Effect of administering a crude equine gonadotrophin preparation to mares on follicular development, oocyte recovery rate and oocyte maturation in vivo.

The research investigates the impact of administering crude equine gonadotrophins on mares’ follicular development, oocyte recovery rate, and in vivo oocyte maturation, finding no signs of significant enhancement or alteration in these biological processes.

Study Context and Purpose

• The study was designed to explore potential methods to increase the availability of small-to-medium-sized follicles in mares for in vivo aspiration, aiming to enhance the overall oocyte yield.
• This increase in yield could help improve methods for in vitro maturation and in vitro fertilization, overcoming the present challenges posed by the limited number of oocytes and variable nuclear maturation at certain stages of the oestrous cycle.
• Specifically, the study examined the potential effects of administering crude equine gonadotrophins on follicular development, oocyte recovery rate, in vivo oocyte maturation, and follicular concentrations of meiosis-activating sterols.

Study Design and Methodology

• The researchers aspirated all follicles greater or equal to 4 mm from 19 pony mares during oestrus.
• Over a period of eight days following the initial aspiration, the mares were treated daily with either 25 mg crude equine gonadotrophins or physiological saline.
• Using ultrasonography, the research team monitored follicular growth between day one and day eight.
• On day eight, all follicles greater or equal to 4 mm were evacuated (second aspiration or A2) and the nuclear maturation of the recovered oocytes was analyzed using orcein staining.

Findings and Conclusions

• The research discovered no significant differences in follicular growth, oocyte yield, or in vivo oocyte maturation between control mares and mares that were treated with crude equine gonadotrophins.
• The oocyte recovery rates at the first and the second aspirations were also found to be similar.
• The study found a significantly higher number of oocytes at the germinal vesicle stage at A2 than at A1, indicating that follicular aspiration during oestrus facilitated the development of a new follicular population and resulted in increased synchronization of oocyte development in terms of cumulus expansion and nuclear maturation.
• The administration of crude equine gonadotrophins during early dioestrus did not affect the growth of small follicles, the oocyte yield after aspiration, or oocyte maturation in vivo.
• Since there were no changes as a result of administering the gonadotrophins, the researchers concluded this approach may not significantly impact in vitro maturation and fertilization techniques in mares.