Breeding from your mare is never a decision to be taken lightly, it takes forethought and planning, not to mention the cost. If you’ve got a horse that is sound, technically gifted in your discipline and has a trainable temperament, it’s so tempting to put her in foal so you can pass her genes on. But you’ve worked hard to get her to the level you’re at and don’t want to take your foot (hooves) off the gas, or retire her. Embryo transfer (ET) is growing in popularity as it allows competition mares to keep performing while passing on their genes to the next generation, without a gap in their career.
The option of ET poses an additional dimension to breeding from competition mares and involves a combination of artificial insemination, sourcing a recipient mare and ensuring ovulations are synchronised. One of the major advantages is that you can breed more than once from your mare in one breeding season. It’s quite usual for two different stallions to be selected and carrying out the ET process twice, enabling one mare to produce two foals by two different stallions.
The ET process involves the transfer of an embryo from a mare who has been covered (or artificially inseminated) to a recipient mare. The recipient mare needs to be at a similar stage in her cycle, usually one or two days behind the donor mare, so that the embryo is being placed in a suitable environment. Synchronising the reproductive cycles can be achieved artificially; the hormone prostaglandin is injected to bring a mare into season when she is in mid-to-late cycle, followed by an injection that induces ovulation, such as Ovuplant. If the donor mare is being artificially inseminated it’s important for her to ovulate as close to insemination as possible, as chilled and frozen semen have a shorter lifespan than fresh.
The embryo is normally transferred at about eight days old and is removed from the donor mare by flushing and siphoning out the uterus with a sterile solution. The solution is then filtered to catch the embryo (it looks like a very small pearl!) before it is inserted through the cervix and into the uterus of the recipient mare. Due to the handling of the embryo there is a greater risk that the process will fail than if the recipient had been covered naturally. Plus embryos from older mares are not as robust as embryos from younger ones. Overall success rates are around 40% per flush so you might need more than one attempt to get a viable pregnancy. While it’s likely that you’ll be able to carry on competing unhindered, the logistics can be tricky; the donor mare may need sedating in order to complete the transfer which means you can’t compete until the drugs have completely left your mares system. Also, due to the intrusive nature of the ET it’s not uncommon for the donor mare to be sore or one-sided so you might need to recruit a chiropractor or equine physio to keep her as supple as possible. The advice from owners who have been through the process is to do your research, know how much it’s likely to cost and employ the best ET expertise you can afford.