Silage Additives | Silage Inoculants

Making silage enables the farmer to store forage, providing a cost effective feed when required. From silage making through to feeding out, the challenge is to ensure that valuable dry matter, energy and protein are not lost. 

An effective silage additive helps to drive fermentation in the right direction, preventing undesirable microbes from robbing valuable protein and energy resources from the ensiled forage.  

Even the best selection of silage additive cannot replace getting the fundamentals of silage making right.

Most silage inoculants are lactic acid bacteria (LAB). Some products contain only homofermentative strains or heterofermentative strains while others are a combination of both types of LAB. 

Homofermentative bacteria such as Lactobacillus plantarum, Pediococcus, Enterococcus and Lactococcus enhance the production of lactic acid, which lead to a faster drop in pH value and improved fermentation, thus reducing DM losses, protein breakdown and growth of undesirable microorganisms. 

Heterofermentative bacteria such as Lactobacillus brevis, L. kefiri and L. buchneri convert forage sugars to lactic and acetic acid. The production of acetic acid will improve aerobic stability of the silage by preventing proliferation of undesirable yeast and mold keeping silage highly nutrient and hygienic.   

In grass silage, the main challenge is acidification—in which case an adequate amount of homofermentative lactic acid bacteria (LAB) should be applied. A combination of homo- and heterofermentative lactic acid bacteria guarantees not only optimal fermentation but also enhanced aerobic stability.  

Silage inoculants are generally applied as the forage is being picked-up or baled, using a specific applicator. While the forage will already have a range of naturally occurring bacteria on them including lactic acid bacteria species, the microbial community present may not drive optimum fermentation and may even have high levels of detrimental bacteria.  

The aim with an inoculant is to supply a sufficient amount of selected strains with known effects on fermentation to help ensure that fermentation proceeds rapidly and in the right direction. 

The rate of 100 000 (1 x 105) colony forming units (cfu) per gram of fresh forage will provide enough microorganisms to dominate fermentation. If a silage inoculant has a lower level than this, or does not even specify a cfu count, then there may be insufficient bacteria to really influence silage fermentation in positive way. 

Be aware that not all inoculant bacteria are equal. Even within the same species, there is wide variation in what effect the bacteria will have on fermentation. Products and the published evidence of efficacy should specify the actual strain numbers to provide assurance to customers. 

Quality of the packaging and storage conditions are also important. These should prevent exposure to oxygen, moisture and heat that could reduce the viability of bacteria. Follow manufacturer instructions on storage and use and ensure that application is even and comprehensive over the whole forage.

The use of organic acids such as propionic and formic acids are aimed at lowering the silage pH to make it less favorable for undesirable bacteria such as Clostridia. Other organic acids and their salts including potassium sorbate and sodium benzoate target the growth of yeasts and mold fungi either in fermentation or during feed out.  

There needs to be sufficient amount of the additive to provide a concentration in the bulk forage that will actually be sufficient effect on the growth of those undesirable organisms. That rate is typically at 5 to 10 kg of active ingredient per ton of forage to preserve the silage or around 1 to 2.5 kg/ton to restrict yeast amount at feed out. Compare those values to what is actually contained in a product that claim a preserving affect. 

At the lower inclusion rate (less than 5 kg/ton of active ingredient), organic acids do not provide full preservation. To ensure adequate fermentation it is advisable to use silage inoculants. Bear in mind that organic acids and silage inoculants cannot be mixed together.  

The aim of adding enzymes to silage is usually to aid the breakdown of plant cell walls (e.g. use of celluloses and hemi-celluloses). The main benefit of this appears to be an increase in the amount of sugars available for LAB bacteria to convert to lactic acid for more rapid acidification.  

While there is some evidence of favorable outcomes of this on silage quality and animal production this is less reliable than general silage inoculant approach. In some cases, there are claims of increasing forage digestibility for livestock but evidence for this is less clear. There are also some enzymes aimed at improving starch availability for either bacteria or livestock but research on this is still at an early stage. 

Literature

Kung, L., 1998. A review on silage additives and enzymes. Proc. 59th Minneapolis Nut. Conf. (pp. 121-135). 
Kung, L., 2001. Silage fermentation and additives. Sci. and Tech. in the Feed Ind., 17, pp.145-159. 
Muck et al., 2018. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 101(5): 3980-4000.