A "pen" of cattle is whatever you work out between you and the feedlot. Generally, there are about 100 head in a pen, but if you want your 50 penned alone, some feedlot operator will likely be willing to do that. At a cost. Some feedlots sort and mingle customer's cattle and market them at an optimum end point. But that cost something, too. You'll just need to talk with specific feedyards to get what you want.
> What determines a "pen"
> of cattle. Is it all the cattle
> one customer sends to the lot, or
> is it a predetermined number?
> Would one owner's cattle be
> grouped and sold with anothers' if
> he sends only a half a pen? Would
> 50 head make a "pen"?