Use of artificial insemination has become commonplace in most breeds today, but the use of frozen semen is gaining in popularity for mare and stallion owners. In this article from the reproductive experts Etta Bradecamp, DVM, Dipl. ACT, DABVP, and Maria Schnobrich, VMD, DACT, of Rood and Riddle Equine Hospital, we will learn the basics of using frozen semen.
The use of frozen semen has become more common in the equine industry (non-Thoroughbred) over the past 10-15 years, and both stallion and mare owners are routinely seeking information regarding the pros and cons of breeding with frozen semen.
Stallion owners often wonder if they should consider having semen from their stallion frozen and what the pros and cons of doing this may be.
Meanwhile, when choosing a stallion to breed to, mare owners often have questions regarding what is involved when breeding with frozen semen.
There are several reasons to consider freezing a stallion's semen. Cryopreservation of semen is a means of preserving a stallion's genetic material for an indefinite period of time, regardless of the lifespan of the horse. Based on current scientific information, once frozen, semen may be preserved for an infinite amount of time before being used. The amount of time frozen does not appear to affect the viability of the spermatozoa once thawed and utilized.
Cryopreservation of semen can also be seen as an “insurance policy” on a stallion's genetic material; in the event of untimely loss of the stallion his genetic potential has been preserved. Storage of frozen semen from a stallion also allows a stallion to continue his performance career uninterrupted by semen collections that would be required for breeding mares with cooled-shipped or fresh semen.
Semen is often collected for cryopreservation when the stallion is not competing and stored until needed. Frozen semen may be shipped to the location where the mare is housed and be stored until needed, eliminating the need for a last minute shipment when the mare is ready to be bred.
Utilization of frozen semen also greatly increases the number of mares that may be bred to a stallion, because geography has been eliminated from the equation. When frozen to meet export and import requirements, frozen semen can be shipped to many countries, while cooled-shipped semen is limited to much smaller geographical areas due to the limited amount of time that spermatozoa remain viable when cooled.
Cryopreservation technology is also utilized to preserve genetic material from stallions that are being castrated for a variety of reasons. If a horse proves himself as a valuable breeding animal after being gelded, semen preserved prior to castration can become a desired commodity. In addition, for stallions that have died unexpectedly, epididymal sperm can be harvested and cryopreserved for breeding at a later date.
Based on data gathered over many years, approximately 25% of stallions have semen that tolerated the freezing process very well with several different freezing protocols, 50% have semen that freezes moderately well utilizing a select few protocols and 25% have semen that does not tolerate freezing well at all.
Test freezes should be performed on all stallions to determine the cryopreservation protocol that provides the best results for an individual stallion. When considering the use of frozen semen for breeding a mare several factors should be considered. More intense reproductive monitoring of the mare is required when breeding with frozen semen as the semen is viable for a shorter period of time within the mare’s reproductive tract compared to fresh or cooled-shipped semen. Because of the semen’s shortened lifespan, insemination must be closer to the time of ovulation, requiring more frequent checks by your veterinarian.
In general the chance that the mare will become pregnant following breeding with frozen semen is slightly lower than with fresh or cooled-shipped semen. Historically, the accepted range of per cycle pregnancy rates for fresh semen is approximately 65-70%, for cooled 55-60% and for frozen thawed semen 30-45%. However, a recently published report showed that pregnancy rates similar to cooled shipped semen can be achieved when using frozen semen.
Obviously this is very stallion-dependent, and stallions with excellent fertility and excellent quality frozen semen can approach per cycle pregnancy rates comparable to fresh semen.
Both mare and stallion can affect the success of the breeding, but in general it is ideal to use mares that are reproductively normal, younger (less than 15 years) and in good health. Mares that have traditionally had difficulty conceiving in the past despite good management are usually poor candidates for a frozen semen breeding program.
An interesting development in recent years in the use of frozen semen is the low-dose deep-horn artificial insemination technique. This procedure involves guiding the insemination pipette to the tip of the uterine horn so that the semen is deposited closer to the site where fertilization will occur. By placing the frozen-thawed semen closer to the oviduct, veterinarians have been able to use smaller doses of semen with the same success as traditional doses. This development has allowed stallion owners to maximize the number of breedings per semen collection, and for mare owners, doses may be split to allow multiple inseminations for the same cost.
However, this is only recommended when there is data available indicating that acceptable pregnancy rates can be achieved using lower numbers of spermatozoa per dose.
There are many advantages to using frozen semen in your breeding program, but all pros and cons must be weighed in making sure it is the best option for you. Understanding the expected pregnancy rates, knowing the intended stallion’s previous reproductive history, and considering all the factors that can affect success will aide in making an educated decision regarding frozen semen use in your breeding program.