Microflora of the digestive tract: critical factors and consequences for poultry

Abstract

The microflora of the digestive tract of poultry is still incompletely known. Microbial populations of varying size and complexity occur throughout the digestive tract and the highest and most complex floras are found in the crop and the caeca. The upper part of the digestive tract is predominantly settled by facultative anaerobes, whereas the caeca are mainly the site of obligate anaerobes. The types, numbers and metabolic activities of the organisms are affected by numerous factors such as individual, animal age, environment, and diet.Bacteria produce various metabolites that can be useful or detrimental to the host. Interactions between bacteria and the gastrointestinal epithelium lead to various structural and functional modifications of the digestive tract. Bacteria can impair lipid digestion and may modify carbohydrate and protein digestion. They cause an increase in energy and amino acid requirements. They have a negative effect on vitamin nutrition. Beneficial bacteria can protect birds against pathogens through a competitive exclusion process. Moreover, the flora is involved in the development of the intestinal immune system. Overall, bacteria have a negative effect on bird growth. They may also have an effect on meat and egg quality.Improved knowledge of the microflora of the digestive tract and its consequences may contribute to its control and beneficial use for birds as well as breeders, consumers and the environment.

The intestinal microbiota and its modulation for Salmonella control in chickens

“…Ducluzeau and Raibaud used "competitive exclusion" (CE) to refer to 'the phenomenon associated with the tendencies of the first organisms to become established as a flora to hinder the establishment of further microorganisms' (in review by Gabriel et al, 2006). Initially, competitive exclusion, or the Nurmi Concept (Nurmi & Rantala, 1973), involved administration of a saline suspension of the contents of the alimentary tract of adult chickens containing a mature microbiota (Mead, 2000) to newly hatched chicks with a deficient microbiota.…”

“…The compositions of the diet and the microbiota and their interactions also affect the intestinal development, mucosal architecture and the mucus composition of the lower digestive tract (Lan et al, 2005). Conventional chickens have greater absolute and relative weight (weight/kg body-weight) of all intestinal sections than germ-free chickens when fed average and higher concentrations of protein (Gabriel et al, 2006;Lan et al, 2005). The intestine is heavier and longer with thicker walls associated mainly with connective and lymphoid tissue.…”

“…CE develops rapidly, is apparently unaffected by breed, sex or immune status of the recipient and is active against all host non-specific serotypes of Salmonella enterica studied (Mead, 2000). Mechanisms of CE agents, or commensal bacteria in general, to prevent/reduce colonization of pathogens include: competition for nutrients; occupation of attachment sites on the mucosal surface of the intestine that may involve specific interference towards pathogen adhesion or other physiological activities; and production of H 2 S and bacteriocins by elements of the microbiota (Barrow, Mead, Wray, & Duchet-Suchaux, 2003;Gabriel et al, 2006;Schneitz & Mead, 2000).…”

“…Colonization resistance consists of: competitive exclusion and immune modulation of the young chick (Brisbin, Haghighi, Kulkarni, & Sharif, 2007;Gabriel, Lessire, Mallet, & Guillot, 2006;Lee, Lillehoj, & Siragusa, 2010;Revolledo et al, 2006). The microbiota also stimulates development of the digestive tract to impact functions such as: nutrient digestion; digestive enzymes; digestive tract development; gut mucosal proliferation; vitamin synthesis and utilization; and utilization of fermentation and endogenous products (Gabriel et al, 2006;Lan et al, 2005).…”

“…The intestinal microbiota is a function of the diet itself as dietary ingredients are also nutrients for bacterial growth (Gabriel et al, 2006). The compositions of the diet and microbiota plus their interaction can affect the mucosal architecture and the mucus composition of the intestinal tract (Lan et al, 2005).…”