Íslenskar landbúnaðarrannsóknir - 01.03.1977, Page 63

ULLARÞUNGI ÁA 61
ástæða til að vega af tvævetlum, enda mestur
breytileiki í ullarmagni við þann aldur.
Erfðafylgni ullarþunga við frjósemi og af-
urðastig bendir til þess, að ullarmagn ætti
að aukast jafnhliða úrváli fyrir aukinni frjó-
semi og vænleika lamba hjá ánum.
Engin mæling á ullarþunga áa er til í
fjárræktarfélögum, en fyrsta skilyrði þess
að kynbætur verði stundaðar til að ná auknu
ullarmagni, er að taka upp mælingar á því.
SUMMARY
Fleece weight of ewes and its relation
to other production characteristics
JÓN VlÐAR JÓNMUNDSSON
Stefán Aðalsteinsson
Og
Jón Trausti Steingrímsson
Aðricultural Research lnstitut,
Keldnaholti, Reykjavík.
The paper describes an investigation on
variation in wool weight of Icelandic ewes,
based on data from four state farms in the
period 1966—’75.
The coefficient of variation was found to
be 18%. Two year old ewes were found to
have the highest average fleece weight, one
year old ewes having 0.9 kg lighter and three
year old ewes 0.4 kg lighter fleeces than
two year old ewes.
The regression of wool weight of one year
old ewes on live weight at 4—5 months,
corrected for type of rearing and age of dam,
was found to be 0.0367 kg/kg.
Ewes which reared a lamb at one year of
age produced 0.26 kg less wool the following
í Ástralíu hafa verið gerðir útreikningar
til að kanna hagnað af skráningu ullarmagns
(Thatcher og Napier, 1976). Forsendur
þær, sem þar gilda, eiga á engan hátt við
hérlendis, og hafa niðurstöður þeirra því
ekkert gildi við hérlendar aðstæður. Aðferð
þá, sem þeir nota við útreikningana, má afmr
á móti nota hér á landi til að meta hagnaðinn
af skráningu ullarþunga.
year than one year old ewes which did not
rear a lamb.
Heritability of wool weight and three other
characters was estimated by several methods
and the best estimates were found to be as
follows: wool veight 0.28, wool class 0.55,
number of lambs born 0.20 and ewes score
for lamb carcass production 0.23. The re-
peatability estimates for the same traits were
0.33, 0.51, 0.24 and 0.32, respectively.
A positive genetic correlation was found
between wool weight and fertility and wool
weight and lamb carcass production score,
but negative between fecundity and lamb
carcass production score. Wool class was
negatively geneticálly correlated with wool
weight and lamb caracass production score
but positively with fecundity. Some of the
above correlations are biased because of in-
tense selection for improved wool class carried
out during the period under study.
The genetic correlation between years for
wool weight was bélow unity. The possi-
bilities for selecting for higher wool weights
are discussed and the necessity of incorpo-
rating wool weight into index selection is
pointed out.