Íslenskar landbúnaðarrannsóknir - 01.03.1977, Blaðsíða 87

THE EFFECT OF RAM ON EWE FECUNDITY 85
within flocks, as these factors did not contri-
bute significantly to the variation in fertility.
The fertility was corrected for age of ewe
by constants found in this same material
(Hallgrímsson, 1966) The terms fertility
in the ram and fecundity in the ewe are
here used in the same way as described by
Hulet et. al. (1965).
RESULTS AND DISCUSSION
Results of the analysis of variances of the
effect of the rams fertility on the ewes
fecundity is given in table 1.
ship classes (coded 1, 2, 3 and 4) was
calculated. The coefficient was found to be
(b) = —0.007. The regression did not
contribute significantly to the variation in
ewes fecundity (P>0.05). As there were
only 409, 357 and 209 observations in
relationship classes 2,3 and 4, respectively,
but 10.133 in class 1, it was decided to group
the observations in classes 2,3 and 4 into
one class and use analyses of variance to find
if there was any difference in ewes fecundity
between these two classes, where the relation-
ship between the ewe and the ram was
none or very little (class 1) or 12.5% or
Table 1. Analysis of variance o£ thé effect of ram on ewe fecundity.
Source of Barren ewes included Barren ewes exciuded
variation D.F. M.S. F D.F. M.S. F
Between rams Residual 983 11369 0.2561 1,02 0.2524 978 11066 0.2186 0.2119 1.03
As can be seen from table 1, the ram has
not had a significant effect on the ewes
fecundity according to the analyses of vari-
ance. The question could be raised if the ana-
lyses of variance is good enough indicator on
the effect of the rams fertility on the ewes
fecundity. However, it has been pointed out
(Dampster and Lerner, 1950) that it will
give resonably good estimates of the variances
to use usual metholds in calculation of the
variance for all-or-none traits if the frequency
is near 0.5. The fecundity of the ewe, defined
as 1 or 2 lambs born per parturition is an
áll-or-none trait, and the frequency is very
near 0.5 in this material.
To test the effect of the degree of relation-
ship between the ram and the ewe, the
regression of the ewes fecundity on relation-
more (class 2). The analysis of variance
showed a significant difference in ewe fe-
cundity between these two classes (P<0.05).
Barren ewes were included in this material.
According to these results the rams fertility
is not affecting the fecundity of the ewe
under ordinary management conditions in
Iceland, although it has been shown in ext-
reme cases that the ram may affect ewe
fecundity measured as lambs born pr. part-
uration and number of return ewes of ewes
mated (Adalsteinsson, 1970). In the case
described by Adalsteinsson and Hall-
grímssson (1977) every second ovum was
found to be lost. This loss was expected to
be due to a chromosomal abnormality in the
rams. Ewes mated to these rams also had
fewer twins than the rest of the flock. The