I talked to our embryologist this morning, and since I had him on the phone, I asked about the possibility an embryo splitting after implantation... He said it does happen occasionally, but not often. He also said he had noticed fertilized eggs under the microscope that appeared to be likely to split...he makes notes of things lime that, and has records of that happening. I think he said he knew of two or three sets in the several years he's been doing ET work.
We also talked about other possibilities for the occurrence of "twins" after ET...he knew of one situation where two calves were born, obviously NOT identical twins, so obviously not the result of an embryo that split. In this case, they tested the two calves, and ONE was an ET calf, the other a natural calf of the recip who obviously got bred during her heat, then they put an embryo in her, and both embryos survived. He also said the embryologist would have to be "highly incompetent" in order for two embryos to end up in the same straw, but he couldn't argue that it wasn't possible.
If the calves are the same sex and look very similar, they're probably identical twins. If they're opposite sex or different colors, then clearly they are the result of two separate eggs. Btw the fact that twins ARE the same sex or the same color doesn't automatically determine they are identical twins. Fraternal twins are genetically just full sibs.
I grew up with Simmental cattle, and I've seen a fair share of twins. Some look NOTHING alike...some really ARE identical, enough so that they're very difict to tell apart. I've even seen this in traditionally marked Simmental with lots of spots, but according to research, identical twins in breeds with spotting don't always have identical markings. I would expect them to be described similarly, but not necessarily absolutely identical. In our experience, we seem to have a lot more fraternal twins than we do identical, but I can think of a few cases that I could barely tell two calves apart because everything about them, even their faces, looked the same!
Didn't mean to get long-winded...I just think it's an interesting subject.
