Íslenskar landbúnaðarrannsóknir - 01.03.1977, Page 33

ÍSL. LANDBÚN.
J. AGR. RES. ICEL. 1977 9, 1: 31-42
A study of data from
the sheep recording associations in Iceland.
II. Ewe production traits.
JÓN VlÐAR JÓNMUNDSSON
Agricultural Research Institute,
Keldnaholt, Reykjavík.
ABSTRACT
Factors affecting the number of lambs and the weight of lambs produced by 37833 ewes in the
Sheep Recording Associations in Iceland for the years 1970 and 1971 were studied.
The age of ewe accounted for 2.7 and 2.4% of the variation in the number of lambs born and
weaned, respectively. The 5 year old ewes proved to be most prolific and had on the average 0.23
more lambs at birth than the 2 year old ewes.
Ewe body weight was found to have a significant effect on the number of lambs born. This relation-
ship was curve-linear with the highest number of lambs at 75 kg body weight.
Age of ewe accounted for 10% of the variation in ewe body weight.
Heritabilities and genetic correlations were estimated for ewe traits by use of half-sib correlations.
The heritability for the number of lambs boxn was 0.19 and for the number of lambs weaned 0.13.
The corresponding value for score of lamb production was 0.21. The heritability estimates for ewe
body weight in October and January were 0.42 and 0.49, respectively. Correlations between traits were
positive.
INTRODUCTION
It has been shown in an economic analysis
(Hannesson and Sigþórsson, 1971) that
the number of lambs weaned per ewe is
the factor which has the greatest effect on
the income of the Icelandic sheep farmer.
The sources of variation in the number of
lambs will therefore be of great importance
in the breeding work with sheep. The weight
of lambs, which is affected by the mothering
ability of the ewe, is also of great importance.
The highest cost item of the sheep enter-
prise is the feed for the maintenance of the
ewes during the winter together with the
cost of labour and housing. The feed require-
ment for maintenance is a function of ewe
body weight. The correlation of the ewe
body weight with ewe production characters
is therefore of importance.
In this paper a study of variation in these
characters for ewes is described.