Embryo-initiated oviductal transport in mares.

This research investigates the theory that equine embryos themselves instigate their transport through the oviduct in mares, providing evidence whose results appear supportive of this claim.

Research Methodology

• The scientists tested the hypothesis that equine embryos play a proactive role in initiating their own transport through the mare’s oviduct. To confirm this, they conducted an experiment whereby day 6 uterine embryos were surgically placed into the oviducts of other mares which were either 2 or 5 days into timed pregnancies. Embryo collection was then attempted 48 hours later, to observe if they have made their way through the oviducts.
• To rule out the possibility that the surgical transfer might have influenced the oviduct, a sham transfer was performed in this study as a control group. This sham transfer involved putting just the medium in the oviducts of day 2 inseminated mares, then also attempting embryo collection 48 hours later.

Findings

• The study results showed that in six out of ten day 2 recipient mares, embryos expedited their transport through the oviduct, arriving by day 4 instead of the typical day 5 or 6. Though less than the nine out of ten successful transports recorded in day 5 recipient mares, statistical analysis showed this difference was not significant, suggesting that introducing the day 6 embryo did instigate early oviductal transport.
• The researchers established that the act of surgical transfer itself does not majorly instigate oviductal transport, as it occurred in only one out of ten sham transfers. This provided further evidence in support of the main hypothesis that the embryo itself played a significant role in controlling its movement through the mare’s reproductive tract.
• They also found no significant difference size-wise between the embryos placed in day 2 and day 5 recipient mares, showing that the size of the embryo transferred does not influence its journey. But, the embryos collected from the uterus of day 2 recipients were significantly smaller than those from day 5 recipients, an important aspect to study further, not directly explained by current findings.
• In one case, an embryo which had already shed its zona pellucida (the outer layer of the embryo) was successfully transported through the oviduct, suggesting the zona pellucida may not be crucial for oviductal transport.