Immune parameters monitored during the production period of laying hens managed with or without single-dose vaccination against erysipelas

BACKGROUND: Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER), is an emerging disease in non-cage housed laying hens. According to Swedish field experience outbreaks seem more common in older flocks and may also occur in flocks vaccinated against erysipelas. This cross-sectional study aimed to assess single-dose vaccination outcome in laying hens with respect to antibody titres to ER and to monitor selected immune parameters to identify putative risk factors for erysipelas. Blood samples were collected from laying hen flocks at 30, 50 and 75 weeks of age. At each time point, 5 unvaccinated flocks and 5 flocks that had been vaccinated against erysipelas once at placement were sampled (20 hens/flock, total n=600). RESULTS: The results showed that the majority of hens were positive for IgY to ER and that the antibody titres were higher in older hens irrespective of vaccination status. Vaccinated hens had significantly higher IgY titres to ER compared to those of unvaccinated hens. This difference was most prominent for the youngest age category. Among the different leukocyte populations studied, blood heterophil, monocyte and γ/δTCR+ T-cell counts were significantly higher in younger hens. Also, serum MBL-levels were significantly higher in younger hens and MBL-levels were positively correlated to heterophil and monocyte counts at the individual level. CONCLUSIONS: Taken together, results indicate that ER or antigenically similar bacteria are common in the hen environment and that this exposure results in antibodies recognising ER that are present at higher levels in older laying hens. In addition, a higher general pathogen load/level of subclinical infections was indicated by altered leukogram patterns and increased MBL-levels in the youngest age category. Nonetheless, among the parameters studied we found no evidence to suggest that antibody responses to single-dose vaccination should fail or why older flocks seem more susceptible to erysipelas outbreaks.