Different Doses of Commercial Eimeria Vaccines Were Not Effective to Induce a Successful Necrotic Enteritis Challenge Model in Broilers

Necrotic enteritis (NE) is often induced in broilers after getting infected with coccidiosis. However, not all sources of Eimeria, as a causative agent of coccidiosis, can successfully induce NE.

This study was conducted to assess whether different doses of Eimeria combinations predispose broiler chickens to NE, compared with the NE challenge model used at UNE. A total of 768 d-old Cobb 500 broiler chicks were assigned to 48 floor pens each stocked with 16 birds replicated 6 times per treatment. The treatments were: unchallenged birds (NC); Eimeria challenged birds with vaccine strains used at UNE model (E. acervulina 5000, E. maxima 5000 and E. brunetti 2500 oocysts, Eimeria Pty Ltd.) (EUNE); NE challenged birds with Eimeria used at UNE (E. acervulina 5000, E. maxima 5000 and E. brunetti 2500 oocysts) plus C. perfringens (UNEM); challenged birds with Emeria vaccine (E. acervulina 5000, E. maxima 5000 and E. brunetti 2500 oocysts) and C. perfringens plus supplemented with in-feed antibiotic and anticoccidial drugs (PC); challenged birds with higher dose of vaccine A (E. acervulina 5000, E. maxima 10000 and E. tenella 15000 oocysts) plus C. perfringens (HVACP); challenged birds with lower dose of vaccine A (E. acervulina 2500, E. maxima 5000 and E. tenella 7500 oocysts) plus C. perfringens (LVACP); challenged birds with higher dose of vaccine B (E. acervulina 5000, E. maxima 10000, E. mitis 10000 and E. tenella 15000 oocysts) plus C. perfringens (HVBCP); challenged birds with lower dose of the vaccine B (E. acervulina 2500, E. maxima 5000, E. mitis 5000 and E. tenella 7500 oocysts) plus C. perfringens (LVBCP). The challenged birds were orally inoculated with Eimeria on d 9 and C. perfringens on d14. Bird performance was measured on d 8-19 and 0-35 and oocyst counts were determined in pooled excreta collected during d15 to17, and in ileal and caecal contents at d 16. The JMP 16.0 statistical package was used for analyzing the data and the female percentage was used as a covariate for performance data after the feather DNA sexing was employed to determine the sex of the birds.From d 0- 35, weight gain (WG) reduced (P < 0.001) in EUNE (2351g) and UNEM (2360) birds compared to NC (2573), PC (2539) and HVBCP (2527) birds, with other challenged groups being intermediate. FCR increased (P < 0.01) in UNEM (1.481) birds compared to NC (1.398), PC (1.421), LVACP (1.421), HVBCP (1.419) and LVBCP (1.423) birds, with the other groups being intermediate. No significant differences for FI were observed between any groups on d 35. From d 8-19, FCR increased (P < 0.001) in EUNE (1.343), UNEM (1.343) and PC (1.365) groups compared to NC (1.268) and LVACP (1.276) groups, with other groups being intermediate. FI increased in PC (885g) birds compared to EUNE (810), LVBCP (807) and LVACP (797) birds, with other groups being intermediate. In terms of oocyst counts, the EUNE and UNEM groups had higher oocyst counts (P < 0.001) in caeca (455222, 455222), ileum (38767, 60833) and excreta (117458, 86958) compared to NC (133, 33, 39), PC (967, 442, 74), HVBCP (7558, 8442, 13060) and LVBCP (1767, 1317, 12244) birds. No significant differences were observed in caecal and ileal oocyst counts between EUNE, UNEM, HVACP and LVACP birds.

The data obtained in this experiment suggest that birds received Eimeria used at UNE, successfully induced NE impairing bird performance and increasing the number of occysts in caecal, ileal and excreta contents but not vaccines.