In order to maintain a high feed value, avoid negative health effects and, therefore, not impair the animals´ performance, it is important to reduce spoilage during storage to a minimum.
The key contributors to spoilage of silage are putrefactive bacteria, yeasts and moulds. They are responsible for changes in colour, smell and consistency of the forage and cause energy and nutrient losses. As infected areas of the forage cannot be fed and may also lead to the loss of an entire forage batch, spoilage always results in forage losses.
These bacteria develop under aerobic conditions, when water and air is allowed in. Infested areas are therefore predominantly located under damaged film, and on the silo borders where the film does not seal the silo stock properly. Putrid silage has a greasy, manure-like consistence and musty smell.
Putrefactive bacteria may also cause a deterioration of the entire silage stock. It is especially at risk if it has already been destabilized due to other effects, such as clostridia. Furthermore, it causes high losses of energy and strong protein degradation.
Caution: areas of putrefaction must not be fed to animals.
Yeasts develop under aerobic and anaerobic conditions. They are especially risky for the aerobic stability of silages and may cause losses due to heat generation. Without oxygen, yeast ferments sugar to alcohol and proliferates only slightly.
Additionally, yeasts consume all energy-rich substances such as residual sugar, alcohol or lactic acid in the presence of oxygen. The decomposition of these substances to carbon dioxide and water results in a rapid and high temperature increase up to and above 50 °C, leading to high energy losses and possible protein degradation. This process is characterized by the smell of toasted bread and such silages are less palatable for animals. As rises in temperatures also promote mould growth, the risk that the entire batch of silage is spoilt is also increased.
Moulds are aerobic organisms, developing only in the presence of air and oxygen. Badly compacted forage layers or air penetration during storage or the feed-out phase promotes these fungi. As they decompose lactic acid, sugar and protein, they are unfavorable for the energy and nutrient content of the silage.
The presence of mycotoxins in fed silage is hazardous to animal health and can result in Diarrhea or abortion. Infected silage must be removed and not be fed to animals.
Energy Losses Due to Spoilage
The table below illustrates the impact of spoilage on energy content.
Energy losses during silage making
Source: Zimmer 1969 and Pahlow et. al. 2011
A certain percentage of energy loss is unavoidable – i.e. losses due to respiration after cutting, crumble losses and lactic fermentation. Such losses constitute a minimum of 5-6 % for silage making.
More interestingly, energy losses may increase up to 50 % under certain conditions. This is mainly caused by faulty fermentation and above all by spoilage due to aerobic transformation in the silo, and reheating, after feed has been removed.