Hoofs and Goofs (1957)

Sister Bertie is reincarnated as a talking horse.

Joe dreams that the stooge's sister Birdie has died and been reincarnated as a horse. The stooges take Birdie home but must conceal her from the snoopy landlord. They succeed, but more complications ensue when Birdie gives birth to a colt. Joe wakes up to suffer some abuse from the real Birdie (Moe in drag), when he tells her he dreamed she was a horse.