Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 53

STUDIES ON AUTUMN WEIGHT OF ICELANDIC LAMBS 51
Table 3. Constants for the effect of type of birth on autumn weight of lambs. ± s.e.
Type of birth group Sexes combined Male lambs Female lambs
Number Constant Number Constant Number Constant
1 X 1 X 1 3764 5.28 + 0.19 1868 6.06 + 0.28 1896 4.68 + 0.26
2 X 1 X 1 494 2.90 + 0.23 264 2.97 + 0.34 230 3.00 + 0.31
2 X 2 X n
1 X 2 X 2 / 241 + 0.24 + 0.28 122 + 0.07 + 0.41 119 + 0.26 + 0.37
2 X 2 X 2 8658 + 1.71 + 0.19 4154 + 1.69 + 0.28 4504 + 1.60 + 0.25
3 X 2 X 2\
3 X 1 X 1/ 25 + 1.43 + 0.66 15 +0.94 + 0.91 10 + 2.11 + 0.96
3 X 3 X 3 35 +4.81 + 0.59 15 + 6.32 + 0.05 20 +3.60 + 0.74
wegian investigations (Eikje 1971, Fim-
land et.al. 1969, Gjedrem 1965, Sang-
olt 1969). One of the explanations is that
in the present investigation the lambs are
younger than in the referred Norwegian in-
vestigations.
Type of birth and rearing.
In the data processed here, the type of birth
and rearing has been recorded three times,
i.e. at birth, at shearing time of ewes in July
and as number of lambs in autumn. Alto-
gether six groups and rearing types were
therefore obtained in the material. Constants
for type of birth and rearing effects are shown
in table 3. The difference between singles
and twins is 6.99 kg and is higher than that
found in comparable investigations elsewhere
abroad (Blackwell and Henderson 1955,
Eikje 1971, Gjedrem 1965, Robertson
1969, Sangolt 1969, Vesely and Peters
1964) but comparable to that found by Að-
alsteinsson (1966). The effect of type of
birth and rearing is more pronounced, both
absolutely and relatively, for male than for
female lambs, which also is in agreement
with the findings of Aðalsteinsson (1966).
Sex.
The constant for sex found in the present
study is 1.47 ± 0.034 kg, which gives a sex
difference of 2.94 kg. Aðalsteinsson
(1966) found a sex difference of 3-6l kg for
single lambs and 2.54 kg for twin lambs.
Sangolt (1969) quotes several Norwegian
investigations which in general show a larger
sex difference than that found here.
Age of lamb.
As mentioned before, a significant curvilinear
effect of age on autumn weight of lamb was
found which, however, explained only a very
small proportion of the total variation. It was
therefore decided to use a linear regression.
The regression coefficients found were 0.165
— 0.004 for sexes combined, 0.178 — 0.007
for male lambs and 0.149 — 0.006 for fe-
male lambs, all expressed in kg/day. The
higher regression coefficient for male lambs
is in good agreement with the findings of
Pálsson and Gunnarsson (1961) which
showed that male lambs have a higher
growth rate on cultivated autumn pasmre
than female lambs.
The coefficients found here are somewhat
higher than those found in Norwegian in-
vestigations on Spaelsau (Old Norwegian
sheep) (Eikje 1971, Gjedrem 1965, San-