I read about this today, it just means the vegetarian feed has no animal by-products in it, therefore less chance of getting a disease from feed. Like above post, mad-cow disease, etc. Feed often has slaughter-house waste in it, the biggest concern seems to be salmonellae. Long-term use of antibiotics has caused antibiotic resistant bacteria. Salmonellae is a huge concern for egg layers, as it is passed from the chicken ova duct into the yolk. I also learned the white has anti-bacterial properties too. I guess it is not exactly a marketing ploy, as I'd always thought.
