At least where I live no organs can be taken unless the patient has a donor card/explicitly allows this. This makes it into a donation, not a forceful taking, which is why they're called donors.
I don't think animals can opt-in to such a system, as such I'd consider it an incorrect usage of the term.
I don't think animals can opt-in to such a system, as such I'd consider it an incorrect usage of the term.