Comparison of the effects of pretreatment with Veramix sponge (medroxyprogesterone acetate) or CIDR (natural progesterone) in combination with an injection of estradiol-17 beta on ovarian activity, endocrine profiles, and embryo yields in cyclic ewes superovulated in the multiple-dose Folltropin-V (porcine FSH) regimen
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Follicular wave status at the beginning of exogenous FSH administration is an important contributor to variability in superovulatory responses in ruminants. Studies in ewes have shown a decrease in the number of ovulations when superovulation is initiated in the presence of ostensibly ovulatory-sized ovarian follicles. Hormonal ablation of large antral follicles with the progestin-estradiol (E-2-17 beta) treatment significantly reduces this variability in superovulated anestrous ewes, but the effects of the treatment in cycling ewes have not yet been assessed. Sixteen Rideau Arcott x Polled Dorset ewes (November-December) received either medroxyprogesterone acetate (MAP)-releasing intravaginal sponges (60 mg) or controlled internal drug release (CIDR) devices (containing 300 mg of natural progesterone) for 14 days (Days 0-14), with a single intramuscular injection of 350 mu g of E-2-17 beta on Day 6. The superovulatory treatment consisted of six injections of porcine FSH (Folltropin-V) given twice daily, followed by a bolus GnRH injection (50 mu g intramuscular) on Day 15. There were no differences (P < 0.05) in the ovulatory responses and embryo yields between the two groups of ewes. In both subsets of animals, the next follicular wave emerged similar to 2.5 days after an E-2-17 beta injection (P > 0.05). A decline in maximum follicle size after an E-2-17 beta injection was more abrupt in CIDR- compared with MAP-treated animals, and the ewes pretreated with exogenous progesterone had significantly more 3-mm follicles at the start of the superovulatory treatment. The metabolic clearance rate of exogenous E-2-17 beta appeared to be greater in MAP-treated ewes, but circulating concentrations of porcine FSH failed to increase significantly after each Folltropin-V injection in CIDR-treated animals. The CIDR-treated ewes exceeded (P < 0.05) their MAP-treated counterparts in serum E-2-17 beta concentrations during superovulation. In spite of differences in antral follicle numbers and endocrine profiles between MAP- and CIDR-treated cyclic ewes receiving E-2-17 beta before ovarian superstimulation, there were no differences in superovulatory responses. (C) 2015 Elsevier Inc. All rights reserved.