To prevent cross-contamination of the virus from different animals, the feed eaten by the breeding hens cannot contain animal products; they cannot test positive for Salmonella enteritidis, Salmonella pullorum or Salmonella typhi, nor for avian flu or avian leukosis viruses; and they must also be free of external hormones and antibiotics.
魏逸之稱呼這些是「clean eggs」──為了避免不同動物體內的病毒交互感染，種雞所吃的飼料不得含有動物成分；牠們體內不得檢出腸炎沙門氏桿菌、雞白痢沙門氏桿菌、傷寒沙門氏桿菌，以及 A 型禽流感、禽白血病等病毒，也不得有賀爾蒙與抗生素的殘留。