Control of ovulation in cycling ewes with a prostaglandin F2[alpha] analogue

[摘要] ENGLISH ABSTRACT:1. Preliminary observations proved that an intramuscular injectionof 62,5pg Cloprostenol terminates the oestrus cycle of ewes.Higher dosages (1251jg, 250pg and 500pg) caused a more abrupttermination of the cycle and more synchronised occurrence ofoestrus. However, 125pg was only effective in terminatingthe oestrus cycle when injected between days 4 and 14.2. In order to overcome this refractory period to Cloprostenoltreatment, (days 15 through oestrus to day 4 of the oestruscycle) ewes were treated with intravaginal progestogensponges for 8 - 9 days and injected with Cloprostenol on theday of sponge withdrawal. A dosage of 31,251ig provedadequate, but conception rates were significantly lower atthe first post treatment oestrus (mean 63,7%) as comparedto the second post treatment oestrus (mean 81,9%). The changein the serum progesterone concentration following the cessation of treatment was not affected by the dosage of Cloprostenol (31,251g; 62,5pg and 125pg), but the position of theLH peak relative to the onset of oestrus varied markedly.The stage of the cycle when the intravaginal sponge treatmentstarted had a significant affect on the interval between thecessation of treatment, the onset of oestrus and the LH peak.3. The time of Cloprostenol administration relative to intravaginal sponge withdrawal (-48, -24 and 0h) showed no significant effect on either the oestrus response or the durationof oestrus. However, for the group receiving the prostaglandin injection at sponge withdrawal (Oh) the intervalbetween cessation of treatment and oestrus showed a markeddecrease as the onset of the progestogen treatment progressed from day 2 to day 17 of the oestrus cycle. The reproductive efficiencies of the three respective treatment groupsdid not differ significantly from each other, neither wasthere a significant difference between the reproductive performances at the first and the second post treatment oestrus.4. An alternative method of bypassing the refractory period ofthe corpus luteum to prostaglandin is by giving two injections of prostaglandin 8 to 14 days apart. In this experiment different dosages (31,25pg; 62,5pg; 125pg and 250pg)of Cloprostenol were injected at a 10 day interval. Mnincrease in the dosage was followed by a significant increasein the oestrus response (50,0%; 56,3%; 81,3% and 100,0%respectively). The higher dosages (250pg) of Cloprostenolcause more rapid and complete luteolysis as is reflected inthe decrease in plasma progesterone concentration, whilelower dosages (31,25pg and 62,5pg) often fail.5. The reproductive efficiencies of ewes treated with the intravaginal progestogen sponge (MAP), an intravaginal progestogensponge (MAP) followed by an injection of Cloprostenol (125pg),a double injection of 250pg Cloprostenol at a 9 day intervaland a control groupwere compared. The oestrus response, theinterval from cessation of treatment to the onset of oestrusand the duration of oestrus did not differ significantly forthe respective groups. The mean conception rate of ewestreated with a double injection of Cloprostenol at a 9 dayinterval was significantly lower (36%) than that of the othergroups (mean of 71,9%).G. In a 2 x 2 factorial experiment the reproductive efficiencyof ewes treated with a double injection of prostaglandin ata 10 day interval and of a group of progestogen sponge (MAP)treated ewes were compared following insemination at observedoestrus and insemination at a predetermined time. The prostaglandin treated group was inseminated at 60 and 72 hoursfollowing the last injection of Cloprostenol and the spongetreated group at 48 and 60 hours following sponge withdrawal.Although the conception rates of the ewes were about 10% lowerfollowing fixed time A.I. as compared to A.I. at obs'arvedoestrus, these differences were not significant.7. The reproductive efficiencies of ewes treated with twoinjections of prostaglandin (Cloprostenol) administered atintervals of 9, 10 and 11 days, were compared. The conception rates of ewes in these treatment groups were 11,1%;40,0% and 70,0% respectively and that of the control group82,4%. These differences indicate the importance of injecting Cloprostenol at an interval of at least 11 days.

[发布机构] Stellenbosch University