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Biomedical subjects

J R Reichl

Publications and source records attributed to J R Reichl.

15 recordsLinked to original sources
PubMed1995

[Simulation of nutrient dynamics in the rumen of sheep and cattle considering the feed composition, level of feed intake and feeding frequency. 1. Model description].

The aim of this work was to develop a dynamic, mechanistic computer-model, which can be used to simulate digestion, outflow and pools of different nutrients in the rumen of sheep and cattle and which reacts on changes of the feed composition, on the level and the frequency of feeding. The model consists of 35 flux- and 17 differential equations and works under cyclic steady-state conditions. The following mechanism are integrated into the model: The three substrates protein, neutral detergent fibre (NDF) and non-fibre-carbohydrates are degraded by three specific groups of microbes. A fourth group degrades NDF and non-fibre-carbohydrates following the principle of competitive inhibition. The fermentation in the rumen serves for supply of energy for growth and for the maintenance of microbes. The rates of degradation are calculated from the turnover-time of the specific substrate and the amount of microbes. Recycling of N occurs through recycling of the microbial protein and the ruminohepatic pathway. If concentration of ammonia in rumen fluid decreases below 50 mg/l then the growth of microbes declines.

Animal Feed↗
PubMed1995

[Simulation of nutrient dynamics in the rumen of sheep and cattle considering the feed composition, level of feed intake and feeding frequency. 2. Model validation].

A mathematical model of rumen fermentation processes was validated with 65 sheep experiments and 45 cattle experiments, respectively. Further, it was shown how the model reacts when the feed composition, the level of feed intake and the feeding frequency was changed. The model predictions were satisfactory for the digestibility of organic matter and neutral detergent fibre (NDF) in rumen, the production of volatile fatty acids and the non-ammonia-N (NAN) flow to duodenum. The partition of NAN in microbial and feed N was estimated with lower reliability. The effects of variation of feeding level, feeding frequency and roughage quality (crude protein, lignin) on digestion processes have been simulated correctly. On the other hand, the effects of the proportion of roughage to concentrate have not been reproduced sufficiently with the mechanisms included in the model. To make correct predictions in this area too, it is necessary to integrate the rumen pH and its effects on rumen processes into the model. A mechanistic approach for estimation of the velocity constants for passage of substances out of the rumen would improve the model.

Animal Feed↗
PubMed1976

A rumen linear programming model for evaluation of concepts of rumen microbial function.

A linear programming model provides for analysis of general input-output relationships in the rumen, for evaluation of competitive relationships among rumen microbes, and for computation of optimal relationships in the rumen. Eight rumen microbial groups defined on the bases of substrate specificity, nutrient requirements for growth, fermentation products, and relative metabolic activities comprise the central core of the model. Relative metabolic rates of microbial groups calculated from their cell sized were used as coefficients in the objective function. The model was used to evaluate effects of different amounts of protein from feed and various carbohydrates upon microbial population and fermentation patterns as accommodated by current concepts. During the several solutions of the model, considerable simplification of the rumen microflora occurred. This implies that current data and concepts, and the hypothesis regarding relative metabolic rate, as represented in the model, do not accommodate adequately competitions among the several rumen microbial species and, thus, that additional data and concepts regarding rumen microbial interactions are required. Also evaluated were effects of ingestion of bacteria by protozoa upon over-all rumen function, absolute microbial cell yields, cell yields per mole of adenosine triphosphate, and factors affecting these.

Adenosine Triphosphate↗
PubMed1975

Rumen modeling: rumen input-output balance models.

Two models of rumen fermentative relationships expressed as systems of simultaneous linear equations and based on requirements for maintenance of balances of elementary imput and output and metabolic pathways are presented in matrix format consistent with solution by linear programs. Matrix entries defining the two models were verified carefully based upon a survey of the literature, and conceptual bases of the models were validated by comparisons of model outputs with experimental data not used in model construction. The models then were used to evaluate interactions among feed composition, volatile fatty acid yields and patterns, microbial growth yields and efficiencies, and microbial metabolic pathways.

Amino Acids↗