1651 The micro gas test: A small scale in vitro system for high throughput analysis

METHOD • The MGT is a small scale in vitro method, conducted in 20 mL gas chromatography vials which serve as reactors for anaerobic digestion. • 14 dried and ground feedstuffs were weighed into the vials, which were subsequently closed with a gas-tight sealing. • Atmospheric conditions were adjusted by previous application of CO2. • Samples were simultaneously incubated in the HGT (n=3) and in the MGT (n=4) at the same feedstuff-inoculate ratio. • Incubation started with dispensing 5 mL inoculate and was carried out in a heating chamber (39°C). Ruminal fluid solution was prepared according to the HFT standard procedure. • The relative pressure increase in the headspace was manually measured at predefined intervals (1,2,4,6,8,16,24h) and the headspace subsequently vented. • In contrast to the HGT no continuous rotation but regular agitation was applied subsequent to pressure measurement in the MGT. RESULTS • To display the measuring range of the feedstuffs within the two measuring systems replicate data points have been plotted (n=3, for MGT 3 out of 4 data point with maximum variances have been selected), see figure 2 on 2nd page • Ranges vary for each feedstuff depending on the measuring system. Straw and (grass) hay standard samples, for instance, scatter more widely in the MGT than in the HGT. For rapeseed meal contrary results were obtained. • In the MGT, material shape and texture of the feedstuffs as well as their floating characteristics influenced the ranges within replicate measurements. • The MGT resulted in a significantly (p<0.05) lower 24 hour gas production as compared to the HGT (ca. 90%). • Linear regression analysis of the 24 hour gas production data set using replicate values (n=3, maximum variances) resulted in a high R2 of 0.97. • For the mean values of the 24 hour gas production data set an R2 of 0.99 was calculated. • Based on this high correlation between the two measuring systems, it is possible to convert the results of the HGT and the MGT directly using the linear equation y=0.88x+1.62. • The relative dispersion of the measured values for both methods are <5% • The mean value of coefficient of variation for the MGT is 2.7% compared to 1.5% for the HGT. 1 2 3 4 The newly developed micro gas test (MGT) is a small scale in vitro method, where gas production is measured through pressure increase. For the method’s validation, a total of 14 feedstuffs, including two standard materials (hay and concentrate), were simultaneously incubated in the Hohenheim gas test (HGT) (Menke et al. 1979) and the MGT. There was strong correlation between the two methods. Compared to the HGT, the MGT gave maximum gas productions of nearly 90% for all feedstuffs investigated. Regression analysis of the mean values of gas production (mL/200 mg dry matter (DM)) from the MGT (y) and the HFT (x), respectively, resulted in the linear equation: y=0.88x+1.62, R2=0.99. The results indicate that the MGT is a suitable method for in vitro feedstuff evaluations. The micro gas test – a small scale in vitro system for high throughput analysis Figure 1: Different scales of three incubation systems (a) MGT; (b) HGT; (c) large scale pressure system