Garryowen was the 7th Cavalry Regimental marching song.  It was derived from an old Irish drinking song, and might have been suggested to Gen. Custer by one of his "melting pot" Irish soldiers, perhaps even Capt. Myles Keogh.  Custer liked the tune since it matched the cadence of a cavalry horse marching in formation.  The music and lyrics may be found under the "Custer Topics" section.

"Dandy" (right) Custer's horse for the long march and hunting, and "Vic" (left) the thoroughbred that Custer used for battle and whenever speed was required were no doubt well acquainted with the regimental song.  The bare spots on the horses in this photo attest to the fact that, the McClellan saddle did not fit many horses too well.