As the breeding season for thoroughbreds is drawing to a close, hopefully the fruits of this year’s work will produce a good crop of 2015 foals.

For sport horse mares the season is still in full swing as many owners like to have foals in the late spring or summer when conditions are more favourable.

A growing number of sport horse mare owners are using assisted reproductive techniques such as artificial insemination and, to a lesser extent, embryo transfer. Such techniques are not available for mares registered with Weatherbys but are commonly used for mares registered in the non-TB books.

Semen for artificial insemination (AI) can be used fresh, chilled or frozen and success rates with each type depends on individual stallions as well as semen handling techniques. The semen from some stallions does not freeze well and is better used fresh or chilled, while other stallions have excellent pregnancy rates using frozen semen. As a mare owner it is always best to be guided by the stallion owner as to what works best for any particular stallion.

Fresh (raw) semen: fresh semen is occasionally used for insemination where the semen does not react well to semen extenders and the semen is collected from the stallion as usual but is inseminated straight into the mare with minimal handling and with no extension.

Raw semen must be used within six hours of collection and ideally should not be exposed to bright light or excessive heat prior to insemination. For convenience this type of insemination is often carried out at the stud where the stallion resides. It is also a good option for mares that are very sensitive to the ingredients used in semen extenders.

Chilled semen: chilled semen generally retains fertilising capacity for 24-48 hours post collection and so mares inseminated with this type of semen can be managed as per natural cover. The semen should contain at least 600 million normal sperm per dose which should then give at least 300 million normal sperm by the time the semen arrives at its destination.

This type of semen is commonly used for mares using stallions based in Ireland or nearby in the UK. It is important that the semen is handled correctly and transported using either an Equitainer (used for longer journeys) or polystyrene transport boxes (used for short journeys within Ireland). When chilled semen is inseminated into a mare the attending vet will usually retain a drop or two to check for motility, semen concentration and morphology (appearance of sperm).

If there is a problem with the semen this can then be relayed back to the stallion owner and, if necessary, a repeat dose can be shipped. Chilled semen contains semen extender which prolongs the life of the sperm.

Frozen semen: frozen semen is normally used where the stallion is dead/retired, lives outside the country or is frequently away from his normal duties at competitions. Freezing the semen does not suit all stallions and some stallions that have very good pregnancy rates using chilled semen have disappointing results with frozen semen and vice versa.

Frozen semen is stored in straws which usually range from 0.5ml to 2ml in volume and each stallion will have a recommended number of straws per insemination dose. The semen is stored in tanks of liquid nitrogen either on the stallion farm, in dedicated reproduction centres or at veterinary clinics.

Frozen semen remains viable for up to 12 hours post-thaw and so the mare needs to be very close to ovulation when inseminated. Deep uterine insemination is usually performed using a long pipette or an endoscope. As thawed frozen semen seems to generate a very strong inflammatory reaction post insemination, the mare needs to be lavaged four to eight hours following insemination. This, combined with intensive monitoring of follicles during the cycle, can make using frozen semen costly.

Embryo transfer: this technique is used primarily for competition mares that an owner wishes to obtain foals from during her competitive career or for sub-fertile mares who cannot carry a foal to term themselves due to a poor uterine environment or physical disability.

The donor mare is bred as usual and any embryo that she produces if harvested eight to 10 days later and placed into a recipient mare that has ovulated on the same day or up to three days after her but has not been bred. Ideally the recipient mare should be a relatively young fertile mare.

Usually embryo transfer is carried out at reproductive centres where herds of recipient mares are managed and await donor mares. The average embryo recovery rate is 50% for donor mares with a pregnancy resulting from transfer approximately 75% of the time. The result is therefore a 35% pregnancy rate per cycle which can have financial implications for the mare owner and embryo transfer should be undertaken with these figures in mind.

Andrea Ryan MVP Cert EP Cert EM (Stud Med) is a member of the Equine Group of Veterinary Ireland and is in practice in Kilcash Equine Centre, Clonmel, Co Tipperary.

Email: hq@vetireland.ie

Telephone: 01-4577976