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The administration of antibiotics to day old chicks as a means of prevention or treatment of suspected hatchery or farm-borne infections is common, especially in developing countries. This practice could contribute to a poor immune response following Newcastle disease (ND)-LaSota vaccinations, in addition to the sluggish growth in broiler chickens. This study was aimed at determining: the antibody titre to ND-LaSota vaccine, live weight, weight gain and feed conversion efficiency (FCE) of broiler chicken exposed early to gentamicin and doxycycline. One hundred, day-old broiler chicks were randomly assigned to four groups (n = 25). Group 1 served as a control, while groups 2 and 4 received gentamycin and doxycycline, respectively. The chicks in group 3 were treated with a combination of gentamicin and doxycycline (1 : 1). All drugs were administered via the drinking water from the 2nd to the 6th day of the chicks’ life. On day 18, the birds received ND-LaSota vaccine intraocularly. At weekly intervals, the post-vaccination antibody titre, live weight and weight gain were determined. The feed conversion efficiency (FCE) of the different groups was calculated at the end of the experiments. The results showed that the NDV antibody titre of the antibiotic-treated groups did not differ significantly (P < 0.05) from that of the control. However, there was a significant (P < 0.05) increase in the live weight, weight gain and FCE of the control birds when compared to the antibiotic-treated groups.