Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 51

STUDIES ON AUTUMN WEIGHT OF ICELANDIC LAMBS 49
Table 1. Number of ewes (n), years and older in May and their average fertility (x) calcu-
lated as number of lambs per ewe alive at lambing.
1965 1966 1967 1968 1969 1970
Experimental ---------- -------------- ------------- ------------- -------------- ------------
farm nx nx nx nx nx nx
Hvanneyri ............. 322 1.63 346 1.55 312 1.52 290 1.57 263 1.55 232 1.26
Reykholar ............. 217 1.48 250 1.61 277 1.56 269 1.62 254 1.61 234 1.44
Skriðuklaustur..... 597 1.63 602 1.57 617 1.54 602 1.49 594 1.38 577 1.55
Holar ................. 448 1.33 454 1.55 425 1.45 436 1.35 441 1.53 420 1.45
Total.................. 1584 1.53 1652 1.56 1631 1.51 1597 1.49 1552 1.49 1463 1.46
was 35.68 kg with a coefficient of variation
(cv) of 14.8 per cent. The average weight of
male lambs was 37.26 kg with a cv of 14.7
per cent and that of the females 34.19 kg
and 13.6 per cent, respectively.
Average age of the lambs at weighing
time was 125.6 days, with a standard devia-
tion of 8 days, the estimates being equal for
bot sexes.
Methods.
Due to the unequal number of animals in
the subgroups, the estimation of the correc-
tion factors must by done by the method of
least squares. This analysis has been described
by Harvey (1960). All the statistical ana-
lyses carried out in this investigation have
been done on a within farm and year basis.
The following basic model was used for
the estimation (Model I):
Yijki_"+ai+bj+ck+bi cxiijki+xi)
+b2<X2ijkl+X2) + b3<X3ijkl+X3) +
e... .where
íjkl
Yijkl =
the 1* observation of autumn
. th
weight of lamb of the k sex,
the j* type of birth and re-
aring and the
.th
age of dam.
p = average autumn weight of lambs.
a.
i
the effect of the i^ age group
of dam; i = 1, ..., 9
o.
J
= the effect of the j type of
birth and rearing; j = 1,... 6
= the effect of the k^ sex;
k = 1, 2
bj = partical regression coefficient of
autumn weight of lamb on age
of lamb
b^ = partical regression coefficient of
autumn weight of lamb on
squared age of lamb
bg = partial regression coefficient of
autumn weight of lamb on date
of birth of lamb
Xlijkl
= age of lamb of the autumn
weight, the k^ sex, thej* type
of birth and the i
of dam
.th
age group