Histopathologic Assessment of Gut for Poultry Production and Applied Research

The ongoing transfer of science and technology is a defining feature of the efficiency and success of commercial poultry production. Meeting the nutritional, environmental, and health needs of every bird is key to realizing genetic potential and providing for well-being. To monitor and quickly identify developing problems, basic knowledge and skills in pathology are learned by almost everyone involved in live production. To add value to the standard postmortem procedure, we describe a method of applying histopathology (microscopic pathology) to digestive health surveys in broilers, turkeys, and commercial layers and to field and floor-pen research trials. 

 

In developing this method, principles were borrowed from toxicologic pathology as well as pharmaceutical and biological safety testing. In these fields, testing is performed in laboratory animals of defined genetics that are kept in controlled environments and fed uniform diets.  Within these systems, the disease is defined as any departure from normal caused by a known toxin, product or infectious agent.    

 

Pathology is a key part of the assessment process, performed at specific times or ages after exposure. The assessments are carried out using standard operating procedures that lead to thorough examinations of either all body systems, or perhaps narrowed to target organs.  The pathology assessment includes recording of any lesions observed at necropsy (animal autopsy, postmortem examination), and lesions that are detected by histopathology.   

 

Fundamental to the pathology examination are 1) presence or absence of a lesion; 2) the lesion severity; and 3) assessment of incidence and severity differences from expected normal for the test population. The latter takes into consideration age, genetics, and spontaneous pathology, and/or comparisons to internal controls in the study.  The process becomes progressively complicated as multiple lesions are found, each requiring assessment according to standard procedures for scoring severity with analysis to determine significance.  It is labor intensive and detailed work performed by a pathologist. Because the process is standardized, however, the results are reproducible (if the protocols are followed) even when the analysis is conducted by independent parties. It also allows development of data sets that can be monitored over time for changes in disease expression within a group or between groups.    

 

From a broad perspective, commercial poultry fit this model reasonably well: animal populations of uniform genetics, consuming a uniform diet, and raised under relatively uniform housing and management programs with good to excellent biosecurity.  From any production program, it is possible to select birds of specific ages, on specific management or nutritional programs, and make a uniform pathologic assessment according to standard procedures, and obtain reasonably reproducible results by persons trained in the evaluation methods.

 

 

 

When combined with surveys of the immune system, the gut issues can be seen from the perspective of lymphoid organ stress associated with viral enteritis, the effect on the bursa of Fabricius of acute and recovery stages of infectious bursal disease, and thymus atrophy from infection by chicken infectious anemia virus following decline of maternal immunity (2, 3).