Comparison of fermentation kinetics of four feedstuffs using an in vitro gas production system and the ANKOM Gas Production System

Abstract Text: The objective of this study was to perform a comparison between two computerized systems that are used to determine the fermentation kinetics of in vitro gas anaerobic incubation of feedstuffs. The evaluated systems were the ANKOM^RF Gas Production Systems^® (aIVGP) and the in vitro anaerobic fermentation system (tIVGP) as used at Texas A&M University. The aIVGP uses a wireless system, while the tIVGP a wired system to collect the measures. Four different samples of ground corn, alfalfa hay, dried distillers grain, and dried forage were used (n = 16). All components of the fermentation were maintained constant between the IVGP systems (sample: 0.20 g to tIVGP and 0.39 g to aIVGP; rumen fluid: 4.0 ml to tIVGP and 7.8 ml to aIVGP; media: 14.0 ml to tIVGP and 27.3 to aIVGP; and bottle volume: 158 ml to tIVGP and 307 ml to aIVGP). After 48-h, the concentrations of methane in the bottle’s headspace was collected and analyzed using a gas chromatographer. The solution pH was measured and the profiles of the feedstuffs were interpreted using nonlinear model. The total gas production (ml/100 mg of DM), fractional production rate of gas (h^-1), pH of the solution and methane concentrations (μmole/ml of gas) were used to compare the systems. The levels of agreement between the IVGP systems were determined using the coefficient of determination (r²) between both predictions (X axis = aIVGP and Y axis = tIVGP), bias correction (Cb); concordance correlation coefficient (CCC) and mean bias (MB). The IVGP systems had similar values for total gas production (mean X = 17.70; mean Y = 21.23; r² = 0.81; Cb = 0.85; CCC = 0.77; MB = 3.58; P = 0.2165), methane concentration (mean X = 2.15; mean Y = 2.66; r² = 0.89; Cb = 0.83; CCC = 0.79; MB = 0.51; P = 0.0787) and solution pH (mean X = 6.35; mean Y = 6.31; r² = 0.90; Cb = 0.98; CCC = 0.93; MB = -0.04; P = 0.6480). However, the estimated values of fractional production rate of gas were different (mean X = 0.1255; mean Y = 0.1031; r² = 0.44; Cb = 0.79; CCC = 0.52; MB = -0.022; P = 0.0032). The results suggest that both IVGP systems had similar fermentations patterns. The difference in the fractional production rate of gas between these IVGP systems may be due to difference in the headspace gas composition.

Keywords: gas production, headspace, in vitro systems