By Dr Balkar Bains
For the past few years there has been a significant and continuing shift in the use of anticoccidial prophylaxis, particularly in broiler flocks. There are several factors that support the current trend, including the incidence of sub-clinical and clinical coccidiosis, potential loss of efficacy of anticoccidial compounds such as Ionophores or development of resistance in case of chemical anticoccidial compounds. The anticoccidial program also aims to prevent the occurrence of a clinical coccidiosis and thus ensures optimum bird health and welfare.
Factors influencing coccidiosis
The incidence of coccidiosis under practical conditions is often influenced by the concurrent husbandry and management practices. In commercial broiler flocks, both the sub-clinical or clinical coccidiosis is most commonly diagnosed and treated between 20 – 28 days of age.
Effective anticoccidial programs
The most popular and effective current anticoccidial programs are aimed at inducing immunity to coccidia in broiler flocks by the age of 35 days. The immunity program necessitates the use of anticoccidials that permits controlled challenge and yet effectively prevents the occurrence of clinical coccidiosis under practical conditions. For the immunity program to be effective, its imperative that immunological competence of the chicken must be at its optimum. The two most common and endemic viral infections in broiler flocks that are associated with immunosuppression include Infectious Bursal Disease Virus (IBDV) and Marek’s Disease Virus (MDV).
Influencing the coccidia lesions
Both IBDV and MDV have the potential to influence the coccidia lesions by negatively influencing immune response to coccidia challenge. The exposure to coccidia challenge and both viral infections frequently experienced during the first two weeks of age. The influence of concurrent infection by single or both viruses in commercial flocks has the potential to exaggerate coccidia lesions, mortality from coccidiosis and adversely effect commercial parameters. The concurrent infection may lead to the misdiagnosis of coccidiosis or misinterpretation of efficacy of anticoccidials in use.
Both of these viruses have the potential to generate pathogenic variant strains that are not effectively controlled by routine standard measures in practice. The poultry industry is well aware of the significant economic losses due to infections caused by both IBDV and MDV in commercial broiler flocks in the recent past. The major causes of economic losses in the commercial flocks were attributed to immunosuppression and higher incidence of concurrent infections such as E.coli and coccidiosis and vaccine failures etc. The current practice of vaccination for the control of both IBDV and MDV is not without potential immunosuppression and thus adversely affecting the immune response.
Both IBD and MDV are not only endemic in commercial poultry flocks but also have caused significant economic losses due to the emerging new strains of the virus that were not controlled by routine measures. There is potential risk that these viral infections individually or concurrently would directly influence the incidence of coccidia lesions, clinical coccidiosis and immunity to coccidiosis. It is also worth considering that the presence of coccidia lesions or inadequate immune response may be an indicator of a concurrent infection with either of the viruses.
Dr Balkar Bains has extensive experience in poultry farming in Australia and throughout Asia from a diagnostic lab and field perspective. With particular focus on optimizing health of broiler and breeder flocks, hatchability and fertility problems in the hatchery, hygiene and food safety issues, and disease prevention and treatment strategies.
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