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 different Salmonella enteritidis oil-emulsion bacterins (an experimentally prepared acetone-killed vaccine and a commercially available vaccine) for protecting laying hens against intestinal colonization following oral exposure to S. enteritidis. Each vaccine was administered twice (4 weeks apart), and all hens were challenged with 10(8) cells of a nalidixic-acid-resistant S. enteritidis strain 2 weeks after the second vaccination. Fecal samples from vaccinated and unvaccinated control hens were cultured at three weekly intervals post-challenge to determine the incidence of intestinal colonization and the numbers of S. enteritidis shed into the environment. Both vaccines significantly reduced the incidence of intestinal colonization (P < 0.05) and the mean number 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 other flock sanitation and infection-monitoring strategies, vaccination with bacterins could potentially reduce the overall level of environmental contamination and thereby also reduce the horizontal transmission of S. enteritidis within and between laying flocks.