Necrotic enteritis (NE) is an important poultry disease that is currently controlled by the use of in-feed antibiotics in many countries, including Australia. The general public demands clean and green poultry products that require the discontinuation of the use of antibiotics in feed. To achieve this goal, the broiler chicken industry must address the impact of NE without the reliance on in-feed antibiotics. The current thesis has examined a variety of nutritional strategies to minimise the impact of NE in broiler chickens using a subclinical NE model.
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Chapter 1 presents the summary of literature related to NE with particular emphasis on the role of nutritional tools in alleviating losses associated with NE outbreaks. Chapter 2 examined the effect of early feeding a high amino acid density diet on performance of broilers under NE challenge. Birds fed the high amino acid diet had greater body weight by d 35 and heightened Lactobacillus content in the ileum at d 16 (P < 0.05). Birds that were fed the high amino acid (HAA) diet after a period of fasting post-hatch performed better regarding feed conversion ratio (FCR) performance under challenge. The findings from this study suggest there are beneficial effects of feeding high amino acid diets to birds in response to external stresses, such as post-hatch fasting and subclinical NE.
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Chapter 3 investigated the effect of the reintroduction of crude ileal and caecal contents from previously NE-challenged chickens on performance, mortality and intestinal lesions of young broilers under NE challenge. Cloacal administration of both ileal and caecal crude flora inoculants significantly (P < 0.05) improved feed conversion efficiency and alleviated (P = 0.049) the severity of NE-associated lesions at d35. These preliminary findings suggest that the gut microbiome of birds plays a significant role in the susceptibility of broilers to NE.
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Chapter 4 examined the prebiotic properties of arabinoxylo-oligosaccharides (AXOS) produced both in situ and in vitro for their activity against the onset of necrotic enteritis in broiler chickens. Birds fed the AXOS diet had numerically less severe gross lesions, improved feed conversion at d0-16 (P=0.043) and lower ileal viscosity (P < 0.001) at d16 compared to birds fed intact arabinoxylans. Caecal short-chain fatty acid (SCFA) concentration was higher in birds fed AXOS compared to other diets and was higher in the challenged birds compared to the unchallenged birds. The results suggest that AXOS appear to be efficacious prebiotics, as highlighted by improvements in feed conversion ratio (FCR) and increased SCFA.
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Chapter 5 explored whether supplementing diets with xylanase, pectinase and protease would alleviate the effects of key predisposing factors of NE, xylans (from cereals), pectic polysaccharides (from vegetable protein sources) and undigestible proteins on bird performance, caecal volatile fatty acid concentration and ileal pH and prevalence of intestinal lesions, in NE challenged birds. The protease enabled higher weight gain compared to that fed xylanase at d0-35 (P=0.040) and d0-24 in the unchallenged birds (P<0.001). Feed intake was higher at d0-35 (P=0.001), and d0-24 (P=0.011) in birds fed protease, resulting in better feed conversion (P=0.009) in birds fed xylanase compared to that fed protease. Findings from this study suggest that enzyme application can be used as a tool to reduce the amount of undigested nutrients reaching the hindgut and hence lessen the growth of pathogenic bacteria.
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Chapter 6 examined the effects of arabinoxylan (AX) and AXOS on net energy and nutrient utilisation in broilers. Ileal dry matter digestibility was higher in birds fed AXOS compared to that fed AX (P=0.047). Ileal digestible energy and total tract dry matter digestibility was higher in birds fed AXOS compared to that fed AX or AX+E (P=0.004 and P=0.001, respectively). Birds fed AXOS had higher ME intake (P=0.049) and nitrogen retention (P=0.001) and a strong trend of higher NE (P=0.056), NE intake (P=0.057) and retained energy (P=0.054) compared to that fed AX. Total ileal SCFA concentration, including lactic and formic acid, was higher in birds fed AXOS compared to that fed AX (P=0.011, P=0.012 and P=0.023, respectively). These findings indicate that AXOS generation in the gastrointestinal tract via the use of enzymes is not as efficient as feeding AXOS directly.