| Avian coccidiosis is a severe parasitic disease caused by intracellular protozoa including several species of Eimeria, which severely hamper the development of pourltry industy. Control of coccidiosis is dominated by prophylactic chemotherapy, but drug resistance is a serious problem, along with the public demand for chemical free meat, so it has lead to the requirement for an effective strategy such as vaccine. However, almost all vaccines used presently are active vaccines, have the risk of causing outbreaks of the disease, so it is necessary to develop a more safe method. As a method of passive immune, specific egg yolk immunoglobulin (IgY) can be produced in egg yolk by immunizing hens with specific antigens, then can be isolated in large quantities from yolk by simple methods without distress to the birds, also has attracted much attention and been recognized to be efficient in the therapy and prevention of many animal diseases. In this study, anti-coccidia egg yolk IgY antibodies were prepared, and its protective effects against Eimeria tenella were evaluated.1. Preparation of egg yolk IgY antibodiesHens were orally hyperimmunized6times with live oocysts of three major Eimeria species, E. tenella, E.praecox, and E. maxima. An indirect ELISA method was established to detect serum antibody and yolk antibody after immunization. IgY antibody from hen yolks were extracted by saturated ammonium sulfate(SAS) method, and the purity and molecular weight of IgY was determined by SDS-PAGE, the titer and stability of IgY were detected by indirect ELISA. Results showed that the titers of serum antibodies gradually raised, specific activity has raised gradually from the lth immunization and finally reached to peak titer on15d after the6th times, while the yolk antibody was generally similar with serum, specific activity can be obtained in a long time. The optimization of dilution with water for egg yolk was1:9, and pH5.1was the optimization value for extraction. The purified IgY was consisted of a70KDa heavy chain and a40KDa light chain with the purity achived98%. The titer of purified IgY achived1:140000per milligram. The IgY was stable under different pH environment and temperature, total145g egg yolk IgY was harvest after freeze drying. Above these provided a reliable basis for the next clinical application.2. Protective effects of IgY against E.tenella infectionOne-day-old chickens were randomly divided into9groups of20each, which contained six groups fed with different additive concentration of IgY for10days, one salinomycin medicated group, two groups served as positive and negative control, respectively. At10days post-hatch, all groups except the uninfected control were orally infected with1×104sporulated E. tenella oocysts. After8days postinfection, chickens were weighted and killed, survival rate, weight gain, lesion score, oocyst output, and the anticoccidial index (ACI)were then measured and compared with those of the controls. Results showed that the protective efficacy in the groups fed with1%IgY and0.5%IgY were significantly higher than postive control group and other IgY treated groups, slightly lower than the medicated group. As food safety economy and were considered, the recommended dose of IgY was0.5%. Above these provided a new and safe method for the control of avian coccidiosis. |
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