SW Wisconsin, I put bulls in around July 20 for May 1 start of calving, I try to pull bulls out and put them in a separate pasture around Christmas or when there's a warm spell. I'd rather not have bulls in with the cows as they're calving in my smaller pastures.

Cows get 45 days (2 cycles) after the first calf is born or they get marked in Cattlemax for the next trip to the sale barn. This includes first calvers. I kept a couple that ended up getting bred later, calving the following September or so. Just screws up my whole system. I don't want fall calves and don't want to feed precious hay to open cows or heifers for 6 months over the winter. Also want to keep herd fertility up. 

Every time I make an excuse for a cow and she has a late heifer that I'm tempted to save I run the risk of lowering the group's fertility. So I'm back to holding the 45 day rule or they're gone.