Stallion owners and managers can encounter reluctance from mare owners to use frozen semen. This may be due, in part, to commonly spread misinformation regarding the fertility of frozen semen and the misconception that frozen semen is difficult to use. This hesitancy seems especially true if the frozen semen of a particular stallion has yet to be used in order to establish evidence of fertility. If one can offer specific credible evidence of the fertility of frozen semen from a given stallion it can go a long way towards promoting the process and breedings to your stallion. For more information please read “Frozen Semen Myths and Misconceptions” as well as our blog article regarding “The Pros and Cons of Equine Frozen Semen”. In this article, Dr. Brian Carroll of Oklahoma City Equine Hospital, discusses why a frozen semen fertility trial should be performed, how to go about performing the fertility trial and provides an example of a frozen semen fertility trial he performed.
Why Perform a Frozen Semen Fertility Trial?
Test breeding a number of reproductively sound mares with a controlled timed insemination protocol and reporting the pregnancy rate, I believe, is the best way to foster willing participation of mare managers in a successful frozen semen breeding program. It also is very helpful in promoting the sale of international breedings via export of frozen semen. Mare owners would perceive added value of the frozen semen because you invested the time and expense to perform the ultimate quality control before offering your stallion through frozen semen. You can click on the following links to learn more about “Questions Every Mare Owner Should Ask” and “What Exactly is a Dose of Frozen Semen?”
Determining the fertility of frozen semen from a stallion can also aid the stallion owner/managers in managing the inventory of frozen semen. Establishing some level of fertility aids in estimating how much semen is needed in reserve whether the intent is to bank semen for international export, domestic use or in the event of temporary or permanent disability of the stallion. Furthermore, establishing fertility encourages confidence for the investment of frozen semen reserves.
Semen frozen within the SBS network semen has been checked and rechecked to insure that a sufficient number of normal spermatozoa are packaged in each dose to maximize the potential fertility of the stallion. The post thaw progressive motility, sperm concentration, and bacterial culture have been standardized in every collection. However, post thaw analysis no matter how extensive, has limitations in predicting fertility. This is due to the complexity of factors that affect fertility. “It Only Takes One, Right?”
Recommendations for a Fertility Trial
The ultimate way to demonstrate fertility is simply to breed mares. At least if a number of mares are bred one can demonstrate the ability to achieve pregnancies in appropriately managed, reproductively sound mares. I must be careful not to imply that by breeding a relatively small number of mares a true fertility rate or minimum effective dose may be obtained. However, you can often establish a trend. In my experience, when you obtain pregnancies in the first few mares bred, fertility tends to be good. If you breed 10 mares to achieve 1 or two pregnancies that doesn’t mean your pregnancy rate will be less than 20% but it may influence the way in which you distribute the semen and implement its use. As a veterinarian or an agent of a mare owner choosing a mating for a mare, the proven ability to produce pregnancies at a given dose has value and definitely influences my decision on choosing a stallion. It demonstrates an honest intent to insure a positive outcome for all parties involved.
I recommend a minimum of 10 test breeding cycles using a timed insemination protocol with two inseminations at roughly 24 and 40 hrs post ovulation induction by hCG or Deslorelin. The number of straws per dose is determined by the post thaw analysis parameters. Follow the link for more information about “What Exactly is a Dose of Frozen Semen?”. My rationale is that if fertility can be demonstrated with a simple, less time consuming protocol in order to minimize veterinary costs for the mare owner, it will be more readily accepted in a commercial setting. One of the myths that breeding with frozen semen is more expensive than breeding with cooled semen is dispelled in the article “The Economics of Cooled and Frozen Semen”. Again there are limitations to only 10 cycles but valuable information can be obtained from a 10 cycle breeding trial. The ideal situation is one whereby a stallion owner has reproductively sound, open mares of their own to utilize early in the breeding season. If not, commercial embryo transfer facilities usually have reproductively sound mares available later in the breeding season and after the season ends that can be used for a fertility trial.
Example of a Fertility Trial
A real-life example may serve as an illustration. Several years ago, some foreign investors wished to purchase a number of breedings from a popular stallion. The semen was in storage in the United States and was qualified for export to their country. However, the frozen semen from this stallion had not yet been used to breed mares. The post-thaw motility of the semen was average with 38% total motility, 29% progressive motility, 48% normal morphology and a concentration of 200 million per milliliter.
The prospective buyers had previously made sizable investments in frozen semen from two other American based stallions but had dismal results obtaining pregnancies. Needless to say, they were hesitant to incur another financial loss yet they really wanted to purchase breedings to this particular stallion. A fertility trial was conducted by an objective third party using embryo transfer recipient mares in August. The frozen semen was used to breed mares on eight cycles. Positive pregnancies were obtained in 5 of the 8 cycles resulting in an overall pregnancy rate of 62.5% for this fertility trial. The following results were reported.
After the investors and their advisors were presented with this information they were much more confident in a positive outcome and followed through with a six figure purchase of the frozen semen. More importantly, based on this information they instituted a breeding protocol that was successful in efficiently producing foals from this stallion in their country.
Valuable information can be obtained in a relatively short period of time using this method. Depending on the value of the semen for the stallion, a breeding trial can usually be done for the cost of three breeding fees or less. I feel this is an especially effective promotional investment worthy of the effort compared to other commonly used advertising methods.
