Íslenskar landbúnaðarrannsóknir - 01.09.1976, Blaðsíða 50

J. AGR. RES. ICEL.
ÍSL. LANDBÚN.
1976 8, 1-2: 48-53
Studies on autumn weight of Icelandic lambs
I. Correction factors for autumn weight of lambs
JÓN VlÐAR JÓNMUNDSSON
Agricultural Research Institute,
Reykjavík, Iceland.
ABSTRACT
A study was made of the effect of some systematic environmental effects on autumn weight of 13217
lambs of the Icelandic breed of sheep. Type of birth and rearing of lamb, age of dam, age of
lamb and sex explained 46 per cent of the variation in autumn weight within farm and year.
The constants obtained for these effects are given in tables and in the text.
Introduction.
Approximately forty per cent of the total
agricultural production in Iceland comes from
the sheep sector. In no other country in Nort-
hern Europe are sheep of such importance
for the agricultural economy.
One of the ways of increasing productivity
of the sheep production is by improving the
sheep population genetically by selection. It
has been shown in several instances that
auffimn weight of lambs is highly influenced
by systematic environmental factors (Aðal-
steinsson, 1966, Gjedrem, 1965, San-
golt, 1969). It is therefore necessary to be
able to adjust for these environmental effects
when estimating the breeding value of indi-
vidual animals and also when genetic para-
meters are being estimated.
Material.
The data used in the present investigation
were collected on lambs from the Icelandic
breed of sheep on four experimental farms
in Iceland during the period 1965 —1970.
Table 1 shows the number of breeding ewes
on these farms together with the average
number of lambs born per ewe alive at
lambing time. On all the farms in the study,
selection against tan fibres in the wool and
for improved pelt quality has taken place
during the period in question.
The data were available on punched cards.
From there they were transferred to a magne-
tic disc pack where the calculations carried
out. Altogether 13217 lambs were included
in the analysis. Excluded were lambs with
missing information and all abnormal lambs,
e.g. sick lambs, lambs which lost their dam
during the grazing period etc. Of the total,
6438 were male, and 6779 female lambs.
The average autumn live weight of all lambs