ARTIFICIAL INSEMINATION

Article series for Horse Daily Planner
By Jos Mottershead
last updated May 21, 2000

Artificial Insemination (A.I.) can be used with 3 different forms of semen: Fresh; Cooled; or Frozen.

Use of fresh semen is also sometimes known as "on farm A.I."; Cooled semen may be used off farm, in which case it is known as "transported", "cooled transported", or "shipped" semen.

Frozen semen may also be known as "cryopreserved semen".

Some of the advantages of artificial insemination are:

1. AI can be used to minimise the spread of infectious diseases by avoiding contact between the stallion and the mare.
2. As there is no contact between the animals, risk of injury to animals or handlers during the breeding process is reduced to almost nil.
3. Use of proper AI procedures will increase conception rates.
4. A.I. will allow the breeding of a stallion or mare that may be unable to complete live cover because of an injury or infirmity.
5. More than one mare can be bred with a single ejaculate.
6. By using transported semen mares can be bred to stallions far away without leaving home.
7. Animals of a different height may be safely and easily bred.
8. Because of frequent evaluations, a stallion's fertility is closely monitored.
9. A.I. encourages better record keeping.

Some of the disadvantages of artificial insemination are:

1. When carried out improperly, conception rates will be dramatically reduced
2. A few Breed Registries (most notably Thoroughbreds) do not permit the use of A.I.
3. There is additional expense in setting up for semen collection and processing.
4. If A.I. is used to overcome certain fertility problems, if successful it may actually be passing those problems on to the next generation if they are inheritable.
5. It is claimed by some that A.I. may lead to fraud or error in identifying sire or dam. As most Registries that permit A.I. now also require DNA or Bloodtyping, this is not as likely as it once was.
6. There is a possibility of the over-use of a stallion, which may decrease the variety in a gene pool, or propagate undesirable traits.
7. Unlike teasing and live cover, A.I. does not cause the mare to release oxytocin, which may lead to a higher incidence of post-breeding endometritis in some mares.

Semen is most commonly collected from the stallion by using an Artificial Vagina (A.V.). There are many different types of A.V. In North America the two most commonly used are the "Missouri" model and the "Colorado" model. Other models seen there include the "Roanoke" and the "Hanover" A.V.'s.

A.V.'s are all similar in basic design in that they have a harder outside shell, with hollow center, which is surrounded by a water jacket that is filled with water heated to slightly above body temperature prior to collection. The water jacket is usually made of some form of rubber, while the outer shell may be leather, fibreglass, plastic or aluminum.

One can use a disposable plastic liner, with or without a filter, in the A.V., which adds to the sterility of the collection process, saves having to clean the A.V. after use, and significantly reduces the chances of cross-contamination if the A.V. is being used to collect multiple stallions. Some stallions however do not like the texture of the liners.

For collection, the stallion will mount either a "jump mare", which is a mare in estrus; or may be trained to mount a "breeding phantom" or "dummy". Jump mares may have had their ovaries removed ("ovariectomised"), which will cause the mare to respond to exogenous hormones, making her display estrus behaviour. Some stallions can even be trained to permit collection of semen using an A.V. without mounting a phantom or a mare.

Other methods of semen collection include manual stimulation of the penis with hot compresses, and chemical ejaculation. These methods are more commonly used with stallions that are sick or injured, although some breeders do use them routinely.

Once the ejaculate is collected it must be analyzed to establish the gel-free volume; concentration in millions per millilitre, progressive (forward-moving) motility, velocity, morphological status of the sperm and the pH value (acidity/alkalinity) of the ejaculate. Although these will vary somewhat with breed and age, minimum "normal" levels for light horses are:

1. Gel-free volume: 40 milliliters
2. Sperm Concentration: 30 million per milliliter
3. Progressive motility: 40%
4. Velocity (on 1 to 4 scale): 2
5. Morphological status: at least 60% normal
6. pH value: 7.33 (range 6.9 to 7.8)

If being used for anything other than on-farm use (and often then too), the semen must have a diluent added. This is called "extender", and is commonly of a non-fat dried milk solid base, with added sugars. The industry standard extender was developed by Dr. Kenney, and is know as "Kenney extender". Extender adds nutrients to the seminal plasma, as well as diluting it. Both actions result in an enhanced sperm life, as seminal plasma is toxic to sperm over an extended exposure period. It also increases the total volume of the ejaculate, making analysis and "splitting" the ejaculate to breed multiple mares from a single collection easier.

If semen is being transported cooled, it must be packaged in containers specially designed to bring the temperature down to 5^o Celsius, and maintain it there. There are several different designs of these containers, but the model considered by many to be the best is the Equitainer. This is a heavily insulated plastic container that has room within for pre-frozen coolant cans, and a device that slows the cooling down to approximately 0.05^o C per minute.

There are also "disposable" semen containers made of cardboard and Styrofoam. It is recommended that they be used not more than five times, and only if there is no sign of external damage. Maintenance of the correct internal temperature in these types of containers tends to be more influenced by the external ambient temperature.

Attention to detail; careful monitoring of the mare by means of rectal palpation or ultrasound; and good communication between the stallion farm and the mare farm are essential for successful breeding with transported semen. Mare owners should contact the stallion farm to establish what procedures are expected when ordering semen for transport.

Rectal palpation and ultrasound are used to establish the size of a follicle on a mare's ovary. This will indicate when she is due to ovulate. As there is a distinct danger of injury to the horse, only specially trained personnel carry out palpations and ultrasound.

Transported semen is most usually shipped "counter-to-counter" with airlines, or by courier. As most semen is only viable for 24 to 48 hours after collection, it is essential that it be transported quickly. Some of the courier companies now offer "tracking services" over the Internet, which is very useful for finding out how your shipment is progressing.

When the semen shipping container arrives, it must not be opened until immediately before insemination is to take place, as the semen would warm up too soon, which would be detrimental to it.

Prior to insemination, the mare must have her genital area cleaned with a cleansing solution such as "Betadine". The cleaning should be performed in the same manner as a pre-surgical scrub, starting at the center, and working to the outside of the perineal area. Her tail should be wrapped, and held out of the way until the insemination is completed.

The semen must be withdrawn from the shipping container into a special all-plastic insemination syringe with an insemination pipette attached.

The inseminator wears a sterile glove, and places their thumb over the tip of the insemination pipette before sliding it into the mare.

The cervix is located, and the insemination pipette introduced through it into the uterus, whereupon the plunger of the syringe is depressed, and the semen is thereby introduced into the uterus. The hand is then slowly withdrawn from the mare, and the insemination is complete.

Frozen semen use is a little different from fresh or cooled semen, in that once frozen it must be stored in a special container at minus 196^o C until thawing immediately prior to use. Additionally, the life span of the frozen semen once thawed is less than fresh or cooled, and it must be inseminated into the mare no more than 12 hours before, or 6 hours after she ovulates. This means that the mare must be monitored much more closely for ovulation, and the use of hormones such as hCG or GnRH may greatly assist in timing the ovulation.

Frozen semen has additional advantages over fresh or cooled semen:

1. The semen can be collected and frozen when it is convenient to the stallion owner, thereby allowing the stallion to compete if desired.
2. The mare owner can order and receive the semen far in advance of the anticipated breeding date, thereby eliminating any problems such as a shipment of cooled semen being inadvertently delayed or diverted in transit, with the result that the mare's ovulation is missed.
3. In the event of sickness, injury or the death of the stallion, his semen is still available.

Frozen semen does however also carry some additional disadvantages:

1. Not all stallions have semen that will freeze and thaw well enough to subsequently achieve a pregnancy.
2. There is additional initial cost in the freezing process, although in the long term often this ends up being cheaper than cooled semen use per insemination dose.
3. As the use of frozen semen requires careful monitoring of the mare, it is essential that the veterinarian or technician that is inseminating be well versed in the process.
4. Thawing of the semen must be done carefully, and exactly following suggested protocols.
5. Not all Breed Registries permit the use of frozen semen.

Semen to be frozen is collected in the same manner as that to be used for fresh or cooled use. It is then centrifuged, and the seminal plasma removed, re-extended with a special freezing extender that contains a buffer and cryoprotectant as well as nutrients. It is then carefully frozen in liquid nitrogen vapor at about minus 160^o C, and finally plunged into the liquid nitrogen before being quickly removed to a storage tank. The freezing process requires special equipment and knowledgeable personnel to perform it successfully.