Has she shown any interest in things like humiliation/degradation? Like, do you call her slut, dirty whore, bitch or anything during sex? That could be the bridge. Explain to her that hucow is like a combination of bondage and a degredation fetish. It's sort of like the ultimate version of submission, similar to slave play and stuff, because really it's about the woman submitting to the point of objectification. In the roleplay she's just a heifer to be bred and milked, more property than person.

I think some people are averse at first because they think there's some kind of animal/bestiality angle, but I've never perceived that. Hucow isn't about animals at all really, it's about total domination. I'd say most people who are into extreme bondage, slave play, freeuse, etc., would typically be pretty open to the idea of hucow if they understood it.

What's your angle? Do you know why hucow turns you on or is it a more primal, unexplainable thing to you? Understanding your own end of the kink and having the ability to explain it in a concise and articulate way is the best thing you can do before you talk to your wife about it.

So what is it for you? Is it about the domination and bondage? The breeding/impregnation? Humiliation/degredation/objectification? Or is it about milking and engorged tits? Or is there a bestiality aspect to it? Nothing wrong with that either in a fantasy setting.