21 November 1997



The main reason for using a

silage additive should be its

proven ability to increase

animal performance, be it

milk production or

liveweight gain.

Jessica Buss reports

PRODUCERS are paid for animal product and not improvements in silage fermentation.

Lower milk prices and meat values make it uneconomic to use a forage additive just to improve fermentation, or as an insurance policy, so additives must be guaranteed to lift animal performance.

So warns Tim Keady, researcher at the Agricultural Research Institute of Northern Ireland, Hillsborough.

Unless an additive is backed by evidence of improvements in animal performance, dont use it. "And it is pointless to use an additive for suckler cows or stores as the value of improvement in animal performance will not cover the cost of the product," he says.

In studies at Hillsborough, Dr Keady has found that animal performance is only improved by formic acid under difficult harvesting conditions – when the silage would preserve badly without additive treatment. Use of effective inoculants has, however, been shown to increase animal performance of beef and dairy cattle across a wide range of conditions. Other additives he tested improved fermentation without improving animal performance.

Evidence supports use of formic acid in difficult ensiling conditions, and in such circumstances it improves the performance of finishing beef cattle and lactating dairy cows, says Dr Keady.

But when the silage would preserve well without additive, in moderate to easy ensiling conditions, formic acid is unlikely to result in an economic response, he says.

Use of an effective inoculant should increase performance of beef and dairy cattle. In the industry it has often been claimed that inoculant treatment will make a good silage better. However, results from recent experiments feeding inoculant treated silage to beef cattle, where the untreated silage was poorly preserved, showed increases in animal performance without having an effect on fermentation at the time of feedout.

"Inoculant treatment lifted carcass gain by 14% compared with the untreated, poorly fermented silage. This was similar to the improvement in carcass gain seen from the formic acid treatment."

Treatment with inoculant has also increased silage intake and altered rumen fermentation beneficially in beef animals. From the mean of 11 more studies, inoculant treatment of wilted and direct cut silages produced similar positive responses in animal performance. Direct cut crops were ensiled with a mean dry matter of 18% and wilted crops at 32% DM. Additive is applied at a given rate/t of grass, says Dr Keady. Consequently, when silage is wilted, less product has to be applied to a given area of land because yield/acre is lower, reducing the cost of application.

However, Dr Keady warns that inoculants can vary greatly in the response in animal performance. The worst inoculant in the Hillsborough studies had no effect on milk yield, while the best one increased it by 2.7 litres/day. The average of 11 studies was an additional milk yield of 1.3kg a cow.

"This indicates the importance of accurate independent research evidence for the additives which you wish to use", he says.

Bacteria in inoculants act during fermentation in the silo and not in the rumen of an animal as has been suggested. One effective product tested improved digestibility, predominantly in the fibre fractions, due to more rapid fermentation immediately post-ensiling, leading to a greater breakdown of structural carbohydrates and a greater retention of soluble components, which increases animal performance.

As for enzyme-only products, these improve silage fermentation under moderately difficult silage making conditions, but there is little research evidence of improvements in carcass gain or milk yield, he warns.

Molasses adds sugar to the crop. During the fermentation in the silage all the sugar is either converted to lactic acid, undesirable acids, lost in the effluent, or converted to carbon dioxide. Application of nine litres of molasses/t of grass did increase the sugar content by 0.4%. However, although molasses improves fermentation, from the mean of nine studies, it did not improve animal performance, whereas formic acid, when used as the possible control, increased it by 17%. Also extra machinery and labour is needed to apply it at the pit during ensiling.

Evidence shows that sulphuric acid improves fermentation, but no published literature shows improvements in animal performance relative to untreated silages.

Beet pulp is often used as a silage additive to retain effluent, but its capacity for this varies depending on the dry matter of the grass and how well the beet pulp is mixed with the grass.

It is better to feed beet pulp dry in winter than use it as an additive, he advises.n

An acid will improve silage fermentation and animal performance under difficult conditions, says Tim Keady.

Ensure that the additive you choose will improve liveweight gain – for example, by using an effective inoculant.