Disappearance of the Growth Response of Chicks to Dietary Antibiotics in an “Old” Environment

THE addition of an antibiotic to a suitably deficient diet can result in large increases in the growth of chicks, while such additions to nutritionally adequate diets usually result in lesser increases. (Waibel et al., 1953; Biely and March, 1951; Coates et al., 1951). These latter can be eliminated entirely when the chicks are kept in a “new” environment not previously occupied by chickens (Coates et al., 1952; Hill et al., 1953; Lillie et al., 1953). The present report describes experiments conducted in one environment over a three year period. For nearly two years, consistent growth responses to antibiotics were obtained but during the third year responses became inconsistent and negligible. The chicks used were the progeny of New Hampshire males and Single Comb White Leghorn females fed diet B-1 of Robblee et al. (1948). They were placed on experiment when one day of age and maintained on raised …