Induction of multiple births has been identified as one of the primary goals in controlled sheep breeding. The results of the present study may provide a basis for devising practical follicle manipulation techniques to increase the ovulation rate in commercial flocks of sheep. However, in cattle, there is evidence, albeit not unequivocal, that oocyte quality is compromised in follicles with an extended lifespan or dominance, resulting in low fertility. Recent studies suggest that this is not the case in sheep, which means that the addition of prolonged lifespan follicles to the ovulatory cohort could effectively increase fertility. In the study by Johnson et al., fertility was depressed by a PGF2a/low progesterone treatment in ewes; however, in that study, treatment was applied from early in the cycle and for a longer duration (Days 5 to 15 after ovulation). In a recent study by Vinoles et al., the pregnancy rate was significantly higher in cyclic Polwarth sheep that received MAP sponges for 6 days (87%) rather than 12 days (63%). buy nexium
In conclusion, a PGF2a/MAP regimen applied late in the cycle of nonprolific Western white-faced ewes increased the ovulation rate, mainly through maintenance of ovulatorysized follicles in the penultimate and earlier waves, and their addition to ovulatory follicles from the final follicular wave before ovulation. Breakthrough ovulations were observed in 65% (17/26) of treated ewes between 1 and 6 days after PGF2a treatment and insertion of MAP sponges. These ovulations did not affect the emergence of successive follicular waves, were not preceded by a preovulatory discharge in gonadotropin secretion, and did not result in CL, but rather, only in transient CH. In the present study, we were unable to show a dependency of the effects of MAP treatment on serum concentrations of FSH/LH or LH pulse frequency, suggesting that the altered follicular dynamics and increased ovulation rate may have been related to other direct or indirect effects of MAP, independent of changes in gonadotropin secretion.