The goats will graze pastures lower if the plants are not as mature when they start grazing. Southern Australia makes most of its milk on grazing, you should be able to reduce feeding costs per litre of milk, or kg of solids by grazing. It should more than pay for the possible reduction in yield. Down here cows and goats get fed a high energy or protein grain ration with buffers and minerals etc while getting milked in the dairy. Some farms also use a partial mixed ration when there is not enough grass to meet the animal requirements. It is adjusted depending on the nutritional value of the pasture they are consuming. New Zealand are the experts on making grass into milk, pehaps search through some of their information as well as Australian info. It takes good management and understanding of the system to get it right. I have also posted to Jim and others our grazing system. Here is a link, ask questions if you like.

http://talk.newagtalk.com/forums/thread-view.asp?tid=489276&posts=9&highlight=kg/dm/ha&highlightmode=1#M3975089