Last week, we identified two critical parameters around winter feed.

The first was quantity and we looked at the importance of measuring how much feed you have in stock this winter, going on to complete a fodder budget to determine if your stocks are sufficient to keep the cattle fed until turnout next spring.

This week, we will look at the second critical parameter of winter feed – quality.

For as long as people have been opening pits or bales, the first reaction is to pick up a lump of silage, smell it, feel it and make an assessment.

There’s no harm in doing so, but quite frankly, a visual assessment is not adequate when it comes to determining the quality of your silage – you need to get it analysed.

The Teagasc/Irish Farmers Journal BETTER farm advisory team of Martina Harrington, John Greaney and Tommy Cox are taking silage samples on all programme participants’ farms.

Now that they are half way through this process, we take a look at the reports coming back from the lab and what the values actually mean.

What to look out for

Dry matter (%)

An important determinant of intake and preservation values. Most silage analysis parameters are expressed on a DM basis. This ranges from 15-45%.

The optimum level for intake is 28-32%. Low values can result in low pH and poor intake. Can reduce aerobic stability at very high values.

pH

This is a primary indicator of preservation quality and fermentation efficiency. pH measures the acidity of the final silage product.

Very acidic (low pH) silage has poor feed intake and rumen stability. High pH in wet silage indicates poor preservation - ammonia is usually high in this case, leading to poor intakes.

Target pH depends on the DM content. A pH of 3.8 to 4.2 indicates good preservation at <28% DM.

Dry or wilted crops (>28% DM) can be well preserved at pH up to 4.5. Wet silage with pH values of > 4.2 are generally poorly preserved.

Ammonia (%)

Ammonia is caused by protein breakdown during preservation, which reduces feed quality and palatability.

High nitrates in grass at ensiling contribute to elevated ammonia. Values of less than 8-10% show good fermentation with little protein breakdown. Silage ammonia levels above 15% indicate poor preservation and will likely result in feed refusals.

Crude Protein (%)

Crude protein (CP) measures nitrogen as an indicator of true protein content. It gives no information on the quality of protein.

Typical values range from 9-15%. CP% is usually higher in leafy/higher DMD silage, but this can vary. High CP in silage tends to be rapidly degradable, leading to poor utilisation if diet energy is lacking. CP <10% may impede rumen microbial growth.

Energy (UFL/UFV)

This is directly linked to DMD value. Increased energy values boost animal performance and reduce cost of supplementation.

Top-quality silage can be >0.90 UFL, but values close to 0.70 UFL are more common. This value drops quite quickly for each day delay in cutting after grass heading date.

Dry Matter Digestibility (%)

The key measure of quality. DMD determines intake and energy values per kg DM. It’s generally low if cutting is delayed beyond the heading date, and/or dead material present in the base of the sward.

Values of 74% are suitable for high performance animals. DMD% below 66% is sub-maintenance feed for most classes of stock. Silage at 68-70 DMD% is adequate for dry cows requiring little body condition gain.

Results to date

Based on 13 farms tested to date, Table 1 shows the average BETTER farm results for first and second cuts and the range in results of both cuts.

In general, the results are good, with average DMDs of 70% and 69% in first and second cuts respectively.

However, there are large ranges in the results for all values. It is here that the real value of taking a silage sample comes to the fore and we can now use the information at our disposal to properly formulate diets for our cattle this winter.

Take for example DMD percentage. Table 2 shows the effect DMD percentage can have on the level of meal required by different types of suckler stock. Valuing ration at €260/t, the difference in feeding 75% DMD silage versus 65% DMD silage is €60/weanling for a 120-day winter.

The protein percentage of silage is another big factor in formulating diets.

Table 3 shows the protein required by different types of beef cattle in their ration, based on what the protein content of silage is.

Given that protein in a ration will likely be driven by soya bean, the less protein needed, the cheaper it should be.

Taking a silage sample

A sample of silage being taken.

For best results:

  • Take the sample from deep inside the silage pit using a corer.
  • Do not take a sample from the face of the pit or directly beneath the plastic cover.
  • For bales, use a corer, or take the sample from the centre of a freshly opened bale.
  • The sample should be placed immediately in an airtight bag (ziploc bag ideally).
  • The sample should be posted to the lab as soon as possible.
  • It should be kept cool and out of direct sunlight in the meantime.
  • Ideally, take samples early in the week, so they are not sitting in on your farm, in the post or in the lab over the weekend.
  • Costs:

    Teagasc now uses FBA Laboratories for silage samples. It costs €32 per sample for forage analysis and €90 per sample for a mineral scan.

    If sending samples privately to other laboratories, expect to pay €30-40/sample for a forage analysis and €85-95/sample for a mineral scan. Results are typically returned within a week.