SUMMARYA rapid method for measuring gas production during incubation of feedingstuffs with rumen liquor in vitro is described. Gas production in 24 h from 200 mg feed dry matter was well correlated with digestibility of organic matter, determined in vivo with sheep. Multiple regression analysis, when it included data from proximate analysis, resulted in an equation (R = 0-98) for prediction of metabolizable energy content, based on 30 experiments with rations varying in protein and crude fibre content, and 59 other experiments with concentrates. Energy content was in the range of 7-7-13-2 MJ ME/kg D.M. (X + S.D. = 11-17 ± 1-08). The residual standard deviation of the equation was 0-25 MJ. Gas production was measured in calibrated syringes. The only chemical determinations needed are dry matter, protein and fat. Differences in activity between batches of rumen liquor are corrected by reference to gas production with standard feedingstuffs (hay meal and maize starch).

Zusammenfassung Eine vergleichende in vitro‐Untersuchung zur Fermentation von energiereichen Zulagen im Pansen Eine Methode zur Inkubation von Futtermitteln mit Inoculum aus Panseninhalt (Menke et al. 1979) wurde eingesetzt, um Fermentationsraten von Weizen, Gerste, Tapioka, Sorghum, Hafer, Roggen, einer Konzentratmischung, Heu und Haferstroh zu bestimmen. Während der Inkubationsdauer von 96 Stunden wurde die Gasproduktion in verschiedenen Zeitintervallen gemessen. Die Fermentationsrate (k) wurde mittels nichtlinearer Regression geschätzt, wobei mathematische Modelle mit und ohne anfänglicher Verzögerung (1) der Fermentation verwendet wurden. Die Schätzwerte für k variierten zwischen 0,024 und 0,140 bzw. 0,035 und 0,135 wenn das Modell die Verzögerung ein‐ bzw. ausschloß. Es werden Probleme diskutiert, welche sich im Zusammenhang mit der Schätzung und Interpretation von 1 sowie deren Einfluß auf Schätzungen von k ergeben. Die Anwendung von k‐ und l‐Werten zur Vorhersage der Pansenverdauung werden ebenfalls diskutiert.

No abstract

1. A method is described for the determination of protein degradation based on measurements of ammonia concentration and gas production (Menke et al. 1979) when a feedingstuff was incubated with rumen fluid in vitro.2. NH, liberated during incubation is in part used for microbial protein synthesis. Production of carbon dioxide and methane can be regarded as a measure of energy available for protein synthesis. The ratio, gas production: incorporation of NH,-nitrogen was estimated by addition of starch to the substrate. The response in gas production was linear in the range C200 mg starch, when starch was added to C200 mg feedingstuff dry matter and 30 ml rumen fluid-medium mixture.3. Linear regression between NH,-N concentration (y, mg) and gas production (x, ml) yielded an intercept (6,) representing that amount of NH,-N which would be released when no fermentable carbohydrates were available and consequently no bacterial protein synthesis took place.4. The difference between this intercept 6, and NH,-N content in the blank (rumen fluid without substrate added) indicated the amount of NH, liberated from protein and other N-containing compounds of the feedingstuff incubated. In vitro-degradable N (IVDN) was calculated as a proportion of total N by the equation:NH,-N at zero gas production (b,-NH,-N of blank Total N of feedingstuff incubated IVDN =

The relationship between gas production and microbial protein synthesis was studied in vitro using the method of MENKE et al. (1979). 150 mg starch or cellulose or a mixture of 10% glucose, 40% starch and 50% cellulose was used as the carbohydrate source. The microbial protein synthesis and gas production occurring during 2 hrs after the 5th, 10th, and 23rd hr of incubation were studied. Total and net microbial synthesis were estimated using 32P as a microbial marker and by the net disappearance of NH3-N respectively. The data indicate that the type of carbohydrate and the rate of carbohydrate fermentation influence microbial protein synthesis per unit volume of gas produced. However, the relationship between total synthesis and cumulative gas production (up to 8 hrs incubation) with carbohydrate mixture as the substrate was linear. With reference to these observations, the possibilities and difficulties in using cumulative gas production as an index of microbial growth potential of the feedstuffs are discussed.