Fertilization rates in superovulated and spontaneously ovulating mares

Area of Science:

• Veterinary Science
• Reproductive Biology
• Equine Reproduction

Background:

• Superovulation in mares can lead to reduced embryo recovery per ovulation compared to untreated controls.
• Understanding the ovulatory and fertilization dynamics in superovulated mares is crucial for improving reproductive efficiency.

Purpose of the Study:

• To determine if superovulatory treatment leads to ovulation or luteinization without ovulation in mares.
• To compare fertilization rates of oocytes in superovulated versus control mares.
• To evaluate the viability of early-stage embryos from both groups when cultured in equine oviductal cell-conditioned medium.

Main Methods:

• Cyclic mares were assigned to receive equine pituitary extract (EPE) for superovulation or serve as controls.
• Hormonal treatments (PGF2alpha, hCG) were administered to induce ovulation.
• Mares were inseminated, and ovaries/oviducts were collected post-ovulation for embryo recovery.
• Recovered embryos were cultured in vitro using equine oviductal cell-conditioned medium.

Main Results:

• Corpora lutea (CLs) in superovulated mares primarily resulted from ovulations (92%) rather than luteinizations, similar to controls (94%).
• Fertilization rates (88% EPE vs. 91% control) and embryo development to morula/blastocyst stages (46.4% EPE vs. 40.0% control) were comparable between groups.
• Embryo recovery rates were 57.1% for EPE-treated and 62.5% for control mares, with no significant difference (P>0.05).

Conclusions:

• Superovulatory treatment in mares stimulates ovulation, not luteinization without ovulation.
• Fertilization and early embryo development are not compromised by superovulation protocols.
• While embryo recovery was lower than anticipated, the reproductive outcomes suggest superovulation is viable in mares.