The Influence of Necrotic Enteritis, Environmental Factors, and Genetics on Intestinal Development Pathways and Disease Occurrence in Broiler Chickens

Intensified poultry production to meet global food demands has faced challenges associated with the removal of in-feed antibiotics due to concerns over antibiotics resistance. The reduction of low-dose antibiotics in feed has allowed for reemergence of intestinal diseases that diminish animal welfare and producer economics. Alternative mechanisms to preventing disease are therefore required. The objective of this dissertation was to examine factors that contribute to chicken development and health including intestinal structure and function, environment, and genetic selection. Chapter 2 investigated the host response to infection of the parasite Eimeria maxima that predisposes chickens to a bacterial infection Clostridium perfringens. Intestinal structure, function, inflammatory response, and epithelial composition was examined during a mild subclinical infection. Analysis of E. maxima and C. perfringens as individual infections revealed how each pathogen contributes to a co-infection. E. maxima caused a more severe inflammatory response, increasing pathology scores, shortening intestinal villi, and elongating crypts in the jejunum at peak infection. C. perfringens was shown to manipulate intestinal epithelial composition by influencing stem cells to differentiate into secretory goblet cells. The most deleterious effects were observed when the pathogens were introduced together, increasing pathology scores further, damaging intestinal villi, and increasing crypt depth. The introduction of C. perfringens and E. maxima also increased signaling for the production of reactive oxygen species, stimulation of tumor necrosis factor- that is involved in innate immunity, and decreased transcription of Hes1, which is involved in Notch signaling towards absorptive cell differentiation. Hes1 has previously been shown to be involved in the inflammatory response and could be an area of interest in determining new treatments to prevent or relieve the effects of E. maxima and C. perfringens. Chapter 3 applied an environmental perspective to disease prevention and examined the properties of C. perfringens that allow it to persist in the poultry house environment. Spores resist treatments used to sanitize poultry houses and litter has been shown to be a reservoir for disease, potentially increasing occurrence in certain houses. The metabolic and physiological properties of C. perfringens were utilized to separate the microbe from other poultry litter bacteria to enumerate spores within houses. A selective and differential medium combined with a heat treatment was developed to isolate C. perfringens spores from poultry litter samples. On average, houses that had histories of necrotic enteritis harbored a greater abundance of C. perfringens spores. Colonies that were isolated on the specialized medium were confirmed using PCR as C. perfringens. Lastly, Chapter 4 examined how genetic selection for multiple traits has influenced early intestinal development compared to divergently selected lines based on eight-week body weight. This study showed the morphological and gene expression differences between lines and revealed that most pathways involved in intestinal development are conserved through genetic selection. The major differences between lines were an increase in peptide transporter PepT1 on d5 and d7 in chicks selected for low eight-week body weight (LWS) compared to high weight selected (HWS) chicks and modern broiler Cobb500 chicks. In HWS chicks, the opposite mechanism was observed with an increase in expression of secretory goblet cell marker Muc2. The findings of these studies give multiple perspectives into poultry production and how major factors in management including nutrition, environment, and genetics can be used to increase efficiency while preventing disease.