It depends on the purpose of the jar for protection or to attract negative energies. Your DNA does not have to be urine if you decide to use the witches bottle for protection as a ward to repel negative energy.
I have used hair, fingernails, coffee or water that I sipped and than released into the jar, just as a starter, you do not need to use urine which personally i find offensive.
Other elements I have used other then my own DNA for a witches bottle include: shells and beach sand, symbol of the water, pennies for a symbol of wealth and prosperity. Various flowers.
There is a great link about witches bottles and all the elements to create and make them and discussing in detail the elements used in the jar, whether for protection or to attract negative energies.