Equine Artificial Insemination using chilled semen
An exercise in logistics
Dr Bruce Syme BVSc (Hons), MRCVS, IVAS (cert)

The process of Artificial Insemination (AI) in itself, is relatively simple. All you need is a fertile, in season mare, a viable semen sample, and an insemination pipette to implant the semen into the mare's uterus. What could be more easy ?? But what if your mare is in Victoria, and the stallion you would like to breed her to is in Queensland ? Can you afford the time and effort to float her all the way there to serve her ??
Generally the answer is no, and many breeders simply elect to use a stallion that is more physically accessible. But, this is where A.I. using chilled semen can provide the answer. So where do you start ?

Firstly, and most important, is to contact the stallion owner to check that the stallion and handlers are equipped to collect semen. Stallions must be trained to use an Artificial Vagina (AV), the device used to collect semen, and the handlers must also be set up with the appropriate equipment and knowledge to perform viable collections and handling of semen. A semen sample must be checked under the microscope for viability (at least 50% progressive motility), diluted with an appropriate semen extender, and then chilled to 4'C. Correct packaging and transportation is also vital. Nowadays there are commercial transportation packs (eg. Equitainer) specifically designed to transport semen at stable (4'C) temperatures for at least 48 hrs or more. Most studs involved in transporting semen will have their own transport packs, but it is worth checking.

The next important step is to book a semen collection. This can be organised to suit your mare's projected insemination date, but if the stallion you are using is very popular, and in heavy work, you may have to work around a specified collection date in advance. This is where timing becomes critical.

The one area, which can cause the most frustration for using chilled semen, is the transport stage. Your semen sample must be collected from Qld and delivered to you in Vic by a courier within a definite time frame. This time is dictated by two factors; the survival and viability of the chilled semen being transported, and the pre-ovulatory stage of your mare. I strongly recommend you discuss transport with the stallion owners, as they may all ready have a reliable system in place. If not, ring around and see if any transport companies have dealt with semen samples before, and try and use one that understands the importance of timing. You do not want thousands of dollars worth of semen left in the depot in Sydney over the weekend !! Make sure they can give you an accurate time frame from collection to delivery at your end, as this is critical to ensure that your semen arrives when your mare is ready for "service".

Once you have organised your stallion, semen collection, and transport, you can focus on your mare. Your goal is to receive the viable semen sample within 48 hours of your mare ovulating.

Make sure she is cycling normally. It is preferable to inseminate later in the breeding season, when you are confident that you mare is ovulating on a regular basis. This can be confirmed by ultrasound scanning during the previous cycle or two. If your mare is very regular in her cycle, you can organise your semen collection to coincide with her next season. If she is unpredictable, or you are restricted to a specific semen collection date by the stallion, then you must prostaglandin (PG) injections to ensure she is well in season when your semen arrives. Make sure you discuss your plans with you vet, so that he is available to scan, PG, and implant the semen at the correct times. PG injections should be given a minimum of 7 days after the last season, and should bring your mare back in to oestrus within 5-7 days, so you must be planning at least 14 days in advance of your semen arriving. Ultrasound scanning from about 4 days after a PG injection will ensure that you can accurately chart follicle growth and predict ovulation / insemination day. The more scans you perform, the more accurate you can be. This may be dictated by the value of the semen you are using.

If your semen providers are flexible, let them know when your mare is due to come on, or when you give her a PG injection, so that they can organise collection and transport at their end. Once the mare's follicles have reached 30-35mm, you are ready for your semen to be collected and dispatched (assuming it will arrive within 24 hrs).

On delivery of your semen sample, your vet or stud manager should check the sample for viability. This stage is critical, as there is no point inseminating with dead semen. A small amount (0.5-1ml) is warmed in a water bath to exactly 37'C and examined under the microscope on a warmed (37'C) slide. Ideally half the sperm should be active and progressively motile (moving forwards). Your mare should have ovarian follicles of 35-40mm in size and be showing / teasing strongly.

You are now ready to implant the semen. Sterility is vital when implanting semen. Use a tail bandage and thoroughly wash and disinfect the mare's perineal and vulval areas. An AI pipette is then advanced through the mare's cervix approximately 2-3 cm into the body of the uterus and the semen sample injected. Flush the remaining semen through the pipette using sterile saline or semen extender. To maximise chances of proper ovulation, a dose of Ovuplant (one implant) or Chorulon (5ml) should be given to the mare immediately after insemination.

The rest is up to Mother Nature (or luck). Re-scan the mare 48 hrs later to ensure that ovulation has occurred, and then start pregnancy check scans from day 14 -17, and again at days 25 and 42 to confirm pregnancy. Ensure there is not a twin pregnancy early (before 25 days) and have your vet deal with it if present.
All events occurring smoothly and precisely, you can look forward to greeting your new foal next season.