Freemartinism

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runnervet

runnervet

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Can someone explain in detail why this occurs? How is the cow/sheep placenta different to allow for this and why is it in some rare instances the female still fertile?
 
Freemartinism happens when the chorionic blood vessels fuse, allowing a common circulation between the male and female twins prior to real sexual development in utero. Admixing blood is not a big deal and does happen in cattle twins, but if you have twins of a different sex, that's where the problem occurs. Certain hormones, testosterone included, secreted by the male fetus inhibit the development of the female and "masculinize it"....90+ percent are infertile, but if for some reason the hormones don't quite inhibit it enough (ie, not fused for a long enough amount of time so the female has a better chance to develop), they can be fertile.

Its much rarer in small ruminants for freemartinism to occur, but it can....there have also been reports of fused membranes and such in pigs and cats, and some "freemartin-ism" findings/theories, but its exceedingly rare.

When goat and sheep chorions fuse, there is a sort of scar line that forms that prevents or reduces vascular anastomosis (or is supposed to - that's the last theory I heard on it) and that's why it's rarer.
 
Damn, I am taking therio now, and pretty much just covered that stuff, and I don't know it nearly as well as you WhtsThFrequency... Not sure all this 'vet' stuff is sticking for me 🙁
 
We just learned this the other day!

It doesn't happen in other ruminants like pigs due to necrotic tips at either end of the placental membrane. Although the membranes may still overlap in a pig, the necrotic tips aren't vascularized, which prevents anastomosis of the blood vessels. Cows do not form very good necrotic tips. The placental membrane in cows have very small necrotic tips, which means fusion is more likely.
 
Braki said:
We just learned this the other day!

It doesn't happen in other ruminants like pigs due to necrotic tips at either end of the placental membrane. Although the membranes may still overlap in a pig, the necrotic tips aren't vascularized, which prevents anastomosis of the blood vessels. Cows do not form very good necrotic tips. The placental membrane in cows have very small necrotic tips, which means fusion is more likely.
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Aren't pigs monogastrics?
 
Necrotic tips to the chorion? Uh....I'd be worried if there was anything necrotic in my chorion...are you sure they didn't mean degenerate or atrophic? And yeah errrr....pigs aren't ruminants 😉
 
The pigs being ruminants thing was an editing error, I had a ruminant listed and changed it to 'pig' and didn't remove 'ruminant'. Oops. I was really confused as to what you guys were talking about because I didn't realize I left that in.

And yes, my notes and my prof use the term "necrotic tip", so... *shrug* I thought it was an odd term myself when she first used it, but if it's there it won't be wrong on the test.

Edit: just did a quick google search, and yes, "necrotic tip" is the correct term. See: http://www.reproduction-online.org/cgi/content/abstract/32/3/539.
 
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Very interesting!.....however, that's a pretty old article - the sources it cites that use the term "necrotic tips" are from anywhere from 1910 to 1968....I imagine the term has been revised at least in some circles.

I know there are avascular areas, but hadn't ever heard of them being referred to as necrotic per se - as in they still have their basic stromal architecture (as far as I know), it's just lifeless, as opposed to necrosis, where I imagine loss of structural remnants (except in a few cases such as single-cell necrosis....things that are avascular/dead but leave structures behind I am more likely to call degenerate, not necrotic). Sort of how, ok, your hair is avascular/lifeless, but it's not necrotic.

Do you have any more recent sources? As is, not a "google search" 😉 From an actual veterinary journal with an appreciable impact factor? I could not find that term referenced any later than 20+ years ago or in journal of note? I'm not trying to get on your back, I'm just curious. Being in pathology, buzzwords fascinate us 😉
 
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My anat & phys Ph.D professor and employer - who taught at a vet school for 23+ years - calls them necrotic tips. Seeing as he taught repro at the vet school and it's still his focus in research - yes, they are called necrotic tips.

Sheep and goats have necrotic tips - hence the reason you'll rarely find freemartins in those species. Good thing, too, since twins or more are common in sheep/goats.
 
You are right; most of the references to "necrotic tips" are in older publications. I did read through a bunch of newer publications to see if there is a newer term that is now in use, but there doesn't seem to be a new term; instead, it seems the newer publications just exclude that factor from their papers, and don't mention avascularization of the placenta at all. However, I was able to find these:

Schlafer, D.H., Fisher, P.J., Davies, C.J. 2000. The bovine placenta before and after birth: placental development and function in health and disease. Animal Reproduction Science 60-61:145-160.

The authors are at Cornell CVM and write:

"The small end of the chorioallantois that occupies the very tip of each uterine horn usually undergoes degeneration and coagulative necrosis. These “necrotic placental tips” are very common and their size varies with some approaching 3–5 cm in length."

Dunlop, R.H., and Malbert, C. (Eds.). 2004. Veterinary Pathophysiology. p.219

This looks like a vet textbook or something, but here it says: "Rarely is there evidence of vascular anastomosis in the developing placentas of early pig fetuses. When membranes abut at the tips, they generally become necrotic. Thus, freemartinism is rare."

Baxter, E.M., Jarvis, S., D'Eath, R.B., Ross, D.W., Robson, S.K., Farish, M., Nevison, I.M., Lawrence, A.B., and Edwards, S.A. 2008. Investigating the behavioural and physiological indicators of neonatal survival in pigs. Theriogenology 69(1): 773-783.

This paper only mentions it once as part of their methods section, but doesn't actually explain it.

At any rate, from what I've read there doesn't seem to be a new term, although if you can find one I'd be interested to know. I'm not entirely sure why newer papers don't seem to mention that concept anymore, and I am completely surprised by the lack of results that come up when searching. I had assumed that anything you'd learn in first year would be fairly basic material/common knowledge type stuff.
 
It might be one of those "people's choice terms" - i.e. some vet profs like to to use it, some don't, based on that they were taught while they were in school. I'm just intrigued because I personally had not heard that term before. Cool! Milkmaid, that's sort of what I was saying - older profs who may have been taught with that term are more likely to use it, and for some reason maybe newer vets don't - interesting how things change. At least it's not as bad as bacteriology...I'm constantly having to research the newest genus for xyz bacteria for the proper classification for boards, ha!
 
WhtsThFrequency said:
At least it's not as bad as bacteriology...I'm constantly having to research the newest genus for xyz bacteria for the proper classification for boards, ha!
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Ugh... don't tell me. That's not something I'm looking forward to. 😛
 
I'll have to ask one of our longtime pathologists here - his specialty is gross pathology especially pigs, cattle, and reproductive stuff...he's away right now but should be back at the end of the month I think.

Ha ha don't worry...unless you're going for path or microbiology residencies, it probly won't affect you too much if you get em wrong occasionally 🙂
 
They taught us "necrotic tips" at UMN, too, although the lecturer is super old.
 
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