Resistance to Challenge of Breeders and Their Progeny with and Without Competitive Exclusion Treatment to Salmonella Vaccination Programs in Broiler Breeders

Abstract

Resistance to Salmonella challenge of breeders under three vaccination programs and of their chicks with and without mucosal Competitive Exclusion (CE) (CHR Hansen) treatment was assessed. Vaccine treatments combined a live Aro-A Salmonella Typhimurium (ST) vaccine and an autogenous commercially prepared (Lohmann Animal Health) trivalent killed vaccine (serogroups B, C₂ and D₁). Treatments combined: 2 live and 2 killed doses or 3 live and 1 killed dose delivered at 1, 21, 77 and 126 d of age; or 2 killed doses delivered at 77 and 126 of age; and a non-vaccinated control (C). At 3, 6, 11, 17 and 22 wks of age, a portion of breeder pullets was removed and challenged per os with 10⁷ cells of a 3-strain mixture of antibiotic-resistant salmonellae. Chicks from eggs laid at 29, 34 and 40 wks of age were randomly divided into two groups, one group received a CE treatment by oral gavage. Both groups were given 10⁷ cells of a 2-strain mixture of antibiotic-resistant salmonellae and kept in isolation units for one and two wks. Ceca and Liver-Heart-Spleen (LHS) samples were cultured for each strain on BGS+antibiotic plates and colonies enumerated. Log₁₀ data were analyzed under factorial designs. Breeder Salmonella counts showed significant reductions between (live) vaccinates and non-vaccinates at 3 (0.82 log) and 6 wks (0.85 log) challenges. By 11 wks, there were no differences in Salmonella levels between vaccinates and controls, indicating that 1-d and 3-wk live vaccine protection had diminished with time. All vaccination treatments reduced breeder cecal counts (1.15-1.30 log) by wk 22. Passive immunity from breeder vaccination treatments was not effective in diminishing chick cecal counts as shown by comparable susceptibility of chicks from vaccinated and control breeders, regardless of breeder age. Chick CE treatment consistently diminished cecal (1.41 log) and LHS (0.306 log) counts. These results show that live Aro-A ST vaccination decreases counts during the first 6 wks of age, as do all programs by 22 wks of age and that competitive exclusion is the most effective treatment in reducing hatchling Salmonella counts.