Íslenskar landbúnaðarrannsóknir - 01.03.1977, Síða 88

86 ÍSLENSKAR LANDBÚNABARRANNSÓKNIR
result found in the present investigation that
the ram does not affect ewes fecundity is in
accordance with Heape (1899) and Blegert
(1939), who bot concluced that the ram did
not have any effect on the ewes fecundity in
the material they studied. However, there are
numerous investigations concering the quality
of the semen of different rams showing
great quality variation (see for example
Terrill, 1937; Webster, 1952; Edgar
1958) Other workers have found close cor-
relation between quality characteristicas of
the semen and ewe fecundity defined as
percentage of ewes having lambs of those
mated. (See for example Wiggs et. al. 1953;
Edgar, 1958; Hulet and Ercanbrack,
1962). Terril (1937) compared the quality
characteristics of ram semen immediately
after the end of the breeding season and
devided the rams into groups according to
if 95 % or more of the ewes got pregnant or
less that 95%. The five rams which gave
over 95% of the ewes pregnant had on the
average superior same compared to the four
rams giving the lower rate of non-returning
ewes. Both Terrill (1937) and Edgar
(1958) showed that the fertility of ram is
not an all-or-none trait but can practically
vary from 0—100%. This is also supported
by Hulet and Ercanbrack (1962), who
constructed an index for ram fertility, con-
sisting of several semen quality criteria. They
defined the fertility of the ewe as number
of ewes having embryos, determined by
slaughtering them and examining the uteri
approximately 25 days after copulation. These
investigations show that there are great dif-
ferences in samen quality and hence we
should expect difference in mating results.
It has also been pointed out that certain
environmental factors affect the semen
quality, and thereby ram fertility (Webster,
1952; Edgar, 1958). As mentioned above
it was found in this material that the blood
relationship between the ewe and the ram
did have a significant effect upon the ewes
fecundity. It is well known that inbreeding
affects the fertility of the ewe (Lax and
Brown, 1968), measured as number of
lambs born. There seems, however, to be
very littíe evidence on the effect of the blood
relationship between the ewe and the ram.
Thus Edey (1969) in a review of prenatal
mortálity in sheep does not mention this as
a possibility of prenatal losses in the sheep.
It is known that lethal genes can cause
prenatal losses in sheep (Morley, 1954),
and this should be more frequent when the
ewe and the ram are related. However, lite-
rature on this matter is very scarce, and more
investigation is needed. Wiggins, et al.
(1953) found that there was a significant
negative correlation between inbreeding of
the ram and percentage of live lambs born
and percentage of lambs weaned.