I believe the correct ratio would be 99.9% human and 0.1% cow.
Today, 0.1% cow, tomorrow - 0.5% pig, the next day - 0.8% monkey, etc. The point here, quite simply, is that this is nothing more than destruction of human life, regardless of the percentage, in favor of a blended life of human and animal.
HUMANAE VITAE
Though it is true that sometimes it is lawful to tolerate a lesser moral evil in order to avoid a greater evil or in order to promote a greater good," it is never lawful, even for the gravest reasons, to do evil that good may come of it (18)—in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of man, even though the intention is to protect or promote the welfare of an individual, of a family or of society in general. Consequently, it is a serious error to think that a whole married life of otherwise normal relations can justify sexual intercourse which is deliberately contraceptive and so intrinsically wrong.
HUMANAE VITAE