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FLEECE MEASUREMENT AND WOOL WEIGHT [Vol. XXVIII, Part III,
quality is being controlled by culling animals with too strong a fibre as judged on
measured diameter. Excessively wrinkly sheep are also culled. In a group of
initially similar sheep run with them as controls, selection is entirely at random.
At the commencement of this part of the experiment, in 1950, the average clean wool
weights of the offspring from the two groups were similar.
After four years, the offspring from the group selected by the fleece measurement
method cut on average of 0.4 lb. of clean wool more than the offspring from the unselec-
ted sheep running with them. The actual average clean wool weights for ewes
16 months old were 7.3 lb. and 6.9 lb. respectively.
The increase over the four years was slightly more than 1.2 per cent per annum
which would be predicted on the basis of the original heritability studies with the
mating system used. There was no increase in body size in the selected group and
there was no appreciable change in fibre diameter. There was, however, a very
slight decrease in the number of crimps, the selected group averaging 11 crimps per
inch compared with the 12 per inch of the controls. Both staple length and "density"
number of fibres per square inch) increased in the selected group.
In another experiment at Gilruth Plains, selection is being concentrated on one
character at a time. Thus, there are contrasting groups for each of several characters,
in one of which selection is aimed at increasing the character to a maximum while in
the other the aim is to reduce it to a minimum.
In contrast to the practice in the previous experiment, culling rates are much
higher than those encountered commercially. This is to ensure that the characters
will be pushed as quickly as possible to extreme values either way. The characters
under selection are clean wool weight, staple length, fibre number, fibre diameter,
body size, and degree of wrinkling. The aim is not only to see how far one character
can be taken by selection, but also to see what happens to other characters during the
process.
A dramatic response has been obtained for every character and in most cases this
response has been greater than that predicted. In the group selected for high clean
wool weight, the mean clean weight for ewes was 7.6 lb. for the two-tooth ewe offspring
in 1956, compared with 6.4 inches the low clean wool weight group. Staple length for
ewes in the group selected for long staple averaged 4.5 inches compared to 2.9
inches in the short staple group. Ewes in the large body size group weighed 86 lb.
as two-tooths (16 months old) while those selected for small size were only 64 lb.
Responses in the other single character selection groups were of the same order.
Of great interest are the recombinations of the various fleece characteristics
that have taken place. Earlier findings, that dense fleeces tend to be finer, and more
wrinkly sheep to have a shorter staple, have been confirmed. Sheep in the group
selected for high density (fibre number) have a much finer fibre than those in the low
density group. Also, animals selected for strength (high fibre diameter) have a
much lower density than those selected for fineness (low diameter).
Because of the negative association between the two characters, selection for
short staple has produced some animals even more wrinkled than those selected
deliberately for wrinkles. Moreover, some of those selected for high wrinkles have
an even shorter staple than those selected for short staple.