The effect of dietary antibiotics upon hepatic and renal xanthine dehydrogenase activity in chicks

Single-comb White Leghorn cockerels were fed a nutritionally adequate, practical-type chick starter diet supplemented with either 15 g. oxytetracycline or 6 g. procaine penicillin per ton in two feeding trials. Fresh liver and kidney homogenates from 4- and 9-week-old chicks were assayed in vitro for xanthine dehydrogenase activity. Oxytetracycline, but not penicillin, significantly inhibited xanthine de-hydrogenase activity per gram of kidney dry matter of 4-week- but not of 9-week-old chicks. Neither antibiotic affected liver xanthine dehydrogenase activity at either age. It is suggested that the growth stimulation observed during the period of rapid growth may be due in part to enhanced nitrogen utilization, resulting from the decrease in renal xanthine dehydrogenase activity.