Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 63

STUDIES ON AUTUMN WEIGHT OF ICELANDIC LAMBS 61
Table la. Applied and potential selection of ram lambs.
Potential
Kept for breeding Sold for breeding selection
Farm Number i Number i i
Hvanneyri ......................... 23 1.04 2 1.52 1.44
Reykhólar ......................... 23 1.16 19 0.91 2.13
Skriðuklaustur..................... 54 0.54 100 0.94 1.88
Hólar ............................. 63 0.78 29 0.62 2.02
Total............................. 163 0.79 150 0.88 2.00
1 = Standardized phenotypic selection differential =.
Xsel [A,
o
q
A G = ------------ ’ where
L., +
M M
IM = genetic selection differential for
male lambs,
Ip — genetic selection differential for
female lambs,
Lj^. = generation interval for male lambs,
and
Lp = generation interval for female
lambs.
Table 1 shows the number of selected
lambs together with their phenotypic se-
lection differential i,n standardized units (i).
The table further shows how intense the
selection would have been if selection had
been applid to autumn weight of lambs only.
The potential selection was obtained by cal-
culating the average corrected autumn weight,
within year, farm and sex, for the same
number of the heaviest lambs as actually
kept for breeding or sold alive in the corre-
sponding groups.
Table 2 shows the average generation in-
tervals that were found in the present study.
Table lb. Applied and potential selection of ewe lambs.
Potential
Kept for breeding Sold for breeding selection
Farm Number i Number i i
Hvanneyri ........................ 258 0.39 6 0.28 1.27
Reykhólar ........................ 260 0.41 23 0.67 1.21
Skriðuklaustur.................... 549 0.41 97 0.37 1.13
Hólar ............................ 380 0.51 16 0.25 1.30
Total............................. 1492 0.43 142 0.40 1.21
i = Standardized phenotypic selection differential —
Xsel [j,
o
P