HOW TO: Assess clamp silage: quantity and quality

As the winter housing period approaches, now may be a good time to assess grass silage stocks and forage quality.

Leafy swards comprising of at least 70% ryegrass cultivars are key to an efficient silage system. The digestibility or ‘D value’ of silage is largely influenced by the growth stage at which the grass was cut and ensiled. Like most other plants, grass goes through a vegetative stage and then a reproductive stage, at which point lignin content increases. This lignin is indigestible to ruminants and can reduce the D value of grass silage significantly. Where seed heads are present within a silage sample, the D value will be below the target figure of 72. Research has also shown that crude protein, water soluble carbohydrate and metabolisable energy content decline as the grass matures (see Figure 1).

nutrient valise of grass before and after heading
Figure 1: Nutrient valise of grass before and after heading

Grass silage should be tested in order to formulate and balance winter feed rations accordingly. AHDB Dairy recently published the ‘5 W’s and 1 H’ guide to getting a clamp silage sample:

Who: It is crucial that the person taking the silage sample follows a technique that allows a representative sample of the feed to be collected, and does so in a safe manner. Always ensure pit faces are stable and not likely to collapse.

What: Most forages can be analysed these days but you should check with the laboratory that will be doing the analysis.

Where: Samples can be collected by coring down through the clamp for one-off feed budgeting and mineral analysis. However, for more routine analysis, a sample should be collected by coring into the pit face.

When:  Samples should only be collected after six to eight weeks, once fermentation has been completed. These can then be used to establish the requirements for purchased feed and also for assessing the mineral content of the silage. For routine diet formulation, samples should be collected on a monthly basis and on a weekly basis for regular DM testing.

Why: Regular analysis of silage samples allows more accurate formulation of the diet and ensures nutrients are not undersupplied or wasted. Equally, a one-off mineral analysis can highlight any potential issues that the stock being fed on the forage may face.

How: This is the most important aspect of the silage sampling process. Research in the USA demonstrated that a large component in the variation of the results of silage analysis was due to individual operator sampling technique.

When sampling the whole clamp:

  1. Using the sample probe, core down through the depth of silage, placing the sample from each core into a clean bucket as you progress through ‘W’ format
  2. Seal the holes with silage tape as you go along
  3. Once all cores are collected, mix the samples thoroughly with your hand
  4. Pour the sample out onto a clean surface and mix again
  5. Separate the sample into four and take small samples from each pile, placing them into a sealable bag. Avoid losing small particles by ensuring your hand is underneath the sample when transferring it to the bag. A sample of approximately 200g is required for analysis, but check with the laboratory
  6. Seal the bag, recording which clamp it came from and the date it was collected. You should also include what type of silage it is, e.g. first cut grass, maize, etc. and whether or not an additive was used
  7. Post the sample immediately. Ideally, samples should be sent at the start of the week to ensure analysis gets completed as quickly as possible.

AHDB Dairy has also developed a spreadsheet which can be used to calculate the amount of silage within a clamp.  Email ku.gr1511447952o.bdh1511447952a@yll1511447952ieR.l1511447952liB1511447952 for a copy of the spreadsheet to calculate amount of silage in a clamp.

Together with Dr Dave Davies of Silage Solutions, AHDB Beef & Lamb is now investigating the factors that impact on the quality and subsequent loss of grass clamp silage on 22 farms throughout England. Background data for silage-making practices on each of the farms has been collected and farm visits are now taking place. The aim is to develop a Better Returns Programmes (BRP) plus document on efficient clamp grass silage production based on the findings from this project.

*Use an FAA accredited organisation for forage analysis -faagroup.co.uk/

More information can be found in the Better Returns Programme (BRP) manual Making Grass Silage for Better Returns.