Teagasc Directory of Silage Additives

Avoid Poor Preservation

Silage is preserved grass. Without good preservation you don't get silage but rather a heap of slowly decaying grass. Poor preservation leads to a reduction in silage digestibility (as the more digestible fractions of the crop are broken down) and a reduction in protein as the protein fraction is converted to ammonia in the silo. Intake will also be reduced resulting in an overall reduction in feeding value, which could require 2 - 3 kg of extra concentrates per day to replace.

Grass Ensilability

The essential factors in the silage making process are an adequate supply of fermentable sugars and anaerobic (air-free) conditions.

For good preservation the sugar content at harvesting should be above 2.5% and preferably up to 3.0% of the grass juice. Lactic acid bacteria can only convert sugar to lactic acid in the absence of air. Therefore, fast filling, good consolidation of the clamp and perfect sealing to maintain air-free conditions are all vital to promote rapid fermentation.

Other factors that contribute to ensilability are:

1. the dry matter content - high moisture levels make ensiling more difficult while wilting aids preservation,
2. high nitrogen applications, over 25 kg per hectare (100 units/acre) or late application, results in more difficult ensiling conditions,
3. contamination with slurry, clay or lime can upset the fermentation process.

Additive Use

The additive market is not as buoyant as it used to be. Changes in livestock farming and in silage making practices that have held to this situation are:

1. the introduction of REPS and higher payments for extensification which has led to farmers making silage from a heavier more mature crop;
2. better management of nitrogen application with a greater period allowed between application and harvesting;
3. with the pressure on contractors for more efficient systems the time taken to fill the pit has been reduced several-fold which has resulted in less respiration (wastage of sugars) and faster exclusion of air;
4. there are now a greater proportion of ryegrass swards being made into silage and these are easier to preserve than the old permanent pasture swards,
5. most grass is pre-mown before pick-up and the small amount of wilting that occurs will help preservation. Pre-mowing can also reduce contamination as there is less scalping of the ground and less "hovering" of clay and dust by the pick-up mechanism.

Despite the improvements in grass type and ensiling techniques there are still examples of poor preservation every year. In these cases the cost of using an additive is very small compared to the cost of lost production or the cost of compensating for poor feeding value by extra concentrates.

The decision on when to use an additive should be based on an assessment of ensilability and return on the investment. Ensilability can be assessed by the use of a refractometer to estimate sugar content or more accurately by sending grass samples to a laboratory for analysis of dry matter, sugar content, nitrates and buffering capacity. Sampling accuracy and speed of analysis are essential for good decision making. As an alternative to measurements, farmers and advisors can attempt to make a decision based on an assessment of the crop and ensiling factors that affect preservation as outlined above.

As a general guide:

1. Preservatives are recommended on leafy crops, harvested up to and at ear emergence, except in very dry weather or where an adequate wilt is achieved. Ryegrass swards are easier to preserve than old pastures.
2. Mature crops are likely to preserve well without additives, provided nitrogen levels and contamination do not interfere with fermentation.

Available Additives

The choice of additive depends on ensiling conditions and the use of forage, e.g. dairy cows in winter milk might benefit from an inoculant additive whereas suckler cows may not. The silage contractor in many cases has a major influence on the use and choice of additive.

1. Acids
   Under difficult ensiling conditions acids are the best choice as an aid to preservation. Apply at 2.3 to 3.5 litres per tonne of fresh grass.
2. Sugars
   Products containing soluble sugars, (molassed beet pulp, citrus pulp) provide extra sugar for fermentation and are effective when used at adequate rates and evenly applied.
3. Enzymes
   Additives containing fibrolytic enzymes provide additional sugar through the breakdown of grass fibre. Experiments have shown that enzyme based products can improve preservation but they may not be adequate under difficult ensiling conditions as sometimes occur in Ireland.
4. Bacterial Inoculants
   There is experimental evidence to show that inoculants can improve fermentation characteristics by speeding up the fall in pH and lowering ammonia levels in the silo.

However, the main claim for inoculants is that they give improved animal performance, even when silage is not perfectly preserved as measured by conventional laboratory tests. Animal production experiments at Grange and Hillsborough provide information on the enhanced feeding value effects of inoculants treated silages. A summary of the Grange experiments suggest that the response to inoculant treatment in economic terms is about break-even when treated silages are fed to beef cattle. The Hillsborough beef experiments indicate a carcase response of 60 grams per day to the use of inoculants. Therefore, over a 140 day finishing period this would result in 8.4 kg extra carcase per head at an estimated value of €21. The cost of treatment for 6 tonnes of silage (7 tonnes of grass) is about €11.

In some dairying experiments at Hillsborough, there was an average response of 1.3 kg milk per cow per day resulting from inoculant treatment. The trials indicate that the best return to inoculant use is got from Autumn or Winter calving cows where there is a relatively long silage feeding period.

Additives on Maize and Whole Crop Cereal Silages

With the expansion of maize and whole crops cereals for silage, a number of new products have become available to prevent heating after these silages are opened. There is a scarcity of independent research to show the effects of using these products in Irish conditions. Additives containing sulphite salts, potassium sorbate and bacteria such as Lactobacillus buchneri are used to inhibit mould growth.

For the 2002 Directory of Silage Additives, click here.