Matthias is arguing the metaphor. Which is a little fair in this case because the metaphor is the meat of the thing, but still, his response is basically "Ok, but imagine a completely different scenario. Isn't it different now?"
Not to mention he has a very, very low opinion of animals. Animals do engage in creativity and play. That we've been able to observe. We honestly don't know if they engage in philosophizing or other sorts of abstract thoughts because we don't speak dolphin. Matthias is basically basing his rebuttal on animals not being sentient. Or at the very least, minimally sentient.
So cows can't tell us if they'd rather go extinct or continue as they are. And I'd imagine that whatever way you formulate the thought, you'd find people who would prefer one or the other. If the people were only as aware as cows; if the people were as aware as normal but treated as cows; a third scenario I haven't thought of.
And there's the question of whether or not we have an obligation on how to treat them. If someone disagrees with that obligation, you have to get over that hump first. Kind of on their terms. Because if they believe we don't have an obligation because cows have hooves, you're not going to convince him that cows don't have hooves. You have to find out why hooves matter to him then find an argument along those lines. Arguing from the sentience of a cow isn't going to cut it. Arguing we have a moral imperative as the most abstract thinkers isn't going to cut it. You have got to argue hooves.
And if you can't do that because his position is so nonsensical there's no way to rationally argue against it, you have to accept he's just not going to understand.