-Starting at the farm with the collection of data on disease history, combined with initial post mortems. Further investigations require a laboratory to proceed with different techniques and disciplines.

 Sample selection

Normal, healthy individuals should provide serum samples for routine serological investigation.  Birds must be in good health (Sick or distressed cull birds) should not be used since their antibody titers are usually not indicative of the general health status of the flock. Blood samples, however, taken from birds displaying the clinical symptoms or lesions of the expected pathogen or syndrome during a possible disease inquiry.
It's crucial to choose birds for caged housing systems from different parts of the house. The same birds (or cages) should be used for blood collection when a flock is enrolled in a routine serology program. When compared to drawing blood from various birds for each test, this will lessen the variation in results. 

Ages for routine blood collection in breeder flocks

1.  10 to 12 weeks .

2.  At time of transfer (grow to lay farm) .

3.  Every 10 to 12 weeks during egg production .

 Ages for routine blood collection in commercial layer flocks  :

1.  One time prior to transfer (grow to lay farm) . 

2.  Every 10 to 12 weeks during egg production  .

 Pathogen detection from suspected material for definite diagnosis :

-Routine samples include whole blood, serum, formalin-fixed tissue and swabs: (tracheal, oropharyngeal, cloacal, organs and joints). 

-For specific investigations, PCR, rt-PCR, whole blood or isolates from any type of swab.

Virology

Poultry is the host of numerous viruses. PCR-based viral infection diagnosis has emerged as the preferred technique due to its quick nucleic acid detection. However, isolation is frequently required to deal with functional elements of the disease or to get antigen for the creation of vaccines. Specific application of PCR is a DIVA (differentiating infected from vaccinated birds) PCR, a method used for screening a vaccinated flock for infections with a filed/virulent strain, The initial isolation of a virus depends mainly on adaptation and propagation in embryonated specific pathogen-free (SPF) chicken eggs and cells obtained from those embryos or hatched SPF birds.

Bacteriology

A certain trend to introduce molecular techniques (PCR) that complement or substitute classical bacteriology. The clinical picture and post mortem findings cannot be attributed to a specific bacteria or fungi. Therefore, one of the main goals of bacteriological and fungal examination in diagnostics is the isolation of the pathogen. In addition to disease diagnosis, culturing of bacteria is also obligatory for some surveillance programs, such as that of Salmonella, which are based on the isolation of live bacteria

Parasitology

Diagnoses of poultry parasites depends particularly on macroscopically and microscopically examination. 

Serology

In contrast to the isolation or detection of infectious agents, especially viruses, serological testing is fast and easy to perform with minimal laboratory requirements. Primarily, it focuses on the presence, absence or level of specific antibodies in the serum. In practice, antibodies can be detected in egg, tears, saliva, and mucus secretion.

Many of the classical serological techniques (e.g., the agar gel precipitation test, plate agglutination tests (RSA), and hemagglutination inhibition tests (HI)) have been employed for decades; standardized reference sera and antigens for many poultry pathogens are commercially available worldwide. Considering the high flexibility, quick turnaround and the large sample size to be processed at a time, ELISA assays have become routine procedures for flock health monitoring and for poultry diagnostics alike, with commercial systems available for the majority of poultry pathogens.

Serology importance:

 The study of serum antibody levels, also known as titers. The immune system develops antibodies that circulate in the blood after a bird is exposed to an antigen, whether by vaccination or exposure to a wild-strain pathogen. Antibodies are found in the serum portion of blood (the liquid portion after the clot develops). Serum is free of all blood cells and clotting factors. The flock’s serum antibody titers are used to monitor efficacy of vaccination programs, evaluate field challenges or diagnose disease. The value of this information depends on the quality of the serum samples received by the laboratory. Poor quality samples lead to erroneous and misleading results. Selection of birds for blood collection, techniques used to collect blood, and handling of blood samples and serum all influence laboratory results.

NB: Selection of Birds For routine serological monitoring, serum samples should be collected from normal, healthy birds. Do not use cull birds that are sick or appear distressed, as their antibody titers are not typically representative of the overall flock health status. During a potential disease investigation, however, blood samples should be collected from birds that are exhibiting the clinical signs or lesions of the suspected pathogen or syndrome.

Number of Samples Twenty good quality serum samples should be collected for routine flock profiling and for disease investigation; however, a minimum of 10 samples may be sufficient to estimate flock antibody titers.