Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Hargis, Billy M.

Committee Member

Caldwell, David J.

Second Committee Member

Tellez, Guillermo

Third Committee Member

Bielke, Lisa R.

Fourth Committee Member

Wolfenden, Ross

Keywords

broiler; hatchery; microbial bloom; model; poultry

Abstract

Formaldehyde fumigation has been used to control the microbial load in commercial hatch cabinets. The hatch cabinet environment promotes replication and dissemination of both apathogenic and pathogenic microorganisms. As the microbial load increases during the hatching phase, formaldehyde eliminates airborne microorganisms circulating in the hatch cabinet environment. Due to the hazardous properties of formaldehyde, non-toxic alternatives to formaldehyde fumigation to control the microbial bloom in hatch cabinets are needed. The objectives of the present dissertation were to develop challenge models using singular or multiple microorganisms associated with the microbial bloom to simulate contamination that occurs in commercial hatch cabinets. Initially, a challenge model was developed to mimic horizontal transmission of virulent Escherichia coli during the hatching phase. Seeder embryos were directly infected by in ovo injection into the amnion. Administration of the avian pathogenic E. coli (APEC) alone at 18 and 19 days of embryogenesis (DOE) was lethal to developing seeder embryos. However, seeder chick hatchability was improved when APEC were co-administered with tetracycline hydrochloride (272ug/mL). Exposure to APEC during the hatching phase significantly (P < 0.05) increased 7-day mortality compared to the non- exposed control group. Additionally, horizontal transmission of APEC reduced body weight gain (BWG) in 2/3 trials compared to the non-challenged control group. An alternative challenge model using wild-type (WT) E. coli strains that were previously isolated from colibacillosis field cases were selected to assess horizontal transmission of WT E. coli during the hatching phase. In ovo administration of either WT E. coli strain at DOE19 had minimal impact on seeder hatchability. As the seeder chicks hatched, the circulating airborne Gram-negative bacteria in the hatch cabinet increased. Gram-negative bacteria recovered from the GIT was significantly (P < 0.05) increased for seeder and contact chicks compared to the non-challenged control group. As suspected, formaldehyde fumigation did not reduce seeder chick Gram- negative enteric colonization at day-of-hatch (DOH). However, formaldehyde fumigation effectively controlled the Gram-negative bacterial bloom in the hatch cabinets. The WT or APEC E. coli seeder challenge models could be used to assess the effect of candidate disinfectants or natural alternatives on the Gram-negative bacterial bloom and horizontal transmission during the hatching phase. Although the models using a singular challenge organism were validated, challenge with a singular species does not reflect real-world conditions in commercial hatcheries. Thus, a challenge model with multiple hatchery-relevant opportunistic pathogens was evaluated. Since the contents of non-viable embryonated eggs contain a plethora of microorganisms, an egg homogenate (EH) was derived from the contents of non-viable embryonated eggs at DOE18. To create the pathogen mix (PM) challenge, bacterial and fungal species were isolated from the EH to artificially replicate the contamination in commercial hatch cabinets. The PM consisted of two E. coli isolates, Staphylococcus aureus, Staphylococcus chromogenes, Enterococcus faecalis, and one fungal isolate, Aspergillus fumigatus. EH or PM challenge was applied to the eggshell at DOE19 to determine which material be suitable for future investigations based on enteric bacterial recovery at DOH, bacterial and fungal recovery from fluff samples collect at DOH, chick rinses at DOH, or air samples collected from the hatch cabinet environment during the hatching phase. Based on overall microbial recovery and practicality, the PM challenge proved to be the more appropriate model to mimic microbial contamination in commercial hatch cabinets in a laboratory setting. These challenge models could be used to evaluate industry-applicable methods to control the microbial bloom in commercial hatch cabinets.

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