Imagine having a handy list of areas where silage-making could be improved. There is a list – your silage analysis. The trick is knowing how to interpret it. It offers a goldmine of tips for making better silage. 

Volac business manager, Ken Stroud, said: “A grass silage analysis doesn’t just provide the basis for ration formulation, it is also packed with clues for potential silage improvements.

"Usually, the main figures looked at on the analysis relate to nutritional quality – metabolise energy (ME), digestibility (D value), protein, and % dry matter (DM).

"These are important, but only half the story. Other figures indicate how efficient the fermentation has been, how well protein has been preserved, and whether there has been soil contamination," Ken continued.

“If the fermentation was particularly poor and silage has become unpalatable, no matter how good it is nutritionally, if cows will not eat it, that is a huge waste.”

Knowing the root cause of these issues provides your ‘to do’ list for making better silage. 

Ken suggests scrutinising the following nine areas:

Use these to assess fermentation efficiency.

“In an efficient fermentation, beneficial bacteria convert sugar in grass into lactic acid, and nothing else. This is efficient because lactic acid is very good at preserving silage, but also because the process of converting sugar only to lactic acid wastes very little energy from the grass. 

"Carbon dioxide is wasted dry matter, while excess VFAs are unwanted because they are weaker at preserving silage and silages with high VFAs are less palatable. 

“Ideally, you want a high ratio of lactic acid to VFAs. A good target is 3:1, but higher if possible, such as 5:1," Ken added.

To achieve this, Ken says a proven additive, such as Ecosyl, can be a huge help.

Where fermentations are carried out without an additive, natural lactic acid bacteria populations can be much less efficient. Even worse, if ‘bad’ bacteria from soil or slurry are present, fermentations can be extremely poor.

The silage’s ash figure helps gauge soil contamination.

“To minimise slurry bacteria, if slurry must be applied between cuts, apply as soon as possible onto clean stubble and ahead of regrowth. This will maximise sunlight reaching the undesirable bacteria to help kill them off, and allow the fresh grass to grow above the slurry. Slurry bacteria can result in poor silage palatability and big DM losses," Ken added.

An ash figure above 9% indicates a problem with soil contamination.

Ken said this can be minimised by rolling fields and checking soil isn’t being introduced into silage by machinery, e.g. by rakes and tedders set too low.

Metabolisable energy (ME), the amount of energy available to the cow, is a nutritional measure and is linked to digestibility (D value), since the more digestible the silage, the more energy she can derive from it.

But it also gives an indication of how good the preservation has been, since undesirable microbes will feed on the most digestible part of the silage first. 

Ken said:

"Younger leys tend to be higher in energy. Also, cut before heading. After heading, grass digestibility falls by about 0.5% per day."

As with ME, a low silage sugar content can indicate an inefficient fermentation, or it can be due to low sugar in the grass. 

“Generally, the higher the sugar content, the better. Aim for above 3%. Wilting concentrates sugars, but it is important to wilt rapidly to minimise the time the crop continues respiring for and using up sugars before it is ensiled," Ken said.

Crude protein is the total nitrogen in the plant, which consists of the nitrogen in actual (true) protein that the animal can use, plus nitrogen fertiliser (N) that the grass had absorbed but not yet converted into useable protein.

Too high a protein content is not necessarily good because it buffers the fermentation. 

Ken said: “A good figure is 16-18% protein; higher often indicates residual fertiliser still in the crop. 

“Since nitrogen fertiliser is not applied to clover swards, they can analyse low for CP but still perform well.” 

In conjunction with crude protein, look at ammonia content, the Volac representative adds.

It gives an indication of protein breakdown, although it can also be produced from excess nitrogen. 

“The lower the ammonia content, the less protein has been broken down, or the less bagged fertiliser is still present as residual nitrogen in the crop. Ammonia should be below nine," Ken outlines.

Ken says: “If silage is too wet or too dry, cows struggle to eat enough of it – which is not wanted with high-yielding cows. 

"To make it easier to reach this DM quickly, cut at the correct growth stage, because lighter, leafier grass is easier to wilt, and assess whether increased tedding may be required."

The more moisture the silage contains, the more acidic (lower pH) it will tend to be, which increases the acid load on the cow. 

"The ideal pH will depend on the %DM, since drier silages need less acidity to make them stable. For silage at 30% DM, aim for pH 4.0. Wilting to the optimum 28-32% DM helps to avoid excess acid loading," Ken adds.

Intake potential is a combination of several factors – including %DM; pH; fermentation quality; chop length, with shorter chop lengths increasing intake potential; and D value, since more digestible silages travel through the cow faster. 

"Aim to optimise each of these parameters because a higher intake potential is important for maximising milk from silage,” Ken explains. “The ideal intake potential is above 100%.

For more information, advice and top tips about the six stages of silage making, click here