Íslenskar landbúnaðarrannsóknir - 01.09.1975, Page 59

OCCURRENCE AND INHBRITANCE ’ýf
TABLE 1.
Wool quality measurements.
No.of Fibre diam. Medullated fibres Tan fibres
Sheep group animals micron % micron % micron
Adult ewes ■ 1) 113 24.9 1.6 56.4 2.1 52.4
One year old ewes . . . ■ 1) 17 27.3 1.0 60.9 1.3 53.1
Adult rams ■ 1) 7 31.0 1.9 78.5 2.8 72.9
One year old rams . . ■ 1) 3 25.7 0.8 56.4 1.8 43.8
Adult rams • 2) 204 30.7 5.8 71.9 0.6 97.4
1) T-welve months growth of wool. Samples taken in spring. overestimated. 2) Six months growth of wool. Samples taken in autumn. Percentage of tan fibres most likely
Scoring for tan colour of lambs at birth,
fleece classification at shearing and classifi-
cation of lamb pelts on live lambs at weaning
have been carried out since 1963 at the Ex-
perimental Farm Reykhólar, and since 1965
at the Experimental Farm Skriduklausmr and
the Agricultural School Hvanneyri.
On the above farms, all lambs are ear-
tagged, and record is kept of the parentage
of each lamb. On four of the farms, i.e.
Hólar, Reykhólar, Skriduklaustur and
Hvanneyri, smdies on the inheritance of tan
fibres have been carried out, and on the
same farms selection against tan fibres has
been practiced since the initiation of the
classification.
A system for converting carcass weight of
lambs per ewe into a score has been deve-
loped and an index for ewe productivity has
also been evaluated (Adalsteinsson, 1971
a). The number of lambs per ewe íambing,
the ewe’s score for carcass weight and the
ewe’s production index, based on number of
lambs at lambing and score for carcass pro-
duction, have been used as criteria when jud-
ging the effect of tan colour on ewe producti-
vity. In order to avoid year affecting the pic-
ture, all records have been expressed as devia-
tions from each year’s average.
RESULTS
1. Wool quality measurements.
Table 1 shows the average fibre diameter
and percentage of medullated fibres and their
diameter and percentage of tan fibres and
their diameter.
The measurements made in Norway show
appreciably higher amount of tan fibres than
those made in Iceland. The former vere
made on wool samples taken in spring, after
a full year’s growth and it is believed that
some fibres with damaged surface have mis-
takenly been classified as tan fibres. The low
average diameter of the fibres in that in-
vestigation favours this explanation.
In the wool samples from adult rams
measured in 1959 (Adalsteinsson, 1961),
the diameter of individual tan coloured and
medullated fibres was measured.
Textfigure 1 gives the frequency distri-
bution of the diameter of all measured fibres
(left side) and also the percentage of all
fibres within each diameter which were either
tan-coloured or medullated. The figure
shows that medullation and tan colour are
absent in fibres below 35 micron, while 50
per cent or more of all fibres above 60