Reading wool certificates a skill

Waimarino Bulletin, Volume 5, Issue 4, 23 June 1987, Page 7

Reading wool certificates a skill

For Woolgrowers, reading a wool test certificate has become a necessary skill. Some figures are a valuable guide to policy on the farm and in the woolshed but they have to be sorted out from others that are provided for the trade. The first purpose of the certificate is to give the clean weight of wool. Although auction bidding is in terms of greasy weight woolbuyers value the wool on a clean basis and it is on this basis that the grower is paid. The certificate carries a number of yields but the grower should look for "IWTO Schlumberger dry combed" and the clean weight beside it. To find the clean price, the grower should divide the greasy price by the Schlumberger percentage yield. Clean prices at auctions reported throughout New Zealand are calculated in the same way using the same Schlumberger yields. The clean weight and price for the line, with the effects of grease, dirt and moisture removed, enables a true comparison to be made between different liries of wool depending on breed, length, fineness and colour. Length does not appear on the certificate but growers will know it. More today are shearing when the wool is at its best. For Crossbreds, the length should be between 75mm and 100mm. Fine wools should generally be more than 75mm. "Vegetable matter base" is the next heading the grower should note. The Wool Board advises growers to keep sheep out of seedy blocks in the

weeks before shearing and to remove seedy necks and "birds' nests" from the backs. If the vegetable matter reading for a Crossbred line is over 0.5 percent, it is significant and the grower should take some action. Fine wools may go higher as they are usually combed, a process which removes most of the vegetable matter. "Fibre fineness (airflow)" is mainly of interest to fine wool growers. The "airflow" refers to the method of measurement. An instrument measures the resistance of a wad of wool to an air current; the greater the resistance, the finer the wool. Fineness is expressed in microns ("mu" on some certificates). Coupled with the prices received for different lines, the micron will show the grower whether the best classing policy has been pursued. The Wool Board's advice is that growers should restrict the number of fine wool lines, with a difference of at least one micron between them. "Colour measurement" is

the final heading of interest. Colour is fast emerging as an important measure for growers of Crossbred wools. The "YZ" reading for yellowness should be less than 4 and the "Y" reading for brightness should be over 60. The grower can relate the measurements on the certificate to the time of shearing and the prices received. Good colour is achieved by shearing early, avoiding a long fleece on sheep through the summer. Good colour for Halfbreds is a "Y-Z" of less than 3 and "Y" above 62; for Merinos "Y-Z" less than 2 and "Y" above 65. Colour measurement is also of value to growers in deciding how heavily to skirt. Penstain, brands, cotts and heavy vegetable matter should always be removed. What to do with the permanently discoloured points depends on the amount of discolouration and the overall colour and brightness of the fleece. The measurement provides the answer; if the first

pieces have a colour reading that differs from the fleece wool by less than 3. units of "Y-Z", then they should not have been removed. "These five measurements - yield and clean weight, vegetable matter, fineness and colour - make up the essential information on the certificates," says the Board's National Wool Production Manager. Mr

L.K.

(Lance)

Wiggins.

"I hope one day they can be presented in a way that is easier for growers to read and to relate to their on-farm wool management."