A study of fleeces exhibited at a national merino fleece wool competition

[摘要] Samples obtained from fleeces exhibited at aNational Merino Fleece Wool Competition were analysedfor physical and chemical properties.Standard methods of analyses anda modified methodfor determining disulphides and thiols polarographicallywith methyl mercury iodide are described.The accuracy of judging was calculated throughr2-values from correlation coefficients. The interrelationshipbetween different characteristics wasestimated by correlation coefficients.The accuracy of calculating clean wool weight fromgreasy fleece weight by means of the estimated yieldvalue, was very high (83 percent). The low accuracyof estimating yield· seems to have a negligible effectand for practical breeding and classing purposes itcan be disregarded.While the accuracy of judging length is low, inpractice the error is negligible because a lengthdifference of one inch is allowed in wool from thesame bale. Judges tend to underestimate length.Spinning count estimation seems to be more dependenton crimps per inch than on fibre thickness.Judges tend to underestimate spinning count as aresult of the undercrimping in the wool. Whilethe Duerden standard, laid down in 1929, is stillused, it is emphasised that a re-evaluation of thecrimp fibre thickness relationship in the SouthAfrican Merino wool must be made. The internationallyeccepted A.S.T.M. standards seem a much moreaccurate basis for judging spinning count of SouthAfrican Merino wool.The large number of fleeces disqualified for beingoverstrong is alarming. If disqualifications had beenbased on measured fibre thickness, a smaller percentageof the fleeces would have been disqualified while theuse of A.S.T .M. standards seemsa more realistic basisand only 13.8 percent of the fleeces would have beendisqualified in comparison with the actual 38.5 percent.The greasy fleece weight is positively correlatedwith the amount of scoured wool ~~ andstaple length.\audn~\ve1y witb spinning count.The amount of scoured wool is positively correlatedwith greasy fleece weight and staple length and negativelycorrelated with spinning count.Spinning count is negatively correlated withlength.The use of greasy fleece weight as a selectioncriterium is recommended.The use of length and a lower spinning count as aselection measure to increase the amount of scouredwool is discussed. Selection f~r length to amaximum of 3! inches is recommended while a decreasein spinning count as a method ';to increase the amountof scoured wool is strongly disapproved of.While no significant correlations were foundbetween quality and other physical wool properties itwould seem from the literature that finer wool hasthe better quality. This corresponds with the definition of quality in the trade.Although data are limited9 it would seem thatdifferences in quality can be ascribed to differencesin the chemical composition of the keratin fibre andthat chemical decomposition of the tip sectionsaffected the estimation of quality.An increase in wool production as a result of anincrease in length may be the reason for the positivecorrelation between the amount of scoured wool andthe thiol content and the negative correlation betweenthe amount of scoured wool and the disulphide bondstatus. A positive correlation was also foundbetween greasy fleece weight and thiol content.Highly significant correlations were found betweenyield and alkali solubility (positive), totaldisulphides + thiols and thiols (negative). Thismay possibly be due to the amount of yolk present inthe wool. Longer fibres tend to contain less yolkthan short fibres. This results in the decompositionof the exposed tip section of long fibres andconsequently the production of thiols from disulphides.The bilateral structure of wool is responsible forcrimp formation and the paracortex contains more and/ordifferent disulphide linkages than the orthocortex.A significant positive correlation between spinningcount and disulphide bond status and a negative correlationbetween spinning count and thiol content werefound. Although data are rather limited it wouldseem that finer fibres contain more disulphide bondsthan coarser fibres, possibly as a result of a higherdegree of keratinization in the paracortex.Accuracy of judging is dicussed and a re-evaluationof crimp fibre thickness relationship for SouthAfrican standards is recommended.Interrelationship between different wool traitsis summarised and the practical applications thereofare discussed.A possible reason for the non-significant correlationsin the ram sample group between physical andchemical properties seems to be the lower variationin the ram sample.

[发布机构] University of the Free State