Hey Mama!
If you ask ten different emu owners, you will probably get 10 different answers. However, one thing that they would probably agree on is that an emu needs a more balanced diet than just cracked corn or lettuce. So, here is my opinion, based on my experience. The easiest, but perhaps the most expensive option is to purchase a prepared ratite feed in pellet form. These feeds are prepared with all of the necessary nutrients, minerals, vitamin, amino acids and protein percentages for a balanced diet. A typical adult emu formula would consist of 14-17% protein, and include trace amounts of ME, Lysine, Methionine, Cystine, Calcium, Phosphorus, salt, and about 1% fat. If your local feed store does not carry a ratite formula, a non-medicated poultry grower/finisher pellet is probably just as good. There is a lady who lives about 15 minutes who has raised hundreds of emus and all she ever feeds them is non-medicated poultry breeder/layer pellets. Some people make their own feeds from a mixture of different feeds, this is perhaps the cheapest way to go, but a bit more trouble. Regardless, any of these prepared pellet formulas would be much better, nutritionally speaking, than a diet of cracked corn.
Typically goat feed has the right protein percentage, (16% +/-) but has more fat content, a higher salt and fiber content, and lower calcium percentage than is generally recommended for emus. In addition, it contains copper and selenium.
p.s.- your poop description sounds normal for an emu!
