Developing an experimental necrotic enteritis model in turkeys - the impact of Clostridium perfringens, Eimeria meleagrimitis and host age on frequency of severe intestinal lesions

Abstract Background: Little information exists concerning the pathogenesis, immunity, microbiota or experimental reproduction of turkey necrotic enteritis. Necrotic enteritis in turkeys and chickens differ with regard to important aspects. The objective of this study was to contribute to the development of in vivo experimental models of necrotic enteritis in turkeys. Results: A four tier (0-3) scoring system with clearly defined degrees of severity of macroscopic intestinal lesions was developed, based on 2312 photographic images of opened intestines from 810 B.U.T. 10 or B.U.T. Premium turkeys examined in nine experiments. Loss of macroscopically recognizable villi in the anterior small intestine was established as the defining lesion qualifying for a score 3 (severe intestinal lesions). The developed scoring system was used to identify important factors in promoting high frequencies of turkeys with severe lesions: a combined Eimeria meleagrimitis and Clostridium perfringens challenge, challenge at five rather than three weeks of age, the use of an Eimeria meleagrimitis dose level of at least 5 000 oocysts per bird and finally, examination of the intestines of 5-week-old turkeys at 125 to 145 hours after Eimeria meleagrimitis inoculation. Numbers of oocysts excreted were not influenced by Clostridium perfringens inoculation or turkey age. Three different outcome variables (median lesion score, frequency of severe lesions and frequency of mucosal pseudomembranes/ulcers/depressions) were compared regarding ability to differentiate statistically between effects of dissimilar combinations of Clostridium perfringens inoculation and turkey age at challenge. Frequency of severe lesions was the superior outcome variable in this comparison. Conclusions: This study represents a first and major step forward in the development of in vivo experimental models of necrotic enteritis in turkeys.