I mean, it's got to be a bunch, doesn't it? Top U.S. exports to Iran over Bush's years in office include corn, $68 million; chemical wood pulp, soda or sulphate, $64 million; soybeans, $43 million; medical equipment, $27 million; vitamins, $18 million; bull semen, $12.6 million; and vegetable seeds, $12 million.http://news.yahoo.com/s/ap/20080708/ap_on_bi_ge/iran_buying_american

I don't think it's necessarily a commodity, sold by the quart or whatever. A prize bull might command a premium, like the semen of a Kentucky Derby winner. But check an agricultural answer board.