In vitro gas production: a technique revisited

Abstract

Summary The stoichiometrical relationship between gas volumes and short chain fatty acid (SCFA) production has been exemplified for an in vitro gas test based on the bicarbonate buffer. It is outlined that, even though variation in the molar proportion of acetate, propionate and butyrate will influence gas volumes, quite similar amounts of total carbon, hydrogen and oxygen are required for widely different SCFA patterns (0.748: 0.194: 0.058 or 0.459: 0.462: 0.079 for C2: C3: C4), namely, 2.20–2.34 mg to produce 1 ml of gas. However, the variation in microbial biomass production per mole adenosine triphosphate (ATP) presents a serious limitation for in vitro gas tests, since these tests reflect SCFA production only. As a consequence in vitro gas tests need to be complemented by a quantification of substrate concomitantly truly degraded to avoid selection of a substrate with proportionally higher SCFA production and lower microbial biomass yield. This intrinsic problem of in vitro gas tests was experimentally demonstrated for 61 roughages, where a gravimetric determination of microbial biomass yield showed a highly significant (r = −0.78, p < 0.0001) negative relationship between microbial biomass and gas volumes in vitro when both were related to 100 mg of substrates truly degraded. The relationship was further examined for 35 roughages, being representative of the 61 samples, using incubations with stable isotopie nitrogen (15N). In these studies, 15N incorporation and gas production were significantly (r = −0.78, p < 0.001) inversely related. An in vitro method is proposed which combines gas volume and substrate degradability measurements to estimate microbial yield and these estimations agreed well (r = 0.82, p < 0.0001) with 15N measurements. Zusammenfassung Die stöchiometrischen Zusammenhänge von Gas ‐und kurzkettiger Fettsäuren ‐ Produktion im Bikarbonat gepufferten in vitro Gastest wurden exemplarisch dargestellt. Es wird gezeigt, daß unterschiedliche molare Anteile von Essig ‐, Propion ‐ und Buttersäure zwar Auswirkungen auf das Gasvolumen haben, die Masse an Kohlen‐, Wasser‐und Sauerstoff, die für 1 ml Gas nötig ist, jedoch für unterschiedliche molare Fettsäurenzusammensetzung (0.748: 0.194: 0.058 oder 0.459: 0.462: 0.079 für C2: C3: C4) mit 2.20 bis 2.34 mg sehr ähnlich ist. Unterschiedliche mikrobielle Biomasse‐Bildung per mol Adenosintriphosphat (ATP) begrenzt jedoch die Aussagefähigkeit des Gastests, da dieser nur die Bildung von kurzkettigen Fettsäuren reflektiert. In vitro Gastests bedürfen der begleitenden Quantifizierung der Menge an wahr abgebauter Substanz, um die Selektion von Substraten zu vermeiden, die eine proportional hohe kurzkettige Fettsäuren‐Produktion aber niedrigere mikrobielle Biomasse‐Bildung aufweisen. Diese Beziehung wurde experimentell für 61 Rauhfuttermittel aufgezeigt. Die gravimetrisch bestimmte mikrobielle Biomasse zeigt, bezogen auf 100 mg wahr abgebaute Substanz, eine hoch negative Beziehung (r = −0.78, p < 0.0001) zwischen diesem Parameter und dem Gasvolumen. Diese Bezieh...

The source of fermentable carbohydrates influences the in vitro protein synthesis by colonic bacteria isolated from pigs

“…The differences in the use of the energy coming from fermentation of substrates for bacterial growth is also reflected by the amount of SCFA produced per gram of fermented substrate (Blü mmel et al, 1997). When pectin was discarded from the database, BNI values tended to be negatively correlated with SCFA production (r 5 20.72, P 5 0.068).…”

“…The production of acetate and butyrate yields 34 mmol ATP per gram SCFA compared with 40 mmol ATP per gram of propionate (Blü mmel et al, 1997). Acetate is typical of fermentation under C-limiting conditions .…”

Proximate analysis and in-vitro gas production of predominant forages in Afe Babalola University rangeland as feed resources for ruminant production

“…Invitro estimations of feed degradation are important tools for ruminant nutritionists. These methods measure either substrate disappearance or fermentation products (Blümmel et al 1997). In the present study, forages with high CP produced higher gas volume.…”

Evaluasi Jerami Sorgum Varietas Samurai 2 Hasil Iradiasi Gamma secara In Sacco

“…Degradasi BO penting untuk diamati karena bahan tersebut adalah total bahan yang difermentasi mikroba rumen untuk menghasilkan sumber energi bagi ternak [20]. Degradasi BO merupakan indikator yang berhubungan erat dengan dengan degradasi BK karena sebagian bahan kering terdiri atas bahan organik [21].…”