A Rumen Linear Programming Model for Evaluation of Concepts of Rumen Microbial Function

Reichl, J. R.; Baldwin, R.L.

doi:10.3168/jds.s0022-0302(76)84225-7

Cited by 15 publications

(5 citation statements)

References 18 publications

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“…However, the application of these equations to predator-prey (here : protozoa--bacteria) systems has been questioned, because of the biologically unrealistic results (Bazin, 1981) and the structural instability of the model (Brown & Rothery, 1993). Reichl & Baldwin (1976) described a linear programming model of rumen fermentation in which eight microbial groups, including protozoa, were represented. Considerable simplifications of the predicted rumen ecosystem occurred and the authors concluded that additional concepts regarding microbial interactions were required.…”

Section: Discussionmentioning

confidence: 99%

Simulation of the dynamics of protozoz in the rumen

Dijkstra¹

1994

Br J Nutr

101

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A modified mathematical model is described that simulates the dynamics of m e n microorganisms, with specific emphasis on the rumen protozoa. The model is driven by continuous inputs of nutrients and consists of nineteen state variables, which represent the N, carbohydrate, fatty acid and microbial pools in the rumen. Several protozoal characterktics were represented in the model, inclnding preference for utilization of starch and sugars compared with fibre, and of insoluble compared with soluble protein; engulfment and storage of starch; no utilization of NH, to synthesize amino acids; engulfment and digestion of bacteria and protozoa; selective retention within the rumen; death and lysis related to nutrient availability. Comparisons between model predictions and experimental observations showed reasonable agreement for protozoal biomass in the rumen, but protozoal turnover time was not predicted well. Sensitivity analyses highlighted the need for more reliable estimates of bacterial engulfment rate, protozoal maintenance requirement, and death rate. Simulated protozoal biomass was increased rapidly in response to increases in dietary starch content, but further increases in starch content of a highconcentrate diet caused protozoal mass to decline. Increasing the sugar content of a concentrate diet, decreased protozoa, while moderate elevations of the sugar content on a roughage diet increased protozoal biomass. Simulated protozoal biomass did not change in response to variations in dietary neutral-detergent fibre (NDF) content. Reductions in dietary N resnlted in an increased protozoal biomass. Depending on the basal intake level and dietary composition, protozoal concentration in the rumen was either increased or decreased by changes in feed intake level. Such changes in relative amounts of protozoal and bacterial biomass markedly affected the supply of nutrients available for absorption. The integration of protozoal, bacterial and dietary characteristics through mathematical representation provided an improved understanding of mechanisms of protozoal responses to changes in dietary inputs. Ruminants: Computer simulation: Protozoa: Mathematical modelIn ruminants the quantity and quality of nutrients absorbed from the digestive tract are generally quite different from those ingested because of the activity of the rumen microbial population. The significance of the rumen micro-organisms in the m e n digestion processes and consequently in animal production has been elaborated by many research workers (see Hungate, 1966). The role of m e n protozoa in these processes has been the subject of much debate and our knowledge of rumen protozoa and their function is poor compared with that of rumen bacteria. The contribution of protozoa to total rumen microbial biomass may equal that of bacteria (Hungate, 1966), suggesting possibly an important role of protozoa in ruminal fermentation processes. Yet, in numerous experiments, their presence has been demonstrated to be non-essential for the ruminant (e.g. Veira, 1986). S...

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Section: Discussionmentioning

confidence: 99%

Simulation of the dynamics of protozoz in the rumen

Dijkstra¹

1994

Br J Nutr

101

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“…The rumen fermentative processes are in the form of linear equations and solved by linear programming techniques, in which the objective function consists of the relative metabolic activities of the eight microbial groups. Considerable simplifications of the rumen microbial groups had to be made though when solving the model, and in their evaluation Reichl and Baldwin (1976) concluded that the concepts represented in the model were not sufficient.…”

Section: Objectives and Brief Description Of Whole Rumen Function Modelsmentioning

confidence: 99%

“…In a large number of solutions of the Reichl and Baldwin model (1975), up to four microbial groups were not represented (i.e. simulated extinction of microbial groups), and the model suggested rumen microflora much simpler than the real rumen microflora (Reichl and Baldwin, 1976). Dijkstra (1994a) only obtained biologically realistic coexistence of populations when autoinhibition effects were included in the model.…”

Section: Microbial Metabolismmentioning

confidence: 99%

A comparative evaluation of models of whole rumen function

Dijkstra¹,

France²

1996

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A review is presented on the representation of various rumen fermentation aspects in whole rumen function models in relation to current knowledge on these processes, and areas in need of improved representation are highlighted. The importance of adequately stating the objective of the model in relation to the level of representation of rumen processes is stressed. No model yet exists which can accurately simulate rumen metabolism in all circumstances. A number of issues related to rumen modelling require further research. The sound representation of rumen microbial metabolism is essential. Aspects of microbial metabolism which deserve further attention include microbial distribution within the rumen, microbial interactions, and chemical composition of microbial matter. The representation of outflow from the rumen requires a more mechanistic approach, which should adequately cover continuous as well as discontinuous feeding regimes. Finally, the representation of VFA production is identified as being inadequate, and future attempts to improve prediction of VFA profile should include provisions for the effect of amount and rate of substrate degradation and microbial species preferences on type of VFA produced. Research 98, 129-152 Van Nevel CJ, Demeyer DI (1988) Manipulation of rumen fermentation. In: The rumen microbial ecosystem (PN Hobson, ed) Elsevier Science Publishers, London, 387-444 Wallace RJ, McPherson CA (1987) Factors affecting breakdown of bacterial protein in rumen fluid. Br

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“…However, explicit representation of microbial recycling within the rumen in models has received limited attention. Reichl and Baldwin (1976) evaluated effects of engulfment of bacteria by protozoa in their rumen model, and showed significant effects on cell yields and end-products of fermentation in the presence of protozoa. The Cornell model makes an allowance for protozoal predation by decreasing the theoretical maximum growth yield by 20% (Russell et ai, 1992).…”

Section: Introductionmentioning

confidence: 99%

“…(Reichl and Baldwin, 1976). Dijkstra (1994a) (Wallace and McPherson, 1987), inability to utilize ammonia as N source (Coleman, 1986), and selective retention in the rumen (Faichney, 1989), affect key nutritional characteristics.…”

Section: Introductionmentioning

confidence: 99%