Some Microbiological Observations on the Antibiotic-Fed Chick ,

MANY growth studies dealing with antibiotic supplementation have included limited bacteriological studies in an endeavor to elucidate the mechanism of growth promotion. Sieburth et al. (1951) found no consistent and reproducible modification of the cecal microflora by low growth-promoting levels of penicillin and terramycin fed to turkey poults over a four week period. Rosenberg et al. (1952) also failed to show a modification of the fecal microflora of chicks fed diets supplemented with five progressively doubled concentrations of terramycin. However, other reports have indicated that the cecal and fecal microflora are significantly altered by antibiotic supplementation of the feed. March and Biely (1952) reported that aureomycin supplementation caused a consistent lowering of the population of lactobacilli of the feces during the five week experimental period. On the other hand, Anderson, Cunningham and Slinger (1952) on the basis of counts made at ten weeks of age, reported an increase in most …