Transfer of immature oocytes to a preovulatory follicle: an alternative to in vitro maturation in the mare?

This research discusses a novel method for maturing oocytes in horses. Instead of using in vitro maturation, the study explores the possibility of maturing immature oocytes in vivo by transferring them into a preovulatory follicle of a recipient mare that is induced to ovulate. The maturation success rate is found to be equivalent to that of in vitro maturation.

Experiment Design and Methodology

In this study, the researchers conducted an experiment to analyze the effectiveness of in vivo maturation of oocytes as an alternative to the traditional in vitro method in mares. The method involved:

• Collecting a group of 3-9 oocytes from donor mares.
• Transferring these oocytes under ultrasound control into the preovulatory follicle of a recipient mare. The recipient mare is primed with equine pituitary gonadotrophin (CEG) to induce ovulation.
• Collecting the transferred and native oocytes from the recipient mare 34 hours post-treatment to assess the stages of nuclear maturation.

Findings of the study

The results from the experimental procedure revealed interesting insights:

• The practice of transferring oocytes didn’t notably hinder the maturation process of the recipient mare follicle.
• The indigenous oocytes of the recipient could be distinguished by their expanded cumulus of yellow coloration resulting from a high hyaluronic acid content. Among these, roughly 58% were mature.
• Of the oocytes that were transferred to preovulatory follicles, approximately 49% were recovered. The majority manifested cumulus expansion. Among these transferred oocytes, about 32% matured, 36% remained immature, and the rest degenerated.
• When the indigenous oocyte of the recipient mare was mature, the maturation rate for transferred oocytes was 38%, a rate similar to that of in vitro maturation.

Conclusion from the Research

The researchers concluded that in vivo maturation of immature oocytes through transfer into a preovulatory follicle in a recipient mare is feasible. This maturation rate is comparable to the standard in vitro maturation rate. The technique enables the production of mature oocytes with an expanded cumulus rich in hyaluronic acid, mirroring the state of preovulatory oocytes. These outcomes hadn’t been achieved with in vitro maturation.