Silage Microbial Inoculants: Use in Hot Weather Conditions

IntrodUCtIon Ensiling is an ancient method used to preserve the nutritive value of forages by packing and storing forage in airtight conditions. Silage fermentation occurs naturally under anaerobic conditions (the absence of oxygen). Plants contain native lactic acid bacteria (LAB), and when silage is placed under anaerobic conditions, these LAB produce lactic acid, reducing the pH to a level in which other bacteria cannot survive. However, LAB are not the only microorganisms on plants. Bacteria like clostridia and enterobacteria, as well as yeast and molds, also are present on plants and compete with LAB for sugars. In addition, native LAB populations on plants are not the same from crop to crop. Native LAB levels are generally lower in alfalfa (Medicago sativa L., 10 colony forming units [cfu]/g fresh matter) and greater on perennial grasses (10 cfu/g fresh matter), corn (Zea mays L., 10 cfu/g fresh matter), and sorghum (Sorghum bicolor [L.] Moench, 10 cfu/g fresh matter) (Pahlow et al., 2003). Environmental conditions also have an effect on native LAB levels. Bacteria are more abundant in warmer than in cooler temperatures, with higher levels at certain maturity stages (Pahlow et al., 2003). In alfalfa, native LAB were higher in warmer temperatures, after a longer wilting time, and when rainfall occurred during wilting (Muck, 1989). Moreover, native LAB are low in the standing crop, increasing exponentially after chopping in both corn and alfalfa (Lin et al., 1992). Use of silage additives is recommended to preserve the nutritive value of the crop when circumstances could compromise proper fermentation (Contreras-Govea & Muck, 2006). Silage microbial inoculants are one type of available additive, and have been classified as stimulators of fermentation (Kung et al., 2003). These inoculants contain LAB that complement the native LAB population, helping to ensure a better fermentation (Muck, 2008; Contreras-Govea & Muck, 2006). The objective of this publication is to provide information about silage microbial inoculants, how they work, and the conditions under which they should be applied for better success in hot weather conditions.