U.S. Department of Agriculture experts knew about sanitary problems at one of the two Iowa farms at the center of a massive nationwide egg recall, but did not notify health authorities, the Wall Street Journal reported.

Bacteria found in chicken feed used at the two Iowa farms was linked to a salmonella outbreak that prompted the recall of more than a half billion eggs, the U.S. Food and Drug Administration said last month.

The Journal said USDA daily sanitation reports viewed by it underscored the regulatory gaps that may have contributed to delays in discovering salmonella contamination.

The Food and Drug Administration, which has overall responsibility for egg safety, said it never heard from the USDA about problems such as dirt and mold in the Wright County Egg of Galt, Iowa, facility, the Journal reported.

The USDA said it didn't give notice because the conditions at the egg plant packing facilities were routine, according to the report.

WSJ said it was not clear whether the sanitation problems identified by the USDA experts had anything to do with the salmonella contamination, which is the largest since the 1970s.

USDA and FDA could not be reached for comments by Reuters outside regular U.S. business hours.