Are riders not obliged to pick up the poo of the horses they're on in the same way that dog-owners/walkers are required to? And, if not, why not as it makes much more of a mess.
So far as I know, dog owners don't have to poopscoop if it's in the road either, but I wouldn't be asking my dog to poo in the road or in the gutter.....way too dangerous.
I suspect the law is as it is because it was the landed gentry that rode horses and they couldn't be considered liable to clear that up as they go. But the plus point i s that vegatarian poo is less potentially dangerous to you than other poo. Which is why you can shovel it up and put it on your rhubarb (before picking & stewing it).
It used to be that dogs were encouraged to poo in the gutter but that is rarely done now for the reasons given, and anyway it is still illegal not to clear it up. Horse poo is totally organic and I can remember the scramble to get the droppings when the rag and bone man had been.