A comparative evaluation of models of whole rumen function

Dijkstra, J.; France, J.

doi:10.1051/rnd:19960638

Cited by 9 publications

(10 citation statements)

References 41 publications

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“…There are almost no differences in the error of predictions when different sources of concentrates are used (10.3%, 8.4% and 9.8% for diets using barley, maize grain or both as a supplement, respectively). As found by others (Neal et al, 1992;Dijkstra and France, 1996), the total NAN flow to the duodenum is predicted by this model with much higher accuracy than for its components, dietary, endogenous and microbial NAN.…”

Section: Nmetabolismsupporting

confidence: 53%

A dynamic simulation model of nutrient digestion in the rumen of dairy cows

Petruzzi¹,

Danfær²,

Nørgaard³

2002

J. Anim. Feed Sci.

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A mechanistic model of nutrient digestion in the rumen of dairy cows has been developed to predict rates of nutrient digestion and passage as well as rumen NDF pool sizes at fixed rates of dry matter intake. Different feed fractions according to chemical and physical characteristics are considered. There are 18 rumen state variables representing carbohydrates, nitrogen and microbes in the model. The model is mainly sensitive to the parameters defining rate constants of passage of small particles and digestion rate constant of NDF. For comparative analysis the model has been tested with diets differing widely in intake level and composition. NDF passage and digestibility, NDF pool, total and non-ammonia nitrogen outflow from rumen are well predicted for the whole range of diets used. For some diets, especially those containing maize as a source of starch the predictions of OM and starch digestibility and partition of NAN outflow between dietary and microbial N outflow are not satisfactory.

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Section: Nmetabolismsupporting

confidence: 53%

A dynamic simulation model of nutrient digestion in the rumen of dairy cows

Petruzzi¹,

Danfær²,

Nørgaard³

2002

J. Anim. Feed Sci.

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“…Although most models represent the effect of intake level on flow rates, equations vary widely among models. This largely impacts predictions, as underlined by Dijkstra and France (1996). A more mechanistic representation of transit has been proposed in some models (Sauvant et al, 1996), and deserves further exploration.…”

Section: Carbohydrate Digestion and Nutrient Fluxesmentioning

confidence: 99%

Carbohydrate quantitative digestion and absorption in ruminants: from feed starch and fibre to nutrients available for tissues

Nozière

Ortigues-Marty

Loncke

et al. 2010

Animal

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Carbohydrates are the main source of energy in ruminants. Their site, extent and kinetics of digestion highly impact the amount and profile of nutrients delivered to peripheral tissues, and the responses of the animal, i.e. ingestion, efficiency of production, N and methane excretion, quality of products and welfare. Development of multi-objective feed evaluation systems thus requires a more integrated quantitative knowledge on carbohydrate digestion and yield of terminal products, as well as on their metabolism by splanchnic tissues. The objective of this paper is to review (i) quantitative knowledge on fibre, starch and sugar digestion, volatile fatty acids (VFA) and glucose production and splanchnic metabolism and (ii) modelling approaches which aim at representing and/or predicting nutrient fluxes in the digestive tract, portal and hepatic drainage. It shows that the representation of carbohydrate digestion and VFA yield is relatively homogeneous among models. Although published quantitative comparisons of these models are scarce, they stress that prediction of fibre digestion and VFA yield and composition is still not good enough for use in feed formulation, whereas prediction of microbial N yield and ruminal starch digestion seems to be more satisfactory. Uncertainties on VFA stoichiometric coefficients and absorption rates may partly explain the poor predictions of VFA. Hardly any mechanistic models have been developed on portal-drained viscera (PDV) metabolism whereas a few exist for liver metabolism. A qualitative comparison of these models is presented. Most are focused on dairy cows and their level of aggregation in the representation of nutrient fluxes and metabolism highly differs depending on their objectives. Quantitative comparison of these models is still lacking. However, recent advances have been achieved with the empirical prediction of VFA and glucose production and fluxes through PDV and liver based on the current INRA feed evaluation system. These advances are presented. They illustrate that empirical prediction of ruminal VFA and intestinal glucose production can be evaluated by comparison with measured net portal net fluxes. We also illustrate the potential synergy between empirical and mechanistic modelling. It is concluded that concomitant empirical and mechanistic approach may likely help to progress towards development of multi-objective feed evaluation systems based on nutrient fluxes.

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“…A avaliação de padrões de alimentação descontínuos podem incrementar a importância da representação das características mencionadas anteriormente. De acordo com Dijkstra & France (1996), a representação de padrões de alimentação descontínuos não recebeu muita atenção em modelos ruminais, e a simulação dinâmica de diferentes "pools" pode ser de importância, especialmente quando são utilizadas dietas sem sincronização na fermentação de nutrientes. Há pouca informação quantitativa em como a freqüência de alimentação afeta o padrão de disponibilidade de nutrientes (GILL, 1996).…”

Section: Pgrunclassified

“…Há pouca informação quantitativa em como a freqüência de alimentação afeta o padrão de disponibilidade de nutrientes (GILL, 1996). Como observado em modelos de digestão (DIJKSTRA & FRANCE, 1996) ou previsão de consumo (SAUVANT et al, 1996), a representação da cinética ruminal requer de representações mecanísticas para indicar os intervalos de tempo mais apropriados entre refeições ou explicar variações no consumo.…”

Section: Pgrunclassified

Modelagem da redução do tamanho de partículas na alimentação de ruminantes

Saenz

2005

Ciênc. agrotec.

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RESUMOO tamanho de partícula influencia o valor nutricional do alimento porque pode afetar o consumo de matéria seca, a digestão e utilização de nutrientes pelos microorganismos ruminais e, o desempenho animal. Alguns modelos são apresentados para ilustrar a evolução da representação da redução do tamanho de partícula. Em geral, as diferentes propostas se comportam adequadamente e provêem informação útil para produção ou pesquisa. Porém, todos os modelos demonstram inexatidão em certos pontos. Nesta revisão são discutidas as razões para esses problemas e é proposta a inclusão de novas variáveis relacionadas com a cinética de partículas, ingestão descontínua de alimentos e liberação do conteúdo celular com o objetivo de aumentar a precisão de futuros modelos de consumo e digestão. Termos para indexação: cinética ruminal, consumo, digestibilidade, modelos de simulação. ABSTRACTParticle size seems to be an important factor influencing the nutritional value of the feed because it may affect dry matter intake, microbial digestion and utilization of nutrients and animal performance. Some models are described to present different attempts to represent particle size reduction. In general, the diverse approaches behave adequately and provide useful information for production or research. All models, however, demonstrate inaccuracy in some points. The reasons for these failures are discussed and the inclusion of new variables related to particle kinetics, pulses of feed and cell content release to increase accuracy of predictions in future models of feed intake and digestion of ruminants is proposed. Index terms: digestibility, feed intake, ruminal kinetics, simulation models. As forragens representam uma fração importante do consumo de energia em sistemas de produção de ruminantes. Existem muitos fatores que influenciam o consumo voluntário de alimentos (CVA) pelos ruminantes. A restrição física do CVA devido a atributos físicos das forragens é um dos mais importantes. Entre esses atributos, o tamanho de partícula pode ser um fator importante que influencia o valor nutricional do alimento porque afeta tanto o consumo de matéria seca (CMS) como a taxa na qual os nutrientes ficam disponíveis para digestão e utilização microbiana. Dependendo da qualidade da forragem, a redução de tamanho de partícula pela moagem ou peletização pode incrementar o consumo de forragens e alimentos fibrosos substancialmente (SOEST, 1994).O tamanho de partícula também afeta a taxa de passagem da ingesta através do rúmen. Quando o conteúdo ruminal chega a um ponto onde incremento adicional não é possível, a taxa de passagem da ingesta determina o consumo de alimento (BOSCH, 1991). A taxa na qual o alimento é reduzido a partículas suficientemente pequenas para atravessar o orifício retículo-omasal, e a taxa de degradação pelos microorganismos, são os fatores mais importantes que limitam o desaparecimento de digesta do rúmen.Por outro lado, embora uma fração das partículas ruminais possuam tamanho adequado para atravessar o orifício retículo-omasal...

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A comparative evaluation of models of whole rumen function

Cited by 9 publications

References 41 publications

A dynamic simulation model of nutrient digestion in the rumen of dairy cows

A dynamic simulation model of nutrient digestion in the rumen of dairy cows

Carbohydrate quantitative digestion and absorption in ruminants: from feed starch and fibre to nutrients available for tissues

Modelagem da redução do tamanho de partículas na alimentação de ruminantes

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