First Impressions
The overall quality of finished silage can be rapidly assessed by noting color and odor. A pleasant, fruity odor and an appealing golden brown or greenish yellow color is often considered to be a more reliable indicator of silage quality than a series of chemical measurements. Good silage should keep for years in anaerobic conditions and is generally very well liked by livestock because fermentation produces a mild acidic taste and that pleasant aroma.
From a chemical standpoint, very good silage is free from butyric acid, mold, and sliminess. Poorly made silage, in contrast, will result in high levels of waste since it is unpalatable and likely to be refused. Spoiled and poorly fermented silage can also make livestock ill. Harmful microorganisms like listeria, botulism, and clostridia are common in soil and can be picked up during harvest. Proper fermentation and storage will prevent these bacteria from multiplying.
Monitoring Acids and pH
Good quality finished silage will have a pH close to 4.7 in legume and grass silages, while corn silage will typically be more acidic, around 4.0. Legume and grass silage should have a lactic acid concentration of 7-8%, while ammoniacal nitrogen should be less than 12% of the total nitrogen in grass and legumes. Corn silage should have lower levels of ammoniacal nitrogen typically between 5% and 7% and will contain 1%-2% lactic acid.
It’s important to understand that the pH of silage is a basic measure of its acidity, but that particular measure can be significantly affected by the buffering capability of the crop. Buffering refers to a material’s ability to resist changes in pH. For example, different silage samples may have the same pH while their acid concentrations differ. Fresh legumes have a higher buffering capacity than fresh grasses or corn, which means that they require higher concentrations of acid to reach their target pH.
Corn silage, on the other hand, with a relatively low buffering capability, typically reflects lower pH than other types of silage, even with comparable acid concentrations. For that reason, dairy cattle fed corn silage are often supplemented with sodium bicarbonate prior to feeding to help buffer the rumen pH, which helps to achieve complete digestion. Some studies have indicated that a similar supplementation practice for feeding beef cattle increases gain rates in young steers.
When pH is Too High
Exposure to air can result in higher than normal pH values, resulting in spoilage. Higher pH is caused by the growth of ammonia-producing yeasts that feed on lactates. Ammonia is alkaline and raises the pH of the silage, encouraging microbial growth and spoilage. This spoilage is exacerbated by warm weather.
Other causes of abnormally high pH include incomplete fermentation which may be caused by ensiling when DM is too high. This may be a result of a delay between sampling time and harvest, and slow or poor packing. Regardless of the cause, silage with a high pH from restricted fermentation cannot inhibit secondary microbial growth and is therefore unstable when exposed to air.
Silage with excess ammonia or urea will buffer the pH and keep acidity high, while high levels of clostridial bacteria consume lactic acid and produce weaker butyric acid, raising the pH. Butyric acid also generates offensive odors in the silage and can lead to metabolic problems in livestock.
Lactic Acid
Lactic acid should be the dominant acid produced during the fermentation process of silage. It’s
10-12% stronger than any other major acids found in silage and contributes the most to the decline in pH. Many studies support inoculating fresh forage during the ensiling process in order to ensure that lactic acid producing bacteria rapidly gains the upper hand in the fermentation process. This reduces silage pH and reduces the activity of microorganisms that cause spoilage.
Acetic Acid
Acetic acid should represent the second highest concentration in quality silage. Appropriate levels of this acid inhibit fungi such as yeasts and molds, improving stability when the finished silage is exposed to air. Too much acetic acid, on the other hand, indicates inefficient fermentation resulting in a loss of energy and nutrients, and the product may have high levels of ammonia.
Butyric Acid
The presence of butyric acid in a finished silage indicates a poorly fermented silage. It indicates the presence of active clostridial bacteria, which leads to losses in DM. High levels of butyric acid emit unpalatable odors similar to rancid butter or human vomit, which may trigger feeding issues.
Alcohols
Ethanol in low concentrations in silage (less than 3-4%) isn’t necessarily a problem for ruminants, where it is converted to acetic acid or directly absorbed by the rumen wall, where it’s available to fuel the metabolism and growth. However, higher levels of ethanol may indicate high yeast populations which can cause silage to spoil rapidly when exposed to air. High levels of ethanol may also cause milk to have an “off flavor.”
Yeasts and Molds
Mycotoxins are produced by a wide range of molds which can be introduced to silage directly by infected crops in the field or carried in by air. Mycotoxins can cause a variety of adverse health effects and pose a serious health threat to both humans and livestock. The adverse health effects of mycotoxins in humans range from acute poisoning to long-term effects such as immune deficiency and cancer. In livestock, mycotoxins can produce toxic effects, such as reduced feed intake and milk production, reproductive problems, and immunosuppression. Death can occur when animals are fed mycotoxin-contaminated diets
Obviously The presence of mycotoxins in silage represents a serious problem. The growth of problematic fungi should be minimized both before and after ensiling. Certain chemical additives or microbial inoculants can reduce contaminations, while careful management during harvest and ensiling can significantly reduce contamination.
During harvest, cutting heights should be set high enough to minimize soil contamination, and the crop should be ensiled immediately to minimize exposure to conditions favorable to fungal growth. During ensiling, the forage should be densely compacted and carefully sealed to minimize oxygen within the clamp. Special care should be taken to compacting and maintaining pressure on the top and shoulders of the silo, which are more prone to oxygen infiltration.
The feed-out stage obviously exposes the silo face to air, and care should be taken to maintain a straight, solid face, while feeding it out at a minimum of 4-6 inches per day to minimize oxygen incursion into the mass. Silage should be fed immediately after removal.
While it’s not possible to completely control exposure to mycotoxins prior to ensiling, good management at all stages of silage production and feeding are essential to reduce the risk of dangerous mycotoxins
