I think you would need to do the ethical thing and discuss the breed/cross you wish to get slaughtered with the abattoir. I know of a pure wild boar which went berserk in the slaughterhouse and gouged the slaughterman's femoral artery with a tusk. This led to the slaughterman nearly losing his life, and to both the farm and the abattoir closing down! I don't know how wild a cross would be, but I think the abattoir has the moral right to make its own informed decision.