Íslenskar landbúnaðarrannsóknir - 01.03.1977, Blaðsíða 79

ÍSL. LANDBÚN.
J. AGR. RES. ICEL. 1977 9, 1.‘ 77-82
Inherited fertility depression in Icelandic sheep.
Stefán Aðalsteinsson
Agricultural Research Institute,
Reykjavík, lceland.
SVEINN HALLGRÍMSSON
The Agricultural Soceity of lceland,
Reykjavík.
ABSTRACT
Three rams of the Icelandic sheep breed were shown to depress markedly the fertility of the ewes
they served. Two of these rams were a sire-son pair, used for '6 and 2 seasons respectively, and the
third, used for one season, was the son of a ewe which had returned on heat with an unusually high
frequency.
All tree rams increased significantly the return rate, and lowered significantly twinning rate of the ewes
they served. Altogether the rams were mated to 265 ewes, of which 18% gave birth to twins, 46%
had singles and 36% returned on heat. The corresponding results for the 770 control ewes were 55,
37 and 8% respectively. The abnormal ewe and another of its sons showed a disturbed sex ratio
among their progeny, the ewe producing 8 males : 0 females and the son 8 males : 1 female.
The fertility depression is suggested to be due to excess embryonic mortality prior to implantation
The mortality rate was estimated to be 0.50 ± 0.08; 0.41 ± 0.04 and 0.53 ± 0.08 for the three
sires, respectively.
INTRODUCTION
Embryonic 'losses are a common cause of
infertility in sheep (for review see Bradford,
1972).
The heritability of failure to lamb, has
been shown to be low, (Purser, 1965, for
review see Turner, 1969) which indicates
that prenatal losses are mainly due to non-
genetic causes.
In his review on paternal contribution to
embryonic losses, Bishop (1964) ascribes a
relatively large part of the embryonic losses
to genetic causes, at the same time pointing
out that these genetic causes need not neces-
sarily be inherited by the parents. One of the
genetic causes for embryonic losses mentioned
by Bishop (1964) is translocations, which
operate as dominant lethals as a result of
chromosome rearrangements at meiosis.
Bruére (1974b) in his review on chro-
mosome anomalies in domestic animals
points out that translocation carrying rams
of the Romney breed in New Zealand usual-
ly have shown normal fertility.