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

Effect of Antibiotics on Growth and Nutrient Absorption of Chicks

“…In previous experiments, chlortetracycline regularly gave a growth increase of 15 to 25% but lost its activity after it was in use for 6 months. This is in agreement with other reports that continuous feeding of an antibiotic results in a decrease in the growth response (Waibel et al, 1954;Libby and Schaible, 1955). Figure 1 illustrates the evolution of the daily weight increase, and Table 2 summarizes the body weight data.…”

Comparison of Growth Response of Chicks to Virginiamycin and Other Antibiotics

“…I T HAS been reported that continuous use of antibiotics for growth promotion of chicks resulted in a decrease in their effectiveness (Waibel et al, 1954;Libby and Schaible, 1955;Sherman et al, 1959). McGinnis et al (1958) reported that erythromycin thiocyonate and oleandomycin phosphate improved growth of chicks while other antibiotics which had been used for several years failed to do so.…”

Further Evidence on the Relation of Coliforms to the Growth Response of Chicks to Antibiotics

“…This may explain why penicillin did not resuit in maximum coliform numbers until 7 days of âge while with other drugs the coliforms reached a peak at 3 days of âge. Waibel et al (1954) suggested the élimination of harmful bacteria through the long-continued use of antibiotics as one possible reason for the disappearance of antibiotic growth response in an "old" environment. A delayed response to penicillin, such as that found in the présent work, has been observed in several récent experiments made in the quarters employed for this trial.…”