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  1. #1
    Join Date
    Feb. 24, 2003
    Yarrow, BC, Canada

    Default Stallion progeny - colts vs. fillies

    Being that it is the stallion that determines the sex of the foal (X or Y chromosome), how predictable is the sex of a foal, given a stallion's progeny? If a stallion has produced more colts than fillies, or fillies than colts, does this make any sort of sex prediction possible? For example, if a given stallion has produced, say, 24 colts and only 12 fillies, does this make it more likely that breeding to this stallion is more likely to produce a colt, or is it still as likely as the flip of a coin? This might be a stupid question, but I'm just curious if there is any correlation. Thanks!
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  2. #2
    Join Date
    Jul. 27, 2005
    Chapel Hill, NC


    I will be interested to see what others think. I was always under the impression that the timing of the AI or LC in reference to ovulation made a difference.
    It would also be neat to see what certain stallions % are.
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  3. #3
    Join Date
    Mar. 28, 2006


    There are certainly a large number of stallions out there that don't have enough progeny on the ground to tell how even the percentages are.

    I was close keeping track of what my stallion has produced, but I never sat down and counted up the gender of the 2008 foals. I need to do that. But with the foals on the ground (around 60) through the 2007 season, he was very close to half and half. It seems that one gender will pull ahead slightly, then the other catches up!
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  4. #4
    Join Date
    Jan. 15, 2004
    Lancaster, PA, USA


    with rare exception I have seen LC foals are close to 50/50, AI with the close to ovualtion timing increases odds of a colt and working with frozen for SUPER close timing ups the odds of a colt even more.
    our stats FWIW:
    LC mares were 56% fillies and 44% colts (so close to half of each)
    AI stats including all foals over the years (our guy and outside stallions used) were 63% colts and 37% about 2/3 colts and 1/3 fillies.

    For our stallion only....he ended up with more girls.....75% fillies and 25% colts.
    Last edited by camohn; Jan. 18, 2009 at 08:01 PM.

  5. #5
    Join Date
    Dec. 12, 2002
    Ontario <Living life for the journey not the destination>


    I can only share my stallions kids... They have a much higher % of fillies than colts.

    Sato is at 67% fillies and 33% colts. Mirabeau is at 62% fillies and 38% colts. Arts Aero is 71% fillies 28% colts. I do keep track Sato is mostly live cover and Mirabeau & Arts Aero are only AI.

    I personally like girls better as I do not have to geld them.

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  6. #6
    Join Date
    Dec. 1, 2007
    Gettysburg, PA


    Since in human fertility there are things they tell me to do to influence sex determination, I would guess there are environmental factors that influence horse sperm. I would think if a stallion produced statistically skewed towards one sex for multiple years, that the trend to produce more of that sex would continue
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  7. #7
    Join Date
    Apr. 29, 2003
    Hartford, Wi. 53027


    I can tell you that Ironman is almost 50/50 colts to fillies, some years it is more 60-40 one way or the other but in the big picture in 8 years of foals, it is almost even. How or why I have no clue.

    Home of Ironman: GOV, BWP, RPSI, CSHA, AWR, ISR Oldenburg, CWHBA, CSHA, CS, and PHR.

  8. #8
    Join Date
    Jan. 3, 2007
    Poulsbo, WA


    I have wondered this as well. Yeager so far has produced 82% colts and only 18% fillies.
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  9. #9
    Join Date
    Mar. 24, 2007


    I breed to a stallion that had had about 22/24 foals when I breed to him.....they were all colts but 2.........guess what we got?????....................


  10. #10
    Join Date
    Sep. 29, 2007
    Northern CA


    There has been some evidence that it may be more than JUST the x/y chromosome thing going on. What about the mare's reproductive environment - is it more conducive to X sperm or Y sperm? There was a thread on this forum some months ago talking about broodmares who consistently threw one sex, and discussion about how that might be. So the stallion is a big part of the equation, but the mare may also be involved in helping determine sex.

    I wonder if we'll learn more about this in upcoming years? We've consistently had more colts than fillies, and I have one broodie that has had at least 5 COLTS that I know of and her first filly this past year. Those are small numbers, hard to draw any statistical conclusions, but those 5 colts had 5 different sires (she had a few foals I know of prior to my buying her).

    Statistically, I'm not sure where the cut off is, but I'd say you need much more than 30 or 40 foals on the ground before you can draw any conclusions! Friesian/Warmblood Crosses, the Ultimate Sporthorse
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  11. #11
    Join Date
    Jan. 18, 2009


    I thought that it was 50/50 chance no matter what, if I recall my grade 12 biology teacher correctly

  12. #12
    Join Date
    Jan. 28, 2002
    Alberta, Canada


    Our stallion has been bred on a strict limit each year, mostly because I believe in not over flooding the market with offspring. Here are the interesting stats for our guy. He has a total of 35 foals on the ground. 63% of those are fillies. When he's been bred live cover, it has resulted in exactly 50% fillies 50% colts. Now, here is the interesting statistic. Every time he has been bred via shipped semen, it has resulted in 100% fillies!!

    A more valid statistic; if you are hoping for a colt, there will be a 100% chance of getting a filly. If you are hoping for a filly, there will be a 100% chance of getting a colt!
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