I have put 650 pound steers on meadow grass including Garrison foxtail and had them put on between 2.5 and 3 PPD during summer and early fall. I'd think 3.7 on corn silage & hay would be a cakewalk. Sliage is labor intensive to put up and store correctly in pits. Hay & grain is much easier to feed therefore the reason some feedlots do it.