Vigour in production-bred flocks, by F. A. Hays and R. Sanborn, Massachusetts Sta. Bul. 242, 1928, pp. 149–175, figs. 4.

The studies reported cover a 5-year period beginning with birds in the flock hatched in 1922 and ending with the flock hatched in 1926. The birds have all been pedigree-bred since 1913, and the greater proportion have been bred for high fecundity, with a limited number for other purposes (E.S.R., 59, p. 72). The chicks have been placed in brooder houses on clean range at 1 day old, and the sexes separated at 8 weeks. The pullets were put in the laying house at 150 days of age. All culling has been done by families only, and no pullets were culled at any time in the laying house.