“…To the best of our knowledge there is no published data on the microbial population of various parts of the intestinal tract of poultry. For example, Lindblad et al (1952) found that increasing calcium and phosphorus levels, from deficient to adequate, caused an increase in aerobic, anaerobic, aciduric, proteolytic, lactobacilli and coliform counts. In view of the findings that the greatest effect of the antibiotics in promoting growth occurs at an early age, (McGinnis, 1950;MacGregor et al, 1952;Heuser and Norris, 1952;and others) and that the response gradually at West Virginia University, Health Science Libraryy on June 25, 2015 http://ps.oxfordjournals.org/ Downloaded from disappears with age, it seems probable that changes in microbial populations as a result of antibiotic administration are not constant but change with time and /or age.…”