PIC Update: Understanding the Role of DHA

The Smoky Joe hen is a unique blind strain of White Leghorn Chicken,
but it is not known exactly why these chickens are blind. It is known,
however, that proper eye development and functioning is supported by
adequate intake of an omega-3 fatty acid

The Smoky Joe hen is a unique blind strain of White Leghorn Chicken, but it is not known exactly why these chickens are blind. It is known, however, that proper eye development and functioning is supported by adequate intake of an omega-3 fatty acid known as DHA (docosahexaenoic acid). DHA is also an important factor in brain development.

With this in mind, Dr. Bruce Holub of the University of Guelph questioned whether there were any differences in the DHA content of eyes, brain tissue and blood serum of sighted and blind Smoky Joe hens. The DHA content of eggs laid by these birds was also of interest as this is important for both the development of the chick and for human health. If differences can be shown in the DHA content of eggs from different hens, then it may be advantageous to selectively breed laying hens for both egg production and nutritional content. Furthermore, it will provide a further understanding of the role of DHA in the blind Smoky Joe hen and possible breed-specific differences in the metabolism and distribution of omega-3 fatty acids in the body.

To begin investigating this, Dr. Holub and his research team collected blood samples from groups of sighted and blind Smoky Joe hens that were being fed identical diets. They then euthanized the birds and analyzed the eyes and brain tissue for fatty acid composition. 

Their findings? Eyes from the blind birds had markedly lower levels of DHA omega-3 fatty acid (by 55 per cent overall) as compared to the eyes from the sighted birds. The average DHA level was 3.64 per cent of total fatty acids in the eyes of the blind birds as compared to 8.09 per cent for the sighted birds. Interestingly, no significant differences were found in DHA levels between the two groups in the case of the blood and brain tissue. It is therefore possible that a defect in the uptake or assimilation of DHA from the circulating blood into the eyes of the blind birds during growth and development may underlie the visual defect. 

Fatty acid analysis of the eggs indicated substantial levels of DHA omega-3 fatty acid, but no significant differences in overall levels between eggs laid by blind and sighted birds.  In future, the research team hopes to compare DHA levels in eggs from Smoky Joe hens with other strains, as it is possible that accumulation of DHA in the egg may vary across breed. This has implications for cost-effective production of omega-3 eggs. To read more about this research project, please visit www.poultryindustrycouncil.ca.

Featured Researcher Research within Professor Bruce Holub’s group is focused on omega-3 fatty acids from fish oils and derived concentrates (enriched in EPA and/or DHA) as nutraceuticals and functional food components for human health and the prevention/management of heart disease and other chronic disorders. The group’s past research has utilized EPA/DHA-containing nutraceuticals, functional foods such as liquid eggs, and microencapsulated preparations of omega-3 fatty acids incorporated into various food products. They have also worked/published on the efficacy of an algal form of DHA in human subjects (both vegetarians and non-vegetarians) in attenuating various risk factors for cardiovascular disease.  In addition, Professor Holub’s group has collaborated with animal and food scientists at the University of Guelph in providing for the production of animal food produce (shell eggs, milk and other dairy produce, meats) enriched in DHA and other omega-3 fatty acids via altered feed formulations. DHA-enriched functional foods will also be an important source of this nutrient for enhancing cognitive performance in young and old alike. His research has been funded by public agencies (NSERC, Heart and Stroke Foundation of Canada, the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA)) and industry (agri-food sectors, including nutraceutical and functional food sectors). Evaluation of the aforementioned products (some of which are now commercially available in the marketplace via Canadian agri-food producers) in controlled human trials as conducted at the University of Guelph provides data for potential health claims in Canada, the United States and elsewhere.  Dr. Holub was commissioned by the Market and Industry Services Branch of Agriculture and Agri-Food Canada to write the extensive report (filed in 2002) entitled: “Potential Benefits of Functional Foods and Nutraceuticals to Reduce the Risks and Costs of Diseases in Canada.”

In-vitro and testing of new vaccine candidates
Dr. Wolfgang Köster, Vaccine and Infectious Diseases Organization (VIDO), University of Saskatchewan

Birds, including poultry used for food production, are an important reservoir for various Salmonella strains causing gastrointestinal diseases in humans. The vast majority of the described Salmonella strains represent serotypes of the pathogen Salmonella enterica. Transmission from poultry to humans occurs predominantly through contaminated food. The reduction of pathogen levels in food-producing animals has been predicted to be the most effective strategy to minimize the risk to humans, but the mechanism of colonization of poultry is not well understood.

Vaccination is a relatively new option for control of Salmonella, and there is considerable interest in the identification of new potential virulence factors in Salmonella enteritidis in order to develop more effective strategies to control this pathogen. Dr. Wolfgang Köster and his research team at the Vaccine and Infectious Disease Organization (VIDO), University of Saskatchewan, have been working to understand the role of specific virulence factors – particularly a specialized export system for folded proteins, and selected components involved in iron homeostasis and regulation.

To begin investigating this, the research team hatched chicks from specific pathogen-free eggs, and challenged them at four and seven days of age to S. enteritidis, including strains carrying mutations in genes related to the specialized protein export system and selected iron regulated genes.  At one, two and four days post-challenge, birds were euthanized and samples were taken from the cecum, liver, and spleen, and tested for presence of Salmonella spp.  The researchers were also interested in developing an effective “seeder challenge” model because this is closer to what would occur naturally compared to a high oral challenge. In this model, birds are infected naturally by pathogen-infected “seeder” birds.  For this experiment, the researchers immunized hens and challenged their offspring with S. enteritidis by having them mingle with different percentages of seeder birds within the flock. Chicks were euthanized on days two and three post-challenge and again, cecum, liver, and spleen samples were collected and tested for presence of Salmonella spp.

Their findings? The researchers have found evidence that the specialized protein export pathway is important for an effective and prolonged systemic infection in chickens, meaning it might be a useful system to identify new vaccines.  It was also found that two genes involved in iron regulation and iron assimilation play a key role in cecal colonization in 7 day-old birds, and are important in maintaining S. enteritidis systemic infection. For the seeder challenge model, immunization of hens resulted in a significant antibody response, and liver and spleen bacterial colony counts were lower in the seeder-infected chicks that originated from vaccinated hens. Overall, the researchers have identified new virulence factors that may lead to the identification of candidates for vaccine development. They have also developed a suitable test system to evaluate the protective effect and efficacy of future vaccine candidates. To read more about this work, please visit www.poultryindustrycouncil.ca.