Auto Draft

The effects of reducing chop length

Reducing chop length:

• Increases the rate at which fermentation occurs;
• Reduces fermentation losses of DM and energy, and degradation the protein fraction;
• Increases the chances of a successful fermentation in forages with low WSC content;
• Increases amount of lactic acid produced in wilted silages;
• Can result in a lower silage pH;
• Reduces the volume of forage transported at harvest, and storage space required;
• Makes compaction of the forage in the silo easier; and
• Can increase effluent production in low DM content silages.

Silage intake by livestock has also been shown to increase with short versus long forage chop length in a number of studies. This is particularly so with sheep compared to cattle, and with young compared to older livestock. Increased voluntary intake improves animal production in almost all cases.

The effects of chop length on animal production are discussed in Chapters 13, Section 13.2.5; Chapter 14, Section 14.2.5; and Chapter 15, Section 15.2.5.

Losses

Even in well-managed systems, losses of DM and energy will occur during silage making, storage and feeding. The type and extent of the losses are influenced by a number of factors:

• Crop type and composition;
• Weather conditions;
• Silage system; and
• Management.

In practice, the most important factor influencing losses is management – poor management can substantially increase losses, greatly reducing the efficiency of the conservation process. There is often considerable debate concerning the level of losses that can occur during the ensiling process.

One source of confusion is whether the losses quoted are ‘typical’ losses observed onfarm or losses that occur with good management. Clearly, the on-farm losses are highly variable and reflect the standard of management.

So it is recommended that the latter be adopted as the benchmark that producers should target. This should also be the basis for any economic appraisal of silage, although a sensitivity analysis to determine the penalty of greater losses due to poor management can be very informative (see Chapter 11, Section 11.2.4).

As there are few Australian studies on losses occurring at various stages of the ensiling process, data from Europe and the United States have to be used.

Loss estimates vary considerably, and there is some concern as to whether DM losses have been over-estimated in some studies due to failure to adequately account for the volatile compounds in silage when calculating DM losses (see Chapter 12, Section 12.4.1).

The sources of DM and energy losses during the ensiling and feedout process are illustrated in Figure 2.12 and Table 2.6. The source of losses varies between silage systems and can be seen to be strongly influenced by wilting (see also Figure 2.13). The data in Figures 2.12 and 2.13 indicate that, with good management, it should be possible to keep DM losses to 12-16% in a wilted silage system.

In a direct-cut maize silage system, where field losses are minimal, DM losses should be kept to about 10%. With good management, quality losses during the ensiling process will be minimal.

With poor management, DM losses can be considerably higher than those illustrated, and silage quality will suffer. Energy losses are usually less than DM losses. This is because some of the fermentation products in silage have a higher energy value than the substrates from which they are produced and the gross energy content of silage is usually higher than that of the parent forage.

Energy losses at various stages of the ensiling process are listed in Table 2.6, and have been classified as unavoidable or avoidable. The avoidable categories can be eliminated with good management. According to this European work energy losses need be no higher than 7%.

Losses during the ensiling process The relative importance of field and storage losses varies with the degree of wilting and the DM content at ensiling (see Figures 2.12 and 2.13). Figure 2.13 shows the expected DM losses in the production of pasture silage, under Australian conditions, given good management.

The data in Figure 2.13 are a composite of results from various overseas studies – there are no Australian data, a deficiency that needs to be addressed in future research. Total losses are likely to be lowest in the DM range of 30-40% when rapid wilting is achieved.

Field and harvesting losses

Field losses include the DM lost during various mechanised operations in the field (mowing, tedding and raking), during harvest and transport to the storage site, and due to the activity of plant enzymes.

Table 2.7 outlines the various components of field losses. The extent of these losses and management strategies to reduce them are covered in more detail in Chapters 6 and 8.

Of the field losses in Table 2.7, the physical losses due to mechanical handling should be minimal, and will reflect the standard of management of the field and transport operations. Forage left in the paddock may be utilised with post-harvest grazing.

If grazing is an option, items 1, 4, 6 and 8 in Table 2.7 account for little loss to the system. Direct harvested crops, such as maize, have considerably lower field losses (<1%, see Figure 2.12) than wilted crops because there is less time for respiration and fewer handling operations.

Respiration and proteolysis can account for significant DM and quality losses, particularly during wilting (see Section 2.2.1). The quality losses will mean reduced forage digestibility and ME content and increased protein degradation.

Some respiratory loss during wilting is unavoidable, but can be minimised (to about 2%) by rapid wilting. As Figure 2.13 shows, field losses increase with forage DM content. The longer wilting period associated with higher DM content increases the susceptibility of thecrop to respiration losses.

At the same time the higher DM forage is susceptible to greater mechanical losses during various handling operations, particularly as DM content increases above 35 to 40%.

Storage losses

Table 2.8 summarises the sources of DM and quality losses during storage. They are:

• Effluent;
• Respiration and aerobic fermentation while oxygen remains in the silo or bale (or if the seal is damaged); and
• The silage fermentation.

These losses are strongly influenced by the DM content at which the forage is ensiled. The effluent losses decline rapidly as DM content increases to 30% (see Figure 2.2). Respiration and fermentation losses decline as DM content reaches 35-45% and then slowly increase (see Figure 2.13).

Effluent losses are influenced by forage DM content, chop length, and the degree of compaction or silage density. Some additives (e.g. molasses, acids and enzymes) will increase effluent production (see Chapter 7), but the most important factor is forage DM content at ensiling (see Section 2.1.1). Chapter 9 covers the effect of management on silage effluent production more fully.

As described in Section 2.2.1, losses due to respiration of WSC by plant enzymes and fermentation by aerobic microorganisms will continue until anaerobic conditions are achieved within the silo or bale. Heating of the freshly harvested forage in the silo or bale is an indication of respiratory losses.

Some heating and losses due to respiration are unavoidable (see Table 2.6).

Direct losses of WSC represent only part of the quality loss. Heat build-up within the silo or bale as a result of respiration can further reduce digestibility and damage to the protein fraction (see Section 2.2.1 and Chapter 12, Section 12.4.4).

Chapter 9, Section 9.4, covers management strategies to reduce these losses – rapid filling, good compaction or bale density, and effective sealing (without delay).

While oxygen is present during the early stages of the storage period, aerobic bacteria, yeasts and moulds will continue to grow. Where sealing is inadequate or the seal is damaged during storage, air entry will allow these organisms to grow. The growth of aerobic organisms will result in silage decay and the development of a surface waste layer, mouldy silage and pockets of rotten silage.

Some loss of DM and energy during the anaerobic fermentation of WSC to lactic acid and other products is unavoidable. However, if the fermentation is dominated by homofermentative LAB, the losses are small (see Appendix 2.A3). Higher losses will occur if heterofermentative LAB play a significant role in the fermentation.

The greatest fermentation losses will occur if clostridia or enterobacteria dominate the fermentation.

Feed-out losses

Losses during feedout have two sources – aerobic spoilage or heating, and wastage of silage by animals (see Table 2.9). Effective management of the feed-out process can avoid most of these losses. Once exposed to air, silage at or close to the feeding face commences to deteriorate as yeasts, moulds and aerobic bacteria become active.

Heating is usually the first noticeable sign of aerobic spoilage of the silage stack or bale (see Section 2.2.3). Chapter 10 covers more fully management strategies that reduce these losses.

Crop type, DM content, silage density, the type of fermentation, the quantity of residual spores present from the initial aerobic phase, ambient temperature during feeding, rate of feedout, and silage removal technique can all affect the stability of the silage after opening. Silage additives can influence aerobic stability (see Chapter 7, Section 7.7).

Wastage of silage during feedout is difficult to estimate and few studies have been conducted. In poorly managed feeding systems, wastage is likely to reach 30-50% of silage DM fed. These losses will be influenced by:

• Quantity of silage offered to livestock – if the silage is not consumed within a reasonable time then losses will increase (irregular feeding intervals or overfeeding should be avoided);
• Measures taken to prevent animals from walking, camping, urinating and defecating on the silage; and
• Wet weather (trampling losses are likely to be higher when silage is fed on the ground).

Animals are also likely to reject silage that is hot (aerobically spoiled), mouldy or rotten. These losses, resulting from rejection by animals, have been accounted for earlier as components of storage losses or aerobic spoilage.