Teagasc: Scope to delay silage after heading date is very limited

Difficult spring weather and poor growth delayed closing and application of fertiliser to silage ground on many farms.

As a result, farmers may consider delaying first cut to ‘bulk up’ silage tonnes.

While grass yield is the most important factor determining silage cost per tonne, other factors should be considered when setting a target cutting date.


Silage quality (DMD) is very much determined by grass growth stage at harvest.

Different categories of stock have requirements for silage of different quality (see accompanying table).

For higher DMD silage, harvest at or just before seed heads emerge.

DMD drops by one unit for every three days’ delay after that.

If the crop lodges, or there is dead material at the base, DMD drops a further three to four units very quickly.


While delaying harvest well beyond grass heading date appears to put bulk in the pit, losses in digestibility mean that total feed available to the animal is not increasing, or is perhaps even declining.

It also slows grass recovery rate and reduces second cut yield.


For spring-calving herds, silage for dry cows should be 68-70% DMD.

The scope for delaying silage cutting more than one week beyond heading date is therefore very limited.


Silage fed to milking cows and young stock needs higher DMD, and should be harvested at an earlier growth stage.

Budget how much of this material is needed (equivalent to three bales per cow for spring/autumn feeding, plus three bales per replacement heifer).

Taking out a small percentage of first cut as bales seven to ten days early helps meet this budget.


An option for silage areas grazed for a second time in April may be to manage this area separately, baling out early at lower yield to provide high DMD material.

Many farmers delay the first cut date to allow these areas to catch up with areas grazed only once.

Research suggests that the gap is not made up, and that DMD values on the once grazed area will have declined too far by the time the first cut date arrives.


A guideline for fertiliser nitrogen (N) is that grass uses up two units of N per day on average.

Fertiliser should be applied approximately 50 days before the planned cutting date.

However, the crop may still be harvested sooner, depending on nitrate and sugar levels.

If weather conditions are suitable, it is advisable to test the grass crop rather than delay cutting based solely on the ‘two-unit rule’.

Wilting to under 28% dry matter is a very effective aid to preservation, if nitrate readings are high.

Add a sugar source (for example, molasses) if necessary.


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