Silage season is well underway in many areas and as most farmers try to get the first-cut completed, attention turns towards the quality of the silage.

Teagasc has outlined some key requirements for producing quality silage.

Grass growth stage will have a large effect on silage dry matter digestibility (DMD) so the advice is to target the cutting date at the correct growth stage for the quality of silage you are trying to produce.

Producing high quality silage

Where high quality silage suitable for milking cows and finishing cattle is targeted (74%+ DMD) leafy grass with no seed head will be required, according to Mark Treacy from Teagasc.

As the seed head begins to emerge, grass quality, and therefore potential silage quality, will decline due to the increasing levels of fibre in the grass.

A drop of 0.5 DMD can be expected for every day cutting is delayed after heading date. Where crops are lodged, quality will deteriorate at a more rapid rate, Treacy explained.

Silage with a DMD of less than 68% DMD is poor quality and should be avoided if possible.

Teagasc has outlined three key factors in the successfully preservation of grass silage:

  1. Grass sugar levels;
  2. Anaerobic conditions;
  3. Buffering capacity.

Adequate grass sugar is required to feed the acid-producing bacteria which can be measured using a refractometer, with 3% or higher considered sufficient.

Where sugar levels are below 3%, options such as delaying cutting until later in the day, wilting, or adding molasses should be considered.


Anaerobic conditions are vital for grass silage because lactic-acid-producing bacteria require these conditions.

Where anaerobic conditions are not achieved, undesirable bacteria may begin to grow.

The creation of anaerobic conditions can be achieved by properly rolling the silage pit both during and immediately after filling, by paying attention to detail with covering, and by checking and retightening the pit covers again a few days after cutting as the pit settles.

Buffering capacity is affected by the N levels in the grass. High N grass has a higher buffering capacity and it is therefore more difficult to reduce the pH to sufficient levels for good preservation.

Teagasc has said that the importance of N levels in the grass is often overstated and where adequate sugar levels are present, grass can be successfully preserved with in excess of 600ppm of nitrate.

Wilting of these crops will reduce the effects of the high N levels, Treacy advised.