Silaging, also known as ensiling, is used by farmers all over the world to preserve forage. It is a common technique based on anaerobic (without oxygen) fermentation. Harvested forage is wilted—especially if it is low in dry matter content and chopped before being compacted and stored in silos, bunkers or other types of enclosed environments. These are covered and made airtight to prevent oxygen getting in, providing the ideal conditions for anaerobic fermentation.
At the start of the fermentation process, the forage is still a living material with plant cell respiration occurring. Also, the crop is covered with microbes. Most microbes are Gram-negative, aerobic (oxygen needing) species with fewer anaerobic species present. When residual plant respiration and the metabolism of microorganisms depletes the remaining oxygen from the forage, anaerobic conditions are created and the fermentation process can start.
For effective fermentation, the aerobic microbes need to be replaced with anaerobic, Gram-positive, lactic acid producing bacteria. This can be achieved by adding bacteria capable of dominating the entire process with minimal nutrient losses. Such bacteria are present in Biomin® Biostabil products. Biomin® Biostabil Maize should be used on corn based forage crops, and Biomin® Biostabil Plus should be used for grass, alfalfa and clover based crops.
With feed costs accounting for 50% to 70% of dairy farm inputs, and forage accounting for 40% to 60% of the ration, it is vital to ensure the quality of the forage produced on farm. There are many sources of spoilage which we will explore further here.
The optimum ensiling process should deliver a quick drop in the pH without a significant increase in temperature. A slight increase up to 37°C is accepted at the beginning of the process when the plant is still respiring, but prolonged and elevated temperatures cause significant loss of nutrients from the ensiled material. However, in warm climates, an elevated temperature may persist in the silage for several months.
An increase in the temperature of the silage results in 1) a loss of energy through CO2 loss, 2) a decrease in nutrient availability, and 3) a decrease in the palatability of the silage material that diminishes intake by animals.
2. pH levels
Heterofermentative lactic acid bacteria (e.g. L. kefiri, L. brevis, and L. buchneri) produce lactic acid and acetic acid within a month of ensiling. Higher pH levels create an environment that promotes the growth of spoilage bacteria and molds, thereby heightening the risk of mycotoxin contamination occurring. Applied fermentation bacteria (e.g. L. plantarum and L. brevis) utilize plant sugars to produce lactic acids within the first 1-2 weeks that stabilize silage at a terminal pH. In turn, this lower pH inhibits spoilage microorganisms that are sensitive to low pH levels. Once a clump or silo is opened, the lactic acid present in the silage would be consumed by aerobic yeast—were it not for the acetic acid which acts as a growth inhibitor.
The negative effect of yeast in silage is often underestimated. Yeasts thrive in both the aerobic and anaerobic phases of silage production. Weather conditions at harvest have a dramatic effect on the number of yeast on fresh forage. Those present at harvest requiring oxygen for respiration will be reduced by the anaerobic phase during storage, and will also be present during feed out at the end of the process. The yeasts are 90% sugar utilizers as well as 90% acid utilizers. The sugar-utilizing yeasts dominate at the beginning of the process during the aerobic ensiling and storage phases. The acid-utilizing yeasts dominate during the feed out phase and are responsible for the aerobic deterioration of the silage. Their activity results in an increase in temperature, reduction of fermentation acids, and elevation of silage pH (Table 1).
Table 1. Negative effects of yeast in the aerobic and anaerobic phases of silage production.
The negative impact of yeast can be reduced by having a proper dry matter content at harvest, cut length, good compaction at storage, and proper feed out methods.
The use of silage inoculants containing heterofermentative strains such as L. kefiri and L. brevis as contained in Biomin® Biostabil will produce a small amount of acetic acid during fermentation, therefore inhibiting the yeast.
In high moisture material, the biggest enemy is Clostridia; an anaerobic endospore-forming bacteria. During harvesting and ensiling, Clostridia contaminates the crops and enters the silage bunkers and pits via either 1) manure from fertilized fields or 2) the soil (e.g. from rain splashing during wilting, loose soil released by machinery).
Clostridia grows only in anaerobic conditions, fermenting sugar, protein and amino acids into butyric acid and ammonia as well as toxic amines. The products of clostridial fermentation are responsible for depressed feed intake, increased risk of ketosis, hemorrhagic bowel syndrome (HBS), and sudden death of animals. Feeding silage with elevated levels of butyric acid should be avoided, especially for cattle at sensitive stages e.g. early lactation.
An efficient and quick reduction of the pH during ensiling will prevent the growth of Clostridia. It has also been proven that lactic acid producing bacteria, such as L. brevis as found in Biomin® Biostabil, can inhibit butyric acid formation in ensiled material.
70-90% of molds and fungal origin mycotoxins are present on the plants at the time of harvest and enter the clamps and silos with harvested material. They enter growing plants through the roots during the seedling stage, travel down through either the silk channels during pollination or through plant wounds from environmental or insect injury. Field fungi (e.g. Aspergillus and Fusarium spp.) are capable of producing mycotoxins, including aflatoxin, deoxynivalenol (vomitoxin), fumonisin, zearalenone and T-2 toxin, which will cause health problems when fed to animals. None of the silage additives or inoculants available on the market today are able to degrade field origin mycotoxins as they are resistant to low pH and anaerobic conditions.
In aerobically challenged silages, fungi that have developed during the storage phase will start to produce additional so called ‘silage born’ toxins when they are exposed to the air during feed out.
Penicillium spp. which are typically bluish-green in color and their toxins (e.g. PR toxin, patulin, citrinin, mycophenolic acid and roquefortine C) are of greatest concern in ensiled forages. It is recommended to screen silage in a lab for mycotoxin contamination on a regular basis, or at least each time there is a reduction in feed intake. Once mycotoxins are detected, or are highly suspected from fungi identification, the ration should be supplemented with Mycofix® Plus. For more information and technical support for your forage production, please contact your local BIOMIN representative.