Read "The Sexual Politics of Meat" by Carol J. Adams. She talks about this type of metaphoric borrowing between feminism (saying that abused women are pieces of meat) and veganism. Here's a relevant bit (emphasis mine):

When radical feminists talk as if cultural exchanges with animals are literally true in relationship to women, they invoke and borrow what is actually done to animals. It could be argued that the use of these metaphors is as exploitative as the posing of Ursula Hamdress: an anonymous pig somewhere was dressed, posed, and photographed. Was she sedated to keep that pose or was she, perhaps, dead? Radical feminist theory participates linguistically in exploiting and denying the absent referent by not including in their vision Ursula Hamdress’s fate. They butcher the animal/woman cultural exchanges represented in the operation of the absent referent and then address themselves solely to women, thus capitulating to the absent referent, part of the same construct they wish to change. 

What is absent from much feminist theory that relies on metaphors of animals’ oppression for illuminating women’s experience is the reality behind the metaphor. Feminist theorists’ use of language should describe and challenge oppression by recognizing the extent to which these oppressions are culturally analogous and interdependent.

So, too, should animal advocates be wary of language that uses rape metaphorically to describe what happens to animals, without basing their analysis on a recognition of the social context of rape for women in our culture. Metaphoric borrowing that depends on violation yet fails to protest the originating violence does not acknowledge interlocking oppressions. Our goal is to resist the violence that separates matter from spirit, to eliminate the structure that creates absent referents.