Fertility Rates

Natural mating: In Thoroughbreds, 50-60% of mares conceive in each oestrous cycle, by the end of the breeding season 89% of mares are pregnant and only 79% of mares go on to produce a live foal.

Fresh / chilled semen: When fresh or good quality chilled semen is used for artificial insemination (AI) we can expect slightly higher (5-10%) per cycle pregnancy rates compared with natural mating. It normally takes 1 – 2 cycles for a fertile mare to conceive.

Frozen semen: The fertility of frozen semen after artificial insemination (Al) is quite variable due to the variability of the “freezability” of different stallions. Thus, the fertility of frozen semen ranges from 0-70% per cycle conception and the average is around 40% per cycle throughout the world. It normally takes 2-3 cycles for a fertile mare to become pregnant.

We recommend

To maximise the fertility of your breeding programme we recommend the following:

Mare age: Older mares, greater than 14yo have reduced fertility. These mares are more prone to endometritis (infection of the uterus) and uterine cysts. We recommend that these mares be inseminated with fresh / chilled semen. Generally, we recommend that insemination with frozen semen is reserved for mares that are less than 14yo to optimize its fertility.

Condition: Obesity can lower pregnancy rates. It is important to have the mare in lean body condition and on a rising plane of nutrition prior to breeding. Keep your mare off lush clover pastures and soya based hard feeds prior to breeding. Both contain phyto-oestrogens which may interfere with normal cycling behavior.

Selenium: Know what your mares selenium status is as low selenium levels can cause fertility issues.

Mare foaling status: Mares with a foal at foot and young maidens (3-10yo) are usually the most fertile group of mares. “A pregnant uterus is a healthy uterus” so we do not recommend resting mares to optimise fertility. Barren or rested mares may benefit from being inseminated with fresh or chilled semen this year and then save your frozen semen for when she has a foal at foot.

Semen quality: There is huge variability between stallions in their fertility after artificial insemination so it is best to use semen from stallions with a record of good fertility. We can obtain semen from almost anywhere if you can provide us with sufficient details of the stud where the stallion stands. It is important that mares are inseminated with high numbers (<300million) motile sperm and that the semen is handled carefully by experienced personnel.