That's certainly not true. Mycotoxins are often invisible, tasteless, chemically stable and resistant to temperature and storage. Field fungi such as Fusarium sp. produce mycotoxins much more likely to be found in composted vegetation.
Don't use antibiotics or feed with antibiotics. Encourage your birds' natural ability to defend themselves by regularly feeding them apple cider vinegar, yogurt, and raw garlic. And give the species just a little credit.