The worry would be residues in the eggs - some residues
might be diminished when cooked, but who knows(?)
Drug residues can be found in the eggs (and sometimes meat), so feeding them back, at least to me, would be giving additional drugs that the chickens (humans, dogs, cats, etc.) don't need. If you fed them back, how would you know how much medication they are getting - too much(?) Then how much drug is in each egg - how much egg did each chicken eat - how long does it take for the chicken to process/digest that egg and for it to go through their system, etc. A whole bunch of questions come up that can't really even be answered - so you err on the safe side and throw the eggs out.
Look up Farad guidelines for withdrawal/slaughter times and articles about residues in meat/eggs - some drugs have not even been studied that much in laying hens - so all we can go by when giving a medication for chickens is to find a reasonable withdrawal time we feel comfortable with. Looking at "slaughter timelines" will get you in the ballpark. You also have to look at what country is using a drug -for instance some medications are approved for use in eggs/meat in Europe, while they are banned in the U.S. The best we can do is research any medication that we give to our animals and go from there.
