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The Importance of Knowing the Nutritional Value of Silage

Eamonn Dempsey, Teagasc Kerry, highlights the importance of knowing the nutritional value of silage and discusses analysis by visual & lab assessment, while Gerard Cregg, Teagasc Roscommon, focuses on the differences in silage quality from grass cut at different times and locations

Watch below as Gerard Cregg, Teagasc Advisor Co. Roscommon discusses silage quality

The timing of silage harvesting is critical in determining the quality of the crop ensiled. Before cutting it is advisable to know the sugar and nitrate content of the grass to ensure satisfactory fermentation. Eamonn Demspey, Teagasc Davisor, Co. Kerry has more advice below.

Visual Assessment 

Silage that is excessively dry will be prone to heating, mould growth and secondary fermentation. Where bad preservation does occur, it further reduces dry matter digestibility as well as reduces intake potential of the silage. Micro- organisms such as clostridia, listeria, and salmonella can occur on contaminated grass. Good preservation will inhibit these microbes while poor preservation will allow them to remain viable. Farmers feeding out such silage should be aware of the risk and monitor animal performance closely. Silage can be analysed by visual assessment. A yellow/green colour silage along with a sweet fruity smell is an indicator of excellent preservation, while silage with a dark brown colour and acidic type smell indicates poor preservation. To test for dry matter just take a silage sample with your hands and squeeze , if no moisture comes from sample, you will have a dry matter of around 25%, if the water runs freely dry matter will be 20% or less. Dry matter digestibility is determined by when the silage was cut and how recently the reseeding was done in that field. On visual examination you are looking for the proportion of leaf and stem, if you have around 70% leaf and 30% stem, then the DMD of that silage will be 70 -72%.

Laboratory analysis

Silage sampling for a laboratory analysis is recommended to get a more detailed report on the nutritional value of silage. Samples should not be taken until at least 5 to 6 weeks after ensiling and follow correct sampling technique to ensure reliable silage analysis results. Silage sampling gives the farmer an early indication of feed quality which is used to formulate the animals overall diet. The higher the dry matter the more energy and protein the animal will receive for every kg of fresh silage eaten. In general low dry matter silage will limit intake and high dry matter silage will stimulate intake. Well preserved silage will have a pH of 3.8 to 4.2 and will keep well over the winter. Wet silage with a high pH shows the silage has not fermented well or contained high levels of nitrogen before it was cut. Intakes of this silage will be low and with high ammonia levels can lead to scouring. Animals throwing up cuds suggests low pH, less than 3.8, this is due to the acid profile of the forage and is not the same as acidosis.

Crude Protein

The crude protein level in the silage analysis shows how mature the grass was at the time of cutting. Young reseeded swards tend to have higher protein levels due to the fact that the protein content is higher in the leaf than it is in the stem. Knowing the protein level in silage is important when calculating the correct crude protein level for ration to be fed with the silage.


Energy drives production and is expressed as the amount of energy contained in every kg of silage dry matter. Young grass will have the highest energy content and mature grass the lowest. High dry matter digestibility values generally gives high energy and protein levels.

Be informed of the ideal nutritional values of silage, take your own silage samples for laboratory analysis, the report you receive will give a breakdown of several key silage quality measures and compare. This comparison will allow you to choose or formulate the correct ration and know the recommended level of concentrate to be fed with the analysed silage. As silage is the main source of feed on most farms, great care should be taken to maximise utilisation and minimise waste.

See more on Quality Grass Silage here

See more on Understanding Silage Test results here