Íslenskar landbúnaðarrannsóknir - 01.03.1977, Side 18

ÍSL. LANDBÚN.
J. AGR. RES. ICEL. 1977 9,1: 16-30
A study of data from the sheep recording
associations in Iceland.
I. Sources of variation in weights of lambs.
JÓN VlÐAR JÓNMUNDSSON
Agricultural Research Institute, Reykjavík, lceland.
ABSTRACT
The effects of environmental factors on weaning weight, carcass weight and dressing percentage were
studied on the basis of data from the Icelandic Sheep Recording Associations for the years 1970
and 1971. The data consists of information on the weaning weights of 57996 lambs.
There were found to be significant effects on weaning weight of type of birth and rearing, sex, age
of dam and age of lamb. The R2 value for the model which includes these effects was 0.388. The
estimated difference in weaning weight between singles and twins was 6.35 kg and in dressing percen-
tage 2.18 units. The sex difference in weaning weight was 2.82 kg and in dressing percentage
0.83 units. The regression coefficient of weaning weight on age on 1. October was 0.197 kg/day.
Heritabilities and genetic correlations were estimated by the use of half-sib correlation. The following
heritability estimates were found: 0.20 for weaning weight, 0.13 for carcass weight and 0.18 for dres-
sing percentage. There was found to be a negative genetic correlation between weaning weight and
dressing percentage.
Out of the total variation in corrected weaning weight 33.6 percent was due to flock variation.
The heritability of the flock average estimated on the basis of information about lambs sired by rams
used through artificial insemination was 0.03.
INTRODUCTION.
Iceland’s agricultural production is mostly
based on production from ruminants, sheep
and cattle. About 40% of the farmers’ in-
come derive from sheep production. Of this
some 85% come from meat but 15% from
wool and skins. Therefore the most important
traits in sheep breeding in Icéland are the
weight of lambs at slaughter and the pro-
lificacy and productivity of ewes.
The purpose of the present study was to
study the effects of different environmental
factors that influence the weight of lambs,
both live weight and carcass weight, and also
to estimate genetic paramenters for these
characters.
MATERIAL
The data in the present study were obtained
from the Sheep Recording Associations in
Iceland for the years 1970 and 1971.