Multiple factors affecting the efficiency of multiple ovulation and embryo transfer in sheep and goats

Abstract

This review offers an overview of the basic characteristics of in vivo embryo technologies, their current status, the main findings and the advances gained in recent years, and the outstanding subjects for increasing their efficiency. The use of superovulation and embryo transfer procedures remains affected by a high variability in the ovulatory response to hormonal treatment and by a low and variable number of transferable embryos and offspring obtained. This variability has been classically identified with both extrinsic (source, purity of gonadotrophins and protocol of administration) and intrinsic factors (breed, age, nutrition and reproductive status), which are reviewed in this paper. However, emerging data indicate that the main causes of variability are related to endocrine and ovarian factors, and so the number of studies and procedures addressing a better understanding and control of these factors may be increased in the future. The accomplishment of this objective, the improvement of procedures for embryo conservation and for the selection and management of recipient females, will allow further development and application of this technology.

A study on the effect of GnRH administration on the ovarian response and laparoscopic intrauterine insemination of Awassi ewes treated with eCG to induce superovulation

“…Superovulated ewes with eCG followed by GnRH injection 24 h after sponge removal may result in increased ovulation rate. Gonzalez-Bulnes et al (2004) obtained similar results. The administration of GnRH earlier after sponge removal affects follicular development and maturation and is preceded by an endogenous LH surge .…”

Features of follicle-stimulating hormone–stimulated follicles in a sheep model: keys to elucidate embryo failure in assisted reproductive technique cycles

“…The objectives previously described can also be applied in animal reproduction, where superovulation is commonly used for either in vivo or in vitro embryo production. In ruminants, the practical administration of superovulatory treatments is still hampered by a high variability in the ovarian response (for review, see Gonzalez-Bulnes et al [9]). The follicular status at start of the gonadotropin treatment has been identified as one of the main causes for these variations in the final outputs.…”

“…To address this question in a more amenable model, the present study was undertaken to evaluate functionality of follicles in stimulated cycles by using a nonprimate model, the sheep, which is a monovular species widely considered to be a good model for evaluation of human reproductive endocrinology and ovarian biology (5)(6)(7)(8). Screening of follicular dynamics by ultrasonography and hormone assessment are techniques that are well established in sheep (9). The current study evaluated oocyte quality in relation to the features of the individual follicles from which they were harvested, after they were stimulated to grow with exogenous gonadotropins by using a protocol very similar to that used in clinical practice.…”

Long-term suppression of reproductive function by a single dose of gonadotropin-releasing hormone antagonists in a sheep model

“…This inhibitory influence mainly is exerted indirectly by suppression of FSH, but the contribution of a locally produced and released factor cannot be excluded (22). The ovaries containing a large follicle yield fewer follicles and oocytes in response to superovulation with gonadotropins (23). It is likely therefore that in the absence of large follicles, most of the follicles in the ovary are healthy and contain oocytes that have full developmental competence.…”