SUMMARY

Serology is widely used by the poultry industry to detect infections, such as by Mycoplasma ssp and certain salmonellae, and to monitor response to many vaccines. Serology can also form a valuable component of the investigation of clinical and sub-clinical diseases. The planning of routine and ad-hoc serological monitoring and the interpretation of results generated is a significant component of the work of the poultry veterinarian. In order to make best use of serology it is important to understand the physiological basis of the tests, their various advantages and limitations\par \par Some serological tests have now been available for over 60 years but it was the development of Elisa assays in the 1980's which led to marked expansion in the number of tests available. In addition to Elisa tests, other methods continue to be used. These include direct serum or whole blood agglutination tests (mainly for bacterial pathogens), double-immuno-diffusion and haemagglutination-inhibition. Regardless of the method to be used it is vital that samples are taken carefully to provide good quality sera and results which are applicable to the population being tested. Long term frozen storage of samples can help avoid unnecessary testing and allow retrospective studies when new diseases occur or new tests become available. The range of Elisa tests available looks set to continue to grow, albeit at a more gradual rate than the past decade. The much more widespread availability of genetic engineering techniques such as polymerase chain reaction (PCR) is likely to facilitate the identification of small numbers of pathogens in clinical specimens. This information may well be very helpful in conjunction with the equivalent serological data. Quality control schemes governing various aspects of laboratory work are becoming more widely used, and serology is no exception. The data management associated with the running of a busy serological laboratory presents many challenges. A computerized system which facilitates sample identification and the scheduling of tests, as well as the recording of results and generation of reports has been developed.

The serological techniques, although suffering definite limitations, can play an important part, both in the initial investigation of a disease problem, and in the evaluation of the results of the disease control program. The advantages of the serological techniques can be usefully exploited in commercial poultry production in the diagnosis of disease challenge (by demonstrating rising antibody titres independently of vaccination), and the monitoring of circulating antibody response to vaccination. Serological tests can even predict the decay of maternal antibody as an aid to timing certain vaccinations.

Charts have been prepared from a data-base representing 68,776 individual sample assays on broiler parent chickens, 53,532 assays from broilers and 3,354 from layers. The results of blood samples from broiler chickens at slaughter are used to illustrate the value of serology in the monitoring of field challenge. Extensive data from broiler parent chickens in the UK can be used to illustrate the monitoring of primary and secondary vaccinal responses.