In early 1972, fourteen year old Donny's voice had changed. This was a major upset to the group's formula that had proved so successful. Not only did this eliminate Merrill's young-sounding co-lead's voice (forcing Merrill's already mature tenor voice to strain to cover most of the higher notes, with audible difficulty, through the next few years), but it also ended Donny's bubble gum like ballads, which became so popular with fans. With this development, Donny spent much of 1972 and then 1973 touring with his brothers but singing his old songs with his new voice, although the success of "Crazy Horses" singles "Hold Her Tight" (#14) and title track "Crazy Horses" (on which Donny did not sing) kept the group very popular through 1973.