123. Equine embryo collection is commonly performed on day 7 or 8 (day ovulation) because
1. the embryo has separated from placenta
2. the embryo has crossed all the developmental stages
3. recovery

are high and the blastocysts can be easily recovered and handled
4. the lifespan of embryo is limited to 9 days

Correct Answer:

3. Recovery rates are high and the blastocysts can be easily recovered and handled

Explanation:

Equine embryo collection is typically performed on day 7 or 8 post-ovulation. This timing is crucial for several reasons, particularly for the successful recovery and handling of the embryo.

1. Blastocyst Stage: By day 7 or 8, the equine embryo reaches the blastocyst stage, which is an advanced stage of development. At this point, the embryo is well-formed, making it easier to recover. Embryos at earlier stages, like morula, can be more difficult to handle and less viable for recovery.

2. High Recovery Rates: Embryos that are collected on day 7 or 8 have a higher recovery rate, which is why this window is preferred. The embryo has not yet attached to the uterine wall, and it is freely floating within the uterine horn, making it easier to collect with minimal risk of damage.

3. Developmental Stages: At this point, the embryo has developed through critical stages, including the morula and early blastocyst stages, ensuring it is viable for transfer or preservation.

4. Lifespan of the Embryo: The lifespan of the embryo is typically limited to around 9 days. After this, the embryo begins to undergo embryo attachment to the uterine wall, making it much harder to recover without damaging it. Therefore, collecting the embryo on days 7 or 8 ensures it is still viable and easy to recover.

Thus, the ideal collection time of day 7 or 8 is primarily due to high recovery rates and the optimal developmental stage of the embryo.

Conclusion:

The best time to perform equine embryo collection is on day 7 or 8 post-ovulation. During this time, the embryo is in the blastocyst stage, allowing for high recovery rates and making the embryo easier to handle. This ensures the best chance for successful embryo transfer or preservation.