Grass silage

As we approach the winter feeding period
 it is looking like an uncertain few months ahead for UK and Irish dairy farmers. Global influences seem to be exerting downward pressure on milk prices, although the feed market is falling due to the adequate global supply of cereals and proteins, which is, at least, having a positive influence on the milk price to feed price ratio. Indeed, at the current milk price to feed price ratio of approximately 1.5 there is still an opportunity for farmers to capitalise by feeding for higher yields.

One problem to be aware of, however, is that with plentiful supply of relatively inexpensive cereals, there can be a temptation to feed more of them. This is not the best approach and it remains important that a balanced diet is fed to ensure adequate rumen function and feed efficiency is maintained across the whole herd. This will ensure milk yields and fertility are optimised.

Of course, there are various environmental and management factors that can have a major bearing on production and fertility parameters, as well as the incidence of metabolic disorders, but from a dietary perspective forage quality is one of the overriding factors.

Approximately 50 per cent of a dairy cow’s diet is typically made up of forage and it is important that the dietary content does not drop too far below this as fibre from forage (and long fibre in particular) is important to balance digestion and fermentation and promote good rumen function. At 50 per cent of the diet, forage quality is extremely important as it represents the feed that can have the greatest impact, both positively and negatively, on rumen function and subsequent performance.

The variable weather earlier this summer has in general resulted in a major variation in the quality of grass silage present on UK farms this autumn/winter. While forage quantity does not seem to be an issue, with most clamps full, table 1 demonstrates the impact that later cutting dates have had on quality when compared to 2013.


Initial 1st cut grass silage analysis - 2013 & 2014 comparison



1st cut 2013

1st cut 2014

2014 range

Dry matter




14.3 - 56





58 - 75.8

Crude protein




6.4 - 25

Metabolizable energy

MJ / Kg



9.3 - 12.1





3.5 - 6.0

Neutral Detergent Fibre

g / Kg



33.7 - 69.3

Lactic acid

g / Kg



16.8 - 127.9


g / Kg



0.1 - 66.6

Intake potential

g / Kg



65.6 - 141.2

Source: Frank Wright Trouw Nutrition International

In general, these results are indicating a trend for grass silages of poorer quality for this year’s first cuts, due to lower digestibility compared to those of 2013. This is reflected in the higher neutral detergent fibre, lower digestibility and metabolisable energy content. Indications are that silages are also wetter than last year and the lower digestibility and dry matter content combine to result in lower intake potentials when compared to 2013.

This is reinforced by the fact that if a farmer was aiming to feed 12Kg/DM per head per day of a grass silage he would have to feed approximately 5 kg more on a fresh weight basis of the 2014 sample based on the average dry matters - something that may not be achievable on a higher NDF sample.

Whilst these initial results are useful at providing an early indication of quality, caution must be exercised when interpreting them. Farmers do not feed ‘average’ silages and the range in analysis from farm to farm means it is imperative for each farmer to analyse their own forages this autumn to get a handle on what they will be feeding.

It is advisable to get a number of samples analysed over the course of the winter as there can be major variation within a clamp of silage.

So what impact will feeding a forage of lower digestibility have on performance this winter and what can be done to mitigate against a drop in performance?

In general, feeding forages of lower digestibility will result in reduced intake 
of that forage due to its slower digestion and fermentation profile in the rumen, resulting in a slower rate of passage through the rumen. This negatively impacts on performance, as the rumen microbes are
 less able to digest the forage, resulting in reduced availability of fermentable energy for maintenance, production and reproduction.

This is also coupled with a lowering in microbial protein synthesis, something that is essential for milk production. There are a number of options that can be taken when feeding a low ‘D’ value silage, which are all focused on supplying increased levels of fermentable energy in the form of starch and sugars to the rumen microbes to make up for the shortfall in energy supplied by the forage.

Synchronising the energy supply, whether it is from forages, cereals or by-products, with the type and quantity of protein supplied will optimise digestion and fermentation in the rumen, leading to optimal intakes, milk yield and milk protein yield.

Increasing the supply of fermentable energy can be achieved by feeding a second forage containing starch, such as wholecrop 
wheat or maize silage, which will also have 
a positive influence on promoting higher intakes. For farmers who do not have access to these forages, feeding extra concentrate to make up for the shortfall in energy supplied may be the only option to meet production targets.

Silage MJ / Kg DM

Silage DM intake

ME intake from silage

Concentrate required for M+30 litres









Table 2

Table 2 demonstrates the extra concentrate that is required in order to maintain performance when feeding a cow for 30 litres with two grass silages of varying quality.

It is worth considering the type of energy that is supplied when feeding extra concentrate, as it is starch and sugars that are of most benefit to the rumen microbes when feeding a stemmy grass silage. Therefore it is well worth consulting your nutritionist or feed representative on the specification of blends and compounds to be fed where a stemmy grass silage is being fed.

For those of you lucky enough to have dry, leafy and highly digestible grass silage in stock, care must also be taken when balancing diets containing this type of forage, as feeding increased levels of fermentable energy as cereals, whether as straights or through blends and compounds, may not necessarily be the right option with such a forage. This could actually be counterproductive and result in sub-acute or acute rumen acidosis depending on the level of dietary imbalance.

The importance of routinely conducting silage analysis throughout the winter cannot, therefore, be emphasised enough so that you know what you are dealing with. Other factors, such as forage chop length, mixing consistency and the dry matter of the TMR, can have a significant influence on rumen function and subsequent cow performance. TMR sorting is minimised when a diet is approximately 45-50 per cent dry matter and where structural fibre such as straw is added, a chop length the width of the palm of your hand is optimal.

How Actisaf can help...

Feeding Actisaf Sc 47 live yeast to your dairy cows this winter will prove very beneficial, particularly where stemmy or highly
 variable forages are being fed. Actisaf has been consistently shown to improve rumen function and feed efficiency resulting in a return on investment of up to 13:1 depending on milk price.

Actisaf works by lowering the rumen oxygen levels present in the rumen. Oxygen in
 the rumen is toxic to the beneficial rumen microbes that digest feed, so adding Actisaf results in increased microbial activity in the rumen leading to increased fibre digestion, meaning there is more energy released from stemmy forages for the cow to use for maintenance, production or reproduction.

The mode of action of Actisaf Sc 47 also results in it promoting a pH stabilising effect, which proves beneficial where higher levels of cereals or leafy highly digestible grass silage are being fed, as these can challenge rumen pH. Actisaf has been shown to
 deliver higher milk yields and reduced bodyweight loss when supplemented to early lactation cows, while promoting improved persistency for herds in mid-to late lactation. Supplementing Actisaf during the dry period is also highly beneficial, as it helps to prepare the rumen for the rigours of lactation and the energy dense diet that will be fed.

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