Bologna sausage, is also known in the USA as baloney and in Europe as Lyoner.
It comes from Italian mortadella which is a finely ground pork sausage that has cubes of lard and originally comes from Bologna in Italy.
Aside from pork, bologna can alternatively be made out of chicken, turkey, beef, venison, combined or soy protein. (source wikipedia)
Can guinea pigs eat Bologna?
Unfortunately, because they are herbivores, guinea pigs are unable to eat any meat products at all.
Instead, give them veggies instead, they will much prefer it.