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My Stallion is Not Settling His Mares...What Do I do? - Part 1

June 02, 2015

Posted by SBS in Stallion Management

istock_Stallion 2 It is around this time of year that we receive calls for advice from anxious stallion owners concerned about a lower than anticipated conception rate for their stallion, in the hopes of finding some resolution and correcting any potential issues before the end of the breeding season. Time is running out to fulfill those breeding contracts and get those mares pregnant. There are so many variables that contribute to successful conception and pregnancy, from both the mare and the stallion side of things. From the stallion owners perspective they are looking to address the stallion’s semen quality, breeding management and reproductive status. But where to start? This article will give stallion owners an overview and provide a systematic guide to troubleshooting a resolution if possible. How a stallion owner/manager responds to and handles mare owner concerns regarding semen quality or fertility can make or break a relationship or reputation.

There is a lot to discuss on this topic, so we have broken this article into two parts. In Part 1 we will discuss the stallion’s breeding history, the importance of a breeding soundness exam (BSE), stallion management practices as well as semen quality and evaluation. Our main focus here is on stallions that are breeding with fresh or cooled semen. Next month, in Part 2, we will review common problems identified after the semen evaluation, the relevance of the mare book and their reproductive status and discuss those stallions who are breeding with frozen semen.


Do you have detailed records of his collection history, and information on reproductive efficiency (e.g. seasonal pregnancy rates, first cycle pregnancy rate, conception rate) from years past? Keeping good breeding records is one of the cornerstone principles of sound reproductive management. Regular examination of such data during the course of the breeding season may identify a problem that could be corrected before it negatively affects fertility, client confidence and your stallion's reputation; plus it may save time and money in the long-term. For more information see our blog articles, Measuring Reproductive Efficiency, A Review of Reports for Reproductive Efficiency and Reproductive Efficiency Reported by SBS Affiliate Labs. When you have no prior records, or if this is your stallion’s first breeding season, it can be difficult to determine if the observed conception rate is normal or abnormal for your stallion.


Training 2 When was the last time your stallion underwent a breeding soundness exam, or BSE? Usually a BSE is performed as part of a pre-purchase for the sale of a stallion, for young stallions entering their first breeding season, when deciding whether to retain a stallion as a breeding individual, or when there is a problem suspected. However, a stallion manager may wish to consider a BSE at the start of every breeding season to identify any changes in physical condition or semen quality, particularly as he ages (See our article on Declining Fertility in the Aged Stallion) or to gain information about the book size a stallion can support. There are standards established by the American College of Theriogenology for how a BSE should be performed, it usually includes the following:

  • Complete medical and reproductive history
  • General physical examination
  • Evaluation of libido and mating behavior
  • Examination of the external and sometimes internal genitalia
  • Cultures for bacteriology
  • Semen collection and evaluation of motility and morphology
  • Additional diagnostics as indicated (e.g. sperm testing, endocrine profiling)

For the semen evaluation section of a BSE, the minimum involves two ejaculates collected an hour apart. To pass, there must be at least a billion progressively motile, morphologically normal sperm in the second collection.

If your stallion is not settling his mares, then a BSE should be performed, particularly if no potential causes for the reduced fertility could be identified by reviewing stallion management practices and semen quality.


There exists a wide variety in stallion management practices throughout the country. Some stallions trailer out for collections or stand at a breeding farm or vet clinic, others may be managed at home. “Home” may be a large successful breeding operation, or a small breeding venture that stands only one stallion. As you can imagine there is even greater variability in the method or standard of semen processing, from the high-tech to the low-tech and from the seasoned professional to those new to the breeding industry. Any and all have the potential to be successful, just the same as the equal possibility of running into problems. Furthermore stallions are valued for breeding primarily due to pedigree or performance traits, sometimes regardless of their fertility. So it is inevitable that there will be some sub-fertile stallions out there in the breeding population. Although a sub-fertile stallion may not pass a BSE, he could be successful in a selective breeding program when managed appropriately.

The following elements of stallion management should be reviewed to determine whether they are contributing factors to the lower than anticipated pregnancy rate.

Mare Book and Collection Frequency

Collection of Stallion The sperm production of a stallion is directly related to his testicular size. Determination of testicular volume and daily sperm output (DSO) is a useful measure that is recorded as part of the BSE. This can provide valuable information on the number of mares a stallion can service and an appropriate collection frequency. Fertility may be reduced in popular breeding stallions collected on a daily basis and shipping semen to multiple mare owners with each collection. Their DSO may not be able to support the number of doses required with each collection. However, rather than turn down a mare owner, a stallion owner may reduce the amount of sperm in each breeding dose in order to satisfy all requests. If mares are bred with less than the ideal minimum of sperm, fertility may be compromised.

If you are unable to provide each mare owner with an adequate dose of semen, then you should consider reducing the collection frequency; instead of daily collections it may be preferable to go to every other day collections in order to maximize the number of sperm available with each collection. It may also be necessary to reduce his mare book; this will not be a popular decision with some mare owners, but switching eligible mares to frozen semen may reduce his book for fresh/cooled semen and allow better management of available sperm.

The opposite situation may also be true - a stallion with a small book of mares could experience reduced fertility because of long periods of sexual rest between collections. Older, stored sperm in the epididymis and efferent ducts of the testis are usually of lesser quality and often have reduced longevity. For some stallions, these older stored sperm may not perform as well in a cooled semen program, demonstrating reduced motility after 24 or 48hrs of storage. This could impact fertility if mare owners are not receiving a suitable dose of viable sperm. A series of clean-out collections, to clear out the older stored sperm, are recommended for all stallions at the start of the breeding season. Occasional clean-out collections may also be necessary throughout the breeding season, or in advance of a shipment request, if the stallion is not being collected regularly.

Breeding Management

A breeding stallion should be able to fulfill the physical demands of life in the breeding shed, he should have adequate nutrition and body condition (see our article Feeding the Breeding Stallion), and be physically fit and sound enough to mount the mare or breeding phantom. The goal of any semen collection attempt should be to obtain semen on one mount, see Value of Collecting Semen on One Mount. Multiple collection attempts and/or excessive stimulation can result in a high volume, Sperm low concentration ejaculate that requires centrifugation in order to appropriately package doses for cooled semen, see Processing Equine Semen for Cooled Transport. This can be a limiting factor for the low-tech breeding farm that does not own a centrifuge.

The cause for the multiple or failed collection attempts should be determined and resolved when possible, this may require assistance from a professional in order to assess libido and behavior. It may also be related to the lack of a suitable tease mare, inappropriate height of the breeding phantom, dissatisfaction with the AV (style and liner type, temperature, pressure), muscle or joint pain associated with mounting the mare/phantom or a physical issue with the penis.

Results of the semen evaluation may direct changes in breeding management of the stallion. For stallions that have a tendency towards high volume/low concentration ejaculates, it may be preferable to collect them first, early in the morning, in order to limit their stimulation. Some stallions are known to be “sperm accumulators”, see Sperm Accumulation in the Stallion. For these stallions a regular collection schedule is important, and to obtain the best quality semen it may be that the stallion is collected twice, the first collection discarded and the second collection processed for shipment.

Breeding Method

For stallions intended to be managed in a cooled, transported, semen program, a longevity test or cooled semen evaluation should be performed as part of the BSE and/or at the beginning of every breeding season. This will provide information on the sperm motility after proper dilution and storage at 5 degrees Celsius, and can be used to identify the most suitable extender for semen dilution. The industry recommended minimum for a breeding dose of cooled semen is 500 million progressively motile sperm at 24hrs. It is preferable that sperm motility is >30% progressive at the 24hr time point also. If semen quality is marginal, or there is reduced longevity after storage at 5 degrees Celsius, the stallion may not be a suitable candidate for a cooled transported semen program using overnight shipping by FedEx/UPS. However, this stallion may have good success if the semen is sent counter to counter through airlines or courier services. With very limited semen quality or longevity, it may be necessary to stand the stallion only to mares who can be bred on the farm using fresh semen.

Some stallions may be able to fulfill the requirement for 500 million PMS at the 24hr time point, but motility significantly drops off thereafter. Two doses of cooled semen may typically be included in a shipment, particularly when sperm numbers are not limiting. However, for optimal fertility with some mares/stallions it may be preferable to breed the mare close to ovulation with the semen immediately upon arrival, rather than relying upon a second dose of semen that is 48 hours from the time of collection. If semen quality is marginal after 24hrs it may be advantageous to include only one dose of semen in the shipment, in an effort to encourage better timing in mare management.


If your stallion’s mares are not getting pregnant, probably the first place you’ll look for answers is with his semen quality. A semen evaluation can be performed as part of a BSE or as an independent evaluation to determine reproductive capability, or when a semen quality issue is suspected. All stallions should have some form of a semen evaluation prior to the start of every breeding season, in order to record changes in semen quality over time and to ensure that a stallion will be able to fulfil his breeding responsibilities. The results of the semen evaluation will help the stallion manager make decisions regarding breeding management as discussed above, for example the size of the mare book, the collection frequency, whether the stallion is a candidate for a transported semen program, and the appropriate sperm numbers for the breeding dose.

Semen Evaluation

CASA It is important to stress at this point the value of having an independent semen evaluation performed. You may have the facilities and equipment available to perform a stallion collection and basic semen evaluation at your own farm, however there are many advantages to having the evaluation performed by a qualified veterinarian or professional. This is especially true if you suspect a problem in your own semen collection and processing methods, or have limited previous experience managing a breeding program. In this respect it can be helpful to have an independent, unbiased person reviewing with you your stallion management, collection and semen processing practices to help identify areas of concern. They may also have additional equipment you do not have in your own lab, for example a computer assisted sperm motion analyzer (CASA; photo left) to determine sperm motility, or a Nucleocounter to get an accurate sperm concentration, plus they may have access to additional sperm function assays.

If your stallion is breeding in a cooled, transported breeding program, you could also ship some semen to an independent lab, like Select Breeders Services (SBS) or a university lab, for an accurate semen evaluation and consultation. When receiving cooled semen for an evaluation at SBS we check the temperature of the semen upon arrival, determine sperm concentration by Nucleocounter, and sperm motility by CASA after 24 and 48hrs of storage. We can also perform sperm morphology, and a bacterial culture of the semen. This can provide valuable information to the stallion owner, and very often identifies the problem. It may be just as simple as replacing the shipping container because it is no longer holding temperature (remember disposable shipping boxes are meant to be DISPOSABLE), or replacing old coolant cans in an Equitainer.

We always recommend that the stallion manager retain a dose or a small aliquot of semen in a storage container within the lab after every shipment, so when concerns are raised about the semen quality by mare owners, they have a "test” sample to refer to. This way they can compare the semen quality reported by the mare owner (or independent lab), with the results of the analysis of their own dose of semen in the lab. This can provide valuable information to the stallion owner regarding the longevity of the sperm motility following each collection, and provides a historical record that be referred to when a problem is suspected.

Next month, in Part 2, we will review common problems identified after the semen evaluation, the relevance of the mare book and their reproductive status and discuss those stallions who are breeding with frozen semen.

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Please Note - photos used in these news articles are available in the public domain, have been purchased through istockphoto or (when referencing breeders or horses) have been submitted to Select Breeders Services Inc. by the breeding farm or horse owner. Photo credit has been provided where applicable. If at anytime you see something that needs to be addressed please feel free to contact us directly.

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