Necrotic Enteritis in Broiler Chicken and its Control with Probiotics: Impact on Performance, Lesion, Nutrient Digestibility, Gut Integrity, Gut Microbiota, and Transcriptional Profile

Abstract

<p>Necrotic enteritis (NE) is a major disease of poultry caused by infection with <i>C. perfringens</i>. Necrotic enteritis disease has increased in occurrence over the years, especially due to the ban of in-feed antibiotics. Losses associated with NE vary depending on the severity of the disease. However, to be able to take steps towards the control of this disease, detailed understanding of pathogenesis is necessary. The current thesis has examined this disease by conducting three animal experiments to evaluate the effects of NE on different aspects of broiler gut health.</p> <p>The first experiment compared the effect of two different <i>C. perfringens</i> strains (NE36 and NE18) on broiler chickens. Performance, lesion score, bacteria enumeration and short chain fatty acid (SCFA) concentrations were evaluated with the induction of necrotic enteritis challenge produced by either one of these strains. Birds challenged with NE36 showed a significantly lower weight gain and higher FCR compared to the NE18 challenged birds. Cecal <i>Lactobacillus</i> and lactate were increased by the NE challenge, and to a greater extent in birds challenged with NE36 compared to the NE18 strain. Broilers challenged with NE36 strain had increased concentrations of lactate and propionate compared to those challenged with the NE18 strain and the control birds. The findings from this study suggest that <i>C. perfringens</i> strains can produce different levels of disease in broiler chickens through modulating the gut environment, intestinal microbiota and SCFA profile to different extents.</p> <p>To further investigate the effects of the two different <i>C. perfringens</i> strains (NE36 and NE18), intestinal gene expression of broilers was evaluated to possibly find the underlying reasons for the different performance responses in the birds challenged with these two strains. Chapter 5 evaluates effects of the strains on the expression of apoptosis, immune related, tight junction and nutrient transporter genes. The NE36 strain significantly upregulated apoptosis signaling proteins, caspas8 (CASP3) and caspas-8 (CASP8), but downregulated glucose transporter-2 (GLUT2) compared to NE18. These results suggest that <i>C. perfringens</i> strains can modulate the expression of intestinal genes coding proteins responsible for apoptosis, gut integrity, immunity, mucus production, digestive enzymes, and nutrient transporters which in turn, can affect the severity of NE disease in broilers.</p> <p>The primary objective of the second experiment was to understand whether the addition of a probiotic (<i>Bacillus amyloliqufacens</i>) can aid the performance and gut health of chickens under NE challenge and/or reduced crude protein diets. Results showed that the supplementation of this probiotic increased body weight gain (BWG) and feed intake (FI) and reduced feed conversion ratio (FCR) regardless of the challenge. Probiotic improved performance, increased<i> Bacillus</i> and <i>Ruminocccus</i> numbers, and also decreased the number of <i>C. perfringens</i> in birds fed with reduced crude protein diets. Birds fed <i>Bacillus amyloliqufacens</i> (BA) supplemented diets showed higher cysteine, valine, and lysine ileal digestibility. Results obtained from this study reflect show that this probiotic could be used to ameliorate the negative effects of subclinical NE disease and of feeding low protein diets in broiler chickens by improving the gut environment and thus microbiota profile and nutrient uptake. Furthermore, intestinal gene expression of this experiment is shown in chapter 7 and supplementation of BA decreased cell death signaling proteins (CASP3 and CASP8) and also increased occludin (OCLD) expression regardless of the NE. Expression of immunoglobulins (IgM and IgG) were upregulated by the supplementation of BA. These findings suggest that supplementation of BA in broiler diets can help improve gut health by possessing positive effects on the expression of important genes related to the mucosal barrier, tight junction and immunity in broilers under NE challenge fed either standard or reduced protein diets.</p> <p>The final experiment was conducted to take a broader look at the differences between NE-challenged and healthy birds using transcriptome analysis. A whole transcriptome analysis was performed on intestinal tissue of NE challenged and unchallenged broilers. Results demonstrated a wide range of differences between the two groups of birds. Approximately 370 genes were deferentially expressed in the challenged birds. The NE challenge significantly suppressed metabolic pathways related to peroxisome proliferator-activated receptors (PPARs) signaling and β- oxidation. Immunity genes, especially those related to macrophage and t-cell activity, were activated in infected birds. Some genes related to skeletal muscle growth were also affected which all these changes could affect the growth of challenged birds.</p>