Studies on the Stimulation of Growth by Dietary Antibiotics

ANTIBIOTICS have been shown to have their greatest effect on growth of chicks reared in an old environment (Coates et al., 1951; Hill et al., 1953; and others). Nevertheless, Waibel et al. (1954) and Libby and Schaible (1955) reported that the continued feeding of antibiotics in a given environment resulted in a gradually decreased growth response. McGinnis et al. (1958) reported that new antibiotics (not previously used in feeds) stimulated growth, whereas antibiotics used for some time in feeds did not. Heth and Bird (1962) found no difference in growth response when antibiotics were fed over an extended period. Penicillin had been used routinely in diets fed in our laboratory since 1950. The growth response to this antibiotic was small, but antibiotics not previously used, such as bacitracin and erythromycin, gave a pronounced response. Therefore, the following summary of experiments over a 3-year period using these antibiotics was made in…