My Basenjis would head right for the horse poop and the only question was whether it would be eating or rolling in it. Usually eating......they preferred to roll in more disgusting things. My niece's GSD was attracted to goose poop. Hard to do a tracking test across a field where geese had been. It can be very difficult or impossible to keep a loose dog out of poop. As Debra says, perhaps you can hose it away. Good luck!
(BTW, this is one of the reasons.....and there are many.....why flex leads are not a good idea. Most owners have no idea what their dogs may be consuming at the end of a long lead.)