Outlining a balance-point model of homeostasis in the small intestine of broiler chickens

Since the removal of in feed antibiotics in the past few years commercial poultry production is especially sensitive to the health of the small intestine. Healthy small intestines balance nutrient absorption and defensive barrier functions to ensure the chicken is able to meet the whole-body nutritional needs and is able to help prevent internalization of pathogens or potentially toxic components. This balance can only be maintained under stable conditions. When a disturbance event occurs the intestine imbalances until a new, and less efficient, balance can be achieved. The objective of this dissertation is to propose a novel model to understanding intestinal homeostasis in the face of various disturbance events. Chapter 2 investigated the effects of Runting Stunting Syndrome on broiler chickens in four different groups of chicks displaying clinical symptoms. The major finding in this study was that in two of the four groups the expression of stem cell gene Olfactomedin 4 was absent from the crypt though other functional genes were found to still be expressed there. Chapter 3 characterized intestinal gene expression following a single challenge of Eimeria acervulina in broiler chickens. During Eimeria infection gene expression of multiple host defense peptide genes were decreased compared to uninfected chickens. Further, Eimeria infected chickens increased cell proliferation within the crypt and post-peak infection showed signs of intestinal recovery. Additionally, chapter 3 developed a novel method for visualizing Eimeria as it infects the intestine. In chapters 4 and 5 cell type population changes during the peri-hatch intestinal maturation process were evaluated. Peri-hatch intestinal maturation is critical for the successful transition from embryonic to post-hatch life. Chapter 4 profiled changes in proliferative cells and gene expression of various stem cell marker genes during the peri-hatch period: the last three days of embryogenesis and the first week post-hatch. The stem cell marker gene Leucine Rich Repeat Containing G Protein-Coupled Receptor 5 (Lgr5) decreased during the post-hatch period while Olfactomedin 4 increased post-hatch. Both stem cell genes were expressed within the intestinal crypt, though prior to hatch Lgr5 was expressed in the lamina propria and villi as well. Additionally, the marker of proliferation Ki67 gene was expressed in cells throughout the intestine prior to hatch but became restricted to the crypts and along the center of the villi. Chapter 5 assessed the effect of providing probiotics to late term embryos via in ovo feeding (IOF). The effects of IOF were primarily observed on embryonic day 20 (e20), roughly 48 hours after IOF. On e20 the embryos in ovo fed probiotics in saline had increased expression in the ileum of Peptide Transporter 1 (PepT1) a marker gene for enterocytes and Mucin-2 (Muc2) a marker gene for goblet cells compared to non-injected control embryos. Also, on e20 the embryos in ovo fed saline only had numerically increased PepT1 and Muc2 compared to non-injected control embryos. The difference in responses between the probiotic and saline fed embryos on e20 suggests different routes of stimulation. These investigations illustrate various possible scenarios and means of investigating intestinal homeostasis during disturbance events.