Field observations suggest genotype-associated differences in susceptibility to infection with Enterococcus cecorum (EC). We hypothesized that slow-growing (SG) chickens show less clinical signs and reduced lesions compared to fast-growing (FG) chickens after experimental challenge with EC. At 1-day post-hatch (dph), 97 FG and 97 SG chickens were randomly assigned to four groups: control, SG (CSG), control, FG (CFG), EC-inoculated, SG (ESG), and EC-inoculated, FG (EFG). After oral inoculation with 107 colony forming units EC or mock inoculation with physiological saline, chickens were monitored for clinical signs and samples were collected weekly for further analysis via ELISA, real-time PCR, and flow cytometric analysis. The final necropsy of 40 chickens per group was carried out at 43/44 dph. Clinical signs and pathological findings were observed in a reduced number of chickens in group ESG compared to EFG. Extra-intestinal colonization with EC at 43/44 dph was significantly reduced in group ESG compared to EFG (P < 0.05). Circulating heterophils and monocytes were significantly increased in groups ESG and EFG compared to the control groups (P < 0.05). Additionally, circulating monocytes were increased and heterophil/lymphocyte (H/L) ratios were decreased in SG chickens compared to FG chickens. We may speculate that SG chickens were less affected by the EC-associated disease due to a more efficient innate immune response and may more vigorously control extra-intestinal colonization after translocation from the intestine. Overall, the use of slow-growing chickens may reduce the incidence of the EC-associated disease in meat-type chickens and therefore increase overall health performance.
Keywords: Enterococcus cecorum; fast-growing; immune response; lesion development; meat-type chicken; slow-growing.