The feed and feces of a continuously fed sheep were analyzed for carbon, hydrogen, and nitrogen, with oxygen as the remainder. The daily feed-feces weight difference was used as the reactant in an equation representing the rumen fermentation. The measured products were the daily production of volatile fatty acids (VFA), CH4, CO2, and ammonia. The carbon unaccounted for was assumed to be in the microbial cell material produced in the rumen and absorbed before reaching the feces. The ratio of C to H, 0, and N in bacteria was used to represent the elemental composition of the microbes formed in the rumen fermentation, completing the following equation: C20.03H36.99017.406N,.345 + 5.65 H20-+ C12H24Ojol. + 0.83 CH4 VFA + 2.76 CO2 + 0.50 NHs + C4.44H.sO2.3sNo.785

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.

No abstract

The feed and feces of a continuously fed sheep were analyzed for carbon, hydrogen, and nitrogen, with oxygen as the remainder. The daily feed-feces weight difference was used as the reactant in an equation representing the rumen fermentation. The measured products were the daily production of volatile fatty acids (VFA), CH 4 , CO 2 , and ammonia. The carbon unaccounted for was assumed to be in the microbial cell material produced in the rumen and absorbed before reaching the feces. The ratio of C to H, O, and N in bacteria was used to represent the elemental composition of the microbes formed in the rumen fermentation, completing the following equation:C 20.03 H 36.99 O 17.406 N 1.345 + 5.65 H 2 O → C 12 H 24 O 10.1 + 0.83 CH 4 VFA + 2.76 CO 2 + 0.50 NH 3 + C 4.44 H 8.88 O 2.35 N 0.785 microbial cells absorbed With C arbitrarily balanced and O balanced by appropriate addition of water, any error is reflected in the H. The H recovery was 98.5%. The turnover rate constant for rumen liquid equilibrating with polyethylene glycol (PEG) was 2.27 per day. Direct counts and volume measurements of the individual types of bacteria and protozoa in the rumen were used to calculate the total microbial cell volume in the rumen, not equilibrating with it. The dry matter in the rumen (582 g) and the nitrogen content (12.05) of the microbes in the rumen were estimated, the latter constituting 85% of the measured N in the rumen. Calculations for rumen dry matter and nitrogen turning over at the PEG rate introduce big discrepancies with other parameters; a rumination pool must be postulated. Its size and composition are estimated. Arguments are presented to support the view that dry matter and some of the microbes, chiefly the protozoa, do not leave the rumen at the PEG rate. One experiment with the same sheep fed twice daily showed significantly less production of microbial cells than did the continuous (each 2 hr) feeding. Analysis of the microbial cell yield suggests that, on the basis of 11 mg of cells per adenosine triphosphate molecule, a maximum of six adenosine triphosphate molecules could have been formed from each molecule of hexose fermented.

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.