Breeding 'Myth'... is there any truth to it?

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Breeding 'Myth'... is there any truth to it?

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    11-06-2009, 07:29 PM
Breeding 'Myth'... is there any truth to it?

I've always, always heard that when you breed a maiden mare for the first time, the resulting foal will not mature to as tall as it should because the mare's body isn't used to the changes that being pregnant brings... and that after the first foal, if the mare is bred back to the same stallion, the second foal will be bigger than the first and will grow to its natural 'mature height', whereas the first foal will be the smaller of the two.

I've always heard that, from the horsey people in my family, from the breeder down the road from me, from the owners of the tack stores and feed store I frequent, from just about everyone around here who owns horses or who has had horses in the past.

But I got to looking at my gelding earlier... he's huge (easily 15.2 hands, and he's growing again, so I wouldn't be surprised it he's 15.3 or almost 15.3 hands now) compared to both his sire (15 hands) and his dam (15.1 hands).

So, is there any truth to the 'myth'? If I were to breed my mare back to my boys sire, would the resulting baby end up taller than my already big boy? I'm not planning on breeding my mare again for a few more years (she's 15 now, but I do want to breed her again... but not for a few more years... and when I do breed her again, I'm breeding her to a different stallion than my gelding's sire... already got the stally all picked out and have it okayed with the stally's owner [a family friend] and my grandmother... but I want to have a steady job and at least be halfway through college before I breed her again... so I'm in no rush...), but I'm just curious...
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    11-06-2009, 07:39 PM
No. Sometimes A maiden mare will not have as much milk as she will when she gets older. You see this more in cattle than horses. Genetics determines the size of the horse not the age of the mare or how many foals she's had.
    11-06-2009, 10:00 PM
I think the belief that maiden mares foal/raise smaller babies is probably based on observation in "some" circumstances-- probably a time/place when mares were bred and foals raised "naturally" without extra mare care, foal feeding, nutritional observation, etc.

I believe that it is true that in some cases maiden mares produce foals with a smaller birthweight, and have less milk, so baby gets a slower start. Now, many of these foals will "catch up" to their genetically potential size as they grow over the next couple of years, but often the farms/ranches that bred and foaled them don't see them after they catch up-- only when they are smaller compared to other foals their same age.

With "modern" programs where the mare and foal are managed much more specifically, I think this is more of a "myth".
    11-06-2009, 11:27 PM
Green Broke
ROFL, sure didn't happen with my mare! She was 14hh, and I know for fact we don't stand many Arab studs around here over 15hh. Zierra hit 14.3hh and she was Zena's first.

However, she also nursed until she was over a dang year old. Actually, it's funny, because I've seen quite the contrary to that myth. Shay-las Mustang/App mare had a buckskin colt as her first foal, she's 15hh and the stud she was bred to was about the same. Bugger was well over 15hh when he matured.

I've never heard that myth, and I honestly cannot see any truth being in it. It doesn't make sense, unless the maiden mare rejects her foal and it grows up an orphan, in which case it's a given he'll likely be stunted.

It wasn't the same stallion, but Zena was bred to a 17hh Warmblood for her second foal and the resulting foal is only an inch taller then Zierra (15hh). However, we also didn't know she was pregnant (she was vet checked, huge screwup, still pisses me off) so she didn't recieve proper care and that could have had everything to do with it.
    11-07-2009, 12:38 AM
Thanks for clearing that up. I know it was a random question... it popped into my head when I was looking at my mare and gelding and realized just how much bigger he is than my girl is... Lol. I decided to get the truth after hearing that 'myth' for so long.

Got another question, though... if a mare and the stallion are about the same size (in this case, 15.1 hands and 15 hands) and the foal grows taller than both, does that mean the grandparents genes or great, etcetera grandparents genes influenced the foal more than the genes from the sire and dam? (I dunno if that's clear... if it isn't, then sorry...)
    11-07-2009, 01:55 AM
I think that the theory is that size is a multi-gened trait-- in otherwords its not as simple as inheriting a "tall" or a "short" from one side or the other-- For example lets say height is controlled by whatever A-B-C-D-E- combinations a horse has-- and if a horse is aaBbCcDdEe OR AabbCcDdEe its short but if it is A-B-C-D-E its taller-- So one short parent passes aBCDE and the other passes AbCDE and the offspring is taller than either parent.

A VERY rough example totally pulled from the top of my head, LOL, (amd NOT based on any actual genetic studies of height) but hopefully it helps. LOL
    11-07-2009, 02:08 AM
It helps.

I'm very... stupid when it comes to equine genetics (or any genetics, lol) and most of the time I need things broken down in kiddy increments to get a basic understanding, but after reading your post a few times, I think I understand a little...
    11-07-2009, 08:18 AM
Well, I think it depends on the mare really. My TB mare is an older maiden (she's 9 now) and so far it looks like her foal is going to be large, certainly larger than anyone expected, being her first...but honestly, I don't think that its too surprising because despite being a TB, my mare is naturally a broader, roomier type.

Mares will only carry a foal as large as their body allows. Once the foal is out however, the foal's genetics take over and it will shoot up accordingly. Also alot depends on the condition of the mare and nutrition the foal gets after birth.

If a maiden mare is very young, say 3-4yrs old and is still growing herself, or perhaps not in top condition, she will not be able to provide as much milk or as good quality milk as a mare in top condition. Therefore the foal will most likely be smaller. If that makes sense.
    11-07-2009, 12:34 PM
Green Broke
You're not stupid Britt! Those are really good questions, and to be totally honest, not ones that have an actual scientific answer to my knowledge. I doubt anyone has actually done a study on your maiden mare question, so in retrospect, it's completely heresay. It could have merit, it could not. I think it boils down to the experience of breeders who've actually bred the same mare to the same stud and seen the results.

Same with the height question - sometimes we're just not quite sure WHY horses turn out the way they do. Traits are typically multi-generational though, hence why it's always good breeding practice to examine the lineage of any breeding pair. Just because the dam and the sire have good straight legs, doesn't mean that darn grandsire can't throw his cow hocks out on your foal. I would think height would work much the same way. In my experience, it usually sticks within the realm of what you'd expect from the dam and sire, but you never know when you're going to get a surprise.

You never get any smarter if you don't ask! And these are excellent discussion questions, since a lot of the answers ride on experience!
    12-24-2009, 12:43 AM
It makes no difference if the mare is a maiden mare. I have both a short baby from a maiden mare and a baby that is taller than his maiden mom at 18 months. Genetics and the size of the mares uterus are what determine size. The baby gets tall or short genes from its parents. Then if the mother is small she will affect the length of the cannon bones. There was a study done with Shires and Shetlands than showed this.

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