WF, I am trying to understand this myself. 

My simplified way of looking at it is that each of these cows has a certain value TODAY, Nov 17th. If we assume each cow has the SAME value on May 1 next spring it makes things simpler.

Between now and May 1, my additional EXPENSE per cow is $333 in hay plus mineral, my labor between now and then and some other figure for land/corral "rent". Let's just say this is about $1 per day for these other expenses to hold that cow until May 1, or a total EXPENSE per cow of about $500. Again assuming cow herself has the same value then as now.

In return my INCOME per cow between now and May 1 is a roughly one 200 lb calf.  

Therefore the CHANGE between now and May 1: $500 EXPENSE/200 lb calf INCOME. 

That calf as of May 1 cost me about $2.50 per pound. And this is additional cash expense from today.

My hay did test well. Not dairy quality but very good mixed hay at $60 per 1400-1500 lb 5 ft wide x 6 ft dia bale. That was a good price in WI this year where it was very difficult to bale good, dry hay.  

Jim at Dawn