Feed Additives to Improve Performance and Gut Health in Broilers Under Necrotic Enteritis Challenge

Abstract

<p>Necrotic enteritis (NE) is caused by the ubiquitous bacterium, <i>Clostridium perfringens</i>, together with one or more predisposing factors e.g. coccidiosis and high inclusion of poorly processed fish meal. Necrotic enteritis is an economically important enteric disease prevalent in the fast-growing broilers, particularly in the post-antibiotic era. Among many feed additives, organic acid (OA) blends and plant extracts (PE) are gaining increased attention in alleviating the effects of NE in broilers due to their known antimicrobial properties. However, the data in the literature are not consistent. Moreover, the potentials of these additives are not well-researched under NE challenge, both under subclinical and clinical challenge. The current thesis has examined the potentials of OA blends and PE in improving performance and protecting intestinal health of broilers under NE challenge, both subclinical and clinical.</p> <p>Chapter 1 presents a brief introduction of the problem, NE control strategies, and the primary objectives to conduct this study.</p> <p>Chapter 2 presents the summary of the literature related to NE and ongoing strategies to control NE outbreaks with particular emphasis on feed additives, OA blends and PE supplementation.</p> <p>Chapter 3 examined the potential of blended short-chain fatty acids (SCFA) with medium-chain fatty acids (MCFA) to improve performance, health and welfare of broilers under subclinical NE challenge. The additives used were A) a blend of SCFA, MCFA, and a phenolic compound (SMP); B) a blend of free and buffered SCFA with MCFA (SMF); C) a blend of free and buffered SCFA with a high concentration of MCFA (SHM). Results showed that the birds fed SHM had higher BWG compared to the challenged control group (CHC) (<i>P</i>= 0.001; d 10 to 24). Birds in all 3 additive groups had lower FCR (d 0 to 35), footpad dermatitis and hock burns compared to CHC group (d 35) (<i>P</i> < 0.05). These findings suggest the potential of OA blends to protect birds from NE indicated by improved FCR, digestibility, and bird welfare.</p> <p>Chapter 4 evaluated the effects of SCFA and MCFA blends and/or phenolic compounds on intestinal integrity, intestinal pH, caecal microbiota, and SCFA profiles of broilers under subclinical NE challenge. Birds fed all 3 additives had decreased fluorescein isothiocyanate dextran (FITC-d) concentration from gut to serum and reduced <i>Bacteroides</i> levels (d 16, <i>P</i> < 0.05) as compared to the CHC group. Birds fed additive SHM had higher concentrations of acetate and butyrate (d 21, <i>P</i> < 0.05) in caecal content than CHC group but were not different from SMP and SMF groups. Birds in all 3 additive groups had similar FITC-d concentrations in serum, acetate, propionate and butyrate concentrations in the caeca, and caecal bacterial loads compared to the BAC group (P > 0.05). However, the SMP group had a higher load of<i>C. perfringens</i>than zinc bacitracin (BAC) group (<i>P</i> < 0.05). These findings suggest the potentials of OA blends as alternatives to BAC in protecting birds from NE as indicated by improved intestinal health.</p> <p>Chapter 5 evaluated the potential of monoglycerides blend (MG), a blend of mono-, di- and tri-glycerides with the main component being 1-monoglycerides, and buffered formic acid (FA) as alternatives to antibiotics on performance and intestinal health in broilers under clinical NE challenge. Results showed that birds fed MG had lower NE-caused mortality than the non-additive control (NC) group (<i>P</i> < 0.05). Birds fed MG had upregulated jejunal tight junction protein1 (<i>TJP1</i>) and immunoglobulin (<i>IgG</i>) gene on d 16, and improved gross energy digestibility on d 24 than NC group (<i>P</i> < 0.05). These findings suggest that supplementation of MG may improve intestinal health and reduce mortality of birds during the clinical NE occurrence.</p> <p>Chapter 6 examined the potential of PE, a microencapsulated product composed of eugenol and garlic tincture, as an alternative to antimicrobial (AM) agent on performance and intestinal health in broilers under clinical NE challenge. Birds fed PE had improved FCR (<i>P</i> < 0.05) and livability (5.8%) compared to the challenged control (CC) group (d 0 to 35). Inclusion of PE reduced ileal lesion scores in male birds (<i>P</i> < 0.05). Birds fed PE had decreased <i>E. maxima</i> and <i>E. acervulina</i> oocyst counts in caecal content (<i>P</i> < 0.05). Birds fed PE had decreased E. brunetti and total oocyst counts in caecal content, and <i>E. acervulina</i> oocyst counts in ileal content in only female birds (<i>P</i> < 0.05). On d 35, PE supplementation reduced variation of BW in both male and female birds. These findings suggest the potential of PE inclusion to improve the feed efficiency and intestinal health of birds under clinical NE.</p> <p>Chapter 7 investigated the underlying mode of action of PE in controlling clinical NE by evaluating intestinal integrity, duodenal histomorphology, jejunal gene expressions, ileal and caecal microbiota. Results showed that birds fed PE had reduced FITC-d, increased goblet cell numbers and <i>Bifidobacterium</i> compared to the CC group (<i>P</i> < 0.05). Birds fed PE had reduced <i>CLDN5</i> expression in male birds, and <i>Bacteroides</i> spp. in female birds than CC group (<i>P</i> < 0.05). These findings suggest that PE supplementation may mitigate the negative effect of NE on intestinal health.</p>