The ongoing shift from conventional cage to alternative housing for layers necessitates a deeper understanding of how commercial rearing systems impact physical development in pullets. My thesis examined the effect of three styles of rearing aviaries, differing in the opportunities for load-bearing exercise available during early life, and conventional rearing cages on musculoskeletal characteristics and proximate composition in two consecutive flocks of Lohmann Brown Lite (B) and Lohmann Select Leghorn Lite (W) laying hen pullets. Aviary-reared birds had stronger radii, humeri, and femora, larger keels, and proportionally heavier flight muscles than those reared in conventional cages. W birds tended to have proportionally stronger femora and tibiae, and larger, more ossified keels, than B birds. The benefits of rearing aviary housing appeared to be broadly realized rather than specific to a particular style. These findings provide further evidence that rearing aviaries profoundly improve pullets’ physical development compared to conventional cages.