Íslenskar landbúnaðarrannsóknir - 01.09.1975, Page 62

60 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
TABLE 6.
Comparison by pelt class of sire of number of lambs born per ewe, score for carcass weight of lambs
and production index of ewes for two year old ewes.
Deviations from average ±95%
Pelt class of sire No.of sires No. of ewes No. of lambs confidence limits Score for carc.wt. Production index
A+B 30 339 0.01 ± 0.05 —0.15 ± 0.1'6 —0.04 ± 0.09
C 13 126 0.05 ± 0.08 0.08 ± 0.27 0.10 ± 0.15
D 26 215 -—0.07 ± 0.06 0.17 ± 0.20 —0.04 ± 0.12
By assigning the values 10, 5 and 0 to
pelt classes A-|-B,C and D, respectively, the
regression of offspring on midparent can be
calculated, giving an estimate of the herita-
bility of pelt class.
The regression coefficient was found to be
0.46 ± 0.05.
In a later investigation on independent
data (Adalsteinsson, 1971 b) the herita-
bility of the above pelt dass values was
found to be 0.49 ± 0.03 by intra class corre-
lation based on 13,489 lambs and 0.54 ±
0.03 by regression of offspring on dam, based
on 3,696 offspring-dam pairs.
These estimates show that the heritability
of pelt class is high compared to other quan-
titative traits in sheep.
3. Effect of presence of tan colour on lamb
weight and ewe productivity.
The connection between tan colour and lamb
weight and ewe productivity has been in-
vestigated to some extent. In one investiga-
tion (Adalsteinsson, 1966) 240 lambs
sired by 6 rams in pelt classes A and B were
compared to 216 lambs sired by 8 rams in
pelt class D. The difference in dressed car-
cass weight between the lambs in the two
groups was 0.11 kg in favour of the group
D rams. This difference, however, was not
significant.
In another investigation the effect of tan
colour on productivity of ewes was measured
in two ways. In the first instance 937 two
year óld ewes were divided into two pelt
class group, i.e. 272 ewes in pelt classes A
and B and 665 ewes in pelt classes C
and D. The difference between the two
groups in number of lambs born was 0.05
lambs per ewe in favour of the ewes in group
C -|-D (not significant), and in score for
carcass weight of lambs the difference was
0.31 points, also in favour of group C +D.
This difference was significant (P<O.05).
The second comparison was done on the
basis of grouping 680 two year old ewes on
basis of the pelt class of their sires. The re-
sults of the comparison are shown in table 6.
The results in table 6 show no significant
deviations from average with respect to eith
er number of lambs per ewe lambing, score
for carcass weight or ewe production index,
except for the lowered number of lambs
from daughters of sires in pelt class D.
The significantly lower carcass weight
score for ewes in pelt classes A and B in the
first comparison could be due to löwered
selection intensity for weight among ewe
lambs in these classes kept for breeding, the
main selection criterion being absence of tan
fibres.
The lighter weight of the selected female
lambs would result in lower inherent weight
as well as some maternal effect on lamb