Semen collection and evaluation is an important component of standing a stallion at stud. Semen collection for a breeding soundness evaluation allows owners to estimate how many mares their stallion can service in a year, determine overall semen quality, and identify any issues affecting fertility. Collection also allows stallion owners to offer fresh-cooled or frozen semen for artificial insemination.

The main collection methods include use of an artificial vagina, ground collection, drug-induced ejaculation, and epididymal sperm harvesting. The most commonly used method is the artificial vagina, with other methods generally reserved for stallions with mobility issues.

The veterinarian evaluates the semen collected from the stallion for key features of the sperm including concentration, motility, morphology, volume, and longevity. These features reflect the stallion’s fertility and number of mares that he will be able to service in a year.

Semen evaluation must be repeated each breeding season due to age-related changes, and if there are changes in the stallion’s lifestyle such as athletic use. Stallions also require separate evaluations if they will be collecting in the winter months, due the effect of seasonality on sperm production.

Semen Collection for Horses

Semen collection and evaluation is a crucial component of the stallion breeding soundness examination in which the stallion’s fertility and ability to service mares is evaluated.

Additionally, semen collection is integral in artificial insemination, one of the most popular methods of breeding mares. Artificial insemination offers several benefits for horse breeders, such as

  • Safety: Reduces the risk of physical injury to both the stallion and mare that can occur during natural mating.
  • Disease Control: Semen can be tested and treated for infectious diseases before insemination.
  • Cost-Effective: Cheaper than transporting mares to stallions for natural service.
  • Efficiency: One ejaculate from a stallion can be used to inseminate multiple mares, and semen can be frozen and stored for future use.
  • Genetic Diversity: Gives breeders access to a wider gene pool, potentially improving the genetic quality of the offspring.
  • Controlled Breeding: Breeders can select specific genetic traits and plan breedings strategically. Detailed insemination records can be maintained.
  • Conception Rates: Advanced reproductive technologies can enhance conception rates in mares that have had difficulty conceiving.

Becoming familiar with semen collection methods, semen evaluation, and factors that influence semen quality is important for all stallion owners, but particularly for those interested in standing their stallion publicly.

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn - Equine Nutrition Consultants | Mad Barn USA

Semen Collection Methods

Several methods of semen collection are available, and the collection method used largely depends on the preference of the stallion. Stallion owners must work closely with their veterinarian to determine the best method of collection for each stallion, particularly if the semen will be used for artificial insemination.

Once trained and with a plan in place ahead of time, collecting the stallion is relatively quick and easy, and is more likely to produce a good quality sample.

Artificial Vaginas

Artificial vaginas are the most common method of semen collection for horses. Several models of artificial vaginas are available, but all have a water or air-filled sleeve that surrounds the penis and provides stimulation. [1][2]

Factors such as the amount of pressure, temperature, and lubrication should be adjustable to the stallion’s preference. [1] The base of the artificial vagina is connected to a collection receptacle and a filter. The filter acts to removes the gel portion of the semen and any contaminants. [1][3] After flowing through the filter, the semen is deposited in a collection receptacle for further evaluation.

Breeding Dummy

Stallions are usually trained to mount a “phantom” (breeding dummy), which gives the veterinarian easy access to position the artificial vagina without the added safety risk of managing two horses. [1] Phantoms are also adjustable in height and angle to maximize comfort for the stallion, particularly for those affected by lameness or back pain. [1]

Training the stallion to mount a phantom typically involves using a tease mare in heat, positioned so that the stallion can see and smell her while he approaches the phantom. [4] Over time, some stallions may not require a mare to be present to mount and service the phantom. [1][3]

Collecting a stallion using a phantom requires at least two people: one is the stallion handler, while the other is the collector. Acting as a team, the handler ensures the stallion mounts the phantom correctly so the collector is safe to approach. When the stallion is on the phantom, the collector then diverts the stallion’s penis into the artificial vagina for collection.

Mount Mare

Some stallion owners and veterinarians prefer to use a mount mare rather than a breeding dummy. This method does not require much additional training of the stallion. [1][3] The stallion will mount the mare, similar to natural service, however the penis is deflected into the artificial vagina rather than penetrating the mount mare. [1]

The major downside of using mount mares is that there is no guarantee that the mare will be in heat during the time when the stallion is collected. To avoid this, some breeders use spayed mares who are consistently in heat. [1][3]

Care must be taken to protect both the stallion, stallion handler, and collector when using a mount mare. Thus, some mares may require breeding hobbles to prevent kicking.

Another option is having a large herd of mount mares, which increases the chances once will be in heat during the desired collection period. [1]

Ground Collection

Stallions who are unable to mount a mare or phantom may be candidates for ground collection. The process for ground collection is similar to using a phantom, however the artificial vagina is placed while the stallion is standing. [1][3]

The semen collector may need to manually stimulate the penis for ground collection to be successful. [1]

Inducing Ejaculation

Several drug combinations can be used to induce standing ejaculation in stallions, such as: [1][5]

  • Xylazine and imipramine
  • Imipramine, detomidine and oxytocin

These drugs provide sedation and reduce the stimulation required for ejaculation, allowing for semen collection. [1]

Prior to drug administration, a plastic collection sleeve is placed over the penis and held in place using a flank strap. [1] Once the drugs are administered, the stallion is left in a quiet location for 15 to 60 minutes to allow time for ejaculation to occur. [1]

Inducing ejaculation is often unsuccessful, with only 25-30% of procedures successfully producing semen. [1][5]

Epididymal Sperm Harvesting

Epididymal sperm harvesting is a salvage procedure typically used to preserve highly valued genetics in the event of a catastrophic injury or death of a stallion. [1][4]

At any given time, the epididymides of the stallion’s testes contain between 12 – 20 breeding doses of semen waiting to being ejaculated. [4] In this procedure, processing laboratories remove this semen from the epididymides for use in artificial insemination. [1][4]

To perform harvesting, the testes are removed from the stallion after death, injury or castration and shipped to a processing facility as quickly as possible. [4] Laboratory technicians separate the epididymis from the testes to allow access to the sperm inside.

The epididymis is then flushed with seminal plasma (the liquid portion of semen) from another stallion or semen extender. [4] Some laboratories may instead mince the epididymis to release the sperm into semen extender, and then filter the product. [4]

Breeding doses from epididymal sperm harvesting typically have lower fertility rates than traditionally collected semen. [4]

Semen Evaluation

Semen is highly sensitive to light, agitation, and temperature, so a collected sample must be immediately transported to the processing area to prevent degradation of the sample. [1]

The first step in processing is to note the total volume of the sample. Next, adding a semen extender reduces the risk of environmental damage to the sample and improves sperm survivability. [1][2] After adding semen extender, evaluation can begin.

The main goal of semen evaluation is to determine the viability and concentration of the sperm. [2] For breeding purposes, this evaluation allows the veterinarian to separate the semen into breeding doses. [1][2]

In a breeding soundness exam, more detailed investigations are performed including evaluating the shape and structure of the sperm, longevity of the sperm in semen extender, and sperm function. [2][6]

Sperm Concentration

To determine the sperm concentration, the veterinarian takes a measurement of the total volume of the semen sample, then measures the concentration of sperm in a small amount of semen. [1]

Measuring sperm concentration typically involves specific equipment such as a spectrophotometer or hemocytometer, which provide a reading of the total number of sperm in the sample provided.

Based on this number, the veterinarian can calculate an estimate for sperm concentration by dividing the total number of sperm by the volume of sample. [1][2] Most stallions produce a concentration of 100 to 500 x 106 spermatozoa/mL. [2]

Sperm Motility

One of the most important functions of sperm is their ability to move through fluids using their long tail. This function allows them to reach the egg and penetrate its wall, forming an embryo.

Evaluating sperm motility involves examining a sample of fresh semen under a microscope. [2] The veterinarian will count the number of sperm that are moving, and identify whether the sperm are moving in an abnormal way that could influence their functionality. [2]

In a quality semen sample, at least 60% of the sperm must be moving in a relatively straight direction that indicates they are functioning properly. [2]

Sperm Morphology

Morphology describes the shape or structure of the sperm, and is an indication of whether the sperm are viable. In particular, the shape of the sperm head can impact the sperm’s ability to travel through the female reproductive tract. [1]

To examine morphology, a semen sample is examined under the microscope using a special stain that highlights the sperm. [1][2] Counting the number of normal sperm and abnormal sperm allows the veterinarian to estimate how many sperm are viable in the sample. [2]

The types of abnormalities are also recorded, as some are more detrimental to fertility than others. Common abnormalities include: [1][2][6]

  • Abnormal head, including too small or too large, or having a pointed or pear-shaped head
  • Detached heads with no tails present
  • “Droplets” or ball-like thickenings of the sperm tail
  • Premature sperm

A good quality semen sample has more than 50% normal sperm. [2]

Sperm Longevity

For sperm used in artificial insemination, the longevity of the semen sample determines how quickly a fresh-cooled dose should be used. The veterinarian measures longevity by evaluating sperm motility shortly after collection, then repeating the evaluation at 6, 12, 24 and 48 hours. [2][6]

The type of semen extender used can also have a significant impact on longevity, and semen from different stallions can respond to each semen extender differently. Many veterinarians will conduct semen extender trials to determine which extender is best suited to each stallion. [4]

Advanced Diagnostics

Stallions that have fertility issues may benefit from more advanced diagnostics on their semen.

Additional tests may include evaluations of: [1][7][8]

  • Integrity of the sperm’s cellular membrane
  • Quantity of mitochondria (energy-producing structures) within each sperm
  • Enzymes within the sperm that degrade the egg wall during fertilization
  • Ability of the sperm to bind to the egg wall
  • DNA damage within the sperm
  • Maturity of the sperm

Factors Influencing Sperm Production

Several factors influence a stallion’s ability to produce sperm, which in turn affects their fertility. The major factors are season, testicular size, age, frequency of collection, and athletic use.

Season

Horses are seasonal breeders, and only breed during the spring and summer months under natural conditions. [1] Although most of the seasonality is driven by when mares come into heat, stallions also experience seasonal declines in fertility. [1]

Seasonal changes in semen production include: [1][9]

  • Reduced sperm concentrations
  • Lower sperm motility
  • Reduced sperm membrane integrity
  • Increased DNA damage in sperm

However, it appears that not all stallions respond to seasonality in the same way, with some having minimal or no effect of season on their semen quality. [9]

Testicular Size

In many species, the size of the testes is directly correlated with daily sperm production. [1] Some veterinarians measure testicular size as part of a breeding soundness examination to estimate the stallion’s potential daily output. [1]

Testicular size can serve as an indicator of declining sperm production, allowing for timely intervention and treatment. [1]

Age

Age impacts both the size of the testes and the number of sperm that the testes produce. In older stallions, the amount of sperm stored in the epididymis is greater. The increased storage capacity allows older stallions to service more mares per day than their younger counterparts. [1]

Similarly, testicular size increases from two (2) years of age to around twelve (12) years old, allowing for increased sperm production. After twelve (12) years of age, testicular size decreases slowly, reducing sperm production capacity. [1]

Frequency of Collection

The number of collections per day can greatly influence the quality of each collection. During every collection, the epididymides of the testes release their stored sperm. With repeated collection, the amount of stored sperm available is reduced, resulting in lower sperm concentrations in subsequent collection.

A period of rest is required to allow the testes to replenish epididymal storage and return semen concentrations to their baseline level. [1] Without rest, the sperm concentration in the semen only reflects the capacity of the testes to produce sperm on a daily basis. [1][4]

For most stallions, collecting once a day or on alternating days allows for peak sperm concentrations in the semen. [1]

For stallions in an intensive breeding program, where they are collected daily or multiple times daily, it is important for the veterinarian to evaluate their breeding capacity based on their “true” daily sperm output, or their output once their epididymal stores are depleted. Collecting a stallion daily for around five (5) days depletes the stored sperm, allowing for evaluation of testicular sperm output. [1][4]

Athletic Use

Competing stallions may have reduced sperm quality compared to non-competing stallions. [10] Additionally, horses that perform in less strenuous sports have higher sperm concentration and improved motility compared to those in more strenuous events. [10]

Increased exercise may impair the hormonal balance that triggers spermatogenesis, resulting in lower sperm concentration and quality in working horses.

Increased body heat due to exercise may also cause reduced sperm quality, as sperm production is highly temperature sensitive. [10]

Summary

  • Semen collection and evaluation is a crucial part of breeding soundness examinations and artificial insemination
  • Artificial vaginas are the most common method of semen collection
  • Evaluating semen for motility, concentration, morphology, and longevity provides an indication of the stallion’s overall fertility
  • Age, season, testicular size, frequency of collection, and athletic use are the most common factors that influence sperm production in stallions

Is Your Horse's Diet Missing Anything?

Identify gaps in your horse's nutrition program to optimize their well-being.

References

  1. McKinnon, A. O. et al. Equine Reproduction. Wiley-Blackwell, 2010.
  2. Crabtree. J. Prebreeding Examination of the Stallion. In Practice. 2010.
  3. Brinsko. S. P. and Blanchard. T. L., Eds. Manual of Equine Reproduction, 3rd edition. St. Louis, Mo: Mosby/Elsevier. 2011.
  4. Dascanio. J. J. et al., Eds. Equine Reproductive Procedures, 2nd edition. Wiley-Blackwell. 2021.
  5. Cavalero. T. M. S. et al. Alternative Protocol Using Imipramine, Detomidine, and Oxytocin for Semen Collection in Stallion with Ejaculatory Dysfunction. Journal of Equine Veterinary Science. 2020. View Summary
  6. Love. C. C. Modern Techniques for Semen Evaluation. Veterinary Clinics of North America: Equine Practice. 2016. View Summary
  7. Ball. B. A. Diagnostic Methods for Evaluation of Stallion Subfertility: A Review. Journal of Equine Veterinary Science. 2008.
  8. Varner. D. D. Developments in Stallion Semen Evaluation. Theriogenology. 2008. View Summary
  9. Crespo. F. et al. Effect of Season on Individual Stallion Semen Characteristics. Animal Reproduction Science. 2020. View Summary
  10. Wilson. M. et al. Variance in Stallion Semen Quality among Equestrian Sporting Disciplines and Competition Levels. Animals. 2019. View Summary