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Posted on 10-03-2014

Why Isn’t My Mare Pregnant?

Part 2: Stallion-related factors

Our last discussion featured management changes that may make the difference between a pregnant mare and an open one.  Now we will focus on the role the stallion played in an unsuccessful breeding season.

Does this sound familiar?

-“The semen was bad.”

-“They only sent one dose.”

- “They used the wrong extender/container/delivery service.”

Alas, the stallion is very commonly blamed for pregnancy failure. (And guilty by association, of course, are the stallion owner, manager and vet!) This may not always be fair and accurate, but there is no doubt that the stallion plays a significant role in conception.  This blog isn’t meant as a guide for stallion owners to improve semen quality (we will address that in a future blog) but as information for the mare owner about what might have gone wrong.

Instead of introducing all of the terms associated with examining a semen sample, I want to approach this topic as a series of problems and potential solutions. The first example will deal with the number or quantity of sperm cells in a breeding dose (this correlates to the volume and concentration.) The second problem occurs when the quality of the semen sample is lacking (problems with motility and morphology.) We will finish with problems related to longevity, as well as other stallion factors.

Problem: Not enough spermatozoa (sperm cells) to fertilize the egg

The number of spermatozoa inseminated into a mare is directly correlated with pregnancy rate; fewer sperm cells mean fewer chances to conceive. The industry standard is 500 million cells per artificial insemination dose. In a well-managed breeding situation, 250 million (or less) can result in pregnancy, but many stud farms try to send one billion cells per breeding dose to make up for the cells that will die in transport. (By contrast, samples of frozen semen generally contain only 300 million per dose.) Stallions with a large book of mares to breed may be forced to send semen samples with lower numbers in order to keep up with demand. Older (and very young) studs may not produce as many sperm cells with each ejaculate; these horses may need special processing of their ejaculates to insure that each breeding dose contains an appropriate number of cells.

Solution:  Know your numbers!

Ask your vet if the semen shipment came with information about the sample, including how many cells are contained in one dose. If that information is not available, and your vet suspects that there may be a problem with low sperm numbers, he/she can test the concentration of the sample. Keep in mind that some mares can conceive with low numbers of sperm cells; however, if your mare didn’t get pregnant, make sure to rule that out.

If you aren’t using artificial insemination, the number of sperm can be difficult to determine.  Ask the stallion owner if he/she has the stallion’s semen tested before and during the breeding season to identify problems with total numbers of sperm cells.

Problem:  Semen quality is poor

The sperm cells must be able to reach the egg cell in order for fertilization to occur. The “swimming” action of the sperm moving their tails is referred to as motility. Poor motility equals sperm stuck in the wrong area of the mare’s reproduction tract. Sperm cells that are shaped abnormally (bent tail, abnormal head for example) likely won’t reach the egg cell or will not be able to fertilize that cell.  Semen samples with a large number of abnormally shaped cells are said to have poor morphology. Other factors affecting semen quality include the presence of dirt, blood, or urine in the ejaculate.  Poor motility can be due to numerous factors: how the semen is collected, handled, extended, the choice of shipping container, external temperature, etc. (Again, we will go in depth in this topic in another blog) From your perspective as the mare owner, the focus is on determining if semen quality may have been a reason why your mare isn’t pregnant.

Solution:  Develop a quality assurance program with your vet

How do you know if there is a problem with semen quality?  The semen must be examined under a microscope immediately after insemination.  The quality is not going to be the same sitting in a box, bouncing around in the vet’s truck all afternoon until he/she has time to examine it.  Yes, vets are busy. Mare owners are busy. But making time to promptly examine a semen sample will help you and your vet determine if the semen quality may be the reason that your mare didn’t settle. You can’t blame it on the stallion if you never look at the semen!

Problem: Semen doesn’t live long enough

The longevity of a semen sample is very important: sperm cells don’t live forever and dead sperm cells can’t fertilize an egg.  Sperm generally live approximately 48 – 72 hours after ejaculation.  Like the other factors we have discussed, sperm longevity is influenced by many factors. There are stallions out there that have semen that appears motile 5-6 days after collection, but that is not something to expect from every horse.  If your mare hasn’t ovulated within 2-3 days of insemination, then chances are good that the semen has croaked.  This brings me to one of my pet peeves: the second dose of semen in the box. Here is the thing; sperm were made to live in the stallion or the mare not, in a shipping box.   So the sperm in the 2nd dose are not going to magically live another 2 days longer, just because they are still in the box.   If a mare is bred and hasn’t ovulated within 72 hours, she needs new shipment of semen. 

Solution:  Don’t be afraid to order semen a second time

Think of that second dose as backup insurance, not 2 for 1!  The second dose is a good way to monitor longevity (if it looks good under the microscope, chance are that it looks even better inside the mare’s body) but it does NOT replace the need for a second (or, gasp, third!) sample if the mare doesn’t cooperate by ovulating when she’s supposed to.  Sometimes even a 48 hour lifespan is asking too much: if the stallion owner recommends that you use an airline for delivery so that you ca have the semen ASAP, take the suggestion!

Problem: Quantity, quality and longevity are good…now what?

There is a lot we don’t understand about why some stallions seem to get more mares pregnant than others.  One way to compare stallions with good semen characteristics is the 1st cycle conception rate. For example:

Stallions A & B both have a book of 20 mares.  At the end of the season each stallion has 18 out of 20 mares in foal.  Sounds the same so far, right?  Stallion A settled 15 out of 18 on the 1st cycle, Stallion B only 5 out of 18 on 1st cycle.  Which stallion would you choose?  There can be a lot of factors involved here, some that are not the stallions fault; nonetheless this is good information for the mare owner.  Ask your stallion owner if they calculate 1st cycle conception rate.  If you are scratching your head at the end of the breeding season about why your mare is not in foal, picking a stallion with a high 1st cycle conception rate can make the difference.

So your management is great, your vet looks at every semen sample at the time of insemination and is confident that the quantity and quality of cells are excellent, but your mare still isn’t pregnant.  What gives?  Sometimes I suggest to clients that they switch to a different stallion in order to rule out that the conception failure is due to stallion/mare incompatibility (something in the combination of this pair of horses even though nothing seems wrong with the semen.)  Let me give you an example:  a client of mine had a mare who had delivered two foals by the same stallion.  This stallion’s semen quality was abysmal!  His sperm cells were less than 10% motile under the microscope but yet this mare got pregnant.  Obviously a super fertile mare, right?  Unfortunately, when we tried to breed her to a different stallion (whose semen quality was phenomenal), she didn’t conceive after 4 tries!  When we switched back to the first stallion we got a pregnancy on the 1st attempt.  I love to bring up this example because it reinforces a few points.  1) Not every stallion with poor semen quality is infertile.  2)  Not every stallion with great semen gets all his mares in foal.  3)  I don’t know everything!  

Solution: Consider a different stallion

Switching stallions can be an expensive proposition, especially if the farm you are working with only stands a single stud, but it can make a difference.  If you have another mare to use, try that too. (In the example I used above, my client substituted her mare’s daughter to breed to the stallion with the great semen and has a beautiful foal to show for it!)  Sometimes it helps to narrow down your choice of stallions by asking for information on their 1st cycle conception rate and how well they seem to settle “problem” mares.

I hope this brief list of factors related to the stallion helps you identify a reason why your mare isn’t pregnant.  I would love to hear your comments, questions and suggestions for future blog topics.  Look for part 3 of this series “The Mare” next week!        




Kathy K said:

What do you recommend when it is a mare who has produced many offspring in her 15 years, and this season has already successfully produced two embryos by studs at one stallion facility, but with 2 different studs at a different stallion farm, she has not produced an embryo on 3 tries. Her daughter was also bred to one of these same studs at this stallion farm, twice, and she did not produce an embryo either, but has successfully this season, with a different stallion and a different stallion facility. Is it the stallion farm? We don't really want to use a "rebreed" with this failure rate.

2015-05-19 14:55:05

Kathy said:

Just wondering if anyone has had the experience we have had. We have a proven producing mare that we have been breeding for 9 years, utilizing AI. Some she has carried, most we have used embryo transfer. She has been bred successfully to several stallions, several times each breeding season, resulting in several foals each year. We have used several different stallion farms/facilities and different stallions over the years, all successfully. There is ONE stallion facility we have tried on more than one occasion, last year and this year. We have tried 3 different stallions at this particular facility, and we have had zero success getting a viable embryo this year, and did get one embryo last year but it did not survive the transfer. We have the "rebreed" since we have not been successful with a live foal, but the rebreed seems to be pointless and I am ready to walk away. We even tried one of the mares daughters with the rebreed, and she did not have an embryo either, after two tries. Could there possibly be something with the way the facility is collecting, extending or shipping the semen, since multiple tries, with two different mares, and three different stallions have all failed? , since multiple tries, with two different mares, and three different stallions have all failed? Of course, the stallion manager insists they have great semen, great stallions and plenty of success and happy customers. What are my options at this point?

2015-05-19 17:56:56

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2016-10-13 17:59:44

epi-fluorescnce microscope said:

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2016-10-15 07:26:55

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