Paper-Lecture42 - Fermentation Substrate and Dilution Rate...

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206 1 Journal Paper No. 12,784 of the Missouri Agric. Exp. Sta. 2 Present address: College of Anim. Sci. & Technol., China Agric. Univ. Beijing 100094, P.R. China. 3 To whom correspondence should be addressed: 111 Animal Sciences Research Center. Phone: 573/882-0834; fax: 573/ 882-6827. Received December 15, 1997. Accepted August 28, 1998. Fermentation Substrate and Dilution Rate Interact to Affect Microbial Growth and Efficiency 1 Q. Meng 2 , M. S. Kerley 3 , P. A. Ludden, and R. L. Belyea Department of Animal Sciences, University of Missouri, Columbia 65211 ABSTRACT: The effect of dilution rate (D) on carbohydrate, fibrous and nonfibrous, and protein fermentation by ruminal microorganisms was studied using a single-effluent continuous-culture system. The diets of fibrous carbohydrate, nonfibrous carbohy- drate, or protein were formulated with soybean hulls (FC), ground corn (NFC), or isolated soy protein (PR) as the primary ingredient, respectively. Six dilution rates (.025, .050, .075, .10, .15, and .20/h of fermenter volume) were used. Digestibilities of DM, OM, and CP for the three diets and of NDF and ADF for the FC diet decreased ( P < .001) as D increased, although the response of the digestibility to D varied with diet. Increasing D resulted in an increase in pH ( P < .001) and a decrease ( P < .001) in ammonia concentration. Daily volatile fatty acid production increased (quadratic; P < .01) for the FC and NFC diets, but decreased (quadratic; P < .001) for the PR diet. Increasing D quadratically increased ( P < .001) the molar percentage of acetate and propionate, but quadratically decreased ( P butyrate and valerate for the FC and NFC diets. For the PR diet, the molar percentage of propionate and valerate increased (quadratic; P < .01), whereas acetate and butyrate decreased (linear; P < .001) in response to increasing D. Molar percentage of isobutyrate and isovalerate decreased ( P < .01) with increasing D for all three diets. As D increased, daily microbial N production showed quadratic responses with maxi- mum values achieved at .126, .143, and .187/h D for the FC, NFC, and PR diet, respectively. There was a positive correlation between microbial growth effi- ciency (MOEFF) and D. A quadratic model fit the data of MOEFF as affected by D, and maximum MOEFF of 37.3, 59.6, and 71.4 g of bacterial N/kg OM truly fermented were calculated to be achieved at .177, .314, and .207/h D for the FC, NFC, and PR diet, respectively. Dilution rate significantly influenced the ruminal microbial fermentation of fibrous and nonfi- brous carbohydrates and proteins, and was positively related to microbial yield and growth efficiency. In addition, microbial nitrogen composition, and there- fore efficiency, was affected by substrate fermented. Key Words: Dilution, Rumen Fermentation, Microbial Activities, Culture Techniques 1999 American Society of Animal Science. All rights reserved. J. Anim. Sci. 1999. 77:206–214 Introduction To determine dietary amino acid needs of ruminants, the flow of microbial amino acids from the rumen must be estimable. Microbial amino acid flow from the rumen is a function of how efficiently microbes use the energy generated from their fermen- tation. Carbohydrate (fibrous or nonfibrous) and
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Paper-Lecture42 - Fermentation Substrate and Dilution Rate...

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