Methodological factors affecting gas and methane production during in vitro rumen fermentation evaluated by meta-analysis approach

Effects of some methodological factors on in vitro measures of gas production（GP, mL/g DM）, CH4production（mL/g DM） and proportion（% CH4 on total GP） were investigated by meta-analysis. These factors were considered：pressure in the GP equipment（0 = constant; 1 = increasing）, incubation time（0 = 24; 1 = ≥ 48 h）, time of rumen fluid collection（0 = before feeding; 1 = after feeding of donor animals）, donor species of rumen fluid（0 = sheep; 1 =bovine）, presence of N in the buffer solution（0 = presence; 1 = absence）, and ratio between amount of buffered rumen fluid and feed sample（BRF/FS; 0 = ≤ 130 mL/g DM; 1 = 130–140 mL/g DM; 2 = ≥ 140 mL/g DM）. The NDF content of feed sample incubated（NDF） was considered as a continuous variable. From an initial database of 105 papers, 58 were discarded because one of the above-mentioned factors was not stated. After discarding 17 papers,the final dataset comprised 30 papers（339 observations）. A preliminary mixed model analysis was carried out on experimental data considering the study as random factor. Variables adjusted for study effect were analyzed using a backward stepwise analysis including the above-mentioned variables. The analysis showed that the extension of incubation time and reduction of NDF increased GP and CH4 values. Values of GP and CH4 also increased when rumen fluid was collected after feeding compared to before feeding（＋26.4 and ＋9.0 mL/g DM, for GP and CH4）,from bovine compared to sheep（＋32.8 and ＋5.2 mL/g DM, for GP and CH4）, and when the buffer solution did not contain N（＋24.7 and ＋6.7 mL/g DM for GP and CH4）. The increase of BRF/FS ratio enhanced GP and CH4production（＋7.7 and ＋3.3 mL/g DM per each class of increase, respectively）. In vitro techniques for measuring GP and CH4 production are mostly used as screening methods, thus a full standardization of such techniques is not feasible. However, a greater harmonization of analytical procedures（i.e., a reduction in the number of available protocols） would be useful to facilitate comparison between results of different experiments.

Effect of lactic acid bacteria inoculants on alfalfa(Medicago sativa L.) silage quality:assessment of degradation(in situ) and gas production(in vitro)

Alfalfa （Medicago sativa） is difficult to ensile successfully because of the low content of moisture and water-soluble carbohydrates （WSC） in fresh alfalfa and the high buffering capacity in fresh alfalfa. Here, we conducted a study to evaluate the effects of three lactic acid bacteria （LAB） inoculants （Lactobacillus case/, lactobacillus plantarum, and Pediococcus pentosaceus） on silage quality, in sitE/ruminal degradability, and in vitro fermentation of alfalfa silage. The first cut of alfalfa was wilted, chopped, and randomly divided into four groups： the control （CON） and control mixed with three separate LAB inoculants （106 cfu g-1）. Simmental steers with a body weight of （452±18） kg and with installed rumen fistulas were prepared for in situ degradation and for in vitro gas production. LAB inoculants had a lower （P〈0.05） content of butyric acid than the CON group. Among them, the L. casei inoculated silage had a higher （P〈0.05） content of water-soluble carbohydrate （WSC） and a lower （P〈0.05） NH3-H content. The effective degradation （ED） of crude protein in LAB inoculation decreased （P〈0.05）, while the ED of acid detergent fiber increased （P〈0.05） in situ fermentation. The alfalfa silage with LAB inoculants produced more carbon dioxide （P〈0.05）. The NH3-H content of mixed incubation fluid in L. casei inoculated silage was lower （P〈0.05） compared with other groups. Therefore, this study showed that LAB inoculants could improve both ensiling quality and degradation. In particular, the L. casei inoculations exhibited better performance by limiting proteolysis during ensiling.