Federal investigators are reported to have concluded their investigation into the farms belonging to two major egg producers -- Wright County Egg and Hillandale Farms, both of which were speculated to bear links with the salmonella outbreak in the nation.

Officials on Monday claimed that federal investigators found large amount of manure, piled up to eight feet high, besides other unhealthy conditions, including live mice, pigeons and other birds inside the hen cages.

The unhealthy conditioned at the two Company’s farms clearly signify that the eggs have been contaminated because of it.

The two major egg producers have recalled over 500 million eggs since Aug. 13 because of salmonella fears.

The recent outbreak linked to massive salmonella infection is deemed to be the largest of its kind ever witnessed since 1970s, leading to over 1,500 reported cases of Salmonella enteritidis due to infection from contaminated eggs, the Centers for Disease Control and Prevention outlined.

Salmonella enteritidis is a form of bacterium that breeds on animal intestines and is usually found in feces and can spread via mice, birds, flies and other living organisms.

In a statement, Wright County Egg posted: “Our team has worked around the clock to address concerns that were raised verbally during FDA's inspection, with many of those being fixed as soon as they were identified".