Why perform a reproductive or breeding soundness exam on a stallion?
There are numerous reasons for performing a reproductive evaluation of a stallion. Reasons can include:

  • Prior to purchase
  • Prior to embarking upon a breeding career
  • Yearly reproductive wellness exam
  • To estimate the number of mares the stallion may be able to breed during the season
  • If breeding problems are encountered such as a lower than expected conception rate
  • A gelding that still exhibits prominent stallion characteristics

What does a reproductive exam include?
Reproductive examinations can vary from cursory examinations to a complete Breeding Soundness Examination and additional testing. Consult your veterinarian or contact us to discuss what options may best benefit you and your horse. Listed below are some of the components that may be performed in a reproductive evaluation.

General physical examination
This is a critical step of a breeding soundness examination. Examples of health conditions that may interfere with a successful breeding career include lameness (particularly hind limb and back), cardiovascular disease, fevers, and mild neurological disease.  Additionally, certain medications and supplements may interfere with semen quality.

Semen collection and evaluation
Semen collection and evaluation is one of the most important components of a stallion reproductive evaluation. This is performed using an artificial vagina (AV), usually while the stallion is mounted on a phantom (dummy mare) or on the back of one of Hagyard’s reliable jump mares. This procedure allows the veterinarian to evaluate the stallion’s behavior, activity, and comfort in the breeding shed.

The semen is evaluated for color, concentration, motility, and morphology (shape).  We use Computer Assisted Sperm Analysis, which allows us to provide objective details about the sperm motility characteristics.

Information from semen evaluation is most useful if the stallion has bred or been “cleaned-out” several times over the previous days. This allows us to evaluate semen recently produced rather than older sperm that have been stored in the epididymis. When estimation of the daily spermatic output is desired, the stallion may need to breed or be collected daily for 7 to 10 days, or, alternatively, two to three semen collections can be performed one hour apart. Daily spermatic output is an estimate the amount of sperm a stallion can produce when breeding daily and is used to estimate the book size.

External genitalia evaluation
Evaluation of the testicles and external genitalia is an important part of regular wellness examinations for any stallion. This allows for early recognition of problems and aging changes that may require adjusting book sizes. This examination involves manual examination, ultrasonographic examination, and measurement of the dimensions of both testicles.

The penis and sheath should also be evaluated. This may also include microbial culture from these areas to detect pathogens that may decrease transported semen quality, potentially cause irritation to the stallion, and may be transmissible to the mare.

Additional tests
Many additional tests are available. Consult your veterinarian with specific questions.  Initial examination results will provide insight regarding additional diagnostics that may be useful. Examples of additional tests are hormone evaluation, sperm chromatin structure assay, various viability assays, endoscopy, ultrasound examination of accessory sex glands and testicular biopsy.

Mare Reproductive Evaluation

Why perform a reproductive evaluation?

  • Identify reason for poor reproductive performance
  • Evaluation before procuring an expensive stallion season
  • Evaluation after difficult foaling
  • Diagnosis of behavior issues
  • Pre-purchase

What does an exam include?
A mare reproductive examination can include all or only some on the procedures mentioned below. What procedures to include are determined by the owner, the veterinarian, and the needs of the mare.

General physical examination:
Physical health and soundness can affect reproductive performance so before the mare’s reproductive tract is evaluated it is important that any physical abnormalities are found and evaluated.

Examine of the external genitalia:
The perineal area, vulva, and anus must be evaluated for tears and defects and conformation that could affect the integrity of the reproductive tract.

Speculum examination:
A visual examination of the vestibule, vagina, and cervix is performed checking for any defects, scars, or injuries.

Rectal examination:
Rectal palpation is performed to examine the ovaries, uterus, and cervix for abnormalities.

Ultrasonic examination:
Ultrasound is used to visualize the uterus, ovaries, and cervix and their contents. The presence of fluid, cysts, and tumors in the uterus, tumors and other abnormal structures in the ovaries, and cervical abnormalities can be visualized with this technology.

Culture, Cytology, Uterine Biopsy:
These techniques provide information on the environment of the uterine lumen and the health of its lining. Diagnosis of infection, fibrosis, and inflammation are made in this way.

Endoscopic examination:
The endoscope allows for direct visual examination of the lumen of the uterus.

Hormonal assays:
Help in the diagnosis of tumors, and behavioral problems.

These evaluations along with the history and information from your veterinarian can help to define a mare’s problem and make her a more productive individual. The help and cooperation of the attending veterinarian is essential for a positive outcome to the problem mare. This must be a team effort and the veterinarians at the McGee Fertility Unit will make every effort to make your veterinarian a part of the team.

What is embryo transfer?
Embryo transfer is the process in which the donor mare is bred, and a surrogate mare carries the pregnancy. Thus, the donor mare is listed as the dam, while the recipient mare is the surrogate mother. This procedure has gained widespread acceptance and popularity among many breeders and breed registries.  Please consult individual breed registries for guidelines regarding embryo transfer and registration of offspring.

Why use embryo transfer?
There are many advantages of performing embryo transfer for the horse owner and breeder.

  • The donor mare can pursue an athletic career without interruption by a pregnancy.
  • Multiple offspring may be achieved during one breeding season by the same or different stallions. Consult the breed registry to ensure that all offspring may be registered.
  • Embryo transfer may enable mares with various types of reproductive disease to produce offspring. Consult your veterinarian to determine if your mare is a reasonable candidate.
  • Offspring can be obtained from mares that may otherwise not be able to carry a foal to term or deliver a foal. An example is a mare with laminitis, other musculoskeletal disease or pelvic fracture.
  • Young mares can produce offspring as soon as puberty is reached.

What are the steps involved?
Embryo transfer involves a few basic steps:

  • We recommend that the donor mare be reproductively evaluated to ensure a reasonable chance for success.
  • The donor mare is bred. This can be performed with any modality (live cover, cooled semen, frozen semen). Remember that conceptions rates may vary between these methods depending on both the mare and stallion. Consult breed registries for guidelines regarding breeding methods.
  • The embryo is removed from the donor mare’s uterus. This is a procedure similar to a uterine flush or lavage. Embryo removal typically occurs 6 to 8 days after ovulation, based on veterinarian recommendation.
  • The embryo is located and evaluated under a microscope for appearance, shape and size. At this stage, depending on the embryo’s size, appearance,and age (days from ovulation), the embryo may be cryopreserved for long-term storage in liquid nitrogen. Additionally, the embryo may be packaged and shipped to the recipient mare’s location.
  • The embryo is non-surgically transferred to a recipient/surrogate mare. The recipient mare is checked for pregnancy about 1 week after the transfer.

What is the success rate of embryo transfer?
Embryo transfer is most successful with a fertile donor mare and a stallion with known fertility in the breeding modality used for the mare. When fertile mares and stallions are used, an embryo is recovered approximately 70% of the time. Mares that are older (older and fewer oocytes or eggs) or have had reproductive trouble produce embryos approximately 30% of the time.

What makes a good embryo recipient?
Embryo recipient candidates should undergo complete physical and reproductive examinations.  Recipient mares are young and reproductively normal. A history of good mothering ability is an added advantage. The recipient mare needs to ovulate closely in time to the donor mare to provide the best chance of embryo transfer success.

Our veterinarians can recommend several large facilities throughout the U.S. that have sufficient mares to receive shipped embryos. At these facilities arrangements are typically made to lease or sell to buy back the recipient mare to the donor mare owner.

Once an embryo is transferred, the recipient mare is typically administered supplemental progestagens. Pregnancy confirmation is performed around 14 to 16 days of gestation (approximately 6 to 10 days after transfer).

For further information about embryo transfer at Hagyard Equine Medical Institute
Please call:  859-255-8741

What is embryo vitrification, why would you do it, and what does it involve?
Embryo vitrification is a process by which a 6 to 6.5 day embryo that measures less than or equal to 300 micrometers is frozen by an ultra-rapid freezing technique. Pregnancy rates following transfer of small vitrified embryos have improved compared to routine freezing and have been demonstated as high as 65% to 75%. Thus there has been an increased interest in embryo vitirification in the equine breeding industry.

There are several situations in which embryo vitrification may be warranted and beneficial to a breeder. Mares that have been superovulated or have had larger numbers of embryos retrieved than recipients available for transfer can freeze the “extra’ embryos for later use. Performance mares that are in training or on the performance circuit can be superovulated and bred in their off season and embryos transferred the following spring. In addition mares that are bred late in the season and would like to have a pregnancy early the following year, can have their initial embryo vitrified for transfer early next year and maintain the following pregnancy herself. Finally, it can be used in breeding diversification in which a mare can be bred to different stallions during one breeding season and potentially have different embryos to transfer the next year.

The process is similar to routine embryo transfer except the embryo is flushed from the donor mare’s uterus earlier, at day 6-6.5 post ovulation. This is important so that the embryo size is small and the capsule not present allowing cryoprotectants to enter the embryo which is imperative for survival.  Once the embryo has been retrieved from the donor, identified, graded and washed it then goes through a number of steps during which it is transferred to increasing concentrations of cryoprotectants and substrates. At the McGee Fertility Center a commercial kit provided by ABT360, a veterinary embryo transfer media manufacturer, is utilized for this process. This four step technique increases the efficacy and ease of the vitrification process. The embryo is then loaded into a 0.25 ml straw and a 0.5 ml straw attached to the open end for labeling and identification purposes. The embryo is then frozen by being placed in liquid nitrogen vapor and then being plunged into the liquid nitrogen. Once frozen the straws are placed in a liquid nitrogen tank for long-term storage. The McGee Fertility Center can recommend storage facilities throughout the U.S. 

Thawing and transfer of vitrified embryos occurs with the use of a water bath for thawing and a Cassou gun for embryo transfer into the recipient. Recipient mares should be screened and synchronized as in the embryo transfer process however transfer will occur one day earlier into the recipient.

Artificial Insemination (AI)
Artificial insemination can be classified as an assisted reproductive technique since it consists of the manual deposition of the correct number of live motile spermatozoa into the mare’s uterus at the optimal time. This can include fresh, cooled, or frozen semen. The advantages of artificial insemination include; breeding large number of mares with one ejaculate, transport semen from distant places using frozen or chilled, adding extenders and antibiotics to semen to increase the fertility of some stallions, not having to transport the mare to the stallion, breeding more mares to a stallion, reduce the risk of disease transmission, have greater access to stallions, earlier detection of fertility problems, decrease the risk of injury to mare, stallion and personnel, and may be easier to breed the mare at the proper time. The disadvantages of artificial insemination include; needing increased knowledge and skills in mare and stallion management, increased equipment needed, decreased revenues for vaning companies and boarding facilities, and a decreased genetic pool. With this known, artificial insemination has become a widely accepted and used technique.

Low Dose insemination: What is it? When and why use it? 
Low dose insemination can be described as using a decreased number of spermatozoa that are deposited at the oviduct or utero-tubal junction, ipsilateral to the dominant follicle. This can be accomplished either by hysteroscopic insemination or deposition blindly manually. This procedure is especially useful when dealing with sub-fertile or deceased stallions, poor quality semen, limited supplies of frozen semen and sexed semen. 1-1.5 ml containing approximately 50 million progressively motile spermatozoa has been used. Therefore uterine horn insemination may improve pregnancy rates by increasing the number of motile sperm that enter the oviduct when deposited at the utero-tubal junction. There have however been differing results reported in pregnancy rates.

What other assisted reproductive techniques are available for mares that are not capable of producing an embryo or have a poor uterus unable to have an embryo survive?
Oocyte Transfer

Oocyte Transfer is a technique in which oocyts (eggs) are collected from the donor mares follicles using a transvaginal ultrasound guided approach or aspiration through the mare’s flank.  This procedure is an alternative for mares in which embryo transfer is not an option.  Mares that may have cervical problems, chronic infection/inflammation/yeast, oviductal or uterine adhesions or failure in ovulation are good candidates.  The success rate in oocyte retrieval is about 75-80% in these mares.  The oocyte is then placed into the oviduct or a recipient mare that has previously been inseminated.  The recipient mare needs to be anestrus or have their dominant follicle aspirated so only the donor mare’s oocyt will be fertilized.  Oocyte transfer is done by a flank incision with visualization of the oviduct and placement of the oocyte into the ampula of the oviduct.  Pregnancy rates after the transfers are determined by the age of the donor mare.  Older mares have been shown to have less viable oocytes and be more prone to fertilization problems or early embryonic death resulting in 25-40% pregnancy rates. Younger healthy mares when  oocytes are transferred into the same recipients had pregnancy rates as high as 60-80%.

Gamete Intrafallopian Tube Transfer

Another option using the oocyte transfer technique that is utlilized with sub-fertile stallions is gamete intrafallopian tube transfer (GIFT).  In this procedure both the oocyte and spermatozoa are placed into the oviduct of the recipient mare.  This allows the use of low numbers of sperm or frozen semen with a limited supply.  Only 200,000 spermatozoa are needed.  Pregnancy rates are similar to oocyte transfer.

Intra-Cytoplasmic Sperm Injection (ICSI)
Intracytoplasmic sperm injection(ICSI) is a procedure that helps with stallions that have extremely low sperm numbers or poor semen quality since only one healthy spermatozoa is needed. It is also a valuable tool in mares that have chronic endometritis, poor uterine biopsy scores or anatomical defects that do not allow the oocyte to be fertilitized, the embryo to descend into the uterus or the embryo to traverse the uterus. Oocytes are aspirated from the donor mare’s follicles such as with oocyte transfer, these oocytes are matured in vitro or in vivo. The sperm is then injected into the matured oocyte and cell division is monitored.  If the embryo develops, it is transferred into the oviduct of an anestrus recipient mare that has been primed with estrogen and progesterone. The embryo is transferred by flank incision with visualization of the oviduct. Pregnancy rates with this procedure range from 20-40% depending on clinician.