EVALUATION OF THE EFFICACY OF OIL-EMULSION BACTERINS FOR REDUCING FECAL SHEDDING OF SALMONELLA-ENTERITIDIS BY LAYING HENS

Two replicate experiments were conducted to test the efficacy of two d ifferent Salmonella enteritidis oil-emulsion bacterins (an experimenta lly prepared acetone-killed vaccine and a commercially available vacci ne) for protecting laying hens against intestinal colonization followi ng oral exposure to S. enteritidis. Each vaccine was administered twic e (4 weeks apart), and all hens were challenged with 10(8) cells of a nalidixic-acid-resistant S. enteritidis strain 2 weeks after the secon d vaccination. Fecal samples from vaccinated and unvaccinated control hens were cultured at three weekly intervals post-challenge to determi ne the incidence of intestinal colonization and the numbers of S. ente ritidis shed into the environment. Both vaccines significantly reduced the incidence of intestinal colonization (P < 0.05) and the mean numb er of S. enteritidis cells shed in the feces (P < 0.01) at 1 week post -challenge. However, the degree of protection afforded by vaccination was only partial, as more than half of the vaccinated hens still shed substantial numbers of S. enteritidis. If used in conjunction with oth er flock sanitation and infection-monitoring strategies, vaccination w ith bacterins could potentially reduce the overall level of environmen tal contamination and thereby also reduce the horizontal transmission of S. enteritidis within and between laying flocks.