Paper-Lecture14 - Microbial Attachment and Feed Digestion...

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Microbial Attachment and Feed Digestion in the Rumenl12 T. A. McAllister*, H. D. Bae”, G. Jones?, and K.-J. Cheng“ *Agriculture Canada, Research Station, Lethbridge, Alberta T1J 4B1 and +University of Saskatchewan, Saskatoon, Saskatchewan S7N OW0 ABSTRACT: Direct microscopic examination of the rumen and its contents shows microbial populations largely attached to feed particles in the digesta. Most feeds contain a surface layer that is resistant to attachment and therefore to digestion. Infiltration of these recalcitrant epidermal layers through damage sites or through focused enzymatic attack is essential for initiation of the digestive process. Proliferation of primary colonizing cells produces glycocalyx-enclosed microcolonies. Secondary colonizers from the ruminal fluid associate with microcolonies, resulting in the formation of multispecies microbial biofilms. These metabolically related organisms associate with their preferred substrates and produce the myriad of enzymes necessary for the digestion of chemically and structurally complex plant tissues. Upon accessing the internal, enzyme-susceptible tissues, microbial “diges- tive consortia” attach to a variety of nutrients, including protein, cellulose, and starch and digest insoluble feed materials from the inside out. Sub- stances that prevent microbial attachment or promote detachment (e.g., condensed tannins, methylcellu- lose) can completely inhibit cellulose digestion. As the microbial consortium matures and adapts to a particu- lar type of feed, it becomes inherently stable and its participant microorganisms are notoriously difficult to manipulate due to the impenetrable nature of bi- ofilms. Properties of feed that place constraints on microbial attachment and biofilm formation can have a profound effect on both the rate and extent of feed digestion in the rumen. Developments in feed process- ing (i.e., chemical and physical), plant breeding, and genetic engineering (both of ruminal microorganisms and plants) that overcome these constraints through the promotion of microbial attachment and biofilm formation could substantially benefit ruminant production. Key Words: Rumen, Bacteria, Fungi, Protozoa, Bacterial Attachment, Feed Digestion J. him. Sci. 1994. 72:3004-3018 Introduction Microorganisms in aquatic ecosystems as diverse as alpine streams and the bovine rumen have a natural tendency to interact with and attach to surfaces (Matthysse, 1992; Pel1 and Schofield, 1993). In newborn ruminants, this natural phenomenon is observable 38 h after birth as bacteria from the ruminal fluid attach to and colonize the tissues of the digestive tract (Cheng et al., 1991a). Bacteria at- tached to the wall of the rumen sequester oxygen, hydrolyze urea and, in conjunction with bacteria in the fluid phase, modify the ruminal environment. Fungi and protozoa become established in the ruminal microbiota within 8 to 10 d and 12 to 20 d, respectively (Fonty et al., 1987, 1988; Stewart et al., ‘Presented at a symposium titled “Current Aspects of Microbiol- ogy of the Digestive Tract” at the ASAS 85th Annu. Mtg., Spokane,
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Paper-Lecture14 - Microbial Attachment and Feed Digestion...

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