Horse owners should pick up horse poo

I wish to complain about horse excrement on the pavement. Why is it that dog owners must pick up after dog excrement yet horse owners don't? Horse excrement is far more obtrusive and smells much worse. I have had the misfortune of seeing both on the pavement. These double standards must be removed.

Either let every animal (including humans) to poo on the pavement, or let nothing poo on the pavement.