Its the 4th set this year, so far. I have never seen anything like it, dad either. I only have 29 cows, 23 have calved so far. I lost one of the twins, born dead. 6 cows to go, for my hobby. I'm lucky to get 1 set a year. I can't figure it out. My heifer to bull ratio is 8 heifers to 18 bull calves.