I was just told to wash quilts in horse soap. It is called "Orvus Paste" and you can get it at Farm & Fleet a lot cheaper than buying it at a quilt shop.
"Get your horses squeaky clean with Procter & Gamble’s Orvus Paste Soap. Just lather them up and rinse them off. It works equally well in hot or cold water and will even clean those stubborn manure stains that are such a problem. Plus, you can use this soap for washing fine washables in the laundry because it contains no phosphorus to fade colors! For a versatile soap, you need Procter & Gamble’s Orvus Paste Soap."
I haven't tried it yet, but plan to buy some soon.
Good Luck