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.

 

[AndyPandy]

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

 

[alleycat]

[ QUOTE ]


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.

[/ 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.

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.

 

[JanetGeorge]

[ QUOTE ]

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?

[/ QUOTE ]

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.


[/ QUOTE ]

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

 

[AndyPandy]

[ QUOTE ]
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.

[/ QUOTE ]

Day length is involved, yes. It's basically decreasing hours of darkness, and increasing average temperature.

During the transitional periods, follicles begin to mature but do not ovulate. This allows for extended periods of estrogen elevation, which is natures own spring cleaning process (it raises immunity in the uterus for long period of time, preparing it to carry a foal).

After continued increases in daylight, and temperature, mares begin to cycle fully. Of course, periods of bad weather (where it gets colder/darker) can disturb cycling and make cycles irregular.

Irregular cycles can also be due to uterine infection/irritation which causes v long or short cycles to occur dependant on the exact nature of the problem.

There are probably other players, but we do not know the details yet

 

[alleycat]

[ QUOTE ]
[ 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.


[/ QUOTE ]

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)

[/ QUOTE ]

This is true if the red ball isn't picked until you reach the last 3. But for every time this happens, for this to represent the true range of statistical chances, there would have to be 3001-3 other bags in which the red ball is removed first, 2nd., 3rd., 4th., etc. In these bags, the chance of the red ball being part of a 1 in 3 chance are: zero!

Another way of putting it is that every ball, at the beginning of the process, has a 3001 chance of being picked at the beginning and a 1 in 3 chance of being picked IF it makes the last 3. What you can't say is whether any particular ball will make the last 3...

Basically, you have assumed the red ball is going to be one of the last left. Real life bears this out with Downs Syndrome. Question is, why THAT egg and not one of the others? This suggests to me a mechanism which either makes the last eggs faulty, or keeps the faulty eggs until last.

 

[alleycat]

Thanks.. AND another question... is the one about a mare conceiving more readily if she is in rising condition (rather than poor, fat or a level plateau of good condition) likely to be true?

Thanks again in anticipation...

 

[MissIndependance]

Excellent post – the only one I was surprised at/hadn’t heard before wa the last one re worming… We haven’t had any problems with scouring foals previously but I think I will add ivermectin to my foaling kits now as a precaution…
Interesting re the iodine – we used Iodine last year on vets advice…But they did also say the blue spray which you use to treat thrushy issues in hooves was just as good…is that the same stuff you mentioned? I can’t remember the long name…!
Karynk that’s really interesting about the little TB stallion.
The Downs Syndrome theory statistically makes a lot of sense, and is something I’d never considered before, but it’s certainly an interesting thought… From how I interpret AP’s post he’s saying that although of course the red ball could be picked each time, that every time it is not randomly ‘picked/released’ that the next time the odds increase.
Ie start off with 4 balls, one of which is red and the first time you randomly pick a ball it is a 1 in 4 chance, but the subsequent times the odds that you pick that red ball (assuming it isn’t released first of course) increase, ie 1 in 3, and then 1 in 2 until you are 100% certain to get it…
Great to see a thread which has got everyone thinking!

 

[AndyPandy]

Let me try again... my analogy might not be that great, but I want to try to say where I'm coming from.

Let's say, at age 14, a girl starts menstruating, and cycles every month until she is 54. She has 480 eggs, and one of those has an extra chromosome, and so, if fertilised will create a downs syndrome baby.

For her first ovulation, the chance of that downs egg being ovulated is 1 in 480 (0.208%). Now, of course, because it is totally random, that downs syndrome egg could be ovulated first time, but it is unlikely that it will be.

So lets assume, for 10 years, that downs egg isn't ovulated.
Now we have 360 eggs left, and the chance of the downs egg being ovulated is 1 in 360 (0.278%), because those are the only eggs now available for ovulation.

At age 44, she only has 120 eggs left, so IF she still hasn't ovulated that downs egg, it's now a 1 in 120 chance (0.833%).

At age 50, she has 48 eggs left! So if that downs syndrome egg is still there, the chance of it ovulating is now 2.08%. And at age 53, if she still has that downs egg, the chance of it being ovulated is 8.33%, so the chance has rocketed up in those last few years.

Now look at the way my description matches up to the risk of a downs baby increasing with age here: http://upload.wikimedia.org/wikipedia/commons/c/c3/Trisomy21_graph.jpg

I think it fits very nicely. I just don't understand why you don't like my stats on this one

If you can make it clearer for me, that would be great. Cheers

 

[AndyPandy]

[ QUOTE ]
Thanks.. AND another question... is the one about a mare conceiving more readily if she is in rising condition (rather than poor, fat or a level plateau of good condition) likely to be true?

[/ QUOTE ]

It is indeed true for some mares - a rising plain of nutrition and body condition may be beneficial, however, using the body condition scoring index, a minimum of 5 and a maximum of 7 is desirable, and the rising plain is unlikely to make a big difference.

 

[alleycat]

I can see where you are coming from;and your maths is right: but it seems to me that though this is true of this one egg, it is also equally true for every other egg.

ANY egg that isn't selected (?) at any given ovulation has an increased chance of being picked next time.

My brain is spinning now. I shall go and follow up your link and try to get my head round it, and come back to you when I've thought it over.

Er....Anyone got 3000 white ping pong balls & one red one that I can borrow?

 

[AndyPandy]

I think the reason it works for me is that, yes any other egg could be picked, so the chance of any particular egg being ovulated is essentially the same. However, for the purposes of this discussion, every egg except the downs egg has the same property (that of being "normal"), whereas the downs egg is unique as it is the only one that carries the extra chromosome. So the chance of ovulation of a normal egg is always higher than a downs egg, because there are more of them

It's confusing, especially when you factor in that a woman is actually born with 2 million oocytes, and only 400,000 of them will ever mature to any degree, and 1000 oocytes are destroyed with every cycle... Aaaaargh! But I'm pretty sure the numbers still work, roughly.

My numbers match up to the graph better if you assume that only 1 in every 2 women has a single downs oocyte

MIND BOGGLING!

 

[AJBliss]

Isn't there some effect of a mare's age upon early embryonic development? I don't know that it would have an effect upon the resultant foal when all is said and done, but there was a significant developmental delay whilst the embryo was still within the oviduct. Also, when embryos from old mares (>/= 20yrs) were flushed and transferred to young (6-10yrs) recipients, only 31% (8/26) resulted in embryonic vessicles, whereas 92% (11/12) of embryos transferred from young mares resulted in embryonic vessicles. The conclusion would be that the subfertility noted in older mares could be due to the oocytes themselves, rather than solely the "environment" of the older mare. This was a study done waaay back in 1995 by Carnevale & Ginther ... has there been much done recently? I would be interested to hear anyone's thoughts!

 

[PapaFrita]

Thanks for that AP

Very interesting.

 

[AndyPandy]

Older mares are more likely to have delayed uterine clearance issues. Embryos are flushed from the uterus. If these older mares were not given aggressive oxytocin therapy, then once the embryo dropped into the uterus, it will have been exposed to potentially unpleasant fluid in the uterus. This fluid is pretty likely to damage the embryo, as well as prevent fixation of the conceptus if it wasn't flushed.

In my opinion, it is probably the uterine-fluid-related-damage to the embryos from these older mares that caused the lower success rate. Unless the paper says that they did use oxytocin and that all the mares were cultured before they work was done.

 

[AJBliss]

Whoops! What you say makes sense. I think I misread my notes! Carnevale's subsequent study in 1995 after the one I mentioned (which was from 1993, not 1995!) actually collected oocytes from preovulatory follicles and transferred them into young, inseminated recipient mares. Guess I should re-read the whole thing. Thanks for letting me geek it up science-style and ask questions on this thread!

 

[alleycat]

I think you've persuaded me AP, with that last post; I think I'm wrong here...

Very patiently explained; and if you've thought that out yourself, I hope you've published it.

So, to change tack a bit, if a (human) female's oocytes don't all mature, does she jettison them at menopause, or are they still available but unused? If so is immaturity a problem? Could a post menopausal woman be an egg donor? (A friend of mine was lamenting the fact that she had never done this. Felt it was Flying in the Face of Nature at the time, but has modified her views; too late).

 

[AndyPandy]

I did think it out myself, but I'm sure other people have as well, so I won't be publishing it!

Anyway, I'm more of an equine repro man than a human repro man. I'm really not sure if a post menopausal woman could be a donor. The problem is that primary oocytes must mature to become secondary oocytes before they have a follicle around then and can be ovulated. I guess, theoretically it would be possible to take an ovaian biopsy (OUCH!) and mature primary oocytes in vitro, however, I imagine that would be extremely time consuming, expensive and painful for the donor.

Also, I don't know if primary oocytes remain viable after the hormonal changes associated with menopause.

 

[alleycat]

Thanks yet again AP- excellent post!

 

[AndyPandy]

No worries. Thank you for adding to the discussion - I was just thinking how excellent this thread is, because people are actually discussing stuff in depth and bringing new ideas to the table

Thanks for the nice comments too, very much appreciated.

 

[Fahrenheit]

I have enjoyed this thread... I have found very informative! I love the bit about the 3000 balls, a great way to explain things!!

I have however been unable to contibrute to the thread on a sensible level because I am still finding myself highly amused that anyone would think...

[ QUOTE ]
I drove my mare to the stud and knocked off the follicle!

[/ QUOTE ]

This comment has given me the giggles, everytime I have read it!!

**HG goes back to the naughty corner... until she can control herself**

 

[lisaward]

great thread very interesting

 

[DAHH]

[ QUOTE ]
.....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.

[/ QUOTE ]

From my own experience I would have to disagree. I think genetics play a much bigger role. I have a 15h2 mare who produces tiny foals. She looks huge when pregnant but gives then no room and evidently keeps all the goodness from feed for herself and passes very little to her foal (this is also highlighted by the fact that she still looks pregnant for months after the birth

)
However her offspring always make up for the slow start. For example the 2 year old colt out of her (and by a 16h2 stallion) was tiny and very weak when born but he is now the biggest 2 year old I have, currently standing at 16h.
Of course I may change my mind in the future as last year I had a foal born to a 17 year old 16h2 mare (by a 17h2 stallion) whos uterus didn't expand enough. The result was a foal the same size as my springer spaniel, only with longer legs! He is still small for his age and I will let you know in a couple of years if I have changed my mind.....

 

[htobago]

Just wanted to say great thread, AP - I seem to learn something new and important every time you post on here!