All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The general rule is the dislike (karaha) of feeding animals that are permissible to eat with impure substances. Sheikh Al-Islam Ibn Hajar Al-Haytami, may Allah have mercy on him, said: "It is disliked to feed an animal that is permissible to eat with impure substances" [Tuhfat Al-Muhtaj, Vol. 9/P.386].
If an animal that is permissible to eat consumes impure substances, it falls under the ruling of "jallalah" - and "jallalah" refers to any animal that consumes excrement and dung, such as sheep, chickens, geese, and others. Its meat is disliked to eat if it changes (in taste or smell); however, if no change is evident in its smell or taste, then there is no dislike according to the Shafi'i school of thought.
Shaykh al-Islam Zakariyya al-Ansari, may Allah have mercy on him, said: "A kid (baby goat) raised on the milk of a dog, or something similar like a pig or a donkey, is like a jallalah" [Asna al-Matalib, Vol. 1/P.568]. Imam al-Sharbini, may Allah have mercy on him, said: "If the meat of a jallalah, whether from livestock or otherwise such as chickens, shows any change, even slightly, its consumption becomes haram (prohibited) – as stated in Al-Muharrar – because it has become one of the impure things. It has been authentically narrated that there is a prohibition on eating it, drinking its milk, and riding it, as mentioned by Abu Dawood and others. It is said that it is disliked due to the unpleasantness of its meat. I say: The more correct view is that it is disliked... If it is fed with pure or impure feed such as barley mixed with impure water or inherently impure substances, as is apparent from the text of Al-Tanbih, and its meat becomes pure by the removal of the bad smell, then what was mentioned becomes permissible" [Mughni al-Muhtaj, Vol. 6/P.155].
Some scholars have restricted the description of "jallalah" to an animal if the majority of its feed is impure. This is affirmed by Imam Nawawi, may Allah have mercy on him, in "Tashih al-Tanbih," as quoted by Imam al-Sharbini, who said: "It is said that if the majority of its feed is impure, then it is established [as jallalah]; otherwise, it is not. This is apparent from the author's statement in al-Tahrir and affirmed in 'Tashih al-Tanbih'" [Mughni al-Muhtaj, Vol. 6/P.155].
Based on the expertise provided, if the additives to poultry and animal feed, from animal-derived protein powders, constitute between 5% to 10%, and the rest of the feed consists of pure materials, then the majority of the feed would be considered pure. Therefore, in this case, such animals would not be classified as "jallalah."
Therefore, if the majority of the feed for these poultry consists of pure materials, they do not fall under the ruling of "jallalah." Moreover, if there is no apparent corruption in their meat, milk, or eggs due to their feed, and experts confirm no harm in consuming their meat, then it is permissible to eat their meat after slaughtering them according to the Islamic method. However, if their entire feed is from impure substances or if there is visible corruption in their meat and milk, it is disliked (makruh) to consume them. The preferred approach is to feed them with pure materials for a period until they are cleansed and accepted for consumption. And Allah the Almighty knows best.