Íslenskar landbúnaðarrannsóknir - 01.09.1976, Side 60

58 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
estimate of 0.27, equal for both sexes, was
obtained for maternal effect on autumn
weight of lambs. Gjedrem (1967) found an
estimate of 0.12 for the same character, while
Eikje (1970) was unable to demonstrate any
genetic variation in this character. Shelton
and Menzies (1968) found a heritability of
0.29 for „total lamb production”. Aðal-
STEINSSON (1971) found a heritability of
0.21 for ewe productivity measured as a score
for carcass production per ewe at two years
of age. Compared to the referred estimates,
the estimate found in the present smdy seems
relatively high.
Sources of bias in this analysis are gene-
rally of the same type as when estimating
heritability of autumn weight of lambs. The
k-value was 5.5, and the genetic relationship
between halfsibs calculated by the formula
given by Osborne (1957) was found to be
0.260 for males and 0.262 for females. En-
vironmental correlations might therefore
have greater effect in the latter analysis.
ÍSLENZKT YFIRLIT
Rannsókni' á þunga lamba á fœti.
II. Arfgengi.
Jón Viðar Jónmundsson
Rannsóknastofnun Landbúnaðarins.
Reiknað hefur verið arfgengi fyrir þunga
lamba á fæti á fjórum ríkisbúum haustin
1965—1970. Arfgengi var metið frá fylgni
When calculating the heritability of ma-
ternal effect, the same daughter groups will
be repeated in successive years. As a result,
the calculations will be based on much fewer
sires than the within year sire groups indicate,
because information on the same animals is
used repeatedly. Therefore, the question of
how sums of squares and degrees of freedom
should be combined has greater actuality in
an analysis on maternal effect than when
analysing autumn weights grouped by sires
of lambs.
It should be pointed out that if the correc-
tion for the effect of age of dam on lamb
weight is incomplete, this might affect the
estimate, because within many of the daugh-
ter groups all the ewes are of the same age.
If the covariance between maternal genetic
and additive genetic effect on autumn weight
of lambs is negative, then the heritability of
maternal effect has been underestimated by
the method used.
hálfsystkina. Hjá 6326 hrútlömbum var arf-
gengi 0.19 — 0.03, en hjá 6645 gimbrum
0.29 ± 0.04.
Arfgengi fyrir móðuráhrifum á þunga
lamba á fæti var reiknað 0.27 * 0.04 og
reyndist jafnt fyrir bæði kyn.
Hugsanlegir skekkjuvaldar í gögnum og
við útreikninga eru ræddir og útkomurnar
bornar saman við hliðstæðar eldri rannsóknir.