Lesion Scoring in Poultry

Gross pathology is a valuable tool for diagnosis; considering the rapid autolysis of tissue in dead animals, it is preferable to sacrifice 5 birds of a flock during the risk periods (chickens of 28 and 35 days old). This allows the  identification of the species by means of appearance and site of the macroscopic lesions. These lesions are specific to each species infecting chickens.

Identification of lesions in birds which are dead for more than one hour could be difficult because of post mortem changes in the intestinal mucosa.

Johnson and Reid (1970) established a scale for the different types of intestinal lesions. Their lesion scores from 0 to 4 are still used today routinely for the diagnosis of coccidiosis and for evaluation of the efficacy of anticoccidials in the control of infections by coccidia. The lesion scores were established more particularly to evaluate the severity of the infection, but they may also help to identify the species of coccidia.

Beginning with the duodenum, the intestine is opened and both the mucosal surface and the serosal surface are examined for lesions. A good light source is essential in order to establish the lesion scores. Scoring the lesions caused by certain species is not always easy during multiple infections or when necrotic enteritis is present. Microscopic examination of the scrapings of intestinal mucous membranes or of faeces then yields better information.

Microscopic examination of the scrapings of mucous membranes taken from different sites of the intestine makes it possible to confirm or refute the presence of coccidia and may help with the identification of species when the site is taken into consideration.