Salam Claudia, ليس بي غير الرأفة بهذه الحياوانات الأليفة الأوفى بين كائنات الأرض: I don't have but mercy/ clemency/ mercifulness to these friendliest animals, the most loyal between the earth's creatures. I just wanted to say, that the adj. here is "most loyal" for the dogs, because the meaning of "loyalist" which is a noun is different. I know the meaning is clear for you already, but I just wanted to give you the full translation for this beautiful sentence about dogs :)

ليس بي غير الرأفة بهذه الحيوانات الأليفة الأوفى بين كائنات الأرض This is superlative form of "وَفِي" "loyal" which means:loyalest; most loyal

This is the superlative of the word " loyal " وفي = loyal أوفى = more loyal الأوفى = the most loyal