Aside from the animal cruelty aspect, premarin is also not very effective at inducing feminization, and contains estrogens that are unique to horses, for which the human body doesn't have the enzymes etc in place to deal with. IIRC, it nearly doubled mortality in the 2002 WHI study, and is the main reason doctors are now so reluctant to prescribe HRT to postmenopausal women. It's an old drug, and would have been abandoned long ago except for slick marketing by the pharmaceutical company that produces it. You're far better off with bioidentical estradiol, which is more effective for feminization and has a much better side effects profile (especially transdermal or injected).