Baling the silage
Introduction
Fermentation losses of Dry Matter (DM) content and energy, and degradation of protein can be substantial.
Clostridial silages have a rancid odour and are unpalatable to livestock. If anaerobic yeasts are present in the forage they will ferment Water Soluble Carbohydrate (WSC) to ethanol.
DM is lost due to the production of carbon dioxide, but the loss of energy is not significant.
Growth of yeasts is undesirable because they deplete WSCs that would otherwise be available for Lactic Acid Bacteria (LAB). Other yeasts present break down lactic acid produced by the LAB.
Remember, the ideal pH of a silage is heavily influenced by the DM content of the forage. Where DM content is high, the fermentation is inhibited, resulting in higher pH values and the quantity of fermentation end products is lower.
The quality of the silage fermentation directly affects the production from animals fed that silage. Some examples of poorly fermented silages are given in Table 2.4. The level of ammonia-N (as a % of total nitrogen) in conjunction with pH are good indicators of silage fermentation quality .
Without supplementation, poorly fermented silages will only support relatively low rates of production compared to well-preserved silages (see Table 2.5).
Once the fermentation phase is completed, the silage then enters a stable phase. Provided that oxygen is excluded, there will be little or no change to a lactate silage during this period.
Feed-out phase
When silage is exposed to air, aerobic organisms that have been dormant during the anaerobic phase multiply (see below). Their activity will eventually decompose the silage. The first sign that aerobic spoilage has begun is heating of the silage at the feeding face.
Experiments with silages undergoing aerobic spoilage have shown that the temperature may rise to 50°C or higher. A laboratory test would also show a rise in the pH.
This process is sometimes incorrectly referred to as ‘secondary fermentation’. In fact, it is an aerobic process, more correctly referred to as ‘aerobic deterioration’ or ‘aerobic spoilage’.
The substrates used early in the aerobic spoilage process are lactic and acetic acid, and any residual WSCs. Their relative importance as substrates depends on the type of fermentation. Unfermented WSC levels are usually higher in wilted silages where fermentation has been inhibited.
Figure 2.9 shows the relationship between wilting, residual WSC in the silage and aerobic stability (time taken to commence heating). The breakdown of proteins and amino acids to ammonia also contributes to a pH rise.
The main organisms involved in aerobic spoilage are listed on this page. It is interesting to note that some strains of LAB are able to ferment lactic acid under aerobic conditions and may play a role in the aerobic spoilage process.
Later in the aerobic spoilage process mould activity breaks down and metabolises cellulose and other plant cell wall components.
