The effects of a combination of sodium benzoate, potassium sorbate, and sodium nitrite on the composition of the microbial community, fermentation, and aerobic stability of whole-plant corn silage and high moisture corn

Date
2018
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
During silage fermentation, lactic acid bacteria produce lactic acid that lowers the pH of the forage mass leading to a generalized inhibition of microbial activity when coupled with anaerobic conditions. If the pH is not low enough undesirable fermentations can occur. For example, yeasts can produce ethanol and decrease dry matter recovery, and enterobacteria can increase proteolysis, producing NH3-N. When silage is exposed to air, lactate-assimilating yeasts can initiate an aerobic spoilage process by oxidizing lactic acid and producing CO2, H2O, and heat. The degradation of lactic acid results in an increase in silage pH and allows the growth of aerobic bacteria and molds that furthers the spoilage process. Spoiled silage is undesirable because it is lower in nutritional value than fresh silage and when fed to cows, can affect animal intake, production, and health. Various silage additives have been evaluated to improve the aerobic stability of silages. Specifically, the use of chemical additives may be warranted especially for silage produced under challenging conditions such as short-term ensiling, air-stress during storage, and warm temperatures at feed-out, or to overcome the risks brought by the high numbers of yeasts present in silage. Although it is assumed that such silage additives exert their effect by altering the microbial communities in silage, the types of microorganisms that are impacted positively or negatively by the additives are usually not known. Such knowledge would be important for attempts at improving additives or even developing novel additives. High-throughput sequencing (HTS) is a useful tool to analyze microbial communities because it enables the identification of unculturable, new and low-abundance microorganisms. Therefore, the objective of this study was to evaluate the effects of a chemical additive containing sodium benzoate, potassium sorbate, and sodium nitrite on the composition of the microbial community of corn silage and high moisture corn by HTS, and to analyze its ability to improve fermentation and aerobic stability under challenging conditions in North America. The effects of the additive were tested in a total mixed ration made with corn silage treated before or after ensiling (Experiment 1, Chapter 2), in corn silage ensiled for short-periods (Experiment 2, Chapter 3), in corn silage subjected to air-stress during storage (Experiment 3, Chapter 4), and in high moisture corn subjected to air-stress during storage and warm temperatures at feed-out (Experiment 4, Chapter 5). Microbial and chemical attributes of the ensiled materials were analyzed with respect to the chemical composition, concentration of organic acids and alcohols, and numbers of lactic acid bacteria, yeast, and molds. The aerobic stability of the silages was also determined. The composition of the bacterial and fungal communities was analyzed by sequencing of the ITS1 region present in fungi and the V4-V5 region of the 16S rRNA gene present in bacteria. In Experiment 1, the additive not only reduced the total numbers of yeasts in silage but also reduced the relative abundance of the lactating-assimilating yeasts Candida tropicalis, greatly improving aerobic stability. The additive was also useful in improving the stability of the total mixed rations when applied to the silage before or after ensiling. In Experiment 2, the additive reduced the concentration of NH3-N and markedly improved the stability of corn silage after short periods of storage (1 and 4 d), probably due to fungistatic (rather than fungicidal) effects. In Experiment 3, in corn silage stored for 63 d, the additive reduced the concentration of NH3-N. The low dose of the additive did not reduce the total numbers of yeasts, but markedly improved aerobic stability. In non-air-stressed silos, the additive reduced the relative abundance of the lactate-assimilating yeasts Candida tropicalis. In air-stressed silos, it overcame the effects of air by inhibiting specific microorganisms that were stimulated by oxygen, such as Pichia. In Experiment 4, the additive reduced the relative abundance of Enterobacteriales and decreased proteolysis in high moisture corn. Moreover, it reduced the numbers of yeasts and lowered the ethanol production, increased dry matter recovery, and markedly improved the aerobic stability, overcoming the adverse effects of air-stress during storage and high temperatures at feed-out. Overall, the effects of the additive on the numbers of yeasts varied among experiments. Still, the additive improved aerobic stability in all Experiments. Therefore, the additive containing sodium benzoate, potassium sorbate, and sodium nitrite has the potential to be applied to improve the aerobic stability of total mixed rations, of corn silage that must be fed very soon after ensiling, of corn silage subjected to air-stress during storage, and of high moisture corn challenged with air during storage and that needs to be fed during warm days.
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Keywords
Biological sciences, Health and environmental sciences, Chemical additive, Forage, High-throughput sequencing
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