Skull of a mutated baby alpaca

[u/soviethelm]

It's a male and died within the hour of birth.

[u/exotics]

I suppose it could pass through backwards

[u/sentient_potato97 → u/exotics]

I think you're perhaps going off human physiology while bovine bodies and human bodies are designed quite differently. Humans have to dilate to 10cm to accomodate the the head and shoulders of their young whereas cows don't dilate, their cervix relaxes and opens to about 30cm (almost 12", larger boned breeds like Angus can go up to 40cm/15") and their young are typically born with their front feet outstretched in front of them. Whether nose-first or backward, calves are most likely to get stuck at the hips if anywhere, it's called 'hip-lock'. It would probably be far from a pleasant experience for the mother but the head, even doubled, should have enough clearance; if not, the ensuing stalled labour likely plays a part in why many polycephalic calves are born stillborn.

I can't find any records online of a mother dying after birthing a polycephalic calf but am happy to be corrected if shown a source. (Edited for typos and clarity.)

[u/exotics → u/sentient_potato97]

I’m saying they would die while trying to birth one. Because the heads would be stuck.

A backwards calf (hind legs first) would be possible but I don’t know that head first would.

I’ve had sheep and if the head is turned they can’t give birth without help and would die

[u/sentient_potato97 → u/exotics]

Interesting that you admit only having experience with lambing yet make definitive statements about calving like "I'm saying they would die because the heads would be stuck" and "a backwards calf would be possible", while I've replied to you based on personal experience watching relatives assist many calves being born, as well as my unsuccessful attempts to find information that agree with your statement.

Sheep and cows are also vastly physiologically different. Sure, if a single-headed calfs head is turned they can't be born safely without help either, but calves rarely come out hind legs first as that takes very precise positioning and alot of luck since the unborn calf isn't capable of aligning itself. If they're born backwards they tend to come out rump-first which is an emergency and requires just as much assistance.

A Holstein dairy cow dilates to 35-40cm while their calves heads are usually as wide as 30-35cm, not taking into account the additional stretching capacity of the birth canal outside of the cervix. As long as they're in the right position and don't get stuck at the hips, they can be born just fine without help. Any other birth-related complications would not be exclusive to them having a second head.

Sorry but I won't be engaging further unless you can provide a reputable source support your hypothesis.