Place the chickens, onions, carrots, celery, parsnips, parsley, thyme, dill, garlic, and seasonings in a 16 to 20-quart stockpot.
Add 7 quarts of water and bring to a boil.
Simmer, uncovered, for 4 hours.
Strain the entire contents of the pot through a colander and discard the solids.
Chill the stock overnight.
The next day, remove the surface fat.
Use immediately or pack in containers and freeze for up to 3 months.
