Íslenskar landbúnaðarrannsóknir - 01.09.1976, Side 62

ÍSL. LANDBÚN.
j. agr. res. icel. 1976 8, 1-2: 60-65
Studies on autumn weight of Icelandic lambs
III. Selection for autumn weight of lambs
JÓN VlÐAR JÓNMUNDSSON
Agricultural Research Institute,
Reykjavik, Iceland.
ABSTRACT
The paper describes a study on seleaion for autumn weight of lambs on four experimental farms
in Iceland during the period 1965—1970. For 313 ram lambs the phenotypic seleaion diffeten-
tial was found to be 0.84 standard deviations, and 0.43 standard deviations for 1634 ewe lambs.
The applied selection should result in an annual genetic gain in autumn weight of lambs of 0.3—
0.5 per cent.
It was further found that only 38 per cent of potential selection had been utilized for ram lambs,
and 36 per cent had been utilized for ewe lambs. The main reason for this is an intense seleaion
for wool charaaers during the period in question. Utilization of potential selection for autumn
weight of lambs would not have lowered selection for feritility.
Introduction.
The phenotypic progress which is registered
in breeding work is usually a result of both
genetic and environmental effects. The gene-
tic progress made is of particular interest,
one of the main reasons being that this pro-
gress measures how effective the breeding
methods have been.
The present paper describes an analysis
which aims at measuring the intensity of
selection for autumn weight of lambs and
how much genetic progress the applied selec-
tion should result in.
Material.
The data for the study are taken from four
experimental farms for sheep in Iceland in
the period 1965 —1970 and has been de-
scribed in a previous paper in this series
(JÓNMUNDSSON, 1976a).
Method and results.
It has been assumed that the selection applied
has been mass selection only, whereby the
lambs have been selected on basis of their
own phenotype. The expected genetic gain
per year (A G) is then: