Ours always run together, about 100 cows, weve done it that way because we don't have anywhere else for them to go, but they are also usually running on stalks at the same time. Have lost a few over the years when we get a bad storm and they bunch up, once in awhile they will get stomped into the mud. Have thought about getting some sheds for the calves, put our "calving pen" has very little in the way of flat area, so we haven't figured out where to put them, but theres some tree piles and a tree filled draw they can get into.

Between the weather and issues like that, later calving is starting to look better all the time. 

We used to be in Jan-Feb, the theory was they cant get stomped in the mud when its froze, but since we moved it back to March-April life has been better for everyone.