The type of silage fermentation and the endpoints of that fermentation are dependent on many factors including – the organisms that are present to undertake the fermentation, the amount of sugar that is available for the fermentation, the aerobic nature/oxygen level of the silage, the ambient temperature, the dry matter and buffering capacity of the silage and the treatment type of the silage.
Historical advice has always been to compact the silage at ensiling as much as possible to remove the maximum amount of air from the silage to speed up the process of anaerobiosis, the conversion of air to carbon dioxide in the bunker/pile.
Silage made below 30% dry matter (DM) will produce effluent. The amount of effluent that is produced is directly associated to the actual DM. Certain factors play a role into how much effluent is produced: silage dampness, short chop length, acidic treatments used elevate production compared to an inoculant; and silage compaction.
Silage is like a sponge – in many ways it contains countless tiny ‘pores’ that are normally filled with either oxygen or carbon dioxide. When the forage is very wet, these pores can become filled with effluent which displaces the gas. When this occurs the organisms that are capable of growing change from the desirable lactic acid bacteria to Clostridia.
In desirable fermentation, lactic acid bacteria convert sugar to lactic acid, rapidly and efficiently dropping the pH of the forage to produce palatable, nutritious silage.
There are 2 types of Clostridial fermentation that occur in silage. Initially Clostridia convert plant sugar to butyric acid at the same time as the desirable bacteria are producing lactic acid, making the initial pH fall. Once the sugar has been used, Clostridia start to convert lactic acid to butyric acid, resulting in a rise of pH, very significant energy, digestibility and DM loss, also highly unpalatable silage. In the worst cases of Clostridial growth, biogenic amines are produced and the silage becomes unusable.
Clostridia are inhibited by rapidly achieving a pH of below 5 and not filling the ‘pores’ with effluent. This means that when producing low dry matter silage, the chop length of the silage should be raised, the silage should not be compacted as greatly, and, with baled silage, it is crucial that the bales are stored upright and not stacked as to stop moisture collecting at the base of the bale and producing a bale with two very separate feed values.
Low dry matter forage, below 28%, will produce effluent irrespective of the forage system that is used to manage it, and this effluent inhibits the effective fermentation of the ensiled forage. When the climate is cold, the fermentation is further impacted as the spoilage organisms contaminating the forage are generally found primarily in the soil and are more acclimatized to growing in cold conditions (below 10C) than the naturally occurring lactic acid bacteria.
When ensiling low dry matter corn below 30% DM, there is little value in kernel processing as digestibility is not improved but the level of effluent produced is increased. Equally, when harvesting low DM, it is important to use longer chop length to reduce the volume of effluent being produced and to raise the cut height of the forager (toward 45cm) to not ensile the most heavily spoilage organism-contaminated forage.
Key Points on Ensiling Low Dry Matter Corn under cooler temperatures
- Raise cut height – reduces soil contamination of corn stalk and the presence of Clostridia
- Increase chop length to 13 – 15mm or longer – reduces the volume of effluent produced
- Don’t kernel process – below 30% DM there is no benefit in starch/kernel digestibility achieved through kernel processing, however the volume of effluent produced dramatically rises when low DM (<30%) corn is kernel processed
- Don’t excessively compact – Reducing the degree of normal compaction to the bunker reduces the volume of effluent production. DO NOT USE TRAIN WHEEL COMPACTORS/DO NOT STACK BALES.
- Consider increasing inclusion rate of Sil-All 4X4+ to help overcome difficult conditions and increase the speed of fermentation.
Effluent and Compaction
Effluent will naturally form a saturated layer of silage which will have a significantly different fermentation profile and intake characteristics. Clostridial silage will be of lower feed value, significantly less palatable and lower intake.
When practical, the Clostridial-fermented silage should be fed specifically to heifers and dry animals. Palatability issues can be slightly overcome by the inclusion of aromatic chemicals: aniseed or citric flavorings, but the farm must be sure that the only issue present within the silage is the Clostridial fermentation and that mycotoxins are not present.
Key Points on Ensiling Low Dry Matter Grass
- Ensure a minimum cut height of 10cm to reduce the level of Clostridia
- Use a high specification inoculant such as Sil-All 4X4+. Low DM silage requires more acid to lower the pH and the acid must be made rapidly before the effluent fills the pore spaces
- Extend the chop length of the grass to reduce effluent
- Ensure the forager blades are sharp to provide a clean cut and reduce effluent production
- Do not over-compact the forage by targeting a relatively low density
- Ensure best possible sealing of the bunker