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

Abstract

Samples obtained from fleeces exhibited at a National Merino Fleece Wool Competition were analysed for physical and chemical properties. Standard methods of analyses anda modified method for determining disulphides and thiols polarographically with methyl mercury iodide are described. The accuracy of judging was calculated through r2-values from correlation coefficients. The interrelationship between different characteristics was estimated by correlation coefficients. The accuracy of calculating clean wool weight from greasy fleece weight by means of the estimated yield value, was very high (83 percent). The low accuracy of estimating yield· seems to have a negligible effect and for practical breeding and classing purposes it can be disregarded. While the accuracy of judging length is low, in practice the error is negligible because a length difference of one inch is allowed in wool from the same bale. Judges tend to underestimate length. Spinning count estimation seems to be more dependent on crimps per inch than on fibre thickness. Judges tend to underestimate spinning count as a result of the undercrimping in the wool. While the Duerden standard, laid down in 1929, is still used, it is emphasised that a re-evaluation of the crimp fibre thickness relationship in the South African Merino wool must be made. The internationally eccepted A.S.T.M. standards seem a much more accurate basis for judging spinning count of South African Merino wool. The large number of fleeces disqualified for being overstrong is alarming. If disqualifications had been based on measured fibre thickness, a smaller percentage of the fleeces would have been disqualified while the use of A.S.T .M. standards seemsa more realistic basis and only 13.8 percent of the fleeces would have been disqualified in comparison with the actual 38.5 percent. The greasy fleece weight is positively correlated with the amount of scoured wool ~~ and staple length.\audn~\ve1y witb spinning count. The amount of scoured wool is positively correlated with greasy fleece weight and staple length and negatively correlated with spinning count. Spinning count is negatively correlated with length. The use of greasy fleece weight as a selection criterium is recommended. The use of length and a lower spinning count as a selection measure to increase the amount of scoured wool is discussed. Selection f~r length to a maximum of 3! inches is recommended while a decrease in spinning count as a method ';to increase the amount of scoured wool is strongly disapproved of. While no significant correlations were found between quality and other physical wool properties it would seem from the literature that finer wool has the better quality. This corresponds with the definition of quality in the trade. Although data are limited9 it would seem that differences in quality can be ascribed to differences in the chemical composition of the keratin fibre and that chemical decomposition of the tip sections affected the estimation of quality. An increase in wool production as a result of an increase in length may be the reason for the positive correlation between the amount of scoured wool and the thiol content and the negative correlation between the amount of scoured wool and the disulphide bond status. A positive correlation was also found between greasy fleece weight and thiol content. Highly significant correlations were found between yield and alkali solubility (positive), total disulphides + thiols and thiols (negative). This may possibly be due to the amount of yolk present in the wool. Longer fibres tend to contain less yolk than short fibres. This results in the decomposition of the exposed tip section of long fibres and consequently the production of thiols from disulphides. The bilateral structure of wool is responsible for crimp formation and the paracortex contains more and/or different disulphide linkages than the orthocortex. A significant positive correlation between spinning count and disulphide bond status and a negative correlation between spinning count and thiol content were found. Although data are rather limited it would seem that finer fibres contain more disulphide bonds than coarser fibres, possibly as a result of a higher degree of keratinization in the paracortex. Accuracy of judging is dicussed and a re-evaluation of crimp fibre thickness relationship for South African standards is recommended. Interrelationship between different wool traits is summarised and the practical applications thereof are discussed. A possible reason for the non-significant correlations in the ram sample group between physical and chemical properties seems to be the lower variation in the ram sample.