I've been thinking about that lately and what I think I will do is wean at the same time of year even though the calves will be younger. Probablay late September or early October. Calves will gain better and will have the cows in good shape going into winter.
I went to a producer meeting the other day and heard a talk on early weaning and I mean early weaning! There are some guys who are successfully weaning calves at 100 days of age. Rule of thumb for them is when they put the bulls in with the cows was when they were pulling the calves off. I know it sounds kind of extreme but the main reason they were doing it is to get their cows in really good shape going into fall, grass went way farther because there wasn't a calf out there eating part of it, and the cost of wintering cows was very little because they were so fat going into winter. Conception rates increased and replacement rates are down to about 10% per year which is a big savings in depreciation. I figure about 15% per year for our operation.
Very interesting concept, I guess now that I think about it if I wean in Sep. some of my calves could be about 100 days old.