Íslenskar landbúnaðarrannsóknir - 01.09.1981, Blaðsíða 52

50 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
erk, 1979). In Iceland, where sheep AI
services have been developed during the
last 40 years (Dýrmundsson, 1977a),
synchronization of oestrus with intravagi-
nal pessaries, within the breeding season
in December, has proved to be an inn-
OUT-OF-SEASON BREEDING
Breeding Icelandic ewes in summer for
lambing in winter clearly necessitates the
induction of oestrus and ovulation by ar-
tiflcal means. In a small preliminary trial
conducted at Hvanneyri Experimental
Station in the spring of 1977, six dry
(barren), noncyclic ewes, which were tre-
ated with sheep pessaries for 13 days and
injected with 750 i. u. of PMSG at pessary
withdrawal, exhibited oestrus and were
mated on 12 June. Only three (50%) of
them produced lambs in the autumn, two
with twins and one with quadruplets. Fo-
ur comparable ewes which only received
the pessary treatment failed to exhibit
oestrus. Thus, as would be expected, a
combined progestagen+PMSG treat-
ovation of outstanding practical value
(Dýrmundsson, 1977b). PMSG (500
i. u.) injected at pessary withdrawal raises
the lambing rate substantially but is only
used in a few flocks. Progestagen pessaries
are seldom used for ewe lambs.
ment was found to be necessary for out-of-
season breeding.
In the summer of 1979 the first out-of-
season breeding trial, including both lact-
ating (20) and dry (14) ewes, was cond-
ucted at Gunnarsholt Farm aimed at pro-
ducing marketable lambs for export in late
winter. The lactating ewes had suckled
lambs for 9—11 weeks when they were
subjected to a hormonal treatment on 3
August. Then their lambs were weaned
and progestagen pessaries (VERAMIX,
Upjohn, U.K.) were inserted. All the ewes
retained the pessaries and were injected
intramuscularly at sponge withdrawal on
16 August with either 500 or 750 i. u. of
PMSG (ANTEX LEO, Lövens,
TABLE 1.
Lambing rate in relation to PMSG treatment.
Litter size
(lambs)
Number of ewes
500 i. u. PMSG 750 i. u. PMSG
(n= 16) (n= 16)
0 ......................................................................... 4 3
1 ....................................................................... 4 6
2 ....................................................................... 5 6
3 ....................................................................... 3 1
Conception rate ............................... 75,0% 81,3%
No. iambs born per ewe lambing ................ 1.92 1.62