Breeding myths...

[AJBliss]

I think with size in ET offspring, there should actually be some credit given to the recipient mare. I recall reading about the Smart Little Lena clones at Texas A&M University, one of which has matured to 16.1hh, the smallest being 14.2hh with precisely the same genetics, but very different placental area and vascularity on the part of the recipient mare! Smart Little Lena himself was, I believe only 14hh tall.

[KarynK]

Twink Allen told us of his research on my course in the 1990's, he showed that identical twin's born of different mares reached different heights at maturity, he concluded that genetics may dictate adult height but a far greater influence was due to the available room for growth in the uterus and that this early disadvantage was not recovered in post parturition growth. We were lucky enough to be able to see the mature identical twins and there was a hand difference in mature height from the foal of the 16hh+ mare and that which was birthed by the pony.

[alleycat]

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My theory of Downs syndrome is as follows:
Women are also born with all the eggs they will ever have. Now say, just for the sake of argument, they have 480 eggs. Only one of those 480 eggs is capable of producing a Downs syndrome child. So, the chance of that Downs egg getting randomly ovulated during the first 20 years (after puberty) are fairly small, but as they woman ages, the chance of this egg being ovulated get higher, and higher, and after 40 years (if you're a super-menopause-avoiding-woman ) then, the only egg left will be that Downs egg. So the probability there is 100% of getting a Downs syndrome baby.

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I don't see how this holds up statistically:

If the Downs Syndrome egg were to be just a random event the chance of it being ovulated at any time would be the same for Super Menopause Avoider as for Schoolgirl Mother.

For it to work as you've described, something would have to delay the use of the Downs Syndrome egg, so that it kept not getting chosen until the very end, like the unpopular child at school when the games teachers' pets were choosing sports teams...

Of course, the more babies a woman has the more chance she has of "picking" that egg, but without some other mechanism at work that egg could be picked as often in a young woman's pregnancy as an older woman's; but older women do seem more at risk of having Downs Syndrome children than younger women. In fact more Downs Syndrome kids would be born to younger women than older ones, in terms of actual numbers since more young women have babies.

So even if this isn't due to damage as a result of having been around a long time (and could not damage occur from being "in Storage?" after all, the cell has to stay alive, and from what you say doesn't have the chance to mend itself) - there has to be some sort of mechanism to explain the statistics; maybe the eggs were the first ones formed before Super Menopause Avoider really got her eye in, and are now reappearring from the back of the queue? Or perhaps faulty eggs are somehow slow in coming forward and get left until last? If there is some such mechanism, I suppose it could exist in horses too?

Really useful and interesting post.

Perhaps you could also clarify what brings a mare into season? I know day length is involved, but mine do seem to go on & off with the weather, and cycle oddly in some years.

[AndyPandy]

I guess the "size is 80% dictated by mare size, 20% by genetics" is pretty true then!

[JanetGeorge]

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I wonder about this question as my foals all have behavioural traits like their dam. If they were ET foals would they have the behavioural traits of the recipient mare?

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Mmm - interesting question. You;re looking at two things where behaviour is concerned - the basic genetic temperament (flighty, laidback, stubborn etc) from the original mare, and then learned behaviour which comes not JUST from the mare that raises the foal - but also the mares and foals (if any) that the foal runs with during those first few formative months.

I have an old RID mare who is wonderfully laidback (to the point of being comatose!) ANY 3 week old foal can push her off her haylage - she is bottom of the pecking order in any herd! The first year I had her she was the only mare I had with a foal - and that foal is the most obnoxious filly on four legs!! Good with people - but DREADFUL with other horses. She is Alpha mare with a capital A! The mare has had 4 foals since - admittedly by a different stallion - and all 4 are as sweet as pie - with people and other horses - because they were raised with other mares and foals who put them in their place!

Generally I've found that bossy mares have bossy foals.

I DID notice one interesting thing with one mare this year. She'd had 2 fillies - and was a rgeat, attentive Mum who was besotted with her foals. Last year she had a colt. She started off besotted with him - but by the time he was 3 months old she was being VERY 'strict' with him - he wasn't allowed to share her haylage (although she'd share with another mare and HER foal!) He is now the best mannered colt of that year - it was as if she KNEW he would need extra discipline!

[ihatework]

I think, and correct me if I'm wrong AP, that what was being said is something along the following lines.
Say (as AP gave as an example) that a female has 480 eggs, of these 1 of these is genetically faulty.
When the female is sexually mature and starts ovulating there is a 1-480 chance of the dodgy egg being fertilised.
Now assume 1 egg a month is released. 12 eggs a year (for arguments sake) and therefore 20 years down the line a total of 240 eggs. This elderly female would now have a 1-240 chance of fertilising the dodgy egg (if it hadn't already been released) - so double the chance.

PS - AP, great thread

[machannah]

Regarding "faulty" eggs, is it the case that eggs are released randomly, or the stronger ones take precidence over the lessers?

[ihatework]

Haven't the foggiest I would guess randomly

[AndyPandy]

[ QUOTE ]
I don't see how this holds up statistically:

If the Downs Syndrome egg were to be just a random event the chance of it being ovulated at any time would be the same for Super Menopause Avoider as for Schoolgirl Mother.


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So you're saying, if I had a huge bag with 3000 white balls, and one red ball, all the same weight, size and texture, and I picked a random ball, I would have just as much chance of picking the red ball here, as if I had a bag with 2 white balls and one red ball?

I don't think so

In the first instance, my chance is 1 in 3001, in the second instance, my chance is 1 in 3!!! If, in the first instance, I keep picking out balls, for every white ball I pick out, the chance of picking the red ball increases. Hope that makes sense (I'm assuming the red ball is equivalent to the Downs oocyte)

[AndyPandy]

Yes, it's random. If there was a mechanism in the ovary for picking the "strongest oocyte" (a sort of blueprint reader that can tell which egg has good DNA and which egg has bad DNA), then there would be far less requirement for natural selection/evolution, and we would have very few, if any birth problems or genetic diseases