Staple tenacity versus staple strength
D.R. Scobie, N.C. Merrick, A.R. Bray
AgResearch, P.O. Box 60, Lincoln, 8152, New Zealand
Proceedings of the New Zealand Society of Animal Production. 1995,
55: 39-41
Staple tenacity is an estimate of the peak force to break a staple
of a certain cross-sectional area at the point of break. Staple
strength is a measure of peak force to break a certain weight of staple.
Using the density of wool and the length of staple broken, both
estimates can be converted to force per unit linear density (N/ktex).
The relationship between these two estimates was examined. Midside wool
samples were collected at shearing from 164 ewe hoggets from lines of
New Zealand Romneys that have been selected for or against staple
tenacity, and a randomly selected control line. Five staples from each
sample were measured for staple strength and staple tenacity. This was
accomplished by defining the cross-sectional area at the break point,
breaking the staple to estimate peak force and then cutting the portion
of the staple from between the jaws and determining the weight of clean
wool after scouring. The High staple tenacity line had a significantly
higher staple strength (P<0.001) and staple tenacity (P<0.001).
Although a similar weight of greasy wool was removed from between the
jaws for each selection line (P=0.336), the weight of clean wool was
significantly greater in the High staple tenacity line (P=0.003).
Covariate analysis revealed that the fitted relationships between staple
strength and staple tenacity for the three selection lines had similar
slopes (P=0.822) but significantly different intercepts (P=0.029).
Staple strength is thus biased relative to staple tenacity in these
lines, because of the differences in weight of wool between the jaws,
for staples which are all the same cross-sectional area at the point of
break. Staple tenacity is therefore more useful for some purposes than
staple strength and vice versa, and care should be taken when drawing
comparisons and conclusions and when considering which to use.
Keywords: NZSAPAB;
staple tenacity; staple strength; yield; selection lines
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Last Updated 25-01-1997
