Early in the show, there was some confusion as to whether Xena's horse Argo was male or female. In some of the earlier episodes (SINS OF THE PAST [#01] and DREAMWORKER [#03]), Argo is referred to as "boy." Starting with the episode THE GREATER GOOD [#21], however, it was made clear that Argo is a mare.
There are actually several horses who portray Argo. Tilly, a palomino mare, is the one most often seen. According to a friend of a friend of the show's horse trainer (our sources are everywhere!), Tilly does the riding and standing, Aztec is the rearing specialist, Honey takes care of the kicking and running, and Mac is the stand-in. Despite persistent rumors, there is no horse named 'Daisy.'