SILAGE MAKING PROCESS,SILAGE FERMENTATION AND ADDITIVES : ______________________________________________________ Common end products of Silage fermentation and their significance. • Ph : Has a positive effect. Low Ph inhibits bacterial activity. • Lactic acid : Has a positive effect, inhibits bacterial activity by lowering Ph. • Acetic acid : Negative effect, associated with undesirable fermentations. • Positive effect also by inhibiting yeasts that cause aerobic spoilage. • Butyric acid : Negative effect, associated with protein degradation,toxin formation and large losses of of DM and energy. • Ethanol : Indicator of undesirable yeast fermentation and high DM losses. • Ammonia : High levels indicate excessive protein breakdown. • Acid detegent insoluble nitrogen : High levels indicate heat damaged protein and low energy content. Table 4. Bellow shows Predominant fermentation pathways in silage. Type of fermentation : 1.Homolactic (glucose). End product—Lactic acid. Theoretical DM recovery (%) --- 100 % Theoretical energy recovery (%) --- 99 % 2.Heterolactic (glucose). End product—Lactic acid,ethanol,CO2. Theoretical DM recovery (%) --- 76 % Theoretical energy recovery (%) --- 98 % 3.Heterolactic (Fructose). End product—Lactic acid,acetate,mannitol,CO2. Theoretical DM recovery (%) --- 95 % Theoretical energy recovery (%) --- 99 % 4.Yeast (Glucose). End product—Ethanol,CO2. Theoretical DM recovery (%) --- 51 % Theoretical energy recovery (%) --- 99 % 5.Clostridia (Glucoseand lactate). End product—Buytric acid,CO2. Theoretical DM recovery (%) --- 49 % Theoretical energy recovery (%) --- 82 % ORGANISMS: Because forage often naturally contains many detrimental types of bacteria, the purpose of adding a microbial inoculant to silage is to add fast growing homofermentative lactic acid bacteria in order to dominate the fermentation, resulting in a higher quality silage. Some of the more common homolactic acid bacteria used in silage inoculants include Lactobacillus plantarum, L. acidophilus, Pediococcus acidilactici, P. pentacaceus and Enterococcus faecium. Microbial inoculants contain one or more of these bacteria which have been selected for their ability to dominate the fermentation. The rationale for multiple organisms comes from potential synergistic actions. For example, growth rate is faster in Enterococcus > Pediococcus > Lactobacillus. Some Pediococcus strains are more tolerant of high DM conditions than are Lactobacillus and have a wider range of optimal temperature and pH for growth (they grow better in cool conditions found in late fall and early spring). Table 5 lists several common and one experimental microbe that have been studied as silage inoculants. Table 5. Bellow shows Some of the common bacteria used as silage inoculants and some reasons for their use : • Lactobacillus plantarum--- ----- Lactic acid bacteria,homolactic---helps rapid production of lactic acid and relatively acid tolerant. • Pediococcus acidlactici, cervisiae--- Lactic acid bacteria,homolactic--- helps rapid production of lactic acid and faster growing than Lactobacillus,some strains show good growth at cooler temepratures,some strains have have good osmo tolerance. • Enterocoocus faecium----------- Lactic acid bacteria,homolactic------ helps rapid production of lactic acid and faster growing than Lactobacillus. • Propionibacterium shermanii, jensenii ----------Propionibacteria------ Propionic and acetic acids,CO2. FERMENTATION AND ANIMAL RESPONSES: Alfalfa, grass, and small cereal grain crops have responded well to microbial inoculation with homofermentative LAB. The fermentation of high moisture corn has also been improved with homofermentative LAB. However, microbial inoculation of corn silage has resulted in less consistent results. When compared to untreated silages, silages treated with adequate numbers of a viable homofermentative LAB should be lower in pH, acetic acid, butyric acid and ammonia-N, but higher in lactic acid content (Table 6). It is reported that microbial inoculation lowered pH, improved the lactic:acetic ratio, and lowered ammonia-N content in more than 60% of studies. Dry matter recovery was improved in 35% of the studies. Dry matter digestibility was also improved in about one third of the cases. Microbial inoculation usually has little or no effect on the fiber content of silages because most lactic acid bacteria have little or no ability to degrade plant cell walls. Decreases in fiber content may be due to partial acid hydrolysis of hemicellulose. Some data suggest that certain microbial inoculants can increase fiber digestion. Bunk life or aerobic stability was improved in only 33% of the studies and in fact inoculation with homofermentative LAB has, in many instances, made aerobic stability worse. This is probably due to a lower content of acetic acid and other potential antifungal end products. This finding is extremely ironic because many producers buy microbial inoculants because they perceive an improvement in aerobic stability. Silage treated with homofermentative LAB can be extremely stable if feeding and silo management is good. There is high positive correlation to microbial inoculants on intake, gain, and milk production (Table 7). Although literature summaries are encouraging, caution should be used when interpreting such data because all inoculants are not equal and the conditions (e.g. rate of application, inoculant viability, species of bacteria, crop, moisture levels) varied markedly among the studies. As many have pointed out in the past, products with organisms with the same name are not necessarily the same organism and may not have the same effectiveness. For example, it is reported that various strains of homofermentative LAB improved silage fermentation but animal performance was improved by only one strain. Table 6. Bellow shows Theoretical effect of adding a microbial inoculant containing homofermentative lactic acid bacteria on the end products of silage fermentation. • DM recovery-------------------------------- ---------Greater recovery • Rate of pH decline and final pH ---------------- Faster decline and lower final pH • Ammonia nitrogen ------------------------------------Lower content • Lactic acid --------------------------------------------- Greater content • Acetic acid ------------------------------------------------Lower content • Butyric acid -----------------------------------------------Lower content • Ethanol ----------------------------------------------------Lower content • Fiber (NDF/ADF) ------------------------------------------No change • Digestibility ------------------------------------------------ Increased • Animal performance --------------------------------------Increased Unfortunately, there is no good way to predict the effectiveness of microbial inoculants. A model developed by Pitt suggested that inoculants would be most effective on alfalfa during cool conditions of first, third and fourth cuttings. However, there are numerous products with little or no research to support claims of improved fermentation or animal performance. Another factor which complicates the evaluating process is that the majority of bacterial inoculants are repackaged for distribution under private label and numbers of bacteria may be low and/or other additives (e.g., enzymes, fermentation extracts, minerals) are included in the formulations. (To be contd)
Posted on: Sat, 24 Jan 2015 12:45:27 +0000
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