YES, there are some products being used currently in Nigeria but not complete replacement of chemical additives. For example Fibrafid L D plus. check www.fibrafid

Do you consider vitamins and amino acids made by the chemical industry but identical to those derived from nature, chemical additives?? If so you have a problem!

But you probably want to avoid the use of coccidiostats and antimicrobials. Applying proper housing, cleaning, desinfection and hygiene during the growing period you will almost never need these supplements. But.... it comes at a price.

So my answer is, the moment the public (in the western world) is willing to pay for their meat and do not chose on the basis of price, we will hardly need any supplements to prevent or combat diseases while raising broilers.

However if you  or the consumer want free range animals, your control over hygiene is almost lost and you will probably need efficacious materials to prevent or combat diseases coming from the environment.

Yes we can use phytogenic feed additive (especially essential oils) to replace antibiotic growth promoters and other chemical feed aditiive. Many commercial preparations are available in market.