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2011 Poultry Production Research Impacts, Part 4

Stress & Poultry Reproduction

Stress-induced ovarian dysfunction is a relatively common phenomenon in a wide variety of animal species. In poultry, genetic selection for increased and more efficient egg production in layers and for increased body weight in broiler-breeder hens often acts as a physiological stressor, compromising egg quality, embryo quality, and reproductive fitness. This phenomenon is commonly seen in laying hens selected for increased egg production and extending laying periods and in broiler-breeder hens selected for increased body weight and rapid growth rate.
Although much work has been done to determine the manner in which central neural circuits disrupt ovarian cyclicity, little focus has been placed on the peripheral stress mechanisms
regulating gonadal function. The influence of stress hormones, such as corticosterones, on ovarian follicles is dependent upon the expression of glucocorticoid receptors on ovarian tissues that can bind corticosterones and elicit intracellular changes.

In order to understand ovarian susceptibility to corticosterones, it is necessary to examine glucocorticoid receptor expression in ovarian follicles as they mature and prepare for ovulation. Elucidation of ovarian susceptibility to stress hormones may enable poultry geneticists to select for laying hens and broiler-breeder hens with ovarian follicles that are more resistant to the negative effect of corticosterones. Ultimately, this understanding may allow for improved reproductive performance and efficiency in layers.


What Has Been Done
Scientists at N.C. State University have characterized the expression of glucocorticoid
receptors in the hierarchical and non-hierarchical follicles of White Leghorns in production, compared the expression of
glucocorticoid receptor expression in free-range vs. caged hens, compared the expression of glucocorticoid receptor expression in germinal disc vs. non-germinal disc regions of hierarchical follicles, and compared the expression of glucocorticoid receptors in broiler-breeder hens differeing significantly in egg production.

With an understanding of the influence of peripheral stress hormones on ovarian function, it may be possible to alter ovarian stress susceptibility in laying hens and broiler-breeders through genetic selection of hens with more "stress-resistant" ovarian follicles. Ultimately, poultry geneticists may be able to determine which laying hens are better able to handle environmental and physiological stressors without negatively impacting egg production.

Funding Sources
North Carolina Agricultural Research Service (NCARS) (for start-up funds)
NCSU Undergraduate Research Stipends (2008-Present)

Dr. Jacquelyn B. Hoffman, Department of Poultry Science, N.C. State University
Improvement of Selenium Use in Poultry Growth & Health

Selenium (Se) is a naturally occurring micronutrient that is essential for several known major metabolic pathways in both mammals and birds. Dietary Se can exist as organic selenomethionine and selenocysteine or in inorganic selenate and selenite forms. It is incorporated as selenocysteine into a subset of specific selenium-dependent proteins (selenoproteins), many of which have still undefined biochemical and physiological functions. Selenoproteins involved in oxidative stress, such as the ubiquitous glutathione peroxidase enzymes and the thioredoxin reductase (TRX) enzymes are best understood, due to the ability to quench oxygen and nitrogen free radicals that can damage proteins, lipids, and nucleic acids. Unchecked and sustained free radical generation affects cellular and tissue functions that ultimately result in organ dysfunctions and physiological disruptions. The dietary requirements for Se must be delicately balanced between the harmful effects of excessive Se uptake, leading to Se toxicity due to inorganic Se forms, and pathology resulting from depressed selenoprotein function during Se deficiency.

Organic Se feed supplements are currently being developed for animals on a worldwide basis, and the basis for organic Se usage in poultry is based largely on work conducted at N.C. State University over the past 15 years.
Ongoing studies at NCSU have focused on understanding Se tropism for certain tissues and selenoprotein synthesis. More recently, NCSU studies expanded to explore the influence of organic Se on gene expression in the chicken genome and to use this data to explain the reasons for improved performance of domestic poultry fed organic Se.

Initial research has shown that selenoprotein P gene expression was enhanced by feed supplementation with organic Se to a great intensity than by sodium selenite, and both Se forms induced SelP compared with no supplemental Se. In liver and brain, SelP expression decreased with age. Additionally, NCSU researchers demonstrated that expression of SelP can be modified by avian reovirus infection, regardless of Se supplement source. In this initial study, they also noted that polymeric immunoglobulin receptor expression in secretory organs and glands associated with the gastrointestinal tract was induced by both inorganic and organic Se. Therefore, additional studies were conducted to focus on the relationship between Se involvement in plgR and secretory IgA expression in the intestinal tract of reovirus-challenged chickens.

What Has Been Done
Avian reoviruses (ARV) cause significant economic losses in the poultry industry. The small intestine is the most common site for ARV infection, regardless of the inoculation route, with infection spread beginning in the villus and crypt epithelium.

Selenium (Se) plays a role in the chicken's ability to resist or regain function after ARV infection. Using either dietary inorganic Se, organic Se, or no supplemental Se, the influence of ARV infection was investigated. Morphological alteration of the ileal villi of Se-fed and
ARV-challenged broiler chickens was quantitifed in this study. The improved profile of the intestinal villus was not evident until 16 days post-infection (p.i.), when organic Se-fed broiler intestines were recovering at a faster pace than those of inorganic Se-fed broilers. Secretory immunoglobulin A (sIgA) is the primary antibody involved in antigen-antibody interactions in the mucosal immune system, providing the first line of defense against pathogens. Polymeric IgA, secreted by plasma cells is conjugated by polymeric immunoglobulin receptor (pIgR), and the complex is then transported to the apical membrane and secreted into the intestinal lumen. Intestinal sIgA was altered by Se form as well as by ARV infection. Using an enzyme-linked immunosorbent assay, time-dependent differences in expression were found, in which the greatest expression occurred in organic Se-fed birds, followed by inorganic Se-fed birds, with the lowest expression level occurring in the control group, early in the challenge trials. However over all intervals during the trial, organic Se-fed birds exhibited higher ileal IgA expression.
Biliary sIgA levels were highest in organic Se-fed birds. IgA transcytosis across epithelial and endocrine cells depends on pIgR existing in a 1:1 ratio with sIgA. Quantitative
real-time PCR analysis showed that Se has a positive influence on resistance to and recovery from double-stranded avian ARV. By 16 days p.i., when ARV had run its course, organic Se-fed birds showed lower levels of pIgR expression, suggesting that this group recovered more quickly.

Selenium thus appears to influence the dynamics of intestinal sIgA and pIgR, which improve intestinal villus integrity.

Over the past 15 years, this group's research has demonstrated the need to reevaluate the form of Se that should be used in formulations of poultry diets.

Reduced dietary Se consumption can have significant effects on levels of selenoproteins, such as glutathione peroxidases, thioredoxin reductases, and methionine sulfoxide
reductases, all enzymes involved in oxidative stress responses deriving from unchecked mitochondrial free radical production or from lipid free radicals produced by membranes. Selenium, through its incorporation into selenoproteins, provides protection from reactive oxygen species (free radicals, ROS)-induced cell damage. Because oxidative stress and subsequent ROS production have been implicated in many degenerative diseases and infectious diseases in poultry, it is important to know the role played by selenoproteins, such as selenoprotein P, a carrier of Se in the body.  The consequence of selenoprotein P deficiency on numerous physiological and biochemical functions can have extensive impact on the viability and growth of poultry species. We know from research experience over the past 15 years that control of ROS and maintenance of antioxidant selenoprotein enzymes can result in improved growth and resistance to the damaging effects of both viral and bacterial diseases.
The previous work with selenoprotein P gene expression and characterization of its response during a viral challenge has
potential to affect every broiler raised in North Carolina and in the whole world since SelP is the major carrier of Se in poultry species and is necessary to deliver Se to cells where antioxidant functions are constantly being conducted. In the current research, we have provided a new tool to be used by veterinarians and poultry scientists to address mucosal immunity in chickens. The observation that Se and Se forms affect the expression of plgR and slgA in the intestine is important due to the fact that slgA represents the first line of immunological defense against poultry pathogens. The relationship between sIgA and pIgR is simple. The deposition of a single molecule of sIgA into the lumen of the intestinal tract requires a single molecule of pIgR for transcytosis and eventual export of sig a into the intestinal lumen. Thus, if an increase in sIgA is found in the intestinal lumen, then there must be an increase in the expression of pIgR to carry the sIgA across the enterocyes of the intestinal tract. Not only does Se influence antioxidant status of the bird and the fact that redox status is also important in the immune responses of the bird, we now have definitive information that selenium also influences IgA secretion. This information along with the previously documented Se influence on expression of SelP, IgG and IgM in poultry indicates that the role played by Se in mucosal immunity is critical. With this knowledge, veterinarians and poultry scientists can better address issues such as vaccine development, nutrigenomics, probiotic supplementation, prebiotic supplementation, and many other immunologically linked processes in poultry. These observations will allow improved production of meat type poultry and promote a safer food supply for the American consumer. While difficult to place a monetary value on the impact of such research, one can make assertions relative to the impact on some sectors involved in poultry production.
The shift from inorganic to organic Se use in breeder diets has improved chick production by about 4 chicks per breeder hen, representing about $1.00 per breeder housed. This figure alone has a potential positive impact of an additional $60,000,000 for the breeder industry just in the USA. World impact represents an is even greater value to the
breeder industry. Further, in the broiler industry, the impact of this technology is even greater impact than it is for breeder production: Taking into account the possibility that each broiler fed organic selenium potentially improves feed conversion and meat yield, broiler growers could realize as much as $0.50 additional income/broiler. This gain would represent a potential national impact of $4,500,000,000, with even greater potential gain in value worldwide.

NCSU selenium nutrition
research has other impacts, also. Increased meat yield of higher quality, an improvement in product value for consumers; and the biomedical implications of improved immunity is of such magnitude that one can only estimate impact value ranging into the hundreds of billions of dollars.

Funding Sources
North Carolina Agricultural Research Service (NCARS)
USDA Animal Health Formula Funds