- At ovulation the mare sheds an egg from her ovary, and the egg quickly travels into her fallopian tube.
- The mare is inseminated post-ovulation.
- Within minutes, the sperm is drawn into the fallopian tube by uterine contractions, not swimming. 90% of mares conceive at this time.
- After fertilization, the embryo will remain in the tube for five or six days, before moving into the uterus.
- Following 10 days of moving around the uterus, the embryo becomes more stationary.
- At about 37 days, the embryo attaches to the wall of the uterus by endometrial cups, which are the beginnings of the placenta.
- The placenta produces progesterone, to help maintain the pregnancy. Before its development and attachment, blood levels of progesterone support the pregnancy.
EARLY EMBRYONIC DEATH
- The highest incidence of early embryonic death occurs before day 11, when the embryo enters the uterus. Often it occurs by day five or six. This happens in about 24% of normal mares.
- The next highest incidence of embryonic death occurs between days 14 to 40, in about 17% of normal mares.
Factors contributing to early embryonic death:
- When mares are bred post-ovulation, the egg may not live as long as the sperm, and may have aged and become defective.
- Stress caused by environment and management may cause lethal stress to the embryo.
- Hormone deficiencies and imbalances, the uterine environment, and the age of the mare can all be contributing factors to early embryonic death.
CONCEPTION STATISTICS FOR FROZEN SEMEN
- The national average for first cycle conception using fresh cooled semen is 60%.
- The national average for first cycle conception using frozen semen is 60-70%.
- The average number of cycles per conception using frozen semen is 2.5 per mare.
- The end-of-season conception rate for both fresh cooled and frozen semen is about the same--70-75%.
- Most mares in good breeding condition will achieve a pregnancy within two cycles, but many settle on one cycle. Few mares take three cycles to conceive.
- The conception rate with frozen semen is at least as good as, if not better than, the rates of live cover and fresh-cooled breeding. When breeders purchase frozen semen with no guarantee, they are very careful to select an excellent mare candidate and an experienced veterinarian, thus improving their conception rate.