Grass is key to Ireland’s agricultural production model, with grazed grass used to feed our livestock during the grazing season and grass silage used during the housed winter period.
This year, the vast majority of farmers will be happy with the amount of silage they were able to harvest. Although many were later in harvesting their crops than planned, the extra bulk obtained was welcomed.
But what about the quality of the harvested forage?
To obtain an accurate silage sample a tool called a silage sampler, or core, is required. Ideally, samples should be taken from the highest point of the pit and driven down to the bottom.
Up to seven cores should be taken from each silage pit. These samples should be mixed, and a representative sample then drawn off.
Discard the top five inches of each core and place the remainder in a container.
The holes created in the plastic should be taped to prevent spoilage. If you have, or only use bales, these should also be analysed.
When testing bales you should take cores from two bales from each batch made, in order to get a fair and representative sample.
Once your forage has been analysed you will receive a report back. It is important that you understand what these figures mean.
Dry matter (DM) is the amount of silage material once water has been removed. Generally, the higher the figure the better, as this will increase intakes.
You should target a DM of 20% plus – this will increase intakes in cows.
pH and ammonia
pH is a measure of acidity, which helps to determine the silage’s ability to store.
Well-preserved silage is more palatable to animals and should result in higher intakes and better performance. Well-preserved silage should have a pH of 3.8-4.2.
Ammonia (NH3) is a good indication of fermentation quality. Ideally you want less than 10%, as values greater than 15% indicate bad preservation.
The crude protein percentage reflects the quality of the grass at harvest, with young, leafy grass having values of over 15% and stemmy grass having values of less than 10%.
Protein levels in silage made in early summer are usually higher than silage made in mid-summer.
Metabolisable energy (ME)
Metabolisable energy (ME) is the usable energy of the silage. Young leafy grass should have a high ME value, while hay would have a low ME value.
Dry matter digestibility (DMD) is a reliable and accurate test of a forage’s feeding value.
This result is used to estimate energy value, expected milk yields or liveweight gain, and required supplementation rates.
Young perennial ryegrass swards cut for silage after six weeks of growth should have a DMD percentage of 75-80%, while older stemmy swards when cut would have a DMD percentage of 60-65%.