Improving The Energy Content of Grass Silage

Roy Eastlake, National Technical Support Manager, Lallemand Animal Nutrition UK

Year in year out, standing grass in early May will have an energy content of around 12.5MJ, yet when clamps / silo’s are analysed the average analysis of grass silages will be around 11.0MJ/kgDM.  Somewhere a significant amount of energy is being wasted to be replaced in diets by more expensive purchased feeds. And why is it that some producers are regularly achieving over 12MJ of energy from their grass silage?

While the typical farmer is losing around 12% of the available energy between mowing grass and feedout, the top producers are losing just 4% which means there is a significant opportunity to increase production from forage.

For every 100 tonnes of freshweight silage at 30% dry matter, an increase in energy content of just 0.1MJ would retain enough additional energy to produce an extra 566 litres per 100 tonnes of silage, or almost £160  extra income at 28ppl.

When you consider the typical dairy farmer in the UK makes around 1500 tonnes of grass silage at 30%DM and that an increase in ME of 0.5MJ/kgDM should be achievable, we are looking at a yield benefit of 42,453 litres, or £11,887 for little additional cost.

When working with producers across the UK technical team commonly come across four areas where attention to detail and changes to management will lead to improved silage quality.

  • The starting point for high energy silage is making sure the crop is cut at the correct time.  Once grass goes past the optimum growth stage quality declines and energy is lost.  The digestibility value is a major determinant of energy content and directly correlated to the ME level, and grass loses three units of ‘D’ per week. There is still a widely held belief that grass should be cut when 50% is in head, around 15th May.  All this means is that 50% of the grass has already gone over in terms of quality, so look to cut sooner.
  • Make sure you are ready to cut at the optimum stage for your sward.  Pre-cut grass testing can help ensure timing of cutting is as precise as possible.  Make sure your contractor knows your objectives for cutting and that they will be able to meet your schedule.  Bringing foraging forward could actually make their life a bit easier.
  • Once the grass has been cut, do not over wilt it especially the later fields to be picked up.  Leaving grass too long between mowing and chopping is one of the biggest reasons for the failure to optimise energy content.  All the time the crop is lying on the ground, it is respiring and this leads to energy and dry matter losses. Wilting for too long can result in over 3% extra dry matter losses which loses energy.   Never wilt for more than 24 hours.  In particularly good weather the rule should be to cut in the morning and pick up in the evening with a maximum eight hours wilting.
  • While tedding can increase the speed of wilting, the physical movement of the crop can lead to physical losses and soil contamination.
  • Once the crop has been harvested achieving a rapid and stable fermentation is the key to retaining energy.  An effective fermentation requires a rapid pH drop to stop the actions of undesirable bacteria, yeasts and other microflora on the crop.  All the time they are active, they are using up energy and releasing carbon dioxide which means you end up with less silage and a poorer quality feed.  Choose a challenge-specific inoculant to ensure a rapid and efficient fermentation to preserve more energy and reduce losses.
  • Then thoroughly seal the clamp.  Any spoilage in the clamp will lead to less energy to feed the cows.  Make sure the sides and top of the clamp are fully sealed with a proven oxygen barrier and that sheets are well-weighted down to keep oxygen out and feed quality in.  Take the time to do this job thoroughly.  The sheeting has got a big role to play preserving forage quality for around 4-10 months.

By focusing on silage quality you are taking control of on farm costs.


Lallemand Animal Nutrition does not purport, in this guide or in any other publication, to specify minimum safety or legal standards or to address all of the compliance requirements, risks, or safety problems associated with working on or around farms. This guide is intended to serve only as a beginning point for information and should not be construed as containing all the necessary compliance, safety, or warning information, nor should it be construed as representing the policy of Lallemand Animal Nutrition. No warranty, guarantee, or representation is made by Lallemand Animal Nutrition as to the accuracy or sufficiency of the information and guidelines contained herein, and Lallemand Animal Nutrition assumes no liability or responsibility in connection therewith. It is the responsibility of the users of this guide to consult and comply with pertinent local, state, and federal laws, regulations, and safety standards.

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My silage this year was 12.4 me 75.8 d value my cattle have never looked so good. And used so much less silage.