Mr. Ed 56 episodes??

Has anyone looked at the cast list, i know Allen Lane did Mr. Ed`s voice, but if you look at casting list it say`s Mr. Ed 54 episodes? Referring to the actual horse? How could this be? There 144 episodes, and it says the horse playing Mr. Ed was only in 54 episodes? I could see them taping alot of horse scenes together in 1 day and using in several episodes, but that still should count as all those episodes. That would be sayin they didnt use the horse in 90 episodes, that is not right! And i read it was the same horse used for every episode, different horse used for photo shoots sometime`s, but was always same horse in show. So was not another horse in those other 90 episodes, can anyone answer this?