To prevent it we should count with a strict biosecurity program, which includes a vaccination plan. The poultry companies have available different types of vaccines, like the classic with active and inactivated virus, the immune complex and vectored or recombinant vaccines, as well as laboratory tools to carry on the evaluation of the flock response to the vaccination program. There are three types of ELISA tests for the detection and quantification of antibodies against the IBD virus. The commercial kits use as viral antigen produced in cell culture, one that uses only the VP2 recombinant protein virus, and one that contains the complete virus produced in the bursa of Fabricius.

To adequately assess the estimated immune response due to vaccination, the most adequate laboratory test, according with the type of vaccine. The base line creation, or serological profiles of the flock that have excellent performance parameters, allow the poultry companies to establish the antibody titers that are considered as normal, as well as the lower and upper limits that constitute the range of the curve of the results of antibodies produced by the vaccination program and the general management of the farm. The comparison of the serological results with flocks with less performance, regarding the expected base line, can help to improve the productive index in those flocks to make them have a serological profile similar to those flocks with a better performance. Besides the serological profile, the effectiveness of the vaccination program can be supplemented by an histological study of the primary lymphoid organs, like thymus and the bursa of Fabricius.

The integrity of these organs will be the indicator of protection of the immunocompetent system, which is related to the health status of the flock and, therefore, with the performance expectation that may be accomplished in the commercial broiler flocks.

The economic investment that is carried out with the periodic serological assessment that follows up the humoral immune response as a consequence of the vaccination will be recovered with profits when the deviations are detected in the expected antibody titers in certain age, and allow to make decisions that amend the situation or reduce the negative impact in such deviations. Maybe, the mayor benefit in the base line is the increase in performance from less productive flocks, by accomplishing a serological profile similar as those in the best flocks. For example, the comparison of the antibody titers at 21 days of age, in some broiler flocks the received a recombinant vaccine HVT-IBD, show that when the antibody titers were higher than 7 000, the feed conversion, the final weight and liveability percentage were better than in the flocks with lower titers than 4 000, regardless if the titers at 42 days were similar.

Dr. Rubén Merino Guzmán