The Effect of Antibiotics on the Growth of White Leghorn Pullets

THE first of the experiments discussed in this paper was started soon after the discovery that one of the commercial vitamin B12 supplements contained an unknown factor that stimulated the growth of young chickens (Stokstad et al., 1949). After it was found that the factor was an antibiotic (Stokstad and Jukes, 1950), the second experiment was conducted to determine whether the inclusion of an antibiotic in their diet during hot weather would stimulate the growth of young White Leghorn pullets fed a diet containing cottonseed meal as the chief source of protein. Because the stimulation of growth in the second experiment was relatively small in comparison with some of the results that were attributed to the antibiotics, it was considered advisable to conduct other experiments during cool weather. The data from the four experiments at the Southwest Poultry Experiment Station, Glendale, Arizona, are given and discussed in this paper. PROCEDURE . . .