Firstly, we were curious as to the process involved in 'harvesting' (correct term??) a mares eggs.
In the equine, harvesting a mare's eggs is a surgical procedure. I think you are looking at harvesting the embryo, or flushing the embryo is more commonly the term used.
How many do the get at one time?
The equine is difficult to "super ovulate". Most other mammalian species can be hormonally manipulated to produce multiple embryos. With the equine, even using eFSH (equine follicle stimulating hormone) it only doubles your chances. The industry average for flushing embryos is 50% - so 50% of the time, you will flush an embryo...with the use of eFSH, you double your chances to, drum roll please...1.
How they collect them?
The mare's uterus is filled with a flush media that is specifically formulated for doing embryo transfers. The flush is then run back through a catheter that has a filter attached that will capture the embryo. The fluid that is in the filter is then viewed under a microscope and the search begins :).
How do they store them?
In most cases, the embryo is immediately transferred into a recipient mare. However, there is now a procedure where the embryo can be frozen and stored. Success rate of transferring the thawed embryo into a recip mare is comparable to those of embryos that are transferred immediately.
How long they can be stored?
It is speculated that they can be stored for as long as frozen semen - 40,000 years.
Also, when they fertilise the egg, I assume they do it in a petrie dish and later insert the fertilised egg in the mare - much the same as they would with a human... Is this correct? If not, how do they do it?
No. Invitro fertilization is not done in the equine - at least not thesame way it is done with other mammals. If one does harvest a mare's eggs, in order to fertilize the egg, ICSI (Intracytoplasmic Injection) must be used where a single sperm is actually injected directly into the ovum.
How do people choose a surrogate mare? Is is simply a matter of convenience, or is there a lot more thought involved (ie, mares conformation, size, previous breeding history, temprement etc) (I'm assuming its the second one, but you never know!)
It is preferred that a mare of comparable size is used, that is under the age of ten and older than four, that has had at least one foal and is reproductively sound. Obviously, you want a mare with a known temperament that is good for nuturing the foal, as well as human friendly.
Hope the above helps!