It’s a Western movie trope based in the socio-economic and cultural fabric of the time.

A horse in frontier times would have been a highly priced possession for the owner, usually the most valuable of all in fact, aside from reflecting connection, trust and personal attachment between the two. Given the unforgiving environment, the loss, sudden absence or injury of one’s horse could be the difference between survival and swift and certain death.

Enter crime. Riding another’s horse would have been highly unusual and indicative of either a dire emergency necessitating such or, most likely, foul play.

The chicken being the hero or cause of calamity for the owner is inherently hilarious.