Effects of dietary yeast β-glucans supplementation on growth performance, gut morphology, intestinal Clostridium perfringens population and immune response of broiler chickens challenged with necrotic enteritis

Highlights

• Yeast β-glucans supplementation decreased C. perfringens-induced NE lesions and Clostridium perfringens colonization.

• Yeast β-glucans supplementation could stimulated intestinal endogenous antimicrobial peptide gene expression and enhanced humoral immunity.

• Yeast β-glucans supplementation improved intestinal health in broiler birds challenged with Clostridium perfringens.

Abstract

Necrotic enteritis (NE) is an enterotoxemic disease caused by Clostridium perfringens that results in substantial economic losses to the global poultry industry. This study was conducted to investigate the effects of dietary yeast β-glucans (YG) on growth performances, gut morphology, intestinal C. perfringens population, endogenous antimicrobial peptide expression, and humoral immune response of broiler chickens infected with NE. A total of 240 one-day-old male broiler chicks were randomly assigned to a 2 × 2 factorial arrangements of treatments with two dietary glucan levels (0 or 200 mg/kg of diet) and two disease challenge status (control or NE challenged). NE model was induced via oral inoculation of mixed strains of Eimeria species at 12 d of age, followed by an oral inoculation with C. perfringens at 16, 17 and 18 d of age. Infected birds fed the glucan-supplemented diet had significantly increased body weight (13 to 21 d, 0 to 42 d), significantly improved feed efficiency (13 to 21 d, 21 to 42 d), increased antibody levels against C. perfringens and improved villi height and villi height to crypt depth ratio. In addition, infected birds that were supplemented with YG had markedly reduced intestinal C. perfringens numbers, and NE gut lesion scores compared with infected birds fed unsupplemented diet. Moreover, YG supplementation increased gene expression of Cath-2, AvBD-4, and AvBD-10 expression at the early infection stage and Cath-1, Cath-2, and AvBD-1 at the later infection stage in the gut compared with unsupplemented birds. Decreased AvBD-10 and LEAP-2 mRNA levels were observed at the later infection stage in the glucan-supplemented birds when compared with that in the non-supplemented control group. In conclusion, yeast β-glucans supplementation improved intestinal health of broiler birds challenged with C. perfringens-induced necrotic enteritis.

Introduction

Necrotic enteritis (NE) is caused by Clostridium perfringens (Cp) types A and C, a Gram-positive anaerobic spore-forming, rod-shaped bacterium which produces a range of necrotizing toxins, such as α-toxin and netB toxin (Van Immerseel et al., 2004, Van Immerseel et al., 2009). Acute or subclinical C. perfringen infections cause necrotic lesions in the gut wall. In poultry, clinical NE is characterized by intestinal lesions, severe morbidity and mortality, whereas subclinical NE is characterized by reduced feed intake and body weight, diarrhea, ruffled feathers and depression (Timbermont et al., 2011). These outcomes impair animal welfare and impose tangible economic burdens on poultry producers. Some of the factors that contribute to the development of NE are coinfection with Eimeria or infectious bursal disease virus, or presence of C. perfringens toxins, high dietary levels of specific cereals and fish meal, disturbance to normal intestinal flora, overcrowding, and a variety of environmental conditions (Shojadoost et al., 2012, Timbermont et al., 2011). Experimental models to induce NE with coinfection with Eimeria maxima and C. perfringens has been successfully established (Lee et al., 2012).

NE outbreaks in commercial poultry flocks are controlled by prophylactic use of in-feed antibiotics (Van Immerseel et al., 2009). However, with the emergence of antibiotic-resistant pathogens and increasing concerns about chemical residue in poultry meat, many antibiotics traditionally used to prevent and control NE have been restricted or banned for use in poultry production. Therefore, there is an urgent need to develop alternatives to antibiotics that can reduce economic losses during NE outbreaks. Dietary immunostimulant supplementation is one strategy to improve immune function, reduce antibiotic usage, minimize drug residue and increase disease resistance in livestock and poultry (Lamont, 1998). Yeast β-glucans (YG), a polysaccharide extracted from Saccharomyces cerevisiae cell wall, have been widely studied and shown to possess immunomodulatory activities involving receptor recognition and be most effective in enhancing host protective immunity against infectious agents in mammalian species (Murphy et al., 2010, Stier et al., 2014, Volman et al., 2008).

In poultry, yeast β-glucans supplementation protects against a number of economically-important pathogens, such as Salmonella enterica, Escherichia coli and Eimeria species and improves gut health and increases disease resistance (Cox et al., 2010b, Huff et al., 2010, Lowry et al., 2005, Revolledo et al., 2009, Shao et al., 2013). Yeast β-glucans supplementation enhances lysozyme and complement levels, improves phagocytic activity and alters tight junction protein expressions (Chen et al., 2008, Chuammitri et al., 2011, Lowry et al., 2005). Broilers supplemented with yeast β-glucans have increased humoral and cell-mediated immune responses (Chae et al., 2006, Cox et al., 2010a, Cox et al., 2010b, Kumar et al., 2011, Redmond et al., 2010, Shao et al., 2013). In addition, supplementation with yeast cell wall extract prevents production loss, regulates intestinal innate immune responses, decreases intestinal C. perfringens colonization and proliferation and reduces gut lesions scores after oral infection with coccidial oocysts and C. perfrigens in broilers (M'Sadeq et al., 2015, Thanissery et al., 2010, Yitbarek et al., 2012).

Antimicrobial peptides (AMPs) are ubiquitous in biological organisms including mammals, birds, insects and plants, and generally expressed in mucosal linings (e.g. skin, intestine, respiratory tract) and constitute a critical component of innate immune responses due to broad-spectrum antimicrobial activity and immunomodulatory properties (Cuperus et al., 2013, Zhang and Sunkara, 2014). Besides having direct antimicrobial activities, AMPs modulate innate immune responses and control homeostasis by inducing chemotaxis and activating leukocytes, inducing and/or inhibiting cytokine production (Lai and Gallo, 2009, Zhang and Sunkara, 2014). Avian AMPs belong to three main families: β-defensins (AvBD-1 to 14), cathelicidins (Cath-1 to −3) and liver expressed antimicrobial peptides 2 (LEAP-2) (Cuperus et al., 2013, Michailidis, 2010, Townes et al., 2004, van Dijk et al., 2008, Zhang and Sunkara, 2014). Although previous research has reported that yeast β-glucans can influence gene expression of AMPs in fish (Marel et al., 2012, Schmitt et al., 2015), there are currently no studies of AMP expression following yeast β-glucans supplementation in chickens infected with NE. We hypothesized that yeast β-glucans supplementation could improve gut health and enhance intestinal innate immunity against NE by increasing intestinal AMPs in broiler chickens. To test this hypothesis, we investigated the effect of yeast β-glucans supplementation on growth performance, gut morphology, intestinal C. perfringens population and endogenous antimicrobial peptides (β-defensins, Cathelicidins and LEAP-2) expression and humoral immune response of broiler chickens infected with Eimeria oocysts and C. perfrigens. In summary, the collected data indicated that yeast β-glucans supplementation improved gut health and enhanced host disease resistance in chickens challenged with NE by inducing endogenous AMPs.