I'm sure if it says chicken it is chicken, otherwise just manure-car. Also very odd. Just imagine the smell. I've never seen such a thing in all my ag hist, but maybe others have.
in other parts of the speech this guy's tone is vy inflammatory & dismissive, e.g., toward environmentalists. so I wouldn't put it past him to say "chicken-manure" just for the connotation of "chickenshit", when in fact he just meant "manure" in general. but if he meant chickens I'd love to know!