MICROBIOLOGICALLY FEED CONSERVATION: THE ROLE OF LACTIC ACID BACTERIA IN THE SILAGE FERMENTATION

Abstract

Silage is now the most common preserved cattle feed in many countries (Cai,
2001; McDonald, 1991). It is well established that lactic acid bacteria (LAB) play an
important role in silage fennentation. LAB is a major component of the microbial
flora which lives in various types of forage crops (Cai et al., 1994, 1998). The LAB
commonly grows with other plant-associated microorganisms during silage
fermentation, and they generally determine the fermentation characteristics of silage. Moist dairy farm silage is based on natural lactic acid fermentation (Cai and
Kuamai, 1994). The epiphytic LAB transforms the water-soluble carbohydrates into
organic acids during the ensiling process. As a result, the pH is reduced and the
forage is preserved. However, due to the low numbers of LAB, especially
lactobacilli present in forage, the amounts of lactic acid produced are usually not
suflicient to yield significantly low pH values, which allows the growth of clostridia
and results in poor quality silage (Cai, 1999, 2001). Therefore, it is necessary to use some bacterial inoculants to control microbes in silage fermentation. The addition of LAB inoculants at ensiling is intended to ensure rapid and vigorous fermentation that results in faster accumulation of lactic acid, lower pH values at earlier stages of ensiling, and inhibition of growth of some harmful bacteria (Cai et al., 1999a, 1999b; Zhang et al., 2000). In this paper, identification of LAB isolated from forage and their application for silage preparation, quality and aerobic stability of silage treated with lactobacilli, and development of a new method for preparation and conservation of tea grounds silage are described.