What must eggs not fit for human consumption, going to be used for animal feed, be?

The correct choice focuses on the requirement for eggs that are unfit for human consumption and are intended for use as animal feed. Such eggs must be marked and denatured to prevent any potential misuse.

Marking and denaturing serve as crucial steps to ensure that these eggs cannot be mistaken for eggs meant for human consumption. Denaturing involves treating the eggs in a way that makes them undesirable or unpalatable for humans, thus protecting public health. Marking further emphasizes the intended use, signaling clearly that these products are not suitable for human dietary needs.

This requirement is vital in maintaining food safety standards and preventing any health risks associated with the consumption of eggs that are no longer fit for human use. By following these protocols, the industry can effectively manage by-products in a safe and regulated manner.

Other options might appear relevant but do not specifically address the necessary safety practices for handling eggs unsuitable for human consumption aimed at animal feed.