Are functional additives necessary in feed?

What kind of role do cysteine, etc., play in feed? This product is used by several big companies, you can study its product manual carefully, and a lot of related research papers have been published! -there are a lot of additives, see you need to use-high-grade materials can not be less, do not know what the landlord does, if it is to breed their own ingredients, it is best to add-benevolence, the wise see wisdom! There is a reason for existence! It is important to restore the functional additives of safeeye138 at present-reasonable use.