Abstract:

Coccidiosis disrupts the intestinal immune homeostasis of the host, serving as a major predisposing factor for Clostridium perfringens (CP)-mediated necrotic enteritis (NE). Among seven chicken Eimeria spp., Eimeria maxima (EM) is the most effective at inducing NE. Accordingly, the objective of this study is to establish a stable and reliable experimental model of NE by evaluating the impact of varying EM challenge doses. A total of 200 14-day-old broilers were divided into 10 groups: the control group, CP challenge group, EM infection groups (with varying infection doses), and EM/CP co-infection groups (with varying infection doses). At 14 days of age, different doses of EM sporulated oocysts were inoculated. 4 days post EM infection, CP isolates were inoculated for the challenge infection. The trial was terminated on Day 20, and all the chickens were sacrificed. The body weights (before the challenge and on Day 20) and the survival rate were recorded, and the lesions of the small intestines were scored. The results showed that with the increase of EM infection dose, the weight gain was gradually reduced in the single EM infection groups, whereas this trend was not observed in the EM/CP co-infection groups. The relative weight gain of the EM/CP1 group was significantly higher than those of the other EM/CP co-infection groups. However, no significant changes were observed across the EM/CP2, EM/CP3, and EM/CP4 groups. The lesion scores in the challenged groups showed a trend similar to the relative weight gains. The intestinal lesions in the EM/CP1 group were less severe than those in the other EM/CP co-infection groups, and there was no significant difference in gut lesions among the EM/CP2, EM/CP3, and EM/CP4 groups. In the EM/CP co-infection groups, the survival rate of the EM/CP2 group was 85%, while the survival rates of the EM/CP3 and EM/CP4 groups were lower, at 80% and 70%, respectively. Based on the comprehensive evaluation of the relative weight gains, intestinal lesions, and mortality, the EM/CP2 group dosage (1×10⁴ oocysts/bird + 1×10⁹ CFUs/bird) was determined to be the optimal infection dose for inducing an experimental model of NE. Consequently, this model provides a valuable research tool for the investigation of NE pathogenesis and the development of vaccines/drugs against NE.

Key words: C. perfringens, Emaxima, necrotic enteritis, dual infection model