I like the idea of spreading out the calves for the locker.  I once did some tech support to an farm/abattoir in Ontario that calved year round (never pulled the bull) on 400 head of cows so that they had something to slaughter every week.

40 head of calves going from 550-1250# (if you were to market all of them as finished cattle) would go through about 100 ton of corn (if corn was the only grain).  So about 2.5 ton apiece.  The calves you sell at 900# would probably take about a ton of corn each (depending on how much corn you let them have).  Rolled Corn has about 106% the energy of rolled barley and about 114% the energy of rolled oats, so you can figure how much small grains the corn will replace.