The costs of producing grass silage have risen and will continue to rise. Land costs, harvesting charges and fertiliser prices all make grass silage a costly feed to produce, but it remains the best and most viable forage option for Irish farms.

Due to changeability in pasture type, cutting date, weather patterns and harvesting/ ensiling technique, grass silage is variable feed source — in terms of nutritional value and ensilability — even from cut to cut on many farms.

This leads to challenges when it is fed to livestock. Where 5kg of a 14pc ration can be fed to animals one year, 8kg of a 16pc ration may be required the following year to meet the same nutritional parameters.

The primary aim when making grass silage is to produce a feed for winter use that best replicates grazed grass.

The mowing, wilting, fermenting, and storing of what was a living plant will result in the reduction of its feed value. We try to limit this reduction through the implementation of best practices at all stages of the silage-making, storing and feeding process.

High-quality grazed grass will have dry matter digestibility of 76-82pc, while many grass silages will fall significantly short of these figures.

So where are we losing dry matter digestibility between the field and feed out time?

Traditionally fertiliser was applied at a standard rate and silage made six weeks later, depending on weather. Little consideration was given to adjusting fertiliser application to account for soil fertility and variability in slurry quality.

Growth rates in the period between fertiliser spreading and grass harvesting can have a huge impact on nitrogen uptake. In some cases, accelerated growth rates can take up available nitrogen within 3-4 weeks.

As an industry we need to move away from this six-week waiting period and focus more on how ensilable the grass leaf is when deciding what date is best to harvest.

The practice of waiting for a silage crop to ‘bulk up’ before deciding to cut also needs to be assessed. This has a place for suckler cow herds that will be feeding silage to dry cows, but certainly shouldn’t have a place where young stock or finishing animals are the primary category being fed.

Once harvested and pitted, we are looking for the clamp to undergo a rapid and stable fermentation. Anaerobic bacteria will feed on natural sugar from the grass plant to produce lactic acid, which will stabilise the pit and inhibit mould activity.

Where this fermentation process does not occur rapidly, there is a significant loss of DMD.

I am often asked for my opinion on silage additives. If a good additive speeds up the initial fermentation process and reduces DMD losses, then there is a huge return on investment.

Up to 50pc of silages made in Northern Ireland are treated with some form of additive, but south of the border, the figure is under 10pc.

While there are many additives on the market, all of which are manufactured outside the country, the ones most suitable for Irish conditions are those that can combat the impact of high nitrogen, moderate sugar levels and low dry matters.

Silage additives that supply high levels of selected lactic acid bacteria will provide a much faster and efficient fermentation — reducing effluent run-off and feed losses, and making for a more stable silage at feed out.

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Gerry Giggins is an animal nutritionist based in Co Louth