Íslenskar landbúnaðarrannsóknir - 01.09.1981, Side 51

ÍSL. LANDBÚN.
j. agr. res. icel. 1981 13, 1-2: 49-54
Out-of-season breeding in Icelandic sheep
Ólafur R. Dýrmundsson.
The Agricultural Society of Iceland
Biendahöllin, P.O. Box 7080,
Reykjavík, Iceland.
ABSTRACT
The paper reports on the (irst out-of-season breeding trials in Iceland. A combined treatment of intravagi-
nal progestagen pessaries and PMSG injection effectively induced both dry and lactating ewes to brced in
summer, outside the normal breeding season.
The rams used in the trials exhibited normal sexual behaviour and most of them achieved mating
out-of-season. However, individual variation in serving capacity was apparent.
Of 32 ewes mated in August some 80% lambed with 1.76 lambs born per ewe lambing. Ewes injected
with 500 i. u. of PMSG had a higher lambing rate than ewes receiving 750 i. u. of PMSG.
BREEDING SEASON
Icelandic ewes have a pronounced bre-
eding season ranging from late November
into May (Dýrmundsson, 1978a). Thus it
is possible to obtain lambings as early in
the year as April and as late as September.
Mating, however, is arranged during only
3—4 weeks in December and early Jan-
uary so that lambing coincides with the
resumption of grass growth in May. Tra-
ditionally, lambs are only slaughtered in
September and October.
Although the ewes have a definite
seasonal breeding pattern, limited spor-
OESTRUS CONTROL
A great deal of research has been devoted
to controlled breeding of sheep, and the
application of techniques using progest-
adic oestrous activity occurs outside the
normal breeding season, resulting in
conception and lambing in any month of
the year. However, according to a recent
nationwide survey (Dýrmundsson,
1979), such sexual activity appears to be
relatively rare, particularly during mid-
summer, and of little practical import-
ance. Moreover, natural out-of-season
lambing in Icelandic sheep occurs at a
significantly lower rate among white than
among nonwhite (coloured) ewes (Dýrm-
undsson and Aðalsteinsson, 1980).
agens and PMSG is now exploited to a
varying extent in some countries (Mau-
léon, 1979; Robinson, 1979; Van Niek-
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