Location: Egg and Poultry Production Safety Research Unit
2024 Annual Report
Objectives
1. Evaluate the impact of flock management strategies in cage-free and other hen housing systems on pathogen transmission and prevalence and egg microbial, physical and functional quality.
1.a. Ascertain the impact of laying hen flock management strategies on the vertical and horizontal transmission of pathogens.
1.b. Determine the influence of laying hen flock management strategies on egg microbiology and quality.
1.c. Assess the impact of egg handling practices on consumer product safety and quality.
2. Evaluate the impact of pullet rearing practices on pathogen transmission and prevalence and resulting egg microbial, physical, and functional quality.
2.a. Determine the transmission and persistence of pathogens in pullets reared under various housing practices.
2.b. Assess the prevalence of pathogens during the pullet phase under various commercial cage-free pullet management programs and resulting egg microbiology and quality.
2.c. Ascertain the influence of egg handling practices on consumer product safety and quality from hens reared under a variety commercial cage-free housing systems.
Approach
The starting point for this research program will be to determine the effects of cage-free housing systems for laying hens and cage-free pullet rearing programs, under U.S. commercial production conditions, on the prevalence of food-borne pathogens in flocks and the production environment and on the microbial, physical, and functional quality of eggs and egg products. These studies will generate a unique and comprehensive assessment of the environmental and management risk factors associated with cage-free egg production systems. This baseline information will then be applied in combination with collaborators’ data about housing conditions and management practices with the greatest potential significance as targets for risk mitigation. The output of this two-stage strategy will be a research-based guide of best management practices for extensive housing systems for the egg industry to maintain high standards of egg safety and quality. These guidelines will also allow the egg industry to make informed management decisions, based on definitive scientific data about the associated risk of individual practices, to effectively manage extensive housing systems, conduct housing sanitation, test to detect environmental contamination, reduce flock infection, and enhance processing facility sanitation. State and federal regulatory agencies will also be able to apply these guidelines to protect public health by reassessing current standards to ensure that safe, wholesome eggs and egg products reach consumers. Through collaboration with university extension personnel, outreach programs will be developed for large and small-scale cage-free egg producers.
Progress Report
Cage-free housing system design, hen use of resources, and resulting microbial and physical egg quality. A study was completed to compare different styles of cage-free housing designs and the hen usage of resources in these systems. Monitored Salmonella shedding during the rearing phase of a flock. Environmental and egg microbiology, as well as egg physical quality were monitored. This study is part of a NIFA IDEA grant in conjunction with Purdue University. Impact of orange corn on hen health and product quality throughout the production cycle. A study is underway to evaluate the influence of the supplementation of orange corn in laying feed on egg production and quality. Purdue University is managing the laying flocks and monitoring egg production, egg efficiency and hen well-being. USDA-ARS is assessing egg size, egg quality and egg functionality. This study is funded by a NIFA SBIR awarded to Nutramaize, with ARS and Purdue University as collaborators.
Utilizing orange corn in laying hen poultry feed for enhanced yolk color. A study is underway to determine the impact of genetically modified orange corn in the diets of laying hens and impact on egg production and quality. Purdue University is maintaining the flocks and conducting all hen management and production assessments. ARS is accessing egg shape, physical quality and functional characteristics. This study is an industry partnership with Nutramaize and Eggland’s Best Eggs in collaboration with Purdue University.
Spoilage microorganisms in eggs under different storage and handling conditions. A study was completed in which eggs were processed under different egg handling conditions, stored for extended intervals at refrigerated and ambient temperatures, and examined for the presence of spoilage organisms. Handling conditions affected the isolation of spoilage microbes from eggshells and egg contents but no spoilage microorganisms were found in refrigerated eggs.
Genetics of Campylobacter isolated from laying hens. Campylobacter isolates obtained from commercial egg-laying chickens in prior field studies were subjected to genomic sequencing. Sequencing information for Campylobacter isolates associated with laying flocks was not previously available and has been submitted to publicly accessible databases.
Persistence and transmission of Salmonella Enteritidis infections in egg-type pullets infected at different ages. In a collaborative experiment between ARS and Purdue University, pullets were exposed to S. Enteritidis at different ages during rearing in a cage-free housing system and evaluated for the persistence of the pathogen in their tissue through the age of sexual maturity and commencement of egg laying.
Environmental contamination and horizontal transmission of Salmonella Enteritidis among egg-type pullets in cage-free housing. A collaborative study between ARS and Purdue University was completed to evaluate environmental contamination and horizontal transmission of S. Enteritidis within groups of layer pullets in cage-free housing after infection just before the age of sexual maturity. The isolation of S. Enteritidis from diverse environmental samples taken from the cage-free housing environment during the first two weeks after the oral infection of different proportions of pullets was correlated with the frequency of recovery of the pathogen from the internal tissues of horizontally exposed birds.
Assessing the effects of Salmonella Typhimurium vaccination on gut microbiota in egg laying chickens. University of Adelaide (Australia) scientists, in collaboration with ARS, compared the effects of three different dilution media used for preparing a live Salmonella Typhimurium vaccine on the gut microbiota of vaccinated layer chicks. The diluent and dosage of vaccine did not significantly affect the diversity of gut microorganisms although the abundance of several important species of intestinal bacteria were found to be much higher at 14 days of age than at 7 days.
Evaluating a novel method for challenging egg laying chickens with Salmonella Typhimurium in vaccine efficacy studies. University of Adelaide (Australia) scientists, in collaboration with ARS, evaluated the sprinkling of contaminated dust as a method for infecting and colonizing chickens with Salmonella as a component of vaccine efficacy studies. Dust sprinkling was found to result in gut colonization of chicks at a similar level as direct oral inoculation, but dust sprinkling led to higher numbers of the pathogen in the liver.
Accomplishments
1. Internal organ colonization by Salmonella Enteritidis in layer pullets infected at two different ages during rearing in indoor cage-free housing. The bacterial pathogen Salmonella Enteritidis can cause food-borne human illness by contaminating the edible interior contents of eggs laid by infected hens, and the ongoing transition of the commercial egg industry from traditional cage-based housing to alternative non-cage systems has raised new questions about environmental influences on food safety. ARS researchers in Athens, Georgia, assessed internal organ colonization by S. Enteritidis in groups of egg-type pullets (immature hens) housed in isolation rooms designed to simulate commercial cage-free barns with nest boxes, perches, and floors covered by wood shavings. At either 9 or 15 weeks of age, one-third of the pullets in each room were orally infected with S. Enteritidis. At 1-2 weeks after infection, half of the birds from each age group were tested to detect the presence of S. Enteritidis in their internal organs; the remaining birds were similarly tested at 21-22 weeks of age. S. Enteritidis was found significantly more often in the internal tissues of pullets infected at 15 weeks of age than in those infected at 9 weeks of age, both for samples collected during the 2 weeks immediately following infection and for samples obtained at 21-22 weeks of age. These results reinforce the importance of attentive and comprehensive pathogen risk reduction practices during the later stages of pullet rearing for diminishing the likelihood that S. Enteritidis infection will persist until the age at which egg laying commences.
2. Influence of egg handling and storage on the occurrence of spoilage organisms in shell eggs. Eggs are a major international trade commodity. Differing international egg handling and storage regulations have become a barrier to the importation and exportation of shell eggs. ARS researchers in Athens, Georgia, collected eggs under four different egg handling treatments: 1) unwashed, 2) washed, 3) washed and oiled, and 4) stored 21 days and then washed. Eggs from each egg handling condition were placed in either refrigeration (4°C) or room temperature (22°C). Eggs from each egg handling treatment and storage temperature were sampled at various timepoints. Beginning at 8 weeks of storage at room temperature, spoiled eggs were observed. Microorganisms associated with stored eggs were identified using MALDI-TOF (an analytical technique which identifies bacteria based on the unique mass to charge ratio of their ribosomal proteins). The egg handling treatment did impact the richness and abundance of spoilage organisms in spoiled eggs. Egg contents of unwashed eggs had less richness in spoilage organisms than washed and oiled eggs. Washed and oiled eggs and eggs held for 21 days and then washed had greater abundance of spoilage organisms in their contents compared to unwashed eggs. Spoiled eggs were not observed in any egg handling treatments held in refrigeration (4°C). An abstract of this study was accepted for presentation at the 2024 Annual Poultry Science Association Meeting. This study shows the importance of refrigeration for shell eggs (regardless of egg handling) to prevent egg spoilage.
3. Genomic sequencing of Campylobacter isolates from laying hens. Campylobacter coli and C. jejuni are similar species and both can cause bacterial food-borne illness in humans. Although poultry meat has been identified as a common source of human Campylobacter infections, shell eggs are not generally considered to constitute a likely source of transmission of Campylobacter to humans. ARS researchers in Athens, Georgia, obtained 65 Campylobacter isolates from collaborative research studies conducted with Michigan State University, North Carolina State University and Purdue University. These isolates were associated with laying hens housed in alternative (non-cage) housing systems, which have recently become more common in the egg industry. The genomic sequences of these Campylobacter isolates (38 C. coli and 27 C. jejuni) were determined and the results were submitted to the NCBI Genbank database and the pubMLST database. Genomic sequences of Campylobacter strains isolated from laying hens have not previously been publicly available. Widespread access to these genomic sequences will provide a resource for comparing populations of Campylobacter from egg-layer chickens and meat-type (broiler) chickens.
4. Optimizing and testing the efficacy of live attenuated Salmonella Typhimurium vaccines in egg-laying chickens. University of Adelaide (Australia) scientists, in collaboration with ARS researchers in Athens, Georgia, evaluated several key issues important for testing and optimizing the efficacy of live Salmonella Typhimurium vaccines in poultry. In one study, an S. Typhimurium vaccine was prepared in three different dilution media and administered to layer chicks at three different doses to assess the effects on the total spectrum of bacteria present in the chicks’ intestinal tracts (the gut microbiota). The vaccine diluent and dosage had minimal effects on the diversity of gut microorganisms, indicating that the vaccine can be administered without causing disruption of the intestinal microbiota important for gut health in the developing chick. Another study investigated S. Typhimurium infection of egg-type chickens via contaminated dust. Contaminated dust was administered to chicks by either sprinkling onto their pens or by direct oral inoculation. Both inoculation methods resulted in consistent colonization of the gut, but dust sprinkling led to higher Salmonella numbers in livers than oral inoculation. Infection of chickens using the sprinkling method at a range of doses showed a threshold for gut and organ colonization as low as 1,000 colony forming units of bacteria per g of dust. This demonstrated that dust sprinkling can be a highly effective way to experimentally challenge chickens with Salmonella as a basis for assessing the protective efficacy of vaccines.
Review Publications
Khan, S., Mcwhorter, A., Andrews, D.M., Underwood, G.J., Moore, R.J., Gast, R.K., Chousalkar, K.K. 2024. A live attenuated Salmonella Typhimurium vaccine dose and diluent have minimal effects on the caecal microbiota of layer chickens. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2024.1364731.
Khan, S., Mcwhorter, A., Andrews, D.M., Underwood, G.J., Moore, R.J., Gast, R.K., Chousalkar, K.K. 2024. Dust sprinkling as an effective method for infecting chickens with wild-type Salmonella Typhimurium and changes in host gut microbiota. Environmental Microbiology Reports. 16(3). Article e13265. https://doi.org/10.1111/1758-2229.13265.
Gast, R.K., Jones, D.R., Guraya, R., Garcia, J.S., Karcher, D.M. 2024. Internal organ colonization by Salmonella Enteritidis in layer pullets infected at two different ages during rearing in cage-free housing. Avian Diseases. 68:141-144.