The days of the singing cowboy were drawing to a close. Three of the best known singing cowboys, Roy Rogers, Gene Autry, and Rex Allen, all transitioned to television. Allen, it happens, was the least successful of the trio.
Allen opted not to parlay his musical career into TV, choosing instead to try a straight dramatic role in Frontier Doctor, a syndicated series that lasted just 1 season (1958-9). It's now in the public domain, or so it would seem, as episodes are readily available on YouTube, and I'm not sure if it's airing anywhere at present, though networks like Get TV or Encore Westerns could be looking for new material.
Right now, let's take a look at the episode, "Queen of the Cimarron". Glenn Strange (Gunsmoke) guest stars. Turns out he's also Rex's cousin.
Growing up, I didn't know about any of Allen's movies, and only knew him as the narrator of Disney's "True Life Adventures" series of films. Son Rex, Jr. had a modest career on the country charts in the 70's & 80's.
So why did Frontier Doctor fail? Some will say Allen was a little too bland or vanilla. I'd say that because there were so, so many Westerns on the air, the show was choked out by the glut.