Design, development and evaluation of a fully automated system for gas production measurement and microbial fermentative kinetic of feeds

The in vivo, in situ and in vitro methods have been used for feedstuff evaluation. Gas production technique is known as a reliable in vitro methods which could be accomplished by manual or automated systems. Manual gas pressure measurement is tiresome, labor-intensive, and less repeatable. Heretofore, several methods are introduced for determining kinetic of feed digestion based gas production volume. Between the conventional methods, the method introduced by Theodorou et al. (1994) was simple and low cost, but it had some disadvantages. Mauricio et al. (1999) suggested a semi-automatic method for gas production evaluation. In most Iranian nutritional lab the manual method using glass syringes is used for gas production assays. This method has individual errors and need to discharge gas at different times of assay. So the objectives of this study were to develop and validate a fully-automated gas production system to facilitate the study of the microbial fermentative kinetics and animal science studies.
Material and Three representative feeds (soybean meal, alfalfa hay, and dairy cow concentrate) were prepared form the education and research farm (Lavark Farm, Isfahan, Iran). Then, the samples were milled using a Wiley mill equipped with 1 mm screen. On the other hand, ruminal fluid was obtained from two ewes in a slaughterhouse. The ruminal fluid was filtrated using 2 layer cheese cloth. Then, the feed samples were incubated with buffered rumen fluid inside the volume-calibrated serum bottles. Gas pressure from the head-space of each bottle was transferred to the pressure sensor through a stainless-steel connection fitting and a CO2-resistant hose. Gas pressure data were recorded on an Excel spreadsheet at 30-min intervals during an incubation period of 72 h. Accumulated head-space gas pressure was vented using an electric gas valve immediately after each gas pressure record. To validate the accuracy of the automated system, another experiment was simultaneously performed and gas volume in each butyl rubber-sealed serum bottle was manually measured using a water displacement apparatus after 2, 4, 6, 8, 12, 24, 48, and 72 h of incubation, and then compared with those measured with the automated system. The Pearson correlation coefficients obtained from two methods of manually and fully-automated methods were analyzed by SAS software (SAS, 2002).
Results showed that alfalfa hay had lower fermentation and gas production rate than those the other samples. In automated method, gas volume produced was about 140 and 180 ml/g DM alfalfa hay after 24 and 72 h incubation, respectively. While, these volumes were 130 and 169 ml/g DM alfalfa hay in manual method. In line with Hervás et al. (2005) the mean fermentation rate for alfalfa hay was 7.77 and 7.78 ml/h in manual and automated methods, respectively. In the present study, after 24 and 72 h soybean meal incubation the gas volume was about 156 and 215 ml/g DM in manual method and 169 and 228 ml/g DM in automated methods, respectively. This results were somewhat lower than that the data reported by Tagliapietra et al. (2011) who tested the soybean meal fermentation kenetic by an automated gas production system. The discrpancy could be attributed to the difference in sample preparing, buffer solutions, rumen fluid collection source and the diet of animal before rumen fluid collection. On the other hand, it is reported that the time of rumen fluid sampling (before and after feeding), the method for determining gas production, vial shaking during the incubation and the mathemtical models are some factors mat affect on gas production data (Cone et al. 1996; Nagadi et al. 2000; Lanzas et al. 2007). Cone et al. (1996) demonstrated that fermentation rate was higher when the rumen fluid collected after morning feeding. Menke and Steingass (1988) reported that rumen fluid collected before feeding had lower differentiation in composition and activity. The Pearson correlation coefficient for several incubation times (6, 24, 48 and 72 h) as well as gas production potential was higher than 90% which verifying the gas pressure data generated by the automated system.
In general, the results of the present study showed that the fully-automated system in compare to manual gas production measurement, had high performance in determining the gas pressure with less labor.