The Condom

Semen collected using the condom method is heavily contaminated by bacteria and debris. This method also requires that a mount mare be in estrus and increases the risk of contamination of the stallion’s penis by vaginal entry or urination or defecation during natural breeding. Many stallions do not tolerate breeding while wearing a condom. Condom and semen loss are also common. However, an occasional stallion accustomed to natural service may be intolerant of semen collection with an AV until adequately trained.

Pharmacologically Induced Ejaculation

Numerous schemes have been published for the ex copula ejaculation of stallions using xylazine, imipramine, xylazine and imipramine, and prostaglandin.^1–3 Semen collected in this fashion is of low volume and very high concentration. The resulting ejaculate can be used for cryopreservation or artificial insemination of mares in a cooled semen shipment program. However, the inability to obtain ejaculates on a predictable schedule limits the commercial usefulness of these methods. In experimental ponies, semen was collected in 10 of 24 attempts using imipramine and xylazine.³

Under very selected cases of debility in the stallion, it may be possible to obtain semen specimens with the aid of pharmacologic agents.⁴ Under farm conditions, semen is obtained in about 25% to 30% of the attempts. It is important that the stallion be kept quiet and undisturbed. Intravenous treatment should be done in a quiet manner. One such successful scheme is to administer 2.0 mg/kg imipramine hydrochloride intravenously. An occasional stallion may appear to hallucinate after the IV use of imipramine. If erection and ejaculation are not induced within 10–15 minutes, xylazine is administered intravenously at the rate of 0.2–0.3 mg/kg. With the use of imipramine and xylazine, ejaculation occurs in association with erection and masturbation.³ If xylazine is used alone to induce ejaculation, masturbation and erection do not occur in association with ejaculation. Ejaculation usually occurs as the stallion enters or recovers from the period of sedation or sleep.⁵ This method of semen collection was used in a cooled, shipped semen program for a stallion with severe tenosynovitis of a rear leg. Although successful about 25% of the time, the procedure was time-consuming and unpredictable for mare owners. Anecdotal evidence suggests that the use of 0.5-ml detomidine hydrochloride (Pfizer Animal Health, NY, NY) IM can induce ex copula ejaculation.

The Artificial Vagina

Semen collection using an AV is the most widely used method of semen collection from stallions. Many models of equine AVs are available. These are fitted with a water jacket that allows for the passive control of the internal temperature of the liner, usually 44° to 48°C. In most cases, the internal diameter of the AV can be modified by the addition of water or air to the water jacket. A lubricant is manually added to the innermost liner of the AV to alter the degree of friction during breeding. Lubricants containing bacteriostatic or spermicidal compounds should not be used to lubricate the AV because these compounds are detrimental to sperm motility.⁶ Petroleum jelly (Vaseline) or methylcellulose (H-R Lubricating Jelly, Carter Products, Division of Carter-Wallace, Inc, New York, NY) can be safely used. A recent clinical trial compared the effect of four different “non-spermicidal” lubricants on the longevity of sperm motility.⁷ Three of the four lubricants tested were detrimental to sperm motility. The lubricant Pre-Seed (Ing-fertility, Valleyford, WA) did not suppress motility compared with controls. Possible reasons for the detrimental effect of lubricants include hyperosmolarity and unphysiologic pH. Careful selection of lubricant as well as the amount used are important factors in the semen collection process. Most commercially available AVs can be modified to allow the incorporation of a filter into the semen collection system, if desired, so that dirt, debris, and gel can be removed from the semen sample. Otherwise, the entire ejaculate can be filtered after collection, or the gel can be aspirated from the sample using a syringe. Sperm losses during the collection process have been determined with one model of AV.^8,9 Most of the sperm lost during collection is accounted for in the filter and in the gel fraction of semen. Between 25% and 30% of sperm in an ejaculate can be lost in the gel and filter. Polyester filters tend to absorb seminal fluid and therefore reduce sperm recovered in the gel-free ejaculate. Nylon filters do not absorb fluid but allow considerable trapping of sperm in the gel fraction.¹⁰

Ideally, the AV is constructed to maintain the desired AV temperature for a significant period, to allow the direct ejaculation into the semen receptacle, and to allow for ease of handling and manipulation by the operator. If the AV is large and heavy, the operator may have difficulty positioning the AV for tall stallions, for stallions not trained to the AV, or when the mount mare moves during collection. It is best if the AV can be held in one hand, at the appropriate position, while the other hand is used to deflect the base of the penis to the side of the phantom or mount mare. This is particularly helpful in stallions that thrust with significant force. Deflecting or stabilizing the base of the penis is stimulatory to most stallions and may help prevent preputial hematomas during the collection process.

Semen collection failures are frequently associated with inappropriate AV positioning for the particular stallion, an AV that has dropped in temperature below a “critical” point for the stallion, the phantom mount set too low, and the use of excess pressure in the AV. The AV should be held parallel to the ventral abdomen of the stallion and in direct alignment with the base of the stallion’s penis. In this manner, ventral or lateral bending of the penile shaft is avoided.

In certain circumstances, it may seem necessary to elevate the internal temperature of the AV to 50°C for stallions with difficulty ejaculating into the AV. However, an effort should be made to have the horse ejaculate directly into the semen receptacle or coned portion of the AV liner to avoid heat shock to the sperm. Sperm cells exposed to excess heat from the AV liner exhibit a circling-type motility, have reduced sperm longevity in raw and extended semen, and may be rendered infertile. Exposure of semen to elevated temperatures for as little as 10–20 seconds is sufficient to cause heat shock damage.

Manual Manipulation of the Penis

Ejaculates collected by manual manipulation of the penis are similar to ejaculates collected in an AV.^11,12 This method of collection has not received widespread acceptance because of the training and dexterity required by the person collecting the ejaculate, and many stallions fail to ejaculate unless well trained for this method of collection. A major advantage of this method of collection is that only one or two individuals are necessary for semen collection. The stallion is usually not in direct contact with a tease mare. Specialized equipment or facilities are not necessary for semen collection by the manual stimulation method.

With manual stimulation of the glans penis for semen collection, the stallion remains standing on the ground or is trained to mount a phantom. The horse is teased until erection occurs. The stallion’s penis is washed with warm water because this process is also stimulatory to the stallion. The stallion may be trained for collection in his stall, an open barn aisle, or a corner of the breeding shed. An estrous mare is usually nearby, but mare stimulation for the stallion is altered based on stallion response. Once full erection is achieved, a plastic sleeve or bag is placed over the penis. One hand of the operator cups and stimulates the glans penis to achieve favorable thrusting and glans engorgement by thestallion. The opposite hand is used to stimulate the base of the penis and urethra. A very warm towel is sometimes placed at the base of the penis to increase stimulation. Training a stallion for this method of collection may require considerable patience, whereas other stallions readily accept the procedure. Stallions trained for this method of semen collection become habituated to the routine of sights, sounds, and activities surrounding semen collection. These stallions may require very little stimulation by a mare.