Embryo reduction before day 11 in mares with twin conceptuses

Area of Science:

• Reproductive biology
• Veterinary science
• Equine reproduction

Background:

• Embryo reduction, the natural loss of one embryo in a twin set, is a critical factor in reproductive success.
• Understanding the timing and mechanisms of embryo reduction is essential for improving equine fertility.

Purpose of the Study:

• To investigate the incidence of embryo reduction before day 11 in mares.
• To compare embryo reduction rates between single ovulators and double ovulators (unilateral vs. bilateral).

Main Methods:

• Comparing ultrasonically detected conceptuses per ovulation in single and double-ovulating mares.
• Matching 50 double-ovulating mares with two single ovulators each.
• Analyzing the effect of unilateral versus bilateral double ovulations on embryo reduction incidence.

Main Results:

• Single ovulators had a higher frequency of conceptuses per ovulation (85%) compared to bilateral (77%) and unilateral (60%) double ovulators.
• Unilateral double ovulators showed a significantly different frequency of conceptuses (none, one, or two) compared to expected rates.
• Bilateral double ovulators did not show evidence of embryo reduction before day 11; each ovum had an equal chance of developing.

Conclusions:

• Embryo reduction before day 11 appears to occur in unilateral double ovulators, leading to a lower pregnancy rate per ovum.
• The reduced success in unilateral double ovulators is primarily due to a higher frequency of mares with no embryonic vesicles.
• No evidence of embryo reduction before day 11 was found in bilateral double ovulators.