Íslenskar landbúnaðarrannsóknir - 01.09.1976, Blaðsíða 65

STUDIES ON AUTUMN WEIGHT OF ICELANDIC LAMBS 63
Table 3a. Annual genetic gain due to selection of ram lambs in 1965 —1970 in per cent.
Applied selection
Method* Potential selection
Farm.............................. 1 2 3 4 1 2 3 4
Hvanneyri ....................... 0.5 1.0 0.7 0.9 1.5 2.5 1.6 2.1
Reykholar ....................... 0.2 0.1 0.8 1.1 0.4 0.2 1.6 2.0
Skriðuklaustur................... 0.4 0.4 0.3 0.4 1.6 1.5 0.9 1.2
Hólar ........................... 0.6 0.4 0.5 0.7 1.4 1.1 1.3 1.8
* See text.
spo
SpR is the measured phenotypic selection
differential and
Spo is the potential phenotypic selection
differential. This proportion was 38 per cent
for male lambs and 36 per cent for female
lambs.
The expected genetic gain per year may
now be found as a direct average of the
genetic gain for the tvo sexes, as each sex
contributes 50 per cent of the genes to the
next generation, disregarding sex linked in-
heritance.
The applied selection for autumn weight
of 'lambs should result in an expected genetic
gain of 0.3—0.5 per cent per year. By utili-
zation of the potential selection the expected
genetic gain would have been 1.0—-1.5 per
year. In that connection it was of interest
to examine how utilization of the potential
selection would have affected other charac-
ters of importance.
Correction factors for ewe fertility have
not been obtained from this material, but the
phenotypic selection for fertility, calculated
from the data without correction seemed to
be about equally effective for potential selec-
tion as for the acmally applied selection.
Potential selection showed even a higher sel-
ection intensity for fertility for male lambs
than the applied selection. This in in agree-
ment with the finding of Hallgrímsson
(1968) based on data from the Icelandic
sheep-breeding associations. This can be ex-
Table 3b. Annual genetic gain due to selection of ewe lambs in 1965 — 1970 in per cent.
Applied selection Potential selection
Farm.............................. 1 2 3 4 1 2 3 4
Hvanneyri ....................... 0.5 0.4 0.4 0.3 1.3 1.2 1.2 1.0
Reykholar ....................... 0.4 0.3 0.4 0.4 1.0 0.8 1.2 1.0
Skriðuklaustur................... 0.4 0.4 0.3 0.3 1.1 1.2 0.9 0.7
Hólar ........................... 0.4 0.3 0.4 0.4 0.8 0.8 1.1 1.0