What is nonsensical is a definition of consent that denies that animals are able to give it. You know how when you try to do stuff to them, and they run away or attack you or whatever? It's not a subtle message they're sending. At least in most cases.

Of course, it's probably important to admit that 95% of Western civilization (and maybe all civilization; and maybe all of humanity) agrees with your perspective on this topic, to my dismay.

Edit: although when you consider all relevant issues about the morality of how humans use animals, the ethics of forcefully inseminating them come pretty low on the list, imo.