Íslenskar landbúnaðarrannsóknir - 01.09.1981, Page 53

OUT-OF-SEASON BREEDING 51
Denmark). All the ewes exhibited behavi-
oural oestrus and were hand-mated with
adult rams on 18 August.
The ewes were housed and fed indoors
from late November and lambing took
place in early January 1980. Two ewes
died, one soon after mating in August and
another in November, and both were ex-
cluded from the fertility data. Of 32 ewes
some 80% lambed with 1.76 lambs born
per ewe lambing. These fertility results
indicated a lower conception rate out-of-
season than generally recorded for Ice-
landic ewes bred at the traditional time in
winter. The lambing rate, however, was
quite comparable. There were no clear
RAM FERTILITY
Icelandic rams are known to be early sex-
ually maturing (DÝRMUNDSSON, 1978b)
but detailed information is scant on sever-
al aspects of their reproductive efFiciency.
Although sporadic matings may occur
out-of-season (Dýrmundsson, 1979) bre-
eding activity is restricted by the farmer to
only a few weeks in winter. Dýrmunds-
son, Sigtryggsson and Thorsteinsson
(1982) have recently established seasonal
variation in testes diameter of adult Ice-
TABLE 2.
Mating performance of adult rams out-of-season.
diíferences in reproductive performance
as to whether the ewes had been dry or
lactating before nrating.
Regarding the two PMSG treatments
Table 1 shows that conception rates were
similar, 75 and 81%, but contrary to ex-
pectations the number of lambs born per
ewe lambing was 1.92 and 1.62 for 500 and
750 i. u. PMSG, respectively. Thus the
higher dose of PMSG appeared to reduce
prolificacy, most likely due to increased
embryonic mortality. Certainly, in Ice-
landic ewes, the lower dose appears to be
suíficient to induce both oestrus and ovul-
ation in conjunction with a progestagen
treatment.
landic rams with the lowest values in the
spring and the highest in the autumn,
indicating seasonal fluctuations in testic-
ular function. However, no information is
available in Iceland on the quantity and
quality of ram semen at diíferent times of
the year. Nevertheless, in the light of res-
ults obtained in other countries (CouROT,
1979; Schanbacher, 1979) it is tempting
to suggest that the lower conception rates
of Icelandic ewes bred out-of-season may
Test date No. tested No. mounted No. mated
12 June 1977
(Hvanneyri) ............................... 9 9 9
18 August 1979
(Gunnarsholt) ............................ 12 12 10
Total .................................... 21 21 19