IGER's David Davies and Rhun Fychan (pictured) demonstrate how careful preparation and management will aid the production of quality silage.

Output from UK grass-based livestock production is valued at more than £8bn, representing over 60% of the total agricultural output of the UK.

While grass is undoubtedly the cheapest source of feed on farm, ranging from £30 to £50/t DM, silage is still the cheapest winter feeding option at £60-£120/t DM. Attention to detail during silage making will result in silage with better feed value produced at a cheaper cost. The old haymakers' saying "a good hay is cheaper to make than a bad hay" is probably more true with silage.

Silage making can be split into three distinct areas (figure 1). To make top quality silage all of the points indicated are equally important and failure to adhere to any will result in poorer nutritive value.

Avoiding spoilage before and during harvest

The ideal silage is formed by the action of the good lactic acid bacteria that either occur naturally on the crop or are added when using an inoculant. But on the crop there is a huge range of other micro-organisms which, depending on forage management practices, can outnumber the good bacteria by 1000 to one.

To ensure the good bacteria have a fighting chance a few important rules need to be followed.

• Last slurry application at least eight weeks before cutting. Slurry contains many millions of the bad bugs, which can survive on the sward for a number of weeks.
• Correct nitrogen application for crops' needs. Excess nitrate in the sward is more likely to result in a silage with high ammonia and butyric acid concentrations.
• Rolling to remove soil contamination from molehills, etc.
• Cut to leave a 2.5-3in stubble. This will minimise soil contamination and ensure a quicker grass regrowth.
• Maximum wilt of 24 hours for grass and 48 hours for legumes such as red clover. Extensive wilting times can result in a 1000 times increase in the level of aerobic spoilage micro-organisms such as yeasts and moulds.

Cutting

The ideal date of cutting will vary from farm to farm depending on factors such as grass varieties used, height above sea level, and latitude. But it will also vary from year to year on the same farm depending on the season.

It is important when producing silage intended to be fed to productive animals, be they dairy cows, beef or sheep, to aim for 67 to 70D. This is equivalent to 50% ear emergence. Research at IGER, where the same grass was ensiled in three different ways, is shown in table 1.

The research aimed to show the effect of different management practices on silage quality and, ultimately, animal performance. Grass was cut at the ideal time with an ME of 12.6 and ensiled using good or poor practices.

A third treatment delayed cutting for about two weeks until the ME had dropped two units to 10.4. Comparing the optimal ME good practice silage with that of the mature grass silage gave a five litres a day difference in milk yield. So maximising grass quality by cutting at the optimum maturity can result in a big difference in milk yield and thus profitability.

Wilting

We recommend a rapid wilt and research conducted in Germany has shown that with the pores on the underside of the leaf open, water loss is 100 litres/t/hour, but when they close it drops to 20 litres/t/hour.

The pores only stay open for about two hours after cutting. So to achieve this it is important to spread the crop as quickly as possible once cut, over as wide an area as possible. Figure 2 shows an IGER experiment indicating the difference in sward drying times between either using a mower conditioner with or without spreading, and a Vicon high performance conditioner (HPC). It is clear that the HPC gives the fastest rate of drying. But tedding the crop does speed up the drying process over not tedding.

Silage management

The importance of good silage management can be seen from the results in table 1. The grass was harvested at the same time for the good and poor management practices, with differences in how the grass was handled between harvesting and ensiling.

While this experiment was for a clamp it indicates how not following best practice can result in poor silage quality, but, more importantly, a 3 litres a day a cow loss in milk yield which represents a £80 a cow loss over a winter feeding period.

While the industry understands the importance of compacting a silage clamp sufficiently during filling, and all the other good management practices associated with clamp silage making, there is a lot more uncertainty of big bale silage management practices. And the costs associated with poor bale management will be similar to those associated with clamp silage.

For instance, preliminary results of a recent experiment with big bale silage wrapped either with four or six layers of film have indicated a 0.5 litres a day increase in milk yield where six layers had been used compared with four layers.

Bale wrapping and stacking

There are a few quick and easy rules to follow to ensure good big-bale silage production.

• Wrap bales close to the stacking area.
• Wrap within two hours of baling.
• Apply a minimum of four layers of film to the whole bale and with crops that are either stalky or of higher value such as red clover or haylage, then a minimum of six layers of wrap is advisable.
• Only stack three high if the silage is 30% DM or greater.
• Store more than 10m away from a watercourse on a surface that is free from sharp stones, etc.
• Protect the bales from bird and vermin damage.

The practical question of how many layers of film wrap to apply is one that IGER has been researching for a number of years through sponsorship by bpi.agri, manufacturer of Silotites and Dow Europe. In a recent comprehensive experiment, grass was wilted for either 24, 48 or 72 hours. Big-bale silage was made at each time point and wrapped with either four, six or eight layers of film wrap.

The results (table 2) across all wilting periods clearly indicated that bales with six layers of wrap had significantly less mould coverage than those with four layers. Wrapping with eight layers showed only a small improvement over six layers. Increasing the number of film layers also improved film seal, reduced DM losses and improved the silage fermentation, producing silage with a higher residual sugar (WSC) concentration.