The Effect of High Levels of Antibiotics on the Growth of Chickens During Hot Weather

THE literature contains many reports about the effect of antibiotics on the growth rate of young chickens, but an extensive review does not seem necessary for the scope of this paper. Rather, it seems preferable to mention only two pertinent reports. The first is that of Couch and coworkers (1952) who found the “best and most constant results have been obtained when a combination of antibiotics is fed” (to broilers). The other is that of Heywang (1956) who found that chlortetracycline at the levels of 50 and 100 grams per ton of diet increased the egg production of apparently healthy White Leghorns kept under high, but normal, environmental air temperatures. In two experiments conducted during hot weather prior to 1954 at the Southwest Poultry Experiment Station, Glendale, Arizona, combinations of low levels of antibiotics were at least as effective as somewhat higher levels of individual antibiotics. In the first of …