Endocrine Abstracts (2005) 9 P48

Fertilization in superovulated sheep is disturbed by oestrogenic anovulatory follicles

A Veiga-Lopez1, A Gonzalez-Bulnes1, JAF Tresguerres2, V Dominguez1, C Ariznavarreta2 & MJ Cocero1

1Dpto de Reproducción Animal, INIA, Madrid, Spain; 2Dpto. de Fisiología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain.

Efficiency of superovulatory protocols in ruminants is affected by occurrence of several reproductive abnormalities, such as anovulatory follicles (Kafi and McGowan 1997, Animal Reproduction Science, 48:137-157). The aims of current study were to characterize, in sheep, the incidence and possible causes of anovulatory follicles, their endocrine functionality in terms of oestradiol production and possible effects on viability of embryos from other follicles. The number and size of all follicles present in the ovaries of 12 Manchega ewes at starting a superovulatory oFSH (OVAGENTM, ICP, Auckland, New Zealand) step-down treatment were assessed by ultrasonography. On Day 3 after subsequent oestrus behaviour, number of corpora lutea and anovulatory follicles were recorded and anovulatory follicles equal and greater than 5 mm in size were aspirated and assayed for oestradiol. Viability of the embryos was evaluated just after surgical recovery from uterus under general anaesthesia. The incidence of anovulatory follicles reached a 34.6 % of the structures developing to preovulatory size. The presence of anovulatory follicles was associated to effects of follicular dominance, since their number increased with higher differences in size between the largest and second largest follicle at the beginning of the superovulatory treatment (P < 0.05, r2 = 0.420). Most of the anovulatory follicles showed signs of functionality failures, indicated by a low mean estradiol concentration (9.9 ± 1.1 ng/ml). However, a 22.4 % of the anovulatory follicles were highly oestrogenic (> 200 ng/ml) and their permanence beyond the ovulation was related to a drop in embryo viability rate (P < 0.005), due to a decreased fertilization rate. These findings indicate that a high release of oestrogens from anovulatory follicles after a superovulatory treatment exerts a detrimental effect on the fertilization process, may be through alterations in sperm or oocyte transport, leading to decreased final embryo yields.

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