| Avian coccidiosis is caused by one or several different species of the genus Eimeria,which parasitize epithelial cells of the intestinal mucosa,and it is one of the most important parasitic diseases with great economic impact on the poultry industry worldwide.In this study,Eimeria necatrix and Eimeria acervulina,which cause substantial losses in chicken production,were studied,and the immune effects of the individual strains of the precocious vaccine strains of E.necatrix or E.acervulina and the mixed strains were compared to analyze whether there was an interaction correlation between the immunity of E.necatrix and E.acervulina.The results of this study will provide baseline data for the production and application of live vaccines for chicken coccidiosis.The optimal infectious doses of the first,second and third immunizations were determined by the relevant research test as 140/feather(or 420/feather),12,000/feather,and 12,000/featherrespectively.The chickens were orally administered the first immunization with E.necatrix and E.acervulina at different doses(i.e.,140/featherand 420/feather,respectively)and a mix of E.necatrix and E.acervulina at 3 days old.The chickens were then orally administered the second and third immunizations,with doses of 12,000/feather,at the ages of 10 days and 17 days,respectively.After the second and third immunizations,the challenge experiments were conducted.The chickens were challenged with individual virulent strains of E.acervulina or E.necatrix at 17 days old and 24 days old.The relative oocyst yield,relative weight gain rate,intestinal lesion score and feed intake were indicators to evaluate the immune interaction between E.acervulina and E.necatrix.After challenging with virulent E.acervulina,the relative weight gain rates of all the E.acervulina immune groups were between 86.41%～95.73% and 94.92%～99.11%,and the intestinal lesion scores were between 0.95 ～ 1.81 and 0.63 ～ 1.96 for two immunizations and three immunizations respectively,showing no obvious difference.After challenging with virulent E.necatrix,the relative weight gain rates of all the E.necatrix immune groups were between 48.92%～72.98% and 80.73%～90.69%,and the intestinal lesion scores were between 1.1～2.85 and 0.53～0.96 for two immunizations and three immunizations respectively,which revealed the immune protection effect of three immunizations was better than that of two immunizations.The results showed that after three immunizations,the relative weight gain rate of the E.necatrix and E.acervulina mixed immunization group was lower than that of E.acervulina-immunized alone in the E.acervulina challenge experiment and higher than that of E.necatrix-immunized alone in the E.necatrix challenge experiment.The intestinal lesion score in the E.necatrix and E.acervulina mixed immunization group was higher than that of E.acervulina-immunized alone in the E.acervulina challenge experiment and lower than that of E.necatrix-immunized alone in the E.necatrix challenge experiment.Therefore,it was concluded that the immune protective effect of the E.necatrix and E.acervulina mixed immunization was stronger than that of E.necatrix immunization alone in the E.necatrix challenge experiment.However,the immune protection of the mixed immunization was slightly lower than that of E.acervulina immunization alone in the E.acervulina challenge experiment,although mixed immunization was still protective against E.acervulina. |
