How to Breed Mares with Frozen Semen by Deep Horn Insemination

1. Introduction

Stallion and mare owners are becoming increasingly aware of the number of foals produced by a variety of low-dose insemination techniques and may request that you, the private practitioner, breed their mares with partial doses of frozen semen. Reproductive veterinarians are breeding mares, including the older less fertile mare, using frozen semen with low sperm numbers, low volume, low progressive motility, and low percentage of normal cells. Stallions may be unavailable due to show schedules, unable to provide good-quality semen, frozen or cooled, or may be deceased. Likewise, some of today’s imported semen from popular stallions can be quite expensive and is frequently sold by the “dose,” without a live foal guarantee.

There are a variety of successful strategies available today to help veterinarians use frozen semen. This list includes estrus synchronization, ovulation induction, timed insemination, endoscopic insemination at the ostium (papilla), and deep horn insemination. All of these techniques require effective participation between owners, managers, and the veterinarian to allow access to mares for treatment and examination. Although frozen semen breeding can be successful in any type of facility with adequate personnel, working areas, and laboratory equipment, most mares being bred with frozen semen in equine practices will come into a hospital or clinic for at least 3 to 5 days. Wherever the mares are bred, the overall success of any frozen insemination is dependent on accurate induction of ovulation; proper timing of insemination; and welldeveloped veterinary skills, including transrectal palpation, ultrasonography, and artificial insemination techniques. Practitioners also must be familiar with the current methods used to properly handle, transfer, store, thaw, and evaluate frozen semen, as it is imperative that semen samples are not damaged before or during the thaw process.^1,2 

An accurate review of the previous literature,³ and results from a large number of mares that were bred using low-dose insemination, are currently available.⁴ It became apparent in our practice over the last 5 to 6 years that the timely use of deep horn insemination (DHI) could result in favorable pregnancy and embryo recovery rates even when fewer straws or lower numbers of sperm were available. It is certainly appropriate to use a full dose of frozen semen from any stallion using standard AI techniques (insemination in the uterine body) and then gradually drop the number of straws used and switch to DHI as pregnancy rate dictates. Splitting the dose, in most cases, will save semen and may also produce less post-breeding endometritis in susceptible mares. It makes sense to use as little semen as possible, conserving semen for another cycle or another mare, particularly when the sample’s quality characteristics or pregnancy rates are known. Frozen semen has the distinct advantage that when handling and storage are well managed, it will last for decades.

The aim of this report is to provide valuable references and descriptions of a technique, which with practice will help veterinarians become successful breeding mares with lower doses of semen. It describes a step-by-step technique for DHI in mares using a disposable commercially available pipette.^a This technique allows mares to be inseminated with multiple straws through one pipette and a reusable stainless steel stylet^b (empties a 0.50-cc straw at the end of the pipette and retrieves it). There is also a similar pipette with an inner tube^c to deliver semen from a syringe when semen is packaged in 2.5- or 5-cc straws. This system does require a rectal-vaginal procedure and consequently veterinary skills, yet it avoids the use of additional extender or an endoscope while delivering the semen efficiently and quickly.
 

2. Materials and Methods

The majority of mares bred by DHI in our practice are placed in breeding stocks for the actual insemination. This is ideal for the mare that will tolerate breeding stocks, as the mare remains more confined during the process. It is also helpful to move mares with foals or have them stabled as close to the lab as possible, so that insemination can be completed in an efficient manner after the semen is thawed while allowing the foal to be contained in a safe manner.

As the mare is being prepared, the correct semen should be located in the storage tank and an appropriate water bath set up. Mare preparation consists of restraint similar to what is needed for palpation of that mare, a rectum free of manure, then a standard perineal cleaning. This particular flexible pipettea is easiest to use when kept warm (in an incubator if possible), because it will be more pliable and will retain the curl that is placed in it before introducing it through the cervix.

When the package is opened, a 3-cc syringe is attached to the external end of the pipette to avoid excessive air from being introduced into the uterus. The veterinarian places a sterile sleeve over the arm for the insemination and puts a full circle curl in the warm pipette (Fig. 1). The pipette is then passed transcervically (should retain about 45 degrees of bend) with the internal tip kept ventrally (Fig. 2). As the gloved hand is removed from the cervix and anterior vagina, the other hand should gently guide the pipette forward. The gloved hand can then be passed transrectally to palpate the pipette tip in the uterine body or base of the horn and assist it in a 90 degree rotation, left or right, toward the appropriate horn (Fig. 3). Transrectally, the fingers are used to gently lift the uterine horn base and facilitate passage of the pipette to the appropriate horn’s tip. The entire process tends to go fairly easy when things are in the right position. One should feel the pipette slide up the horn, the rounded tip close to the ovary, and thus the shaft of the pipette is palpated inside the chosen horn. Good palpation skills, knowledge of the mare’s uterine position, and some experience using the technique is necessary.
 

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