maize hybrids underwent typical fermentations for this crop. No relationship was found between adequacy of silage fermentation and epiphytic LAB numbers or species on the pre-ensiled crops. Neither were pH changes during the fermentation explained by the epiphytic LAB count or population succession. Rather, the well fermented alfalfa silages were those ensiled at a high dry matter (DM) content (> 360 g/kg) and low buffering capacity (< 450 meq/kg of DM). Only a few of the LAB strains were shown to be the same among the crops, thus indicating the specificity of LAB strains to an ecological niche.