They’re animals. Artificial insemination is no more or less rape than any other means of reproduction. Bulls don’t exactly get consent, or give a shit if the cow is actively resisting for that matter. This is an instance where nature is more fucked up than what happens on farms, not less.
We artificially inseminate cows when they are in heat. This argument of heat == consent is nonsense to pad out the argument and make it sound more grey than it is.