The Impact of Exotic Sheep Breeds

Since the mid eighties there have been increasing numbers of breeds of sheep being imported into Australia from South Africa. Western Australia has by far the largest numbers, most being meat breeds which are being crossed with Merinos for the Middle East live market. However, more recently other breeds have been imported, which can service the meat market and also have the dual purpose of growing quite respectable Merino wool. The most common are Awassi, Damara, Karakul and Dorper, all of which are kept mainly for their meat characteristics. In particular, purebred Damaras and Dorpers provide some economic advantages as they shed their wool so they don't need to be shorn and they can survive on very poor country. However, all the breeds have wool with a wide range of fibre diameter and can contain coloured fibres of varying degrees. The main cause of controversy, which has accompanied the introduction of the South African breeds, is the wool produced by the crosses, or in some cases the fact that the fibres shed by the lambs may contaminate the pure Merino wool of their mothers. Some of the wool produced is either brown or black and is easy to identify. But much of it in the greasy state appears white, although when scoured is off-white with noticeable amounts of coloured fibres spread throughout. It is this situation that is worrying the wool industry.

Since last July most wool brokers are asking growers who have some of the African breeds running with Merinos, to identify wool which may have cross contamination, and for those farmers who are able to separate the breeds successfully to provide a vendor declaration stating there are no mixed fibres. So far this is providing an element of comfort to the industry. However, because there are market penalties for the potentially contaminated wools, there is a temptation for such instances not to be declared.

It will take only one serious case of this mixed wool finding its way into a large processing batch for the situation to explode.

More recently there have been some breeds imported that generally aren't seen to be a problem if mixed fibres are present and this will appeal to some growers. Breeds such as the South African Mutton Merino (SAMM) and Dohne are examples. The SAMM is a fast maturing breed with merino wool of only average quality, while the Dohne is a similar type but with quite good wool characteristics. Generally the wool from the latter is impossible to distinguish from similar merino wool, processes well and has some very desirable features such as low CVD.

SARDI (South Australian Research & Development Institute) and AWTA Ltd have been co-operating in the development of a presale test to identify the amount of coloured or medullated fibres prior to sale. The methodology utilises the CSIRO Dark Fibre Detector, which was originally developed for semi-quantitative analysis of dark fibres present in wool tops. Wesfarmers Landmark has assisted this investigation by providing commercial samples. The major benefit of such a test, if it proves feasible, would be to reassure international wool buyers that they are purchasing pure merino wool thereby minimising the possibility of a price penalty being imposed on the grower. If an accurate and reliable presale test could be developed the possibility of WA's wool clip being suspect to mixed fibre problems and thereby being penalised as a result, would be less likely to occur.

In the wool processing industry there are instruments that can identify and measure the number of coloured fibres in carded sliver or wool top. But in this case the fibres have been cleaned and aligned so that they are roughly parallel to each other, therefore simplifying presentation of a relatively large amount of sample to the instrument. In the case of greasy core samples this is not the case, and despite the fact that the fibres are cleaned during the normal yield and diameter testing process, they remain very much entangled.

The other major challenge is the detection level required. Normally topmakers would wish to see less than 10 dark fibres per hundred grams of wool top. Translating this back to greasy wool, the detection limit needs to be about 6 dark fibres per hundred grams. The system currently under investigation examines about 0.5 grams of fibre at a time, which means that many such examinations need to occur for every sample if contamination at the level of 6 fibres per 100 grams is to be detected. The technique is extremely tedious and very subjective and consequently requires several hours for each individual examination. The only mitigating circumstance is that research using the technique has shown that where contamination does occur it is usually spread throughout the wool, so the probability that some fibres will be present in core samples taken from such lots will be reasonably high.

For any testing system to be successful it seems that the equipment must be able to examine sufficient sample material very quickly and identify any dark fibres reliably. Image analysis systems offer the most promise of being able to do this but unfortunately considerable difficulties remain to be overcome.

However, it is important to the industry that effective management systems are developed, and implemented. In the short term this must mean on-farm management, accurate labelling of product before it is placed in the market and the availability of at least a semi-quantitative measurement technique for providing some reassurance where there is suspicion that contamination has occurred.

Further information is also available on AWTA Ltd's website:

Dark Fibre Control in Sheep and Wool
http://www.awta.com.au/Publications/Fact_Sheets/
Fact_sheet_14.htm

Wool Contamination: pigmented & heavily medullated fibres.
http://www.awta.com.au/Publications/Fact_Sheets/
Fact_sheet_15.htm

Exotic Sheep Breeds in Australia
http://www.awta.com.au/Publications/Fact_Sheets/
Fact_sheet_16.htm

Editors Note:
This section of the Newsletter is published to enable a range of opinions to be expressed. Reference to specific commercial enterprises, methodologies, strategies or opinions must not be construed as an endorsement of them by AWTA Ltd.