Superovulatory response to FSH treatments after different progesterone primings in ewes

An experiment was conducted to compare the effect of superovulatory treatment initiated after 0, 4 or 10 days of progesterone priming, on ovarian response and embryo quality in ewes. Superovulatory treatment included six FSH equal-dose (total 200 mg NIH-FSH-P1) regimen, plus two half doses of a prostaglandin F-2alpha analogue, given together with the last two FSH injections. In eight ewes superovulatory treatment was initiated immediately after detection of ovulation by ultrasonography (D0, no primed or control group). Fourteen ewes received, after detection of ovulation, a controlled internal drug release (CIDR) device containing 0.3 g of progesterone and superovulatory treatment was started at Day 4 (D4 group; n = 6) or Day 10 (D10 group; n = 8) after CIDR insertion. CIDR's were withdrawn together with the last FSH injection. After superovulatory treatment, ewes were mated with rams of proven fertility. Six days after mating a laparotomy was done and the number of corpora lutea (CL) and anovulatory follicles > or = 8 mm were recorded. Embryo collection was performed and recovered ova/embryos were evaluated for fertilization and quality. Daily blood samples were collected during all the experimental period by jugular venipuncture to determine progesterone profiles. Mean (+/- SEM) number of CL (9.3 +/- 1.8, 10.5 +/- 2.4 and 16.9 +/- 4.0 for groups D0, D4 and D10, respectively), ova/embryo-recovery rates (52.7% +/- 9.6, 61.3% +/- 16.0 and 55.3% +/- 7.2) and mean number of ova/embryos recovered (5.5 +/- 1.4, 7.2 +/- 2.6 and 8.0 +/- 1.2) were not significantly different among groups. The three groups yielded similar mean number of transferable grade 1 and 2 embryos (3.1 +/- 1.5, 3.8 +/- 1.5 and 4.1 +/- 1.0 for groups D0, D4 and D10, respectively) but the long progesterone-primed ewes (D10 group) yielded significantly more poor-degenerated embryos (0.6 +/- 0.3, 0.7 +/- 0.3 and 3.6 +/- 1.2; p < or = 0.05). Mean progesterone levels during the 3 days of the stimulatory regimen were similar between D4 and D10 groups (4.6 +/- 0.1 versus 4.0 +/- 0.2 ng/ml) but significantly lower in D0 group (0.6 +/- 0.2 ng/ml; p < or = 0.01). In conclusion, after different periods of progesterone priming (i.e. 0, 4 and 10 days) a similar ovulation rate was obtained, but an impaired embryo quality was observed with the longer priming. Present work suggests that if progesterone priming is effectively important on subsequent superovulatory response this effect is probably more related to a previous action of the hormone on characteristics of the follicular pool challenged than to its own concentration during the period of gonadotropin stimulation.