Maximising grass silage quality

Arthur Owen from Bodsgaw Isa, along with Dave Davies of Silage Solutions, explore the principles and benefits of producing high-quality silage and how Arthur aims to increase his milk from forage and improve silage quality.

Bodysgaw Isa silage targets

• Arthur wants to increase milk from forage to over 4000 litres/cow
• The herd is autumn calving so improving silage quality is a key target as peak lactation milk is coming from silage
• Increase sugar content of silage

Ruminants have evolved to eat forage so if we can feed more forage we will have healthier cows.

To feed more forage and maintain high milk production, forage must be:

• High in available nutrients
• High in digestibility

When making high quality silages, the challenge is to produce a concentrate in a forage.

Silage system at Bodysgaw Isa

• 3 cuts of grass, third cut variable depending on the year
• Whole crop bought as a standing crop
• Clamp 1 (indoors) – 1^st cut, some 2^nd cut and some whole crop
• Clamp 2 (outdoor) – remaining 2^nd cut and whole crop with any 3^rd cut
• Mows without a conditioner, spreads out crop and teds once generally
• First cut is raked in and picked up in 48 hours from cutting, second cut usually in 24 hours

Bodysgaw first cut silage analysis from 2020 harvest

Dry matter was 38.3% – slightly too dry for clamp silage, it can store up problems and increase quality losses in field. Arthur’s target is 30-32%.

Protein was 15.4% which is in top 25% of Welsh silages but for a dairy herd it should ideally be 16-17%.

Sugar level is 0.5%. Sugar analysis by wet NIR is poor quality, so sugar content could be higher than reported. Arthur wants to improve this and should be able to quite easily.

NDF is low at 43.6% which is good – shows it has been cut early (also reflected in the D value which is good). Digestible NDF is the proportion of NDF which is digestible – Arthur’s is very digestible at 77.5% meaning cows can maximise utilisation of the forage.

Oil B (5%) and Ash (9.6%) are both high as the digestibility is high, showing the grass was leafy. When grass is leafy it has more minerals per kg/DM as it has not yet gone to stem. We should also analyse all grass silages for minerals – higher D value means more minerals in the silage.

Lactic:VFA ratio is 3.91:1 which proves a very good fermentation and preservation process as there’s a higher level of lactic acid and lower level of undesirable VFAs.

Two important targets for high quality silage

1) Maximise the nutrients in grass immediately before cutting

• Nutrient management, fertiliser applications
• Cutting time
• Target crude protein 17-18% - protein too low and ruminants need concentrate protein supplementation – too high and the fermentation is challenged
• Target ME 11.5 MJ/kg DM = 72% D value

2) Minimise the loss of nutrients from grass between mowing and feeding

• Reducing plant activity
• Reduce microbial activity – things that degrade nutrients into undesirable products that reduce intake and quality

Nitrogen requirements

Each farm is different and should be looking at fertiliser and slurry applications field to field in terms of what the crop needs.

There is a calculation you can do to work this out:

• Assuming a yield of 5 tonnes DM/Ha of silage removed
• If crude protein target is 170 g/kg DM, we need to convert that back to nitrogen (dividing by 6.25) = 27.2 g/kg DM of N
• Multiplied by yield = 136 kg N/Ha removed

For the next crop, this N needs to go back to get the CP level up. It doesn’t all need to come from fertiliser or slurry as some will come from natural soil processes and rainwater etc., but it shows how much N you need available for plant to grow properly.

Pre-cut grass analysis can help you gauge fertiliser rates for future years and cuts.

How to improve ME/D value

Choose good grass varieties with high D values.

Have grass mixes within fields that head at a very similar time to hit yield and quality target at the same time.

Cutting time has the biggest effect – during last week of growing, the digestibility decreases significantly as lignin increases.

Consequences of delaying cutting by a week:

• 10% increase of dry matter yield
• Digestibility drops by 3.5% units
• ME reduces by 0.6 MJ/kg DM
• Higher field losses due to heavier crop
• Slower regrowth – lower annual yield
• Increased NDF – intakes are lower so concentrate use is higher

Early and more frequent cutting will improve yield on an annual basis.

Improving sugar content of silage

Research suggests 3% sugar is needed in fresh grass to make a good quality silage.

Sugar content of silage is affected by:

• Time of day when mowing – sugar content increases throughout the day but is lost during wilting
• Length of the wilt
• Dry matter content of the silage
• Use of an additive

Ideal time to maximise sugar content:

• Good wilting weather – cut after the dew has risen in the morning, pick up the same day in the evening
• Poor weather/heavy yield – cut in the afternoon, pick up the next day
• Target 28-33% dry matter

 Managing the silage clamp to reducing losses

Better density of the silage clamp reduces losses of dry matter

• Adequate but rapid compaction during filling – maximum 15cm layer depth
• Changing from 15cm to 25cm layer depth will reduce the density by 120 kg/m³

Sheeting correctly

• Side sheet down to half a metre on the floor, when clamp is filled the side sheet is pulled in
• Top sheet on, make sure there isn’t a gap between top sheet and side sheet as this will let in oxygen and reduce quality
• Gravel bags around the side to stop air going in or out
• Reduce oxygen – once it’s out keep it out

Crop quality at the start

• Harvest the quality the animal needs
• Reduce variability by good silage management and reducing variability in the field

Using silage additives

Additives are the icing on the cake, they won’t make poor grass into good silage but they an make good grass into better silage

The key is to improve the speed of pH decline to preserve nutrients

Types of additives:

• Homofermentative inoculants – contain bacteria that just produce lactic acid from most grass sugars e.g. L. plantarum, Pediococcus – improve animal performance
• Heterofermentative inoculants – bacteria product a mix of lactic and acetic acid and CO₂g. L. buchneri, L. brevis, L. hilhardii, L. kefira – no evidence to improve silage utilisation in the animal but can improve aerobic stability
• Many inoculants contain a mix of both the above - these or heterofermentative only additives should NOT be used on silage with a dry matter less than 30%
• Chemicals that contain food grade preservatives e.g. potassium sorbate, sodium nitrate – inhibit undesirable organisms, both fermentation organisms and aerobic spoilage organisms