Testing for Vegetable Matter (VM) is performed as a standard component of the pre-sale testing procedure. The figure that is published in wool-sale catalogues is the percentage of VM found in the greasy wool core-sample.

The presence of VM in wool is considered a disadvantage as its removal during processing can be costly. Depending on the severity and type of Vegetable Matter, the wool may need to undergo additional processing called Carbonising. Carbonising is a relatively complicated and expensive process which adds to the cost of the final product. It involves passing the wool through sulphuric acid bowls and ovens, before rollers crush the brittle VM that remains. As well as being slower, carbonising usually involves higher fibre loss than other processing methods.

Vegetable Matter type is allocated into 7 main types with the AWEX-ID typing system.

• B - Burr (barrel medic, burr medic)
• E - Seed (sub clover, carrot seed, scotch thistle) 
• S - Shive (barley grass, wild oats)
• N - Noogoora burr
• T - Bathurst burr
• M - Moit
• F - Bogan Flea

In combing wool, fibrous types of VM (S) are the most difficult to remove for processors as they align themselves with the fibre during combing and can pass through to the final fabric. Consequently these types of VM carry the largest discounts. Burry types of VM such as those belonging to the medic group generally sit on type of the staple and are considered easier to remove during processing. Higher percentages of Burr are usually acceptable by processors for this reason.

Discounts for Vegetable Matter are relatively minor in the market place for those types testing less than 1.5%. Penalties start to apply when fleece wool approaches the 2% level and increase rapidly over 2%, reflecting the higher costs and lower throughput for the processor.

VM Discounts - Fine Wool

VM Discounts - Medium Wool

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Vegetable matter trends

The trends in the Vegetable Matter (VM) discounts in the fine and medium wool categories are shown in the charts below.

In the finer microns discounts for high VM levels began to contract in the 2001/02 and 2002/03 seasons. The low point was reached in 2003 when the penalties where halved from the 2000 season levels.

After bottoming out the discounts began to drift out in the first quarter of the 2004/05 season where they began to approach longer term levels.  The ongoing dry conditions have increased numbers of high vm types recently which has resulted in larger discounts for sale lots with 8%vm and greater.

In the medium microns, discounts for 4% types have tended to remain static, trading in a 40 to 70 cent range.  Meanwhile 8% types fallen sharply lately with discounts approaching levels close to those in the finer microns.  In the last quarter the margin was approximately 160 cents clean.

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Wool vegetable matter tips

There are a number of ways to reduce Vegetable Matter (VM) in your wool clip.

Grazing environment

The conditions that sheep graze under can have a large effect on the amount of VM that ends up in the fleece. Your location within Australia will play a large part on both the levels and types of VM that appear in your wool, however a number of strategies exist to reduce problematic levels of VM.

Pasture management tools include herbicide spraying or slashing at key times of the year. You could also consider changing pasture types, however this may have other long-term management implications.

Grazing tools include the overall set stocking rate during the course of the year, and the implementation of strategic grazing techniques such as cell grazing.

Shearing

Shearing can be timed so that sheep are in short wool at the time of greatest exposure to seeds, burrs and other contaminants.

This would generally require shearing sheep before seeds mature on the plant. Frequency of shearing can also have an impact on the levels of seed and burr in the wool, although more regular shearing (more than once per year) is uncommon and generally seen as uneconomical.

While it can be tempting to skirt heavily at shearing time to reduce high levels of VM in fleece wool, studies have shown that this practice is not economically efficient.

Sheep coats

A recent AWI study of 1200 sheep in Western Australian found that vegetable matter could be reduced significantly by the use of sheep coats.

While fleeces from non-coated animals had an average VM of 2.0%, those from coated sheep had an average of 0.7%. The coats also improved yield and reduced the incidence of fleece rot.

The report found the use of sheep coats improved the value of the wool sold on average by $3.40 per head but in some cases was up to $8.51 per head.

Economic Viability of Sheep Coats for Wool Production (Australian Wool Innovation Limited) -  Final report (PDF 350Kb)

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