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Breeding your Mare

  • So you've decided to breed your mare this year?! You may find yourself having a lot of questions when it comes to e.g. choosing the right stallion, preparing your mare, or what you need to know about your new born foal. Below you will find some helpful information about:

  • Preparing your mare for artificial insemination
  • Breeding a Mare with Transported Semen
  • Shipment of the semen
  • Caring for your newborn foal

             Preparing your mare for artificial insemination


  • The estrous cycle of the mare is about 22 days. During those 22 days mares usually display receptivity (heat) to the stallion for 4-8 days. Most mares ovulate 24 to 48 hours before the end heat.
  • Most mares go through winter anestrus, the dormancy period when the ovaries take a break and shut down. The mare will not cycle during this period, which is Mother Nature's way of assuring that she's not going to conceive and subsequently give birth at an inopportune time when conditions are not optimal for the foal's survival. The first estrus of the spring will last for 10 to 12 days, but it's not the estrus you want to breed on. Most breeders will tell you that to breed on this cycle when the hormonal ebbs and tides are coming back into play is often a waste of time. It's best to let her go through that. However, you want to watch when that ends, count 14 to 16 days, then plan on trying to have her impregnated during one of the next several cycles.
Breeding mares with frozen/thawed semen is an exciting challenge as it opens doors to gene pools all over the world. It can add fun and endless possibilities to the breeding program of your horse.
  • There is a tremendous amount of effort that goes into timing the insemination of thawed semen. Selection of the mare is as important as selection of the stallion, in a frozen/thawed semen breeding program. In general young (4-12), foaling mares have been reported to have the highest first cycle pregnancy rates, followed by maiden mares, and the least fertile are barren mares, especially mares that have been barren two years or more. Gypsy Horses are known to be one of the most fertile of all breeds and therefore breeding older mares should be no problem. It is best if mares going to be bred with frozen/thawed semen are fully examined by a veterinarian experienced in equine reproduction. Most experts agree that rectal palpation, transrectal ultrasound of the reproductive tract, vaginal exam, uterine culture, uterine cytology and in selected cases uterine biopsy are current standards of practice in evaluating a mare for breeding. Mares that have fluid accumulations within their uterus, mares that have inflammatory cells or uterine cytology, mares with multiple endometrial cysts, or mares with signs of chronic inflammatory changes indicated by the uterine biopsy are no candidates for breeding with frozen/thawed semen.
  • To increase your success rate the mare should be examined with transrectal ultrasound and palpation at least daily during the heat until the mare develops an ovarian follicle > 35 mm. Then the mare needs examined every 6-8 hours transrectally. 
    Rectal palpation of the ovaries is an important tool in determining optimal breeding time.

Follicular size: most light breed horses will ovulate when the dominant follicle is around 40-45 mm. Draft breeds ovulate at a larger size. You will typically see ovulation around 55-60 mm in the draft horse, as well as the Gypsy Horse.

Timing of ovulation is critical to proper insemination of the mare.

                   Breeding a Mare with Transported Semen

Article By Josh Mottershead


There are probably two major keys to successful transported semen breeding - preparation and communication.
Carefully preparing your mare, and the associated monitoring of her estrous cycle will hopefully result in a timely breeding. It is essential that the mare's estrous cycle be followed carefully, and ongoing follicular activity monitored (this is known as "following the follicle") and recorded. In order to do this, a person experienced in palpation or ultrasound use is needed - most usually a veterinarian. Hormonal manipulation of the estrous cycle may also be called for, in order to pinpoint ovulation more easily or accurately. This is especially important if the stallion is not always available for collections - some stallions are not collected if they are showing; some farms will only collect on an every-other-day basis; and some farms will not collect on weekends. 
This is where the "communication" aspect starts to come into play. Communicate with the farm where the semen will be collected. Make sure that you are aware of any limitations on collection BEFORE your mare is ready to be bred. Ask the farm if semen from the desired stallion is always available; ask if they have a preferred protocol for ordering semen - some farms require one to have called in the order no later than 8.00 am on the day the shipment has to be sent. Other farms require a call the evening before that.

An added note concerning communication by the mare owner to the stallion farm - show consideration in the timing of your telephone calls! The farm manager - especially if it is a busy breeding farm - will be receiving many phone calls during the breeding season, in addition to completing the regular days work. I'm sure most managers will appreciate it if you make sure that you call at a civilized hour - so remember time zone differences!

Once your mare enters her estrus phase ("heat"), it is often helpful to call the stallion farm to advise them of the fact. They will then be aware that they will probably need to be shipping semen to you within the next 3-5 days. If you have already had the mare palpated or ultrasounded at this stage, tell them the results. Follicular size will be a rough indicator for them as to how many more days before you will need semen - the follicle typically grows at between 3 and 5 mm per day, and is unlikely to ovulate prior to being 35 mm in diameter. Remember that although at this stage it seems as though your whole life is focusing around getting your mare bred, you may only be one of many mare owners contacting the stallion farm, and therefore they need to schedule their collections.
Make sure that your palpator and inseminator are available at all times. It's no use having a mare ready to be bred and the semen in your barn if there's no one to inseminate! Likewise, if your mare is palpated with a 3 centimeter follicle on a Friday, will your palpator be prepared to come out on Sunday and palpate if the farm needs to know by Sunday night for a Monday collection and shipment?


                               Shipment of the semen




Find out what method of transport the semen will be shipped by. Will it be a courier company, or a counter-to-counter airline shipment? If it's a courier, find out if they will be able to deliver by a certain time of day (this usually depends on your location - some remote locations are a 2 day shipment, which will probably be useless for the semen). If you wish to pick up the shipment at the courier depot, it must be marked "hold for pickup". Picking semen up often results in your being in possession of it sooner than if you wait for a delivery. If the semen is being shipped counter-to-counter by an airline in North America it is essential that the shipping farm has "verified known shipper status" with the airline being used. 
Without that status, due to security constraints, the semen will not be accepted for shipment. Also be aware that this status is not a blanket status for all airlines, but must be obtained separately from each airline used. Someone will need to be available to pick it up at the airport. What time will it arrive, and when does the freight department close? Note also that if you are using different airlines in your counter-to-counter shipment, with a transfer in the middle, you will require someone to physically carry the container from one airline's counter to the next. Neither airline will be likely to provide that person, and that the person must have "verified known shipper status" in order for the shipment to be accepted by the second airline! Remember too if the semen is traveling between Canada and the US, even though there is no longer a requirement for agricultural inspection, it will still have to "clear Customs", and there must be an officer present to do that. Many of the smaller International airports do NOT have Customs officers present around the clock. 
For semen entering Canada, remember that it is likely that you will be required to pay Canada Customs "GST" or "HST" on the value of the semen when it arrives and the shipment must be accompanied by a Customs Invoice. If this is a repeat shipment and you have already paid the tax, make sure you take your receipt with you, as you are not required to pay the tax more than once if it is a repeat breeding on a mare that did not conceive.

If your semen is being shipped by one of the larger airlines or courier companies, get a Bill of Lading number from the stallion farm, and you can "track" your shipment over the Internet. ("Click" on the following company names to go to their tracking sites: FedEx; Purolator; UPS to track courier shipments). This will enable you to find out when your shipment left the stallion farm, where it is en-route, and if it has been delayed. If you note that it is sitting a long time at one location, make sure that you contact the transport company immediately to find out if there is a problem.

If you have any questions at any stage of the shipping or breeding process, do not hesitate to ask someone. Remember that the only stupid question is the one that's not asked! If your mare ends up not pregnant as a result of some silly hitch that you weren't aware of, you will be very annoyed with yourself!
What to do after the arrival of the frozen semen
So you have the semen, and you're starting to breath a sigh of relief! The inseminator is on their way, your mare is in flaming standing heat, and everything is looking good.... What should you do now? Well, whatever you do, DO NOT open the semen shipping container! It must stay closed until immediately prior to the semen being removed for insemination. Avoid extremes of temperature for the semen container. If the weather is hot, keep it in a cool place; if cool, keep it in the warm. Have your mare in a stall, tail wrapped, and ready to be inseminated. Have a bucket of warm water ready, and sit and wait for your inseminator to arrive!

Once the inseminator does arrive, upon opening the container, make sure that they confirm the identity of the stallion whose semen it is! A competent and thorough semen collection facility will have sent a collection report with the semen that will identify the stallion. If the stallion is not identified in some way on the semen container, make a note of that on any registry AI report - it could save you, the mare owner, considerable grief if next year the foals DNA does not match the sire and dam! Other information that will be provided on paperwork by the responsible stallion operation may include the time the collection took place, the motility at that time and the number of sperm shipped, as well as the type of extender and antibiotic used. Once identification and paperwork is checked, ensure that the inseminator gently mixes the semen before they inseminate. 
Often the sperm will settle to the bottom of the package during shipment. All that is necessary is to invert the package three or four times before the semen is drawn into the insemination syringe. The type of syringe used is important too. Make sure it is an all-plastic syringe, without a rubber seal on the plunger such as is seen on regular syringes. It has been determined that standard syringes can be highly spermicidal with some stallions semen.

Once the mare is inseminated, or indeed, if you have enough assistance available before she is inseminated, a small sample of the semen should be evaluated to determine the sperm percentage progressive motility. Make sure that this sample is warmed prior to evaluation, as in the cooled state motility will be alarmingly reduced. If your inseminator does not have a slide warmer or incubator, a temporary one can be easily made using a bowl of warm water, and "cling film" kitchen roll, a Zip-Loc bag, or a rectal sleeve filled with warm water. (Click here for a description of this). Using the information from the semen collection report that hopefully accompanied the shipment, multiply the total number of sperm shipped by the percentage of progressively motile sperm that you are now seeing. Ideally you will want to have inseminated 500 million progressively motile sperm. 
The lowest number that is acceptable is 100 million - and that only if ovulation is imminent. If the number is below that, notify the stallion farm of your concern. Only do this though, if you are sure that the sample was mixed and warmed prior to evaluation, and after evaluating several samples. It is very frustrating for the stallion manager to be told that the semen was not of an acceptable quality, only to find later that there was nothing wrong with the semen, but the evaluation was sub-standard!

One of the big debates in transported semen is whether to inseminate two insemination doses at the same time if two are shipped, or whether to hold one until the following day. There are valid arguments to be made for both schools of thought. Generally I will take action according to whether I feel confident that the mare will ovulate within the 24 hours after insemination, or not. Also, my decision will take into account the number of progressively motile sperm present in the insemination dose upon receipt.

If I believe the mare is going to ovulate within the next 24 hours (which is certainly what we aim for), and if the progressive motility of a single insemination dose yields more than 100 million progressively motile sperm, then I will inseminate just a single dose. The greater the volume of the insemination dose, the greater the possibility that a mare with a delayed uterine clearance problem may be incapable of clearing it - more commonly older or multiparous mares. Hopefully a single insemination dose has been calculated to be 1 billion sperm. That will then provide between 100 and 500 million progressively motile sperm at the time of insemination. As research has shown that inseminating greater numbers of sperm does not increase pregnancy rates1, there is nothing in my opinion to be gained, and yet much to be lost by inseminating both doses at once.

If I feel that the mare is not likely to ovulate within 24 hours, then I will usually retain one insemination dose for use the next day - but this second insemination will not be performed until at least 24 hours after the first in order to avoid placement of sperm into a still-inflamed uterus. Recent research2 has suggested that sperm that are stored in extender rather than seminal plasma have an increased binding tendency to the inflammatory cells, therefore lowering pregnancy rates substantially. Extended semen does usually contain seminal plasma, but it may be diluted, so this effect, although not as pronounced as with all of the seminal plasma removed, may still be apparent.

It is important to note that the post-breeding inflammatory response is a perfectly natural occurrence, and indeed is essential for the successful establishment of pregnancy under normal circumstances. When one looks at the mare's perineum 16 or so hours after breeding and sees pus dripping from vulva, what is being seen is typically normal clearance of the post-breeding inflammatory response (not a "reaction to the extender"!).
 In susceptible mares however - usually older or multiparous mares, but not always - the mare is unable to clear this fluid, and the result is an inhospitable environment in the uterus for the conceptus. Consequently the pregnancy is lost shortly after descent of the conceptus into the uterus about 5.5 days after fertilization. This problem can be very easily, cheaply and successfully managed with the use of oxytocin in such a manner as is laid out in the article available here.

One area that I very definitely feel is a false economy in the transported semen breeding process, is not following up with a palpation or ultrasound the day after breeding to make sure that the mare did indeed ovulate. Some mares will "hold on" to the follicle just to prove everyone wrong! If the mare has not ovulated 48 hours after insemination, you should be considering obtaining another shipment for insemination as soon as possible.

The use of transported semen is not complicated, and although there can always be unfortunate errors during the experience. If planning and communication are good, those errors will be kept to an absolute minimum, and hopefully your transported semen experience will be straightforward and successfully result in a pregnancy.
Click here for many more articles concerning artificial insemination.

                                    Your newborn foal


  • There is a system in the foal's gut that allows absorption of immunoglobulins during the the first 12 to 24 hours of life. The level of absorption decreases during that period, which is why it is essential to have the foal nurse as soon as possible after birth. This  is also why it is important to inoculate mares against tetanus and other infectious diseases in the last thirty days of pregnancy, as this will assist in ensuring that there are suitable antibodies transferred to the foal in the colostrum. Another associated important point is that of transferring a mare to her foaling location preferably no fewer than 30 days prior to her anticipated due date. This allows the mare to develop suitable antibodies to any organisms present that the foal will be exposed to in the first few hours of it's life, and these antibodies should then be available to the foal in the mare's colostrum.

Straw for survival

The wrong bedding and high fluctuation in a stable can be deadly, according to a research of the department for agriculture. They conducted a study in 4300 stables which proved that both factors are a risk for new born foals. If mares and their foals didn't stand on straw, more foals (three times as much) died within 48 hours. It is assumed that bacterias can multiply better in straw alternatives. They also increase the risk of diarrhea in new born foals.
How your foal will look like as a mature horse can best be determined in the first three days of their life and again in their third week. Already as yearlings, horses have grown to two third of their final height. The final height of a horse can be determined to 70% by the size of their dam.
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