Equine Reproduction Services

Services provided:

  • Freezing semen
  • Artificial insemination with frozen, cooled or fresh semen
  • Stallion collection & shipped semen
  • Mare breeding soundness exam
  • Training young stallions
  • Ultrasound – rectal and transabdominal
  • Miniature horse reproduction – rectal and transabdominal ultrasound
  • Goat artificial insemination – Dr. Leith
  • Embryo Transfer

Reproductive Workup

General Health The mare should be optimal weight, have recently floated teeth and a low fecal egg count (dewormed if necessary, and vaccinated prior to breeding. If your mare is in excellent physical health several months prior to breeding, she will have a higher probability of conceiving and maintaining a pregnancy.

Vaccination should include rabies, Eastern, Western, Venezuelan encephalitis, influenza, West Nile, and rhinopnuemonitis. Depending on geographical location, the mare may require additional vaccines. If the mare is to be bred to an EVA (equine viral arteritis) positive stallion, she should be vaccinated at least one month prior to breeding.

Uterine Culture and Cytology Uterine culture and cytology – a sterile uterine swab is utilized to sample the mare’s uterus for bacterial infection and inflammation. Ideally, the culture should be taken during estrus.

Prebreeding Ultrasound/Rectal Exam The veterinarian examines the ovaries, uterus and cervix with both the ultrasound and digital palpation. Any abnormalities such as intrauterine fluid and endometrial cysts can be identified and treated if needed.

Uterine Biopsy The biopsy evaluates the uterus for inflammation and fibrosis (scar tissue). Older multiparous and maiden mares undergo endometrial changes that will impact their ability to carry a foal to term. This tool will assess the mare’s ability to carry a foal to term. Often, inflammation can be treated whereas fibrosis and scaring are permanent conditions. The uterus is placed into one of four categories:

Expected foaling rates of mares according to endometrial biopsy grade

Grade Degree of endometrial change Expected foaling rate (%)
I Absent 80-90
II A Mild 50-80
II B Moderate 10-50
III Severe < 10


Lights – Mares are long day breeders, they are receptive to the stallion, ovulate, and become pregnant during the spring and summer months. Mares are transitional prior to and following the spring and summer. One of the most efficient methods to hasten the onset of cycling and ovulation is through the use of lights.

Beginning in November, exposing the mare to 16 hours of continuous lights per day will mimic the onset of spring. Usually, 50% of the mares will ovulate following 70 to 80 days of artificial light. Bring the mare into a stall prior to sunset and leave the light on until 11 pm. The light must be bright enough to read newspaper print from anywhere in the stall. The mare must not be able to place her head in a dark space, out a window or stall door.


Breeding your mare with cooled semen enables the horse owner to select stallions that may not be available locally. Shipped cooled semen refers to breeding mares with semen that is chilled (not frozen) to 41 degrees Fahrenheit (5 degrees Celsius). Chilled semen is usually fertile for 1 to 3 days after collection.

Prior to breeding your mare, a uterine culture and cytology may be required by the stallion farm. Culturing maiden mares is not necessary if the owner has knowledge that the mare has never been bred. If the horse owner can determine that the mare is in heat (estrus), the next step is to have the veterinarian ultrasound her reproductive tract. A mare that is in heat will demonstrate a large follicle 30mm or greater and endometrial folds (the uterus takes on a particular appearance). The veterinarian will contact the breeding farm and coordinate the shipment and insemination of semen.


Frozen semen is frozen in liquid nitrogen to – 196 Celsius (-320 Fahrenheit). Frozen semen has an infinite shelf life (as long as the liquid nitrogen tank is maintained adequately) until thawed. Breeding with frozen semen can be very successful, but the appropriate mares should be selected. The advantage to frozen semen is that the stallion’s show career is not interrupted; overseas stallions are available to mare owners (importation of semen is rigorous), stallion illness/death, and decreased concerns with overnight/airline shipping. Not all stallions freeze well, approximately 25% poor, 50% adequate and 25% acceptable/good. Therefore, the mare owner should ask the stallion owner “What is the post-thaw motility” prior to purchasing straws. An additional point of interest is the breeding dose; the dose has ranged from 300 million to one billion total sperm. This breeding dose can be in 4 to 6 one half ml straws. If 6 straws contain 500 million sperm cells and the post thaw motility rate is 50%, then there are 250 million progressively motile sperm available for that breeding.

Advantages Disadvantages
Access to international stallions Lower fertility rates
Access to stallions despite illness, death or competition schedule Not all stallions freeze well; 25% freeze well, 50% freeze acceptably, 25% freeze poorly
Overnight shipment errors Breeding dose ranges from 300 million to one billion total sperm per dose*


*The total sperm number refers to all progressively motile and dead/circling sperm. Therefore if the breeding dose contains 800 million sperm but has a post thaw motility of 20%, only 160 million sperm are available for fertilization.

The goal with frozen semen is to breed within a window of 6 to 8 hours prior to ovulation up to 6 hours post ovulation. Accordingly, once the mare receives either HcG or Deslorelin, ultrasound exams occur every 6 hours to evaluate for impending ovulation. There are several options for breeding with frozen semen; the Arizona Equine doctors will work with the owner select the ideal protocol for their mare.