Those of us who work with stallions are routinely asked to determine a stallion’s fertility prior to breeding mares or to investigate the cause of low fertility. Often this requires sending the stallion to a specialized veterinary clinic or a veterinary school. Advances have been made in stallion fertility evaluations through the use of computerized sperm motion analyzers (CASA) and flow cytometry.
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Fertility of Equine Frozen-Thawed Semen Stored Cooled After Thawing
There are numerous advantages of frozen semen. If maintained properly in liquid nitrogen, frozen semen will last indefinitely. This allows frozen semen to be shipped to the mare and the mare bred at the most opportune time, close to the time of ovulation. One other use of frozen semen that seems to be gaining in favor is for farms to ship frozen semen to mares when there is a shortage of cooled semen. Alternatively, the breeding farm uses frozen semen to breed mares housed at the farm and ships out the cooled semen. Thus, frozen semen becomes the "backup plan" for breeding mares. You can find additional information to consider when deciding if frozen semen is a fit in your breeding program by reading these articles on the SBS Website: ‘Why Freeze Stallion Semen?’, ‘The Pros and Cons of Equine Frozen Semen’ and ‘The Hidden Value of Frozen Semen’.
Endocrine Diagnosis of Infertility in the Stallion
Diagnosis of infertility in stallions usually starts with a complete reproductive history and then collection of semen to evaluate seminal parameters, testis size and the potential presence of bacteria in the semen. A more detailed evaluation might also include drawing blood for hormonal analysis.
Measuring Hormone Levels in Mares
Endocrine diagnostics certainly have a place in the routine management of mares and stallions as well as in diagnosis of problems and diseases. However, there are likely more applications for measuring hormones in mares than stallions. Dr. Ed Squires will discuss the hormones tested in mares in this article and will then cover the testing of stallion hormones in a subsequent article.
Trends in Equine Assisted Reproduction
It has been almost 20 years since I started an assisted reproduction program at Colorado state University. The purpose of that program was to develop techniques to preserve equine genetics. It is beyond the scope of this article to discuss all the goals of that program but I would like to focus on production of foals from old mares and stallions via in vitro technology (aka test tube horse).
Is the Volume of the Inseminate Important for Fertility?
A common question asked by many breeders is whether the volume of semen deposited into the mare affects fertility. When a mare and a stallion mate naturally the entire ejaculate is deposited into the mare. This volume is usually 50 ml or more and includes several billion sperm. However, when breeding mares using artificial insemination, good fertility can be achieved with as little as 1/2 ml of semen. I have been telling breeders for years that the volume of the ejaculate is not important as long as the stallion is producing good sperm numbers. For example, a stallion can produce 8 billion sperm with 80 ml of semen at a concentration of 100 million sperm/ml or 20 ml of semen at a concentration of 400 million sperm/ml. Volume of the ejaculate and concentration are inversely related (i.e. if volume goes up then concentration goes down).
Suppression of Stallion and Mare Behavior
Once young colts and fillies reach the age of puberty their behavior may become an issue in the show ring or on the race track. Castrating a colt which you intend to use for breeding purposes may not be an option and mares are not typically permanently sterilized. Their sexual behavior may also cause problems with housing, trail riding, etc. In this article, Dr. Ed Squires discusses some of the common ways stallion and mare owners suppress the behavior of their horses.
Recent Updates on Freezing Equine Embryos
The majority of equine embryos are collected from the donor mare and transferred immediately as fresh embryos or shipped cooled to a recipient station for transfer within 24 hr. You can learn more about the basics of embryo transfer (ET) in our article, Embryo Transfer and Frequently Asked Questions. Very few equine embryos are frozen despite the numerous advantages of embryo cryopreservation. We discuss the process of freezing embryos in our article, Cryopreservation of Equine Embryos. However here is a quick review of some of the advantages of freezing embryos:
A Stallion Breeding Soundness Exam
In our previous article, My Stallion is Not Settling His Mares…What Do I Do?, we discussed possible causes for the decline in a stallion’s fertility and areas of reproductive management one can investigate further to determine if the infertility can be suitably managed or resolved. One tool a stallion owner/manager can use to better understand the reproductive status of their stallion is to have a breeding soundness exam (BSE) performed. In this article, Dr. Ed Squires outlines the components of a routine BSE which include: physical exam, reproductive history, testes palpation and/or ultrasound, semen evaluation, cultures and an assessment of his sexual behavior. Whether the stallion passes or fails, a BSE provides valuable information on how to manage the stud and gives an indication of the number of mares he could breed.
Effect of Number and Timing of Equine Frozen Semen Inseminations on Fertility
Further expansion in the use of frozen semen is dependent upon developing simplified strategies for insemination. SBS has developed a timed insemination protocol where mares are only examined once per day during estrus and inseminated at 24 and 40 hr after hCG or 30 and 40 hr after GnRH. This approach allows frozen semen mares to be managed similar to those bred with cooled shipped semen. A couple of arguments against this approach with frozen semen is that it takes too much semen when mares are bred twice in one cycle and that if the mare is inseminated more than once per cycle the fertility will be lowered because of post-breeding induced endometritis.