Nowadays using of live and killed vaccines is usually done to prevent Newcastle disease of poultry; however, some of the poultry farms are being encountered with this disease, because the available vaccines do not produce enough antibody titres. In this research, an attempt was made to investigate the effect of using an immune stimulator named Hypericum perforatum on antibody production against Newcastle vaccine. 450 broiler chicks (Ross 308) were divided into five groups and three replicates of 30 chicks per replicate. For six weeks, various doses of dry extract (16, 20/5, 24/5 and 28/5 mg/kg) ofH. perforatum were administered in drinking water to four treatment groups and placebo was administered to the control group. All groups received Newcastle vaccines on days: 11, 19 and 38. Subsequently, on days 10, 25, 34 and 42 blood samples were taken from each group and Newcastle antibody titres were defined by HI test. This experiment showed that the use of H. perforatum in each of the foregoing doses, had increasingly effects on antibody titres and this fact is significant between the control group and treatment groups. By using Duncan multiple range test, it was determined that this effect is significant in the case of 1st, 2nd and 3rd groups at 25th days results, but at 34th and 42nd days results, all groups show the same range of titres.
Key words: Hypericum perforatum, B1, La Sota, antibody titers, HI test and broiler chicks.
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