I'm not kidding you.  Had it happen.  Neighbor had on calve a week before she turned a year.  I will be more then happy to give you the name of my vet.  He bought my last party girl years ago and calved her out.  She was over a year when she had it and he had to C section her, but I know she wasn't more then 13 months.  It happens when you feed molasis tubs in the pasture, it seems.  We quit that and the problem went away.

E mail is in profile, I'll send you his name and phone number.