All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The fact that the animal is vegetarian does not necessitate its prohibition just by feeding it with meat if this meat is lawful, whether this meat is pure meat or it is mixed with plants [like grains]. However, if the meat is impure, like the meat of a dead animal, then you knew from the Fatwa you referred to the details about its ruling. So, if the food of the animal in general is impure meat, then it takes the ruling of Al-Jallaalah (the domesticated animal fed on impurities).
The view that it is forbidden to eat Al-Jallaalah if most of its food is impure is the view of the Hanbali School of jurisprudence, whereas the view of the majority of the scholars is that it is disliked and not forbidden.
Allaah Knows best.