its an archaism. a modern understanding of animal behavior and ethics have both pushed that training modality out, and probably the more successful animal trainers of yore never really relied on it, but people absolutely used to beat the shit out of animals. perhaps not often, and perhaps not horribly, but animal cruelty was certainly common enough to enter the lexicon. see “carriage whip”. see “spurs”. see “bearing rein”. see “branding iron”. etc etc. hell theres even the phrase “spare the rod, spoil the child”.

and this is not the worst place a study of the history of language will take you. remember that european and white north american cultures both (among others) unabashedly practiced chattel slavery for centuries, if not millennia for older cultures.