Totally. Well I guess you have to define free will to really answer that. Is an animal a slave to the hunt? Is a child a slave to their parents? Is a drunk a slave to alcohol? Is a rich person a slave to their spoiled sensibilities?
Discussion
Freewill is only of humans, the rest act by instinct and programming.
OK, maybe slave is a strong word. Caged chicken sounds better. Featherless caged chicken to be more precise.
we have no proof that other animals, especially all other animals, are only following instinct and "programming" ... I am personally quite convinced of the opposite. Most humans on the other hand, don't know what freewill, or more strongly "libre arbitre" truly means.
a better word for a slave without leach is vavassal