RETFORD EQUINE VETERINARY CLINIC

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This is the time of year when a lot of horse owners are thinking about using artificial insemination (A.I.) on their mares. The advantage of AI is that a mare does not have to travel to a stallion that may be located in another state or country. For this method semen is basically available in two forms: chilled and frozen.


CHILLED SEMEN

Chilled semen is collected from the stallion preferably the day before insemination, diluted with extender and cooled prior to shipping. Cooling reduces the sperm’s metabolic rate which allows the sperm to survive longer before having to be used. The semen is shipped in a special container overnight, usually by courier. Chilled semen should be used within 48 hours (although the sooner the better). Success rates with this type of semen are higher than with frozen semen and the timing for insemination does not have to be as precise.


FROZEN SEMEN

Frozen semen can be kept for years in liquid nitrogen, even after the stallion’s death. The semen is collected from the stallion at any time, placed in special straws that are frozen and stored in liquid nitrogen tanks. However, the success rates can be quite poor for some stallions. The general industry success rate for frozen insemination is around 30-40%. This method also uses the least semen general 5ml compared to 50-100ml for chilled, the mare’s must no have any reproductives issues when inseminated. The timing of insemination also has to be much more precise and pregnancy is best achieved within 6-12 hours of ovulation.


PROCEDURE

When the mare is in season she develops follicles or eggs that grow and eventually fill with blood and ‘ovulate”. The size of her follicle is monitored by rectal ultrasound until it reaches 3.5 to 4cm. When it reaches this size she may be implanted with an ovulatory agent which stimulates the follicle to develop and ovulate 36-48 hours later. The mare should be inseminated as close to ovulation as possible for best chances of a pregnancy.

If chilled semen is being used it is ordered at least 2 days before and can be used as soon as it arrives. Ovulation should take place within 24 hours of insemination.


Frozen semen requires that the follicle is monitored frequently, every 3-6 hours so that insemination can take place within 3 hours of ovulation for best results. This type of semen is thawed using specific laboratory techniques and the mare is inseminated immediately.


In some cases the administration of Oxytocin is required after 12 hours of insemination which stimulates the uterus to contract and remove any dead sperm and fluid that may have accumulated.


A further scan is performed 24-48 hours after insemination to check if any fluid has accumulated in the uterus. A combination of antibiotics is infused into the uterus to prevent any possible uterine infections that could hinder the early pregnancy, then your mare is ready to go home.


The mare is then scanned for a pregnancy 15-16 days after the insemination. The early pregnancy test is especially important to rule out any possible twin pregnancy which are not ideal in horse and can be managed at this early stage. Then a further 45 day pregnancy test is performed and pregnancy certificate is issued.