Stallion Breeding Soundness Examination

  • The goal of a stallion breeding soundness examination is to select stallions for fertility, eliminate stallions with heritable defects, alert owners of subfertile stallions, and determine any cause of infertility.
  • It is important to note that the fertility is assumed for time of examination only, since conditions may arise shortly after the examination that affect fertility.

  • The foaling rate is a good indication of fertility.
  • Check the foaling rate of the last breeding season.
  • Check the reproductive history of the mares, as barren or infertile mares may make stallion look like he has subfertility.
  • Record the services/foaling, but be careful as abortions etc. that are not associated with the stallion may alter the number of foals born.
  • Calculate the services/conception for maiden, barren, and foaling mares.
  • If a problem shows up, you may also want to check the management (breeding and housing) of the mares to help rule out a management problem.
  • Determine the intended use of this stallion
    • Natural service vs. AI
    • Fresh cooled semen?
    • Frozen semen?
    • Size of book (expected number of mares to be bred
  • The stallion should be free of Equine Infectious Anemia , Equine Viral Arteritis , CEM.

  • Positive identification is essential.
Who am I?
  • A tattoo is the best identification, but a photo is also a good idea.
  • In any case, make sure you positively identify the stallion to avoid legal complications later!

General physical exam
Examine the stallion for:
  • Conformation,
  • Lameness,
  • Vision,
  • Inherited Defects,
  • Cryptorchidism, 2 scrotal testes
  • Combined Immunodeficiency,
  • Parrot Mouth,
  • Hemophilia,
  • Complete Mature Cataracts,
  • Aniridia,
  • Wobbler,
  • Multiple Exostosis.
  • A breeding sound stallion should be free from these defects.
  • Ultrasound
    • Although we usually think of the mare when we consider reproductive ultrasonography, there are a number of uses for ultrasonography in the stallion. 
    • Ultrasonographic examination of the testes is an accurate method for determining testicular size, as well as identifying pathologic features. 
    • Testicular parenchyma can be examined, testicular trauma evaluated and tumors identified. 
    • The central vein is an easily identifiable landmark. 
    • Scrotal contents such as bowel or excessive fluid can be visualized. 
    • Hematocele can be differentiated from hydrocele. 
    • The internal genitalia can also be examined. 
    • The accessory sex glands are better evaluated using ultrasonography than by palpation alone.
Semen collection
  • Semen is collected with an artificial vagina. 
    • A stallion ejaculates based on the temperature and pressure exerted onto the penis by the vagina, or in our case, the artificial vagina. 
    • Each artificial vagina is designed to produce the correct pressure and temperature to make a stallion ejaculate. 
    • Each model has advantages and disadvantages.

Artificial Vagina

Models of Artificial Vaginas
Colorado (ARS - Animal Reproduction Systems)
  • This is a commonly used model. It forms a water jacket using a hard shell and a rubber liner. A second rubber liner or a disposable liner is inserted into the AV to collect the semen.
  • The advantage of this system is that it holds a large volume and will retain its heat very well in cold climates.
  • A disadvantage is that it contains a large amount of water and is fairly heavy.
  • Another disadvantage is that after ejaculation the semen is retained in the confines of the water liner. If the water is not drained out quickly, the sperm cells are subjected to a deleterious temperature.
  • The ARS version has an entire setup (liner, filter, collection bottle) available which includes a disposable liner to prevent contamination of the sample and contamination between stallions. The disposable liner also facilitates clean up. The latex liners are reported to cause lower sperm motility, but some stallions object to the disposable plastic liners.
  • The system also includes an in-line semen filter to filter out the gel fraction of the ejaculate.
  • If the ARS is completely filled with 50o C water, it will equilibrate to 45o C in about 10 minutes.
  • The pressure is adjusted by opening the valve, inserting your arm into the AV and letting water out to the desired pressure (unfortunately this is only a guess).
  • If more pressure is desired or the temperature needs to be increased, more water must be added (this is a pain when you are out collecting a stallion).
  • Dr. Eilts' least for stallion collection.

  • The Missouri AV contains the water between two soft liners, instead of a hard shell.
  • Advantages of this system include:
  • You can easily adjust the pressure by blowing air into the water bladder.
  • The semen does not remain in contact with the water after ejaculation.
  • It is very light.
  • Disadvantages include:
  • It does not hold much water, so it drops in temperature relatively rapidly in cold weather.
  • It is difficult to get and insert disposable liners into it, so it must be cleaned with alcohol between each stallion. This results in a greater chance of contamination.
  • The leather case does not always hold the AV firmly when the stallion's penis enters the AV.
  • A special "coupling nut" is needed to attach a collection bottle to it
The Hannover AV 
  • Somewhat of a Nishikawa - Colorado hybrid
  • Outer case is made of hard rubber
  • Has a partially closed distal end for the stallion to push the end of the penis against
  • Disposable liners, filters, collection bottles are available, similar to the Colorado
  • Dr. Paccamonti's favorite............for collecting stallions.

Japanese (Nishikawa)

  • This is basically an aluminum Colorado.
  • It has a small hole in the cap that is designed to vent water and automatically adjust the pressure as the stallion's penis enters the AV.
  • There is also a rubber ring in the end of the AV that is designed for the stallion to push his penis against and supposedly feel more natural.
  • It is smaller and made of aluminum, so it loses heat rapidly.
  • The collection 'bottle' is a rubber cone, which can be contaminated easily.
  • These are no longer available.

Krakow - Polish

  • This is just a short model used for not stallions that have a short penis........for fractionating the semen sample.
  • It is most useful in situations when you want to examine the ejaculate to determine where a particular problem originates.

See the French IMV by clicking here

AV Preparation
  • Most stallions want a temperature of 45-48o C (depends on stallion's preference).
  • Adjust the pressure to stallion's preference just before you are ready to collect him. This keeps a lot of water in the AV and helps prevent cooling.
  • Use about a tablespoon of non-spermicidal lube when you are adjusting the pressure. Only lubricate abut the first third of the AV. Lubricate just before collection to avoid drying out the lube and to check for foreign objects (thermometers) in the AV. Studies have shown that even non-spermicidal lubricants can have detrimental effects on sperm due to changes in osmolarity. There are some reports coming out about how spermicidal lubes are. These reports tended to use a lot of lube placed into the semen (5% by volume).

  • Commercially available
  • Hard to put on and keep on
  • Have seen human condoms used on mini stallions (best to use two)

Manual stimulation

  • This can be used for stallions that have difficulty mounting.
  • You can attempt manual massage of the erect penis with moist towels while the stallion is standing or while he is mounting.
  • Experimentally it took about 1 1/2 training sessions to train stallions to do this.
  • The semen (except for pH) is the same as if done by an AV collection.

  • This can also be used for stallions that have difficulty mounting.
  • Erection and ejaculation are primarily alpha, whereas arousal beta stimulation.
  • Xylazine
  • It has both alpha and beta actions.
  • Use 0.3 mg/lb after sexual stimulation.
  • Experimentally semen was obtained in about 40% of stallions.

  • Imiprimine is a tricyclic antidepressant used in humans. (It was noted that a side effect of the drug in humans was ejacualtion)
  • It is only used experimentally now.
  • The 'current' method used by Sue McDonnell and sent on the Equine List server 3/4/02
    • "We now (2002) use the oral imipramine instead of injectable. (We had trouble getting injectable preparations that didn't result in some worrisome hemolysis.) 

    • For a 1000 pound horse we now get best results starting with 1000 mg imipramine  hydrochloride orally approximately two hours before 200 mg. xylazine IV. Ejaculations when they occur, tend to be at about 2 minutes after xylazine  or at 15-20 minutes after xylazine, either when the horse is just becoming sedate or just regaining alterness.  We adjust the dose for subsequent attempts based on the horse's response.  If he goes from normally alert to fully sedate (head down to about 8 inches from floor) very gradually over 120 seconds after xylazine, then we consider that is a good level of xylazine. If he goes down abruptly (less than 1 minute) or to very deep standing sedation (wobbly swaying, snoring with nose on floor), then too much xylazine.  If he never gets fully sedate (head down to about 6-8 inches from floor, and not alert and responsive to surroundings) or not fully sedate until several minutes after xylazine, then we just that not enough xylazine. These induced ejaculation protocols based on imipramine and xylazine have always worked best with with a quiet stallion that tolerates injections well.  We deliberately do the procedure at quiet times and have a minimum of people to disturb the horse (only one). We attach a collection bag over the prepuce on a girth strap so that after a queit approach and injection, we can tip toe out of the stall and leave the stallion undisturbed. we either monitor on remote video monitor or "peak" around the corner quietly.

    • Also, with this protocol the semen will likely be very concentrated, with a small volume.  That's due to the imipramine enhancing contractions of ampullae and inhibiting somewhat the contractions of accessory sex glands.It's great for freezing, but needs immediate careful handling to avoid cold shock. We've had some over 1 billion per ml.  the total count is usually higher than what you would get in an in copula ejaculate from that horse. 

When to collect
  • Semen collection after sexual rest is not indicative of how many sperm cells a stallion can produce under normal use.
  • It is best to collect a stallion when he is at his Daily Sperm Output (DSO). 
    • The DSO estimates the number of cells the testicular parenchyma can produce daily. 
    • This is when all the cells he is ejaculating equals the cells he is producing every day.  
    • It may take 7-10 days in some cases to get to the DSO.
    • Normally the sperm output will stabilize at the daily sperm output. 
    • The mean of last 3 daily collections is DSO. 
    • You can estimate the DSO by taking 27.5% of second ejaculate (taken 1 hr apart). From testicular measurements:
    • DSO=-3.36 X 109 + (0.066 X 109)(SW in mm)
    • DSO=(0.024)(TV)-0.76 .     (TV=(4/3)π(0.5* height * 0.5 * width * 0.5 * length).


  • It would be a good idea to collect a stallion at his normal use schedule.

Semen Collection
  • For a stallion not trained to a dummy, an estrous mare is needed. 
    • If possible pick one that is calm and does not like to kick. 
    • If you do not have a mare in heat , an anestrus mare given 1 - 2 mg estradiol cypionate (ECP) will show signs of heat. 
    • An ovariectomized (OVX) mare given 2 mg ECP 2-3 days in advance is ideal, in that the temperament for the mare OVXd can be selected, and you 'always' have a mare in 'heat'. 
    • A dummy or phantom is ideal if the stallion is trained for it. Dummies do not move or kick!
  • Wrap the mare's tail and tie it off to the side.
  • Make sure the restraint is adequate for both mare and stallion.
  • Stallion preparation
  • Tease the stallion to erection.
  • Wash the penis with warm water only (no soap....soap can lead to overgrowth of harmful bacteria on the stallion's penis) !!
  • Take cultures of the urethra before and after ejaculation, and the penile shaft. 
    • Culture the fossa, corona, etc. if there is a concern or a problem. 
    • You can expect no abundant pathogens, and there should be only garden types (mixed culture) seen on the cultures. 
    • You should not get a pure culture of anything.
  • It is advisable to pull the shoes if at all possible to avoid injuring the mare or any of the collectors.

The semen collection

Click the movie icon to see a video of semen collection in the stallion.


  • All the handlers should be on left side and everyone is advised to pull to the left if there is a problem.
  • The entire collection has to be a choreographed effort by everyone involved in order to get a sample and keep everyone safe.
  • Approach the mare at an angle and allow the stallion to mount the mare.
  • Let the stallion thrust and guide or allow the stallion to insert his penis into the AV.
  • Gently touch the ventral penis and feel the urethra for the ejaculatory pulses. Others can watch for the flagging of the tail that indicates ejaculation.
  • After the sample is collected, keep open of the AV upright to avoid spilling the semen out.
  • Immediately drain the water out to prevent the continued exposure of the sperm cells to hot water. The water jacket also forms a 'dam' that will prevent the semen from draining into the collection bottle.
  • Protect the semen from light and cold shock and then begin to analyze it as soon as possible.

Semen analysis

Stallion specifics
  • The sperm cells may make large circles due to normal abaxial midpiece, but this is normal for stallion semen.
  • If an in-line filter was not used during collection, remove the gel with sticks or by pouring through a filter or some gauze.
Longevity testing
  • Use individual longevity tests for motility as well as looking at fresh samples.
  • Motility - immediately examine raw and extended samples.
  • Make sample consisting of a raw (neat) sample and samples extended 1:1 and 1:4.
  • Keep the samples at room temp and prevent light or air contact.
  • Estimate motility hourly until the motility is less than 10 %.
  • The goal is to have at least 10% at 6 hours.
  • If the motility is < 10 % after 3 hours, the stallion generally has poor fertility.

  • Check the pH immediately with a pH meter.
  • Normal pH is about 7.
  • A higher indicates soap contamination, urine contamination, inflammation, or problems with the accessory sex gland fluid.

Genital exam
  • A genital exam is best done after semen collection, because the stallion will be much calmer.
  • Make sure the penis is free from:
  • Summer Sores (Habronemiasis).
  • Sarcoid.
  • Melanoma.
  • Coital Exanthema (Herpes).

Testes and scrotum
  • Check for edema of scrotum and adhesions between the testes and scrotum that will inhibit thermoregulation.
  • Testes
  • A stallion must have two!!
  • Average size is 9x6x5 cm.
  • The total scrotal width (TSW) should be > 80mm.
  • Ultrasound exam is best
    • Measure height, width, length of testes to determine testicular volume
    • Examine testicular parenchyma, epididymides
    • Best way to examine scrotal contents (hydrocele, hematocele, hernia)
  • The consistency should be the same throughout.
  • The head is anterior, the body is dorsolateral and the tail is posterior.
  • The orientation of the epididymis can help determine if a testicular torsion exists. Transient torsions are fairly common, and does not cause any clinical problems.

Rectal Palpation

  • There are few problems diagnosed by rectal palpation and the risk of routine exams probably does not justify the rewards.
  • You can check the accessory sex glands, which include the prostate, ampullae, and seminal vesicles.
  • You can also palpate the inguinal rings for hernias.

Second semen collection
  • A second semen collection should be performed one hour after the first collection.
  • The second collection, in relation the first, should have:
  • Same Volume.
  • 60 % as many cells
  • Same motility
  • A pH that rises slightly.
  • If this relationship between the first and second ejaculates is not seen, then one of the ejaculates is not representative !!!

Criteria to pass BSE
  • The stallion must have normal libido, normal behavior and a normal gait.
  • He should have 2 scrotal testes and there should be no scrotal or penile abnormalities.
  • The testes should have at least 80 mm TSW.
  • The cultures from the penis and urethra should have inconsistent bacterial types, and there should be fewer colonies after the first ejaculation. There should be no pathogens.
  • The stallion should not have contagious equine metritis  (CEM) or EIA.
  • If the stallion does not pass, recheck him again at a better time in the season or recheck him in 60 days.

Stallion management

  • A stallion produces sperm cells seasonally, just as the mare cycles seasonally.
  • Therefore, the season may affect the results of the BSE.


  • Advantages of transported fresh semen
  • All the advantages of on-farm artificial insemination with fresh semen
  • Reduced chance of disease transmission
  • Increased book size for stud owner
  • Less chance of injury to horses and handlers
  • Less expensive to ship semen than horses
  • Decreased cost of broodmare care at studfarm?
  • Decreased stress and chance of injury to mare and foal due to shipping
  • Breeding can continue while stallion is engaged in other activities
  • Increased availability of superior stallions or uncommon breeds
  • Semen evaluation possible at time of breeding
  • Disadvantages of transported fresh semen
  • Lower fertility with some stallions
  • Lower fertility with prolonged shipping times
  • May be increased cost realized due to processing semen
  • May be increased cost due to lower per cycle pregnancy
  • Requires additional equipment and training for semen processing
  • Requires better mare management
  • Requires good stallion management
  • Requires good communication between all parties
  • Requires advance planning, semen may not be available every day
  • Factors influencing success with transported semen
    • Pregnancy rates with transported, cooled semen are similar to those obtained after using fresh semen, provided mare management, semen quality and semen handling are good and shipping times are relatively short (< 24 hrs). Shipping times greater than 24 hrs are associated with some degree of reduction in pregnancy rates, possibly as much as 50%. For these reasons, proper techniques of semen evaluation, extending and packaging are essential.
  • Semen quality / stallion fertility
  • Motility, concentration, volume and morphology before extending
  • Quality after storage / shipment
  • Type of extender used
  • Concentration, dilution ratio of extended semen
  • Type of packaging system used
  • Cooling rate
  • Lowest temperature reached
  • Ability to maintain stable temperature
  • Duration of transport
  • Number of normal, motile sperm inseminated
  • Timing of insemination: ability to predict ovulation, use of hCG or GnRH analogues to induce ovulation and avoid need for repeat shipments
  • Mare management / fertility


    • The shipment and use of fresh cooled semen is experiencing increasing popularity. Restrictions enforced by the various breed associations are the main factor preventing its widespread use. Semen extenders are an essential component of fresh cooled semen.
  • Semen Extenders
  • Semen extenders are an important adjunct to an artificial breeding program. Use of semen extenders makes it possible to ship semen overnight while preserving fertility. Their beneficial effect is also used at times in natural breeding by infusing the extender into the uterus in conjunction with mating.
  • When an extender is added to fresh semen, it is not unusual to see an initial increase in motility. As time passes, motility of the extended semen remains higher and is maintained longer, than the motility of the unextended, or raw, sample. In addition, semen extenders containing antibiotics help to reduce the contamination introduced into the mare's uterus at breeding. For these reasons, semen extenders may improve the fertility.
  • Composition
  • Semen extenders provide substances for the metabolic activity of the spermatozoa, buffer against changes in acidity and protect against cold shock. Glucose is the primary nutritive component of most extenders. Depending on the particular recipe, egg yolk or milk normally provides the protective effect against cold shock. If milk is used, either half & half, which is heated in a double boiler and the scum removed, or nonfat dry skim milk are usually used. Nonfat skim milk is very easy to use, however, only brands without added preservatives are suitable. Most commercially available extenders rely on non-fat dry skim milk as a base. Antibiotics are usually added to the extender to inhibit growth of bacteria in the semen during storage. Studies indicate that the antibiotic polymyxin B is not suitable for storage of semen, therefore it is not used in extenders for transported semen. Although other studies have indicated slight differences in motility after storage with various antibiotics, from a practical standpoint antibiotics such as ticarcillin, gentamicin or amikacin all give satisfactory results and are commonly used.
  • Osmolarity and acidity are critical factors in the preparation of an extender. After preparing an extender, both pH and osmolarity should be checked before use. If instruments are not available to check pH and osmolarity, the extender should be tested to verify that sperm viability is maintained before the extender is used for shipping. Some antibiotics may significantly alter the pH of the extender and sodium bicarbonate must be added to restore it to a suitable range.
  • Semen extender may be prepared in large quantities and then frozen and stored in smaller aliquots, such as 100 ml, for later use. Properly stored, the semen extender will be preserved for 3 to 6 months and reduce the need for frequent extender preparation. Commercially available extenders are very easy to use and are formulated to provide the correct pH and osmolarity. They usually consist of a packet of dry ingredients and a small vial of diluent which are mixed together at the time of use. Most are available in convenient 100 to 125 ml sizes so that extender is made as needed rather than pre-made and frozen.
  • Dilution Ratio
  • Sperm will quickly metabolize available substrates in seminal plasma so motility will decrease rapidly. Therefore, after the semen is collected, it should be mixed with extender as soon as possible, preferably within 10 or 15 min. Ideally, the ratio of semen to extender should be at least 1:2, and a ratio of 1:4 or 1:5 is preferable. Nevertheless, it is the final concentration of sperm in the extended sample that is the critical factor. Longevity of the sperm cells is maximized if extender is added to give a final concentration of sperm cells of 25 - 50 million/ml. With an adequate extender at a proper dilution, sperm will retain their fertilizing capability for up to 24 hours at room temperature (20oC), depending on the individual stallion. Therefore a semen:extender dilution factor should be calculated based on the initial concentration of sperm to give a final concentration of 25 - 50 million sperm/ml before shipping.
  • For example:
    • Concentration at collection = 267 million/ml

    • Desired concentration = 50 million/ml;

    • 267 / 50 = 5.3 total parts semen + extender

    • 5.3 total parts - 1 part semen = 4.3 parts extender needed

    • Therefore, use 5 parts extender : 1 part semen to give a final extended concentration of 45 million sperm / ml
  • If a stallion provides an ejaculate with a low concentration, so that dilution at a 1:4 ratio, for example, would result in the final concentration being less than 25 million/ml, centrifugation is recommended. Centrifugation can be used to concentrate the semen so that dilution at a recommended ratio can be achieved while maintaining a concentration of 25 - 50 million/ml.
  • Recommendations for centrifugation are to begin with a force of 500 X g for 10 minutes. Less time or fewer g’s will result in less damage to the sperm from the force of centrifugation but a softer pellet and more viable motile sperm in the supernatant that will be discarded. Centrifugation for a longer time or at higher g’s will achieve a better recovery and minimize sperm losses in the supernatant but result in more damage to the sperm cells. Centrifugation technique can be altered within a range of g’s and times to achieve good recovery while minimizing cellular damage.
  • After centrifugation, the supernatant is removed and discarded. Studies have shown that a small portion (a minimum of 5%) of the seminal plasma must be left with the sperm to preserve viability. The pellet is then resuspended using sufficient extender to achieve a final concentration of 25 - 50 million/ml.
  • Preservation of semen quality depends to a large extent on the initial quality of the semen, and varies from stallion to stallion.
  • Determination of insemination dose
  • Prior to shipment of semen from a stallion (and periodically during the breeding season) it is advised to do a trial run with the chosen shipping system and determine the motility after 24 and 48 hours of storage. This allows you to determine the "recovery rate" and make adjustments in the number of sperm shipped so that an adequate insemination dose will be provided when the semen reaches its destination.
  • In addition, it is advisable to maintain a record of the collection data. Such information may help in determining the collection or shipping frequency, shipping dose and number of doses to expect from an average collection.
  • The recommended insemination dose is usually 500 million progressively motile (normal) sperm, although acceptable pregnancy rates can be achieved with as few as 250 million normal, progressively motile sperm. The volume of the inseminate is not critical. Although pregnancy can be achieved with very small volumes, the recommended minimum volume used for insemination is usually 10 ml. Usual insemination doses with fresh cooled semen range from 20 to 120 ml. Although some veterinarians are reluctant to inseminate volumes greater than 60 ml, studies have shown no decrease in fertility when larger volumes were inseminated, provided the inseminate was not real dilute.
  • To determine the volume of semen to package for shipment, divide the desired number of progressively motile sperm (usually 500 million) in an insemination dose by the product of the concentration times percent motility at the end of the storage period. For example, if we have extended our semen to a concentration of 50 million/ml and our motility after transport is 40%, we should package at least :
  • 500 / (50 X .40) = 500 / 20 = 25 ml. Unless a stallion is in very high demand it is best to package more than the minimum amount needed. For example, with the above stallion, packaging 50 ml would insure that more than adequate numbers of sperm were available for fertilization of the oocyte. Furthermore, a more conservative method is to include percent normal morphology into the equation. For the stallion above, if normal morphology is 70%, the equation becomes:
  • 500 / (50 X .40 X .70) = 500 / 14 = 35 ml
  • Semen Packaging
    • The pre-warmed extender should be added slowly to the semen. The extended semen should be placed in a container such as a Whirl-Pak bag, from which air can be excluded, and sealed. This container should then be placed in a second container from which air is again excluded and the second container also sealed.
    • It has become commonplace for some people to place two insemination doses in the shipping container, intending one to be used upon arrival and the other to be used the following day. In fact, there is no physiological basis for such practices. The ideal place to store spermatozoa is in the mare’s oviducts. Man-made semen transport devices are a means to transport semen from the stallion to the mare without transporting horses. They are not meant to take the place of the mare as a site of sperm storage until fertilization. All semen received in a transport device should be inseminated into the mare at the time of arrival. This should be kept in mind when preparing the semen for shipment.
    • Ideally, the semen should be extended and placed in the cooling device within 10 minutes of collection. The rate at which extended semen is cooled is critical. If the cooling rate is too fast or too slow, sperm viability is decreased. A cooling rate of -0.05 to -0.1 C/min is desired between 20 and 5 C. Ideal storage temperature is 4-6 C.
    • Numerous types of containers for fresh, cooled semen are commercially available. Reusable containers such as the Equitainer as well as inexpensive disposable systems are in use worldwide. The systems vary in their cooling rates, minimum temperature reached, time required to reach the minimum temperature, length of time they are able to maintain the minimum temperature, etc. Performance of the different systems also varies depending on environmental conditions. Some of the disposable systems such as the Equine Express and BioFlite compare very favorably with the Equitainer system, while others such as the ExpectaFoal compare less favorably, reaching temperatures below 0 C.
    • Some reports indicate sperm viability is decreased due to contact with the rubber plunger on syringes. Syringes constructed of all plastic are therefore recommended by some researchers. In actual practice, however, the extended semen is not in contact with the plunger very long and the numbers of sperm cells being inseminated are great enough that toxicity from the syringe is probably of little clinical significance. If semen is held in syringes for any length of time, however, as in some types of shipping devices, syringes of all plastic should be used.
    • An information form should be included with each shipment. Minimum information required on the form includes stallion identification, date of collection, concentration and volume of inseminate shipped (i.e. numbers of sperm), initial motility, type of extender used, numbers of doses shipped and any special instructions.
    • Prior to shipment of semen from a stallion (and periodically during the breeding season) it is advised to do a trial run with either shipping system and determine the motility after 24 and 48 hours of storage. This allows you to make adjustments in the number of sperm shipped so that 500 million motile sperm will be provided when the semen reaches its destination.
    • Use of some of the more common packaging systems are described in more detail:

        Equitainer I & II

        • The Equitainer system is a very durable, hard plastic insulated container. In the center of the Equitainer is a well. The system is designed to cool a volume of 120 to 170 ml of fluid at the optimum rate. The extended semen sample is nestled in ballast bags in a plastic cup so that the total volume of the semen plus the ballast bags is between 120 to 170 ml. Each ballast bag holds 60 ml of a colored fluid. Ballast bags should be warmed in an incubator (37oC) for 4 hours before use. The plastic cup containing the semen is placed into the "isothermalizer". One or two (depending on the model of Equitainer) specially designed freezer packs are placed in a plastic bag and loaded into the well of the Equitainer. The isothermalizer is then loaded into the well on top of the freezer packs. Records should be enclosed that identify the source of the semen and for the person breeding the mare to fill out. The particular forms may differ depending on the breed involved. The container is then closed and latched. It is a good idea to seal the container so that it will be evident if any tampering occurs.
        • A sample of the extended semen that was packaged in the Equitainer should be kept in a similar manner for evaluation 24 hours later, as a quality control. If a second Equitainer is not available, the cooling and storage procedure can be simulated by placing a sample in a Whirl- Pak bag which is then placed in a polypropylene cup. The cup is then placed in a water bath of approximately a pint of water in a container about 6 inches in diameter, which has been prewarmed to 37oC. Place the whole assembly into a refrigerator set at 5oC. After a 24 hour interval, warm the semen to 37oC and assess motility.
        • Various models of the Equitainer system are available. Models differ somewhat in the length of time they will maintain the semen chilled and whether a lead shield is present. It should be remembered, though, that shorter storage times result in improved fertility.

  • A number of "disposable" semen shippers are currently available, one of which is the Equine Express. It is inexpensive and consists of a cardboard box with styrofoam inserts and compartments for the semen and a freezer pack. The semen is packaged in all-plastic syringes. After collection, evaluation and extension of the semen, the extended semen is placed in an all plastic syringe. The syringe containing the extended semen is placed in the styrofoam box along with another syringe containing an equal volume of water as "ballast’ to moderate the cooling rate. Alternatively, the semen can be packaged in 2 syringes of equal volume. A styrofoam sheet is then placed in the box over the syringes and a specially formed freezer pack placed on top of that. Breeding forms and other pertinent information should be enclosed before sealing the box.



  • Another inexpensive yet dependable disposable shipper is the BioFlite. It is similar in some ways to the Equine Express, in that it consists of a styrofoam box with a lower compartment to hold the semen, an upper compartment that holds a freezer pack and a styrofoam sheet between the compartments. In previous models the semen was packed in plastic bags that were then placed in a plastic specimen cup. In newer models of the BioFlite the semen is packaged in all-plastic syringes.  BioFllite also makes a model for shipment of canine semen.
  • EST

Made by Plastilite, Inc.  Either a cardboard or plastic outer shell is available, and either a styrofoam or special insulating linerr are available.

  • Transport and Insemination
    • After packaging, the container is shipped by commercial carrier or airline to be delivered within 24 hours. Some concerns have been raised about x-radiation of semen as it passes through airport security. Studies examining the effects of doses of radiation used in airport security have found no adverse effects on spermatozoa. However, there are indications that the airports will soon increase the level of radiation in an attempt to improve security and the effect of the increased level of radiation is unknown. The Equitainer system has a lead shield in the transport container to shield the semen from the radiation and any possible harmful effects.
    • When the semen arrives at its destination, the mare is prepared for artificial insemination. Either while the mare is being prepared or after she is inseminated, the semen should be examined to determine percent motility. Care must be taken to maintain the semen at the chilled temperature in the container until ready to place it into the mare. The best place to rewarm the semen is in the mare's uterus. Prewarming the semen before placing it into the mare decreases conception rate. A drop may be removed from the sample container and placed on a warm microscope slide on a slide warmer. A warm cover slip is placed on top and motility estimated in the same manner as during a breeding soundness examination. Motility will improve as the sample is allowed to warm. The concentration may also be determined if it is unclear how many intended insemination doses were sent.


  • Shipping
    • The use of fresh, cooled semen provides a number of advantages. It is much easier to ship a container of semen to a mare than to ship a mare and foal to a stallion. Not only is cost decreased by shipping semen rather than horses, but stress on the horses is greatly reduced also. Fresh, cooled semen allows more efficient use of a stallion, not only for shipping, but for temporary storage on the farm to reduce the frequency of collection. For example, a stallion can be collected, the ejaculate extended and a portion used to inseminate mares that day. The remainder can be cooled and used to inseminate mares 24 to 48 hours later. Shipment of semen increases the availability of superior stallions or stallions of uncommon breeds and allows a stallion to breed a greater number of mares in a season.
    • Some slight disadvantages are inherent in the use of shipped, fresh cooled semen. For unknown reasons, considerable variation exists between stallions in the ability of their sperm to remain viable during the cooling and storage process. For all stallions, however, fertility is generally higher if the storage period is shorter. If care is taken in the preparation of fresh, cooled semen and mares are managed well, pregnancy rates using fresh, cooled semen can be as high as those with a natural breeding program. An important consideration if semen is being shipped in to breed a mare is the advanced planning required. This may be complicated by the fact that semen may not be available every day of the week due to the work schedule of the shipping company. In addition, use of shipped semen requires good mare management. Good record keeping and a good teasing program are integral components of a successful breeding program. Ability to predict ovulation is essential in order that semen arrive before the mare ovulates, and to avoid repeated shipments of semen during a single estrus. Research has shown that breeding too long after ovulation results in decreased pregnancy rates and increased early embryonic death.



Stallion Infertility

  • Check the mares to make sure that the mares are not the source of the problem.
  • Overuse may lead to oligospermia, so it is important to check sperm output at normal use levels.
  • If the stallion is being overused, you may need to decrease the stallion's use to get greater numbers of sperm in the ejaculate and improve fertility.

Behavioral Problems (Click on the logo to visit the U Penn Web site on behavior)


  • Often times sexual behavior is induced by punishing normal sexual behavior.
  • It may take much retraining to change this sexual behavior.

Low Sperm Motility
  • Abnormal cells may result in low motility. There is not an immediate cure for this.
  • A problem with the accessory sex gland fluid may decrease sperm cell motility. 
    • You can extend the semen to see if diluting the seminal fluid will negate the effects of the accessory gland fluid. 
    • You may need to remove almost all the accessory gland fluid by centrifugation (900 g for 20 minutes does not normally harm the sperm cells).
Sperm Stasis
  • This may be a storage problem in the ampullae.
  • You need to increase the frequency of collection to improve motility.
  • Treatment options: ampullary massage followed by daily collection; administration of oxytocin or PGF

Anti-sperm antibodies
  • Anti-sperm antibodies, as a result of testicular trauma, can cause low sperm cell motility.
  • Corticosteroids have helped in this condition.

Testicular degeneration
  • There are numerous causes for testicular degeneration.  Although not clearly documented as it has been in other species, age related testicular degeneration probably occurs in stallions.  A diagnosis of testicular degeneration can be made on the basis of history, physical examination and semen evaluation.  Observations on physical exam include somewhat soft testicles initially with a noticeable change in size being evident later on in the course of the disease.  Without frequent or sequential examinations, however, slight changes in consistency or size are difficult to discern.  Findings such as a relatively large epididymis may indicate that the testicle has decreased in size. 

  • In many cases, only one testis is initially affected and the other eventually follows, leading to the belief that degeneration in one testicle affects the other testis, leading to degeneration in it as well.  Examination of the ejaculate often reveals a low concentration of sperm, low (<20-30%) motility and increased numbers (40-60%) of abnormal sperm resulting in a low number of morphologically normal, motile spermatozoa.  

  • Hormone testing presents a challenge.  GnRH cannot be measured directly in the peripheral circulation. Therefore, concentrations of testosterone and LH are used to infer the release of GnRH.  Because of the pulsatile release of GnRH and the variation by time of day, the concentrations of testosterone, LH and FSH are not constant but vary greatly.  Therefore, several blood samples must be collected  at frequent intervals over the course of a day.  In addition, concentrations which are apparently adequate for normal function vary between individuals and measurement of the gonadotropins varies greatly between laboratories.   Seasonal variation also complicates the picture.  Nonetheless, hormone testing is usually recommended in order to establish a baseline with which to compare the effects of treatment.  GnRH challenge tests are sometimes used to evaluate the pituitary response to the hypothalamus and, provided that is normal,  the subsequent response of the testis.   An hCG challenge test bypasses the hypothalamic-pituitary portion of the axis and assesses testicular response to gonadotropin stimulation.  Subfertile stallions respond to challenge tests with little or no response.  In the early stages of degeneration, hormonal imbalances may not be evident but with time an increase in FSH and a decrease in estrogen and inhibin will be observed.  When sperm concentration begins to decline, a decrease in testosterone will also be evident.

  • Roser's work suggests the problem is at the level of the testis, not at the hypothalamic-pituitary axis.  If this is so, GnRH therapy would be expected to be of little benefit.  Evidence supports the existence of a paracrine/autocrine system in the testis which is important for normal function.  Roser proposes that idiopathic infertility begins at  the level of  the testis with an initial decline in important testicular factors necessary for interactions between the Sertoli and germ cells.  Subsequently, a decrease in inhibin is observed, accompanied by abnormal sperm production, an increase in FSH release, Leydig cell dysfunction, a decrease in testosterone production and an increase in LH.  

Urospermia (urine in the semen)

  • This happens when the stallions urinates as ejaculation occurs.
  • The pH of the ejaculate is higher than normal.
  • Oftentimes you can smell the urine, but you can also use an Azostix and see if it turns green at 10 seconds.

  • The increased osmolarity is the primary cause of the low motility.
  • Have the stallion urinate before ejaculation (training).
  • 'Urospas' is a drug used in humans to increase the sphincter tone.
  • You may try imipramine or bethanocol to prevent urination during ejaculation.

  • It is the RBC component, not the plasma that is harmful to the sperm cells.
  • The cause is usually trauma or overuse.
  • The result is granulation tissue in urethra. A secondary result is bacterial urethritis and seminal vesiculitis.
  • The blood may be may be from an exterior blood contaminant also.
  • Collect semen in AV and look to see if blood is in it.
  • Fractionate the ejaculate to find the source of the blood.
  • Presperm is bulbourethral, sperm rich is the prostate and ampulla (high in ergothionine), post sperm is the seminal vesicles (high in citric acid) and the tail end is the ampulla and seminal vesicles.
  • A fiberoptic exam of urethra may reveal ulcers, but you may not see any until the penis is erect. You may see clots at the ducts where the vesicles enter the urethra. The bulbourethral glands have multiple ducts on the midline, the ejaculatory ducts (ampulla and seminal vesicles) are paired and are dorsal to the bulbourethral ducts, the prostatic ducts are lateral to the ejaculatory ducts.
  • Radiography using barium contrast may reveal erosions and pits.
  • Determine the cause before treating.
  • Sexual rest may solve the problem.
  • Antibiotics such as pessaries placed in the urethra may be needed.
  • A urethrotomy sometimes allows the erosions in the penis to heal.
  • clotting agents such as Vit K have been recommended.
  • Urinary acidifiers have also been recommended.
  • Surgical treatment of strictures caused by stallion rings may be a sequel.
  • Do not cauterize the lesions. This will result in stricture formation.

View of the duct entrances when doing endoscopy of the penis.


Shy breeders

  • 0.02 mg/lb Valium 10 minutes before breeding may allow a shy breeder to breed more efficiently.

Venereal diseases


Contagious Equine Metritis (CEM)

  • Caused by Taylorella equigenitalis
  • Signs are usually in mares, not stallions.
  • Culture
  • Complement fixation is good for carrier state. It takes 10 days to become positive.
  • Serum agglutination test is very good and there are no false positives or negatives.
  • It is a reportable disease
  • Topical 4% chlorhexadine scrub followed by nitrofurazone dressing for days.

Pseudomonas, Klebsiella, E. coli
  • Seen when normal commensals are destroyed.
  • Must subtype and match to the organism grown in them.
  • These bugs are almost always on the sheath and not from the accessory sex glands.
  • The treatment is using a minimal contamination breeding technique.
  • Here is a nice link to an Acrobat file from the UK standard of practice (If the link does not work you can cut and paste it into your browser:

Equine viral arteritis (EVA)
  • Shed in semen post infection for years after infection
  • Shedding stallion
    • Notification of mare owners of shedding
    • Only seropositive mares may be bred
    • Mares vaccinated > 21 days  or mares previously exposed to virus
  • Sero-positive stallions
    • Must differentiate vaccinated stallions from carriers
    • Documented seronegative before vaccination
    • Virus isolation on semen
Vaccination- controlled by individual States

Coital Exanthema
  • Caused by herpes 3 virus.
  • Vesicles form on the penis and eventually form ulcers.
  • There is no transmission after the ulcers heal.
  • Treatment
  • Sexual rest for 3 weeks.
  • Topical antibiotics.
  • Control: Do not breed mares or stallions with active lesions

  • Trypanosoma equiperdum
  • Signs
  • A mucopurulent urethral discharge.
  • Penile paralysis
  • 50-70% mortality
  • Diagnosis is isolation of the organism.
  • This is not in the United States.

Testicular degeneration

Other Stallion problems
Testicular / penile trauma
  • Kicked by mare during breeding
    • Swelling, edema, and possible hematoma formation.
    • You must reduce the swelling and inflammation ASAP by using hydrotherapy and anti-inflammatories. Frequent short applications of hydrotherapy and cold packs are preferable to infrequent long periods. Don't overdo the cold packs because you can get a rebound inflammation from making the scrotum too cold ("frostbite syndrome").
    • Do not use invasive measures unless, you are going to perform a unilateral castration. Unilateral castration may be advised in some cases, because degeneration of one testis often affects the other testis, plus damage to one may result in production of anti-sperm antibodies.
  • Cryptorchidism
  • Penile Paralysis
  • Penile Hematoma
  • Penile Sarcoids
  • Penile Habronemiasis: treatment / prevention - ivermectins
  • Squamous Cell Carcinoma of Penis
  • Testicular Torsion
    • May be acute or chronic
    • Acute is usually accompanied by signs of abdominal pain (colic)
    • Chronic may be intermittent and without clinical signs or may cause intermittent discomfort during sexual activity and reluctance to ejaculate

Abnormal Position of the epididymis.
(Rear view with the left rear leg adducted)

contributed by Bruce E Eilts and modified on 1 November 04
assisted by Emma Jones  

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contributed by Bruce E Eilts on 25 September 2012


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