INTESTINAL HUMORAL IMMUNE RESPONSE AND RESISTANCE TO SALMONELLA CHALLENGE OF PROGENY FROM BREEDERS VACCINATED WITH KILLED ANTIGEN

Authors: Bailey, Joseph; ROLON, A - UNIVERSITY OF GEORGIA; HOFACRE, C - UNIVERSITY OF GEORGIA; Holt, Peter; WILSON, J - UNIVERSITY OF GEORGIA; Cosby, Douglas; Richardson, Larry; Cox Jr, Nelson

Submitted to: International Journal of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2007
Publication Date: 6/1/2007
Citation: Rolon, A., Bailey, J.S., Hofacre, C.L., Holt, P.S., Wilson, J.L. 2007. Intestinal humoral immune response and resistance to salmonella challenge of progeny from breeders vaccinated with killed antigen. International Journal of Poultry Science. 6(6):417-423.

Interpretive Summary: Salmonella in broiler chickens continues to be a primary concern for regulatory and public health agencies and the U.S. Poultry Industry and these groups acknowledge the need to develop effective on-farm intervention strategies to reduce consumer exposure to Salmonella. Different combinations of live and killed cell Salmonella vaccines were administered in a commercial operation to broiler breeders. The immunological response was measured in breeder birds and the response to Salmonella colonization was measured in their progeny. Vaccine treatments were shown to elicit an immunological response in breeders and progeny, but progeny were not protected from Salmonella colonization unless a live vaccine was administered. Data from this study will allow poultry producers and vaccine companies to make scientifically proven informed decisions about the best times and types of vaccination treatments to help reduce Salmonella in broiler breeders.

Technical Abstract: Salmonella vaccination programs using killed bacterins in breeders and live auxotrophic-strain vaccines early in the life of their progeny have gained popularity in today’s poultry industry. In this study we evaluated the intestinal humoral immune response to a live auxotrophic vaccine used on hatchlings with and without maternal antibody, and related this response to challenge with a blend of two antibiotic-resistant Salmonella marker strains. Forty wk-old ISA Brown® (Institute de Selection Animale, France) breeders from a Salmonella-free flock were vaccinated twice at a three wk interval with commercially-prepared autogenous trivalent bacterin, serogroups B, C and D1 (Lohmann Animal Health International, Gainesville, GA), or a serovar Enteritidis bacterin (Fort Dodge Animal Health Inc, Overland Park, KS). Half of the progeny from these treatments (hatched from eggs layed 3 wks after second bacterin dose) were given a live Salmonella serovar Typhimurium (LiveST) mutant vaccine (Fort Dodge Animal Health Inc, Overland Park, KS), by coarse spray on arrival to the brooding premises. On d 3, 13 and 34, intestinal Immunoglobulins (Ig) A and G were sampled and measured on enzyme-linked immunosorbent assay plates coated with Salmonella serovars Enteritidis (SELPS) or Typhimurium (STLPS) Lipopolysaccharide. On the same days, a second group of birds was challenged with a blend of antibiotic-resistant serovars Enteritidis and Typhimurium strains. Cecal and composite liver-heart-spleen samples obtained 7 d post-challenge were cultured and colonies enumerated. Maternal IgG observed up to 13 d had no effect on subsequent LiveST-stimulated antibody production. No protective effect of maternal antibody was demonstrated, except when combined with LiveST given to the progeny. Killed vaccines delivered to the breeders combined with a live vaccine delivered to the progeny resulted in reduced invasiveness after challenge, as shown by a reduction in liver-heart-spleen Salmonella counts. One dose of LiveST enhanced intestinal IgG (Optical Densities (OD) >0.576) up to 34 d when measured on STLPS, but only to 13 d when measured on SELPS, with titers decreasing with age. Increased IgA was observed only at 13 d. Three and 13 but not 34 day bacterial counts were decreased by the live ST vaccine treatment, for both cecal (1.05 and 1.09 log) and liver-heart-spleen (0.32 and 0.06 log) samples, indicating that a second dose might be necessary for prolonged protection. The protective effect of the live vaccine, but not of maternal IgG, leads us to hypothesize that protection might be due to stimulation of cell-mediated intestinal immunity, and/or a competitive exclusion effect of the LiveST vaccine. Reduction but not elimination of Salmonella colonization by vaccination highlights the importance of vaccines as complementary tools, and not substitutes of integral biosecurity programs to control Salmonella in poultry.