If they calve a month earlier in WI and the north, the heifers are calving in the snow and mud. Unless you have some special facilities.

I think the idea of breeding at 15 months and calving at 24 is they should be big enough to breed at 15 (instead of pushing earlier as mentioned in a couple posts above) and, provided a reasonable CED bull is used and the dam had reasonable CE, they should be able to calve in the pasture on their own at 24 months with the rest of the cows.

Calving for the first time at 24 months is also not likely to hurt their breed back, at least for BCS 5 to 6 Herefords. And if breed back is the same as the cows after a first calf at 24 months then the long term production of the hiefer seems likely to be unaffected (by calving at 24 mo) also.

Jim at Dawn