Effect of organic acids or probiotics alone or in combination on growth performance, nutrient digestibility, enzyme activities, intestinal morphology and gut microflora in broiler chickens

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The gastrointestinal (GI) tract system is of high importance in the production of animals, contributing to growth rate and successful feed efficiency. The optimal gut health is directly involved in the balance of gut microflora, the control of the immune system and its inflammation, the protection of enteric pathogens and the digestion and absorption of nutrients. While the global production of poultry meat has been growing fast, the use of antibiotics has significantly improved animal health by lowering the incidence of diseases (Diarra & Malouin, 2014), enhancing growth and feed efficiency as well as reducing mortality in broiler production. However, their use was introduced without rigorous testing (Graham, Boland, & Silbergeld, 2007) and in recent years, the nature of antibiotic use in poultry production has changed considerably because of concerns about potential negative consequences for human health caused by their use (Singer & Hofacre, 2006). For example, the European Union has banned the use of growth‐promoting antibiotics (AGPs) and their use is being reassessed in the United States. Therefore, current research is focused on finding alternatives to antibiotics in the production of sustainable animal food products to allay environmental and food safety concerns (Kogut & Arsenault, 2016) as well as finding alternative supplements, such as organic acids and probiotics.
The acidification of diets using various weak organic acids such as formic, fumaric, propionic, lactic and sorbic acid has been reported to decrease colonization by pathogens and the production of toxic metabolites, as well as improving the digestibility of protein and of Ca, P, Mg and Zn which can serve as substrates in intermediary metabolism (Hassan, Mohamed, Youssef, & Hassan, 2010; Kirchgessner & Roth, 1988). In the extensive rearing of broiler chickens, organic acid supplements in their diet can enhance their utilization of nutrients and improve their growth and feed conversion efficiency (Agboola, Omidiwura, Odu, Popoola, & Iyayi, 2015). Organic acids and their salts can penetrate a bacterium's cell wall and disrupt its normal physiology as well as reducing the pH of the digesta, increasing pancreatic secretion and can also have trophic effects on the mucosa of the GI tract of animals (Adil, Banday, Bhatm, Mir, & Rehman, 2010). Moreover, the creation of an acidic environment (pH 3.5–4.0) in the gut of broiler chickens by organic acids favours the development of lactobacilli and inhibits the replication of Escherichia coli, Salmonella and other gram‐negative bacteria (Chowdhury et al., 2009; Kopecký, Hrnčár, & Weis, 2012), thus improving their gut health and feed conversion ratio (FCR).
Probiotics are viable micro‐organisms which provide beneficial effects to their host by modifying the intestinal microbiota (Fatufe & Matanmi, 2011). In livestock nutrition, Bacillus, Enterococcus and Saccharomyces are the most common organisms used (Simon, Jadamus, & Vahjen, 2001). The mode of action of probiotics in poultry includes maintaining normal intestinal microflora by competitive exclusion antagonism, lowering the pH through acid fermentation, competing for mucosal attachment and nutrients, producing bacteriocins, stimulating the immune system associated with the gut and increasing the production of short‐chain fatty acids (Sarangi et al., 2016). Both Pirgozliev, Murphy, Owens, George, and McCannin (2008) and Agboola et al. (2015) have reported the beneficial effects of dietary additives (organic acids and probiotics) on energy and protein utilization in poultry. Both constituents are able to modify the microflora which can be the origin of GI sickness and favour a healthy intestinal microflora (Çelik, Mutluay, & Uzatici, 2007; Conway & Wang, 1997; Youssef, Mostafa, & Abdel‐Wahab, 2017).
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