The timing of introducing the semen into the ovaries of the mare is critical to the successful fertilization of the egg. Rectal palpation of the follicles is the best method of assuring the semen is introduced at the correct time.
As the follicle begins to expand, it should be monitored regularly, as often as once every 12 hours. Ovulation normally occurs when the follicle reaches about 45mm (with a normal range of from 35mm to 50mm). As ovulation nears, the shape of the follicle changes from spherical to more teardrop.
It is necessary for the semen to be introduced within 12 hours of ovulation or its chances of success are nil.
Fertilizing the egg in the mare may be accomplished in a few basic ways:
Natural cover is the good old fashion way. It is the only method you can use with thoroughbreds that you want to register with the Jockey Club.
Your advantages of using natural cover are:
1. There are no dangers of affecting the motility of the semen in handling as there are in other methods.
2. More semen is normally introduced into the ovaries.
Insemination - A veterinarian places the semen into the mare.
The semen used for Artificial Insemination may be Fresh, Cooled or Frozen
The type you use depends upon what is available. All other factors being equal, the chances of pregnancy is best for the fresh semen and worst for the frozen semen. I have read one study from Equine Reproduction Concepts in Virginia stating that their results with frozen semen was better than with cooled semen. They theorized that there was less chance of damage in shipment with the frozen semen and that a few days delay would have no effect.
Others disagree!
The egg of a mare is placed in a petri dish with the semen of the stallion.
In vitro fertilization (IVF) is considered an experimental procedure. An egg from a mare is placed in a petri dish with the sperm of a stallion and after the egg is fertilized, it is placed in the recipient mare as described on the embryo transfer (ET) page.
As I hear more about this procedure and find links, I'll post it here.