This study was conducted to determine the effects of some different antibacterial drugs used in the poultry industry for their effects on the immune system of poultry. This experiment was carried on a hundred and fifty Ross PM-3 type, daily broiler chicks. Oxytetracycline and amoxicillin used in treatment of drinking water, and zinc bacitracin and salinomycin capable of being continuously added to feed in anabolic and preservative concentrations were chosen as antibacterial drug samples. In the first 21 days of their lives the broilers were fed with a chick starter feed, that did not contain any antibacterial or anticoccidial agents, later with chick development feed ad libitium. On the 19 th day of their lives blood samples were taken from all chicks and maternal antibody titers against Newcastle disease virus were determined. According to the experimental alternatives chicks were divided into five experimental groups of 30 animals and live Newcastle vaccine was applied in drinking water on the 19 th day. While one of the groups was left as a control group, oxytetracycline and amoxicillin were given respectively to the 2 nd and 3 rd groups in drinking water at treatment dose for 3 days, also zinc bacitracin and salinomycin were given to the 4 th and 5 th groups respectively continuously in the feed. For 3 days after the application of the drug, by taking the blood samples from the 2 nd and 3 rd groups, the concentration of the antibacterial drugs were determined and at the 7 th , 14 th and 28 th days the antibody titers against Newcastle were determined. Twenty-eight day after vaccination 10 animals were slaughtered from each group to determine the lymphocyte concentration of Bursa fabricius and timus. The results were as follows: The maternal antibody levels developed against Newcastle vaccine were 4.4 in 19 day old chicks, four weeks later, an increase was found in the control group, vaccinated under the same conditions. At the end of the same period of time, Newcastle antibody levels reached approximately 7.7, while the antibody levels stayed at 5.7, 5.8, 6.1 and 5.6 levels and did not show any increase in the and 3 rd , 4 th and 5 th groups, respectively. On the 47 th day of the experimental period the live weights of all chiks were determined. All experimental groups treated increased liveweight 8.5-19.46 % compared with the control group. The weights of Bursa fabricius (BF) and thymus (T) of slaughtered animals increased (BF/T) 6.7/18 %, 4.4/21 % and 17/22 % in chicks treated with oxytetracycline amoxycillin and zinc bacitracin, respectively and were decreased 57.2/1.4 % in chiks treated with salinomycin compared with the control group. The average Iymphocyte concentration of BF and T of all groups were determined to be lower than in the control group. The lowest value was observed in the fifth group, effect followed by the second, third and fourth groups. It is concluded that and amoxicillin with a therapeutic effect and zinc bacitracin and salinomycin with an anabolic effect can depress the cellular immunity and according to this can depress the humoral immunity. Therefore the expected effect of immunisation after vaccinations can be reversed.

This study was conducted to determine the effects of some different antibacterial drugs used in the poultry industry for their effects on the immune system of poultry. This experiment was carried on a hundred and fifty Ross PM-3 type, daily broiler chicks. Oxytetracycline and amoxicillin used in treatment of drinking water, and zinc bacitracin and salinomycin capable of being continuously added to feed in anabolic and preservative concentrations were chosen as antibacterial drug samples. In the first 21 days of their lives the broilers were fed with a chick starter feed, that did not contain any antibacterial or anticoccidial agents, later with chick development feed ad libitium. On the 19 th day of their lives blood samples were taken from all chicks and maternal antibody titers against Newcastle disease virus were determined. According to the experimental alternatives chicks were divided into five experimental groups of 30 animals and live Newcastle vaccine was applied in drinking water on the 19 th day. While one of the groups was left as a control group, oxytetracycline and amoxicillin were given respectively to the 2 nd and 3 rd groups in drinking water at treatment dose for 3 days, also zinc bacitracin and salinomycin were given to the 4 th and 5 th groups respectively continuously in the feed. For 3 days after the application of the drug, by taking the blood samples from the 2 nd and 3 rd groups, the concentration of the antibacterial drugs were determined and at the 7 th , 14 th and 28 th days the antibody titers against Newcastle were determined. Twenty-eight day after vaccination 10 animals were slaughtered from each group to determine the lymphocyte concentration of Bursa fabricius and timus. The results were as follows: The maternal antibody levels developed against Newcastle vaccine were 4.4 in 19 day old chicks, four weeks later, an increase was found in the control group, vaccinated under the same conditions. At the end of the same period of time, Newcastle antibody levels reached approximately 7.7, while the antibody levels stayed at 5.7, 5.8, 6.1 and 5.6 levels and did not show any increase in the and 3 rd , 4 th and 5 th groups, respectively. On the 47 th day of the experimental period the live weights of all chiks were determined. All experimental groups treated increased liveweight 8.5-19.46 % compared with the control group. The weights of Bursa fabricius (BF) and thymus (T) of slaughtered animals increased (BF/T) 6.7/18 %, 4.4/21 % and 17/22 % in chicks treated with oxytetracycline amoxycillin and zinc bacitracin, respectively and were decreased 57.2/1.4 % in chiks treated with salinomycin compared with the control group. The average Iymphocyte concentration of BF and T of all groups were determined to be lower than in the control group. The lowest value was observed in the fifth group, effect followed by the second, third and fourth groups. It is concluded that and amoxicillin with a therapeutic effect and zinc bacitracin and salinomycin with an anabolic effect can depress the cellular immunity and according to this can depress the humoral immunity. Therefore the expected effect of immunisation after vaccinations can be reversed.