Náttúrufræðingurinn - 1980, Side 34

Pálsson, Iialldór. 1962. Augmentation of
fertility of Iceland ewes with pregnant-
mare serum in successive years. J. Re-
prod. Fert. 3, 55—63.
Yeates, N. T. M. 1949. The breedingseason of
the sheep with particular reference to its
modification by artificial means using
light. J. agric. Sci., Camb. 39, 1—43.
SUMMARY
Puberty and breeding activity
of Icelandic sheep
by Dr. Ólafur R. Dýrmundsson
The Agricultural Society of Iceland
Bœndahöllin, P. 0. Box 7080, Reykjavík
The paper reports on studies which have
been in progress since 1972 concerning
various aspects of sexual development and
breeding activity in both females and males
of the Iceland breed of sheep.
Most Icelandic lambs are born in May
and they are found to be early maturing.
Thus ewe lambs normally attain puberty in
their first year of life, on average at 7 months
of age, as indicated by the onset of oestrous
activity. Exceptional cases of late summer or
autumn born ewe lambs attaining puberty
and conceiving at 4 months of age have been
reported. Most ram lambs appear to have
attained physiological puberty by 4 months of
age, judged by their anatomical develop-
ment. In either sex marked individual vari-
ation is evident both in puberal age and
body weight, largely due to differences in
growth rate.
Ewe lambs generally show oestrus slightly
later in the season than mature ewes and
they have a shorter breeding season (1 — 4
months) than ewes (4—6 months). Further-
more, the duration of oestrus is shorter and
the cyclic activity is less regular in the young
females. With seasonal breeding of Icelandic
ewes ranging from November to May the
mid-breeding season occurs some 4 — 7
weeks after the shortest day, i. e. consider-
ably later than what is generally found in
breeds with seasonal breeding patterns. It is
suggested that the distribution of sexual
activity over the season may be an inherent
characteristic evolved by natural selection in
the breed and its North European ancestors
in the past.
Although Icelandic ewes have a pro-
nounced breeding season, limited sporadic
out-of-season oestrous activity (May —
November) may take place resulting in con-
ception. However, such cases appear to be
relatively rare, particularly during mid
summer, and are of little practical import-
ance. A comparatively high ratio of out-of-
season lambings has been recorded in
coloured (nonwhite) ewes.
Icelandic rams appear to display normal
mating behaviour when introduced to ewes
in oestrus outside the normal breeding
season. They do not seem to have a distinct
seasonal breeding pattern corresponding to
that experienced by the ewes.
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