New trends and opportunities in the development and use of inoculants for silage

Inoculants are used as silage additives to improve preservation efficiency and to enhance animal performance. In most commercially available inoculants, homofermentative lactic acid bacteria (LAB) have been used because they are fast and efficient producers of lactic acid, improving natural silage fermentation. Specific LAB inoculants may also have beneficial effects on animal performance even if there is no effect on fermentation. However, these types of inoculants are not always advantageous. They do not necessarily prevent secondary fermentation by clostridia in moist silages, and they sometimes impair the aerobic stability of grass and small grain silages, Therefore, new criteria for silage inoculants should be established which consider the specific needs of the crop being ensiled. New approaches which are being taken to develop improved inoculants for silage include the following: (1) using LAB isolates which are more specific to the target crops; (2) inclusion of heterofermentative LAB to produce volatile fatty acids to inhibit yeasts and moulds upon aerobic exposure; (3) inclusion of organisms other than LAB in inoculants to inhibit detrimental microorganisms; (4) selection or engineering of LAB strains to inhibit specific microorganisms; and (5) cloning and expression of genes which would enable selected LAB strains to utilize polysaccharides in crops which are low in soluble carbohydrates. Many of these new strategies for formulating inoculants are being tested, but further research is needed to determine the most successful approaches.