Date of Graduation

8-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Erf, Gisela F.

Committee Member

Sun, Xiaolun

Second Committee Member

Kwon, Young Min

Third Committee Member

Zhao, Jiangchao

Keywords

Antibody; Inflammation; Microbiome; Poultry; Salmonella; Vaccines

Abstract

Salmonella vaccination is a widely accepted practice in the United States poultry industry. These vaccines stimulate a strong humoral response to Salmonella serovars and significantly reduce Salmonella load in the bird. In general, a Salmonella vaccination program for an egg-type pullet flock consists of two administrations of a live attenuated Salmonella vaccine at 1- and 6-wk-of-age followed by one administration of a Salmonella bacterin at 12-wk-of-age. Although these vaccines are regarded as effective against paratyphoid Salmonella infections, there are incidences of breakthrough Salmonella infections and severe injection site reactions after bacterin administration. Therefore, the main objective of this dissertation was to conduct longitudinal studies to assess local (growing feather, a dermal test) and systemic (blood, spleen, liver, cecal tonsil) cellular- and humoral-immune responses to live attenuated- and killed-Salmonella vaccines in egg-type chickens. In Chapter 1, intradermal (i.d.) injection of commercial Salmonella vaccines or vaccine components (lipopolysaccharide or water-oil-water emulsion) into the pulp of growing feathers (GF) of non-vaccinated (primary response) and Salmonella-vaccinated (secondary response) Light-brown Leghorn pullets revealed that a secondary administration of Salmonella vaccines prolongs heterophil recruitment and stimulates local T helper (Th)-17 cell-mediated responses at the site of injection. In Chapter 2, specific pathogen-free White Leghorn pullets were administered a multiphase Salmonella vaccination program (two administrations of a live attenuated Salmonella vaccine, POULVAC® ST, followed by an intramuscular administration of killed S. Typhimurium, or ST, bacterin) and found that CD4+ T cell levels decreased in peripheral blood and liver while γδ T cell levels increased in the spleen and cecal tonsils after live vaccine administration and booster administration of the bacterin. At the end of the Salmonella vaccination program, GF pulps of Salmonella-vaccinated (sensitized)- and non-vaccinated (non-sensitized)-chickens were i.d. injected with ST. Sensitized chickens that were i.d. injected with ST had greater heterophil-, macrophage-, and B cell-localization at the site of injection when compared to those of non-sensitized birds, while non-sensitized birds i.d. injected with ST had prolonged γδ T cell localization. When assessing Salmonella-specific antibody responses in peripheral blood, there was evidence of a T cell-mediated IgM-to-IgG isotype switch in sensitized birds. In Chapter 3, cecal pouch microbiota was assessed prior to vaccination and at 10 d post-vaccination during the multiphase Salmonella vaccination. There was a compounding effect with repeated vaccinations on the cecal pouch microbiota alpha diversity in Salmonella-vaccinated chickens, where indices were higher in Salmonella-vaccinated chickens at 12-wk-old when compared to those of 12-wk-old non-vaccinated chickens. Additionally, the compositions of cecal pouch microbiota in Salmonella-vaccinated- and non-vaccinated-chickens had distinct clustering in Jaccard and Bray-Curtis PCoA plots during the entire vaccination program, where Salmonella-vaccinated birds had lower relative abundances of Lactobacillus with higher abundance of Lachnospiraceae when compared to that of non-vaccinated chickens. The results of these studies, when assessed together, provide qualitative descriptions of leukocyte profiles and ceca microbiota status during a longitudinal assessment of multiple Salmonella vaccine administrations. Future studies investigating interactions between vaccine responses and gut microbiota status in poultry can provide valuable insights into improving vaccine regimens in the future.

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