Aside from pork, bologna can alternatively be made out of chicken, turkey, beef, venison, a combination, or soy protein. Typical seasoning for bologna includes black pepper, nutmeg, allspice, celery seed, coriander, and like mortadella, myrtle berries give it its distinctive flavor, U.S. Government regulations require American bologna to be finely ground and without visible pieces of fat.
Resources
Bologna sausage, Wikipedia
Sausages and Food Safety, USDA