I am looking for a very tight calving period. Like to have all calves born on first 23 day cycle and will cull any cows that have not calved within 45 days/2 cycles of the first calf. These "over 45 day" cows will get culled at weaning along with any cows that preg check open in November.  I had no over 45 day females and no opens in my small herd last fall.

However I put my bull in during early June and leave him in until weaning in November. this makes it easier to manage the rotational grazing, the bull is happier and less trouble. My bulls are in a separate field from the females from mid November until they go in with the cows and heifers in June.

You can tighten up calving and maintain fertility in a couple different ways. 

I am using two bulls this year so instead of the bulls going in with the cows, I will be splitting the cows into two groups in separate fields to go in with each bull for 45-50 days then they will all go back into one group August 1 so they are easier to manage for rotational grazing.

Jim at Dawn