The influence of chlortetracycline on the immunological reactivity of chickens

Morphological examination of spleen and bursa of Fabricius of chickens fed on a diet without or with the addition of chlortetracycline (50, 100 and 200 CTC mg/kg) has shown that both low and high doses of antibiotic in the diet do not influence significantly the structure and reactivity of the lymphatic tissue following the antigenic stimulation. Certain differences were found in the number of lymphatic follicles in the spleen between control and experimental animals which received the highest dose 200 mg CTC/kg but even the greatest differences found on the fifth day after vaccination were not significant (P<0.1). On the other hand, the study of the level of agglutinin titres in the blood of control and experimental broilers has shown that the doses 100 and 200 mg CTC/kg in the diet have significantly influenced their production. After such doses the latent period was slightly lenghtened and both the highest and the average titres were lowered during the whole postvaccinal period to a degree which correlated the magnitude of dosage of the antibiotic.