Sounds a bit like here. We had 3 sets of twins out of the first 7 bull bred cows to calve. We weren't even at day 281 post bull turn out yet. Lost the first set because one was coming butt first and we didn't realize it soon enough. I was afraid it was going to keep up, but those three were the only ones. I wonder if when you first turn out bulls, it can cause some cows who weren't cycling to go into some kind of super ovulation mode. Most of our twins have come in the first week or two of calving. We don't seem to have many out of cows that don't settle in the first few weeks.