Abstract:
This study was carried out to investigate the efficacy of PGF2a
for oestrus synchronization (ES) in Awassi ewes to which were
administered the progestagen–PMSG combination, and to
evaluate the effect of the exogenous GnRH administration
immediately after the artificial insemination (AI) on their
pregnancy rate and lambing performance during the breeding
season. The ewes (n ¼ 33) were treated with an intravaginal
sponge impregnated with 30 mg fluorogestane acetate for
12 days and were injected with 500 IU PMSG at the time of
removal of the sponge. The ewes were then divided into three
equal groups of 11 ewes each. One millilitre of physiological
saline (0.9% NaCl; placebo) was administered to each ewe in
Group 1 at the time of second AI. Approximately 4 lg GnRH
(busereline) was injected to each ewe in Group 2 immediately
after second AI. A total of 150 lg PGF2a (cloprostenole) was
injected at the time of sponge removal on day 12 and 4 lg
GnRH immediately after the second AI was also treated to
each ewe in Group 3. Intracervical AI with diluted fresh semen
was performed twice at 12 and 24 h following the onset of
oestrus. The injection-oestrus onset and injection-oestrus-end
interval in Group 3 was significantly (p < 0.001) shorter than
both Groups 1 and 2. Although the pregnancy rates of Groups
2 and 3 (81.8%; 9/11) were numerically higher than of Group 1
(63.6%; 7/11), the difference among the groups was statistically
insignificant. The multiple birth rate of Group 3 was
found higher than Groups 1 and 2. However, the number of
single lambs of Group 1 was also higher than Groups 2 and 3
(p < 0.05). Despite the litter sizes of Groups 2 (1.27; 14/11)
and 3 (1.55; 17/11) being numerically higher than Group 1
(0.73; 8/11), the differences among all the groups were
statistically insignificant. In conclusion, the administration of
PGF2a at the time of removal of the sponge shortens the
injection oestrus-onset and oestrus-end interval in Awassi ewes
treated with progestagen–PMSG. Additionally, exogenous
GnRH treatment immediately after the AI increases the
multiple birth rate of Awassi ewes synchronized with progestagen–
PMSG–PGF2a combination.
