Pregnancy can wait. Why doesn't the bull fuck her mouth, then her cunt, and finish off by fucking and then cumming in her arse?
But wait, there's more. She then straddles her fuckwits face (I meant cuckolds mouth), then extrudes (OK, shits) the combination of shit and cum down his throat?
Afterwards the bull shows his tacit approval of the act by shoving his semi hard cock down the faggot cucks mouth and pissing down his gullet.
His passive receipt of such filth from both shows he'll take any shit from her, so it should be less of a concern if the bull next impregnates his wife.
They will slowly accustom him to be the working drone to provide for them both (later three).