I will sure try. 

The three large cows I sold weighed a total of 5200 lb. To save some time I will cut and paste. Here is the calculation from my original post above for three large cows totaling 5200 lb:

using 3% of body weight of hay per day consumption I have reduced my winter hay requirement by 5200 lb x .03 x 150 days (in WI to greenup) = 23,400 lb = 16.71 1400 lb & $60 bales of hay = $1002 of hay alone.

These three cows are due to calve around April 1, greenup and turnout on grass is usually about May 1.  Therefore these THREE cows' calves, assuming everything goes ok are costing me $333 EACH in hay alone between now and May 1 at which time they will be one month old.

Here is the same calculation for three 1200 lb cows totaling 3600 lb:

using 3% of body weight of hay per day consumption I have reduced my winter hay requirement by 3600 lb x .03 x 150 days (in WI to greenup) = 16200 lb = 11.57 1400 lb & $60 bales of hay = $694 of hay alone.

These three cows are due to calve around April 1, greenup and turnout on grass is usually about May 1.  Therefore these THREE 1200 lb cows' calves, assuming everything goes ok are costing me $231 EACH in hay alone between now and May 1 at which time they will be one month old.

So the 3 calves from the 1200 lb cows will cost me $231 in hay between now and May 1 compared to $333 in hay cost for 3 similar calves from the three larger cows.

Conclusion in my situation with $60/bale purchased hay:

There is a savings of at least $100 per calf from overwintering three 1200 lb cows compared to overwintering three larger cows totaling 5200 lb on purchased $60/1400lb bale good hay.

Note that a key part of this conclusion is whether or not the calves from 1200 lb cows are essentially identical (or can be with the right genetics) to the calves from 1730 lb (5200/3) cows.  From my last few years of data there is no doubt in my mind that a 1200 lb cow can produce as heavy a 205 day calf as a 17-1800 lb cow.

If I have made a mistake here please point it out. Interesting question.

Jim at Dawn