Simmental are fertile myrtles. So, I have always had numerous twins. But, years ago, they always seemed to get tangled up bad and "kill" each other. I really hate to actually say this (bad luck???) but, we have been having an extremely good run of cows just spitting them out.
Since my nephew moved in with my (after Ken died) we have had 1 set of twins that we had to call the vet. It was the first month Phil got here. Vet didn't have any trouble pushing one back & getting both out.
Maybe it has something to do with the smaller calves??? I still have some whoppers (110 - 125#) from cows that just likes to grow them - in & out of their bodies!!! but, can just spit them out.
Last year I had two sets of EMBRYO twins - heifers - all 4 identical pedigree from same flush. I have an ET full sib/flush mate due in about 2 weeks. As successful as they have been, I still do not like twins. Never have, never will.
One cow had her first set of twins at age of 8 in March, next year set of twins in Feb, and the next year set of twins in January. She came up open, but she is safe in calf for a fall baby.