Looking beyond the headline figures on your silage analysis will ensure diets are better balanced and more cost-effective

New parameters included in silage analyses give a much better indication of how the forage will perform in the rumen, allowing more efficient supplementation and purchased feed costs savings according to Dr Liz Homer from Trouw Nutrition GB.

“Most farmers and nutritionists don’t go much further than metabolisable energy (ME) and crude protein when assessing the quality of silages,” she comments.  “However, and significantly these parameters do not indicate how a feed will perform in the rumen and the type of supplementary feeds which will be required to best balance the diet.

“The consequence will be diets which do not perform as expected leading to poorer production.”

Dr Homer explains that cows do not produce milk from silage, but from the products of digestion when feeds are fermented in the rumen or pass through to the intestines.  New parameters included on most silage analyses now better predict what these products of fermentation will be and Dr Homer advises farmers to ensure their nutritionist makes full use of them.

“These parameters describe how feeds will perform when eaten, what the rumen bugs require and also how much bypass energy and protein is needed to balance the overall diet.

“Unless the rumen is balanced in nutrient terms, but also in terms of rate of fermentation cows will not perform as expected,” she continues.

She advises farmers and their advisors to ration cows based on NDIP which is the metabolisable protein available to the cow and Dynamic Energy (DyNE) which is the net energy available to the cow.  She explains that DyNE is the sum of all energy sources fermented in the rumen including sugars, NDF, residual organic matter and even lactic acid and protein which explains why silages with the same ME content can have different levels of DyNE.

Alongside these she says attention needs to be paid to the amount of Total Fermentable Carbohydrates and Protein and the Rapidly Fermentable proportions.

“These describe how much of the energy and protein will be fermented in the rumen and an indication of how rapidly this fermentation will happen.  Overall the diet will need to be balanced for fermentable energy and protein and also the speed of fermentation.”

Finally, she says the acid load and fibre index help predict the impact of a silage on rumen function.

“Based on these parameters, it is possible for two silages with the same ME level to perform very differently in the rumen and consequently require different supplementary strategies.

“The table compares two silages which are both first cuts with a similar dry matter and both are 11.3MJ/kgDM so on first assessment would be expected to perform similarly.  Although the ME is the same, the DyNE varies, primarily due to the amount of NDF and lignin.”

Silage one is higher in crude protein and in fermentable protein but has lower total fermentable carbohydrates than silage two as a result of being lower in NDF.  Silage two has more rumen fermentable energy but less fermentable protein.

“When we look at the balance of rumen fermentable energy and protein, silage 1 has an excess of protein while silage two has a shortage of fermentable protein, in part due to having lower crude protein.  This means, that despite having the same ME, they will need to be balanced differently.

“Assuming they are correctly balanced and if cows are consuming 10kgDM, then the DyNE in silage one will support M+7.3 litres while silage two would give M+8.3 on this basis.  But if incorrectly balanced, both will under-perform.”

Dr Homer says diets based on silage one would need to be supplemented with Slowly Fermented Carbohydrate sources to balance the excess protein.  This could include feeds like soya hulls and beet pulp.  She advises not feeding too many rapidly fermented carbohydrates like cereals as the acid load of the silage is high, increasing the risk of acidosis.

With silage two, the need is for supplementary feeds to supply fermentable protein to boost the supply of microbial protein.  Consequently, diets based on this silage would benefit from distillers, soya or rape.

“Accurate description of how feeds perform in the rumen is paramount if maximum value is to be made of forage to help support margins this winter. These new parameters allow nutritionists to go further than traditional parameters used to assess silage quality such as ME and crude protein. 

“By balancing the diet more effectively, thinking outside the box and not always buying the same compounds and supplements we calculate the savings could be around £180/cow per year for a 9000 litre herd.”

		First Cut Silage 1	First Cut Silage 2
Dry Matter	%	37.17	37.74
Crude Protein	% DM	14.58	13.59
ME	MJ/kg DM	11.30	11.30
NDF	% DM	42.40	45.85
Rapidly Fermentable Carbohydrates	g/kg DM	208.10	204.92
Total Fermentable Carbohydrates	g/kg DM	440.51	477.05
Rapidly Fermentable Protein	g/kg DM	91.12	81.45
Total Fermentable Protein	g/kg DM	109.58	101.19
Acid Load		49.98	48.26
Fibre Index		171.08	184.57
DyNE	MJ/kg DM	6.05	6.35
NDIP	g/kg DM	62.42	64.91
NFEPB	g/kg DM	13.86	-0.64
Milk from DyNE	Litres	7.3	8.3

Mycotoxin Outlook

As farmers begin to dip their toes into cereal crops around the country, yields are the focus for every arable farmer. AHDB has predicted a UK wheat crop that could be as low as 10Mt, which would be the lowest seen this millennium. Winter barley also looks to have struggled through the spring drought, although the total barley crop is likely to recover due to the large amounts of spring barley planted.

As there is plenty of wheat around the world it is still likely to play a significant part in winter rations this year. However, it is also predicted that imports of maize will be higher and likely to feature in many winter rations. It is important that we are aware of the mycotoxin threat posed by crops grown in different climates as maize for example is especially susceptible to mycotoxin contamination – we see a very high proportion of maize samples having at least one mycotoxin through our Mycocheck service.

Considerations for Imported Feedstuff

1. The Different Climate

Cereals crops are imported from around
the world with the majority coming from
a warmer climate than the UK. Fusarium moulds are the most common in the UK and Ireland, with the temperate/wetter climate and this leads to the production of the mycotoxins such as Deoxynivalenol (DON) and Zearalenone (ZON) amongst others.

Aspergillus moulds that produce Aflatoxins are much more common in warmer & drier climates with higher temperatures. Due to the higher levels of imported feeds, we will see this winter, farmers and feed companies should be on the lookout for symptoms associated with Aflatoxins, as well as the more common DON and ZON mycotoxins from Fusarium moulds.

2. Transportation and Storage

Most moulds that produce mycotoxins are produced in the field before harvesting, however, transportation and storage can also pose a risk, especially when travelling long distances in hot confined containers. These warmer conditions tend to favour Aspergillus moulds and the production of Aflatoxin.

Symptoms of Aflatoxin Contamination

The most common symptoms to look out for with high level of Aflatoxin contamination are:

• Depressed milk yield by as much as 25%
• Significantly reduced reproductive efficiency • Reduced rumen efficiency
• Gastrointestinal upset

How does mould produce mycotoxins?

Moulds produce metabolites at different stages during their lifecycle:

1. Primary metabolites are produced continuously during the exponential phase of growth and are involved in primary metabolic processes such as respiration.

2. Secondary metabolites are compounds produced and are not required for primary metabolic processes, e.g. during reproduction.

Mycotoxins are poisons generated from the secondary metabolic process which occurs naturally in a wide variety of moulds.

Mycotoxins can be present even if there isn’t visible mould on the feedstuff

It has been estimated that over 80% of all mycotoxins are formed pre-harvest with mould growth being present in the stalk or grain of the plant or in the soil. When the crop is then harvested the mould is dispersed through the feed. This allows the mycotoxins to be present in the feed without being visible, so the threat often goes unnoticed.

What does it mean if there is visible mould on the clamp face/feed?

The colour of the mould is an important factor
in understanding its metabolic stage (primary or secondary) and also the type of mycotoxin risk it presents.

• White mould: Commonly seen on feedstuffs especially on open clamp faces. White mould
is still in the primary metabolic phase so it isn’t producing mycotoxins but it is still damaging the feedstuff (Figure 3). When the white mould starts to reproduce, the spores are pigmented and the colour of these spores help to identify the type of mycotoxin present.

• Pink/Red mould: Indication that the feedstuff is contaminated with a fusarium mycotoxin (DON, ZON, T2) (Figure 4). In UK & Irish climates this is the most prevalent mycotoxin.

• Green mould: Indication that aspergillus mycotoxins (aflatoxin) are present.

• Blue mould: Indication of a penicillium mycotoxins.

Top Tips

1. If using homegrown cereals, walking the field pre-harvest and checking for visible mould will provide an indication of whether the feed is going to present a risk to animal health and performance.
2. If you spot white mould growth on feedstuffs, then continue to monitor any changes in the colour/size of the mould, as environmental triggers can cause the mould to enter the reproductive stage, producing mycotoxins