| Objective: To understand the prevalence of respiratory diseases in large-scale chicken farms in Xinjiang,and to master the immune effects of AI,ND,and IB diseases in these chicken farms.In this study,epidemiological investigation on respiratory diseases was carried out in large-scale chicken farms in some areas of Xinjiang.Some chicken farms with serious respiratory diseases were selected for dynamic monitoring of immune antibodies and maternal antibodies against AI,ND,and IB.Finally,the immune scheme was optimized according to the above research results.Methods:(1)The incidence and mortality of respiratory diseases in 10 large-scale chicken farms in Xinjiang were investigated by field epidemiological investigation from December 2020 to December 2021.(2)Immune antibodies against AIV(H5,H7 and H9),NDV and IBV in four large-scale chicken farms with serious respiratory diseases were dynamically monitored by the hemagglutination/hemagglutination inhibition test(HA/HI)and ELISA methods.(3)The decline changes of maternal antibodies AIV(H5 subtype,H7 subtype and H9 subtype),NDV and IBV in the above four large-scale chicken flocks were studied by HA/HI and ELISA methods.(4)Based on the comprehensive analysis of the above test results,the original immunization program was optimized and a new immunization program was developed.300 chicks were randomly divided into 6 groups and immunized with the optimized immunization program and the original immunization program respectively,blood samples were collected at 35,50 and 70 days of age respectively,and the level of AIV antibodies was detected by HA/HI test.Results:(1)The morbidity and mortality of respiratory diseases in large-scale chicken farms in Northern Xinjiang were generally higher than those in southern Xinjiang.Incidences in the first Farm and the second farm of Northern Xinjiang were most serious,in which the morbidity rate were 39.8% and 36.6% respectively,and the mortality rate were 25.8% and 24.5% respectively.(2)During the whole feeding cycle,the average antibody titers of H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV(Re-3)and H9 subtype AIV were maintained between 3log2 and 6log2,and the antibody qualification rate were maintained between 60%and 90%;The average antibody titers of NDV were above 6log2,and the qualified rate of antibody were maintained between 85%～95%;The antibody qualification rate of IBV were maintained between 70% and100%.The immune antibody level and qualification rate of NDV and IBV immune antibodies were both high,which can protect the immunized chickens from the invasion of NDV and IBV,the immune effect of NDV and IBV were both good.But the immune antibody level and qualification rate of AIV were generally low,which can not completely protect the immunized chickens from the invasion of AIV.So it is necessary to further optimize the AIV immunization program.(3)The maternal antibodies against NDV,AIV and IBV all reached the peak at 1 day of age,then decreased gradually with the increase of the age.The maternal antibody level of H9 subtype AIV was the highest and maintained for the longest time,while the maternal antibody levels of IBV,NDV,H5 subtype AIV and H7 subtype AIV were relatively low.The half-lives of maternal antibodies of NDV,H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV,H9 subtype AIV and IBV were 4.85 d,5.58 d,4.25 d,5.09 d,6.03 d and 3.99 d respectively.(4)The antibody titers of H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV(Re-3)and H9 subtype AIV in the optimized immune program group were significantly higher than those in the original immune program group at the age of 28～70 days(P < 0.01).The antibody level titers of H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV(Re-3)and H9 subtype AIV in the chicken flocks with the optimized immunization program were maintained between5 log2 and 9 log2,and the antibody qualification rate all reached above 90%.The immunization effect was significantly better than that of the chicken flocks with the original immunization program.It is indicated that the optimized immune program is superior to the original immune program of the scale field.Conclusion:(1)The morbidity and mortality of respiratory diseases in large-scale yellow feather broiler farms in Northern Xinjiang were higher than those in southern Xinjiang.(2)The half-lives of maternal antibodies of NDV,H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV,H9 subtype AIV and IBV were 4.85 d,5.58 d,4.25 d,5.09 d,6.03 d and 3.99 d respectively.(3)When Implement optimized immunization procedures,the antibody level titers of H5N1 subtype AIV(Re-11 and Re-12),H7N9 subtype AIV(Re-3)and H9 subtype AIV were maintained between 5 log2 and 9 log2,and the antibody qualification rate all reached above 90%.It indicates that the optimized immunization program is effective. |
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