Association between numbers of ovarian follicles in the first follicle wave and superovulatory response in ewes

• Published in: Animal reproduction science 2007-08, Vol.100 (3), p.391-396
• Main Authors: Mossa, F., Duffy, P., Naitana, S., Lonergan, P., Evans, A.C.O.
• Format: Article
• Language: English
• Subjects: Animals; Chorionic Gonadotropin - pharmacology; Cloprostenol - pharmacology; diurnal variation; dosage; dose response; Embryo; embryo (animal); equine chorionic gonadotropin; Estrous Cycle; ewes; Female; Fertilization in Vitro; Follicle; follicular development; hormonal regulation; Ovarian Follicle - physiology; ovarian follicles; Sheep; Sheep - physiology; Superovulation; Superovulation - drug effects; Superovulation - physiology; yields
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2006.10.016

The aim of this study was to examine the variability in the number of ovarian follicles in sheep and to determine if the average number of follicles per day influences the response to superovulation and resulting embryo quality. Ewes ( n = 83) were synchronized and the number of follicles (≥2 mm diameter) in the ovaries were counted daily between Days 0 and 4 of the oestrous cycle using transrectal ultrasonography. Fourteen to 21 days later, 47 ewes were randomly chosen from the group and were treated with an intravaginal progestagen pessary for 12 days and superovulated with 1500 IU eCG administered as a single injection 10 days after sponge insertion. Ewes were mated and reproductive tracts were recovered after slaughter on Day 6 of pregnancy. The number of corpora lutea was counted, uterine horns were flushed and the morphology and developmental stage of the recovered oocytes/embryos was assessed. The mean daily number (±S.D.) (≥2 mm diameter) of follicles per ewe was 8.5 ± 2.8 (ranging between 3 and 16). After superovulation animals with few follicles (Low group: