The netB-positive Clostridium perfringens in the experimental induction of necrotic enteritis with or without predisposing factors.

The netB-positive Clostridium perfringens has been considered as the requisite to consistently induce necrotic enteritis (NE). However, use of a netB-positive strain did not guarantee consistent NE reproduction unless high protein diets or Eimeria, conceived as 2 major predisposing factors, was incorporated. To establish a refined model, the roles of dietary fishmeal inclusion, Eimeria inoculation, and netB-positive C. perfringens challenge in NE induction and the confounding effects of Eimeria infection on NE were examined. The results showed that the use of netB-positive C. perfringens without a predisposing factor failed to induce NE. Fishmeal incorporation promoted the occurrence of NE but did not significantly affect the incidence of the disease in conjunction with challenge of netB-positive C. perfringens. However, the additional participation of Eimeria infection in the same induction procedure produced significantly higher numbers of NE cases and promoted more severe lesions in chickens (P < 0.05). Inoculation of Eimeria resulted in a significant higher incidence of NE compared to the non-Eimeria treated group (P < 0.05). The results demonstrated that both netB-positive C. perfringens and predisposing factors were required for the reproduction of disease. Mild-to-moderate coccidial infection (coccidial lesion score ≤ 2) was noted in NE cases in this model but severe coccidial infection did not correlate with the occurrence of NE, indicating mild coccidial infection may be beneficial for the development of NE. If multiple species infection of Eimeria precedes the challenge of C. perfringens, days 19 to 21 (1 to 3 D after the last clostridial challenge) was the time period favorable for observations of NE lesions. The time after this period may be subject to bias of severity, incidence, or mortality of NE owing to the profound coccidial lesions in the intestinal region. This study demonstrated that the co-infection with netB-positive C. perfringens and Eimeria species under fishmeal incorporation produced a desirable NE model, being of value in studying the effectiveness of novel feed additives and alternative mitigation strategies to prevent NE.