Study Of Associative Effects Between Starch And Neutral Detergent Fiber In Ruminants

The present research was conducted to compare two in vitro gas production systems: Syringe system and reading pressure technique (RPT), and correlations between the gas production at 24 h (Gp_24h) was established. Suitable system was adopted to investigate the associative effects (AE) between rice straw and corn in pelletized rice straw, and between different sources of neautral detergent fiber (NDF) and starch. By using real-time PCR, the cellulolytic bacteria and ethanogens were quantified. Considering the cellulose activities and methane production, the mechanisms of AE between NDF and starch were explored.Experiment 1. An investigation was conducted to compare the syringe gas test system with the reading pressure technique (RPT). A series of mixtures of neutral detergent fibre (NDF) and maizestarch were incubated using both systems and the ratios (wt/wt) of maizestarch in the mixtures were 0, 10.0, 20.0, 25.0, 33.3, 50.0, 55.6, 62.5, 71.4, 83.3 and 100 %, respectively. The gas production (GP) was recorded at 0, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h. The volatile fat acid (VFA) and methane production were determined. There was no significant difference in potential GP between two systems (corrected to 200 mg substrate basis) (p>0.05), while the GP values at a short time of incubation were lower in the RPT system than in the syringe and the rate constant of GP was significantly higher in the syringe (p<0.05). However, a strong relationship was observed between the 24 h GP values (Gp_24h) in the syringe system and the RPT, which was described by: (Gp_24h) for the syringe system (ml) = 1.2628× (Gp_24h) for the RPT system (ml) + 6.2592 (R²=0.9784; p < 0.01; n = 132). It is indicated that the (Gp_24h) in the two systems can be revised reciprocally. The total VFA from RPT system was lower than syringe system (p<0.01), but there was no significant differences in the ratio of acetic to propionic and methane production between two systems at 24 h incubation time. It is indicated that the fermentation characteristics were the same in two systems. In summary, the in vitro feed evaluation system based on gas production from either syringe orreading pressure technique has respective advantages, and could be chosen for use in practice depending on the purposes of research. The syringe system may be used to record the gas values at different times of incubation, and analysis of fermentation parameters may be conducted for the inoculants at the end point. If the continuous analyses of the fermented end products would be expected, the reading pressure technique is proposed.Experiment 2. Syringe system was conducted to investigate a series of pelletized feedstuffs consisting of rice straw and ground corn by compounded chemical treated. The NDF contents of the pelletized rice straw were ranged from 53.6 % - 66.6 %, while the other nutrinents and ratio of concentration to roughage were all the same. The AE values between rice straw and corn were different significantly (p<0.01), which were ranged from 0.6 % - 17.2 %. A high quadratic relationship existed between the AE values and the ratio of corn to rice straw. Regression analysis of these relationships resulted in: Y = -1.0919 X2 + 34.23 X -243.97(11 ^ X ^ 13) (R2= 0.9841) , where Y is the AE values (%) and X is the ratio (%) of corn. The results demonstrated that not the ratio of concentration to roughage but the ratio of NDF to corn was the main effect of AE between roughages and readily fermented carbohydrates in ruminants.Experiment 3. The RPT system was used to investigate AE between comstarch and neutral detergent fibre from rice straw. The ratios of comstarch were 0, 10.0, 20.0, 25.0, 33.3, 50.0, 55.6, 62.5, 71.4, 83.3 and 100 %, respectively. The GP was recorded at 0, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h. The cellulolytic bacteria and methanogens in the fermented end-products of comstarch, straw fiber and the mixture that presented the greatest AE were quantified using real-time PCR. The VFAs and methane production were determined. Positive AE was observed for all the mixtures at all times of incubation. The greatest response was pronounced when the ratio of comstarch was at 33.3 % at 36 h of incubation. The observed cellulase activity, quantities of cellulolytic bacteria, total VFAs and methane production from the mixture was significant higher than the predicted values. It is inferred that theincreased activities of cellulolytic bacteria is one of the mechanisms for the positive AE between fibrous and starchy feeds.Experiment 4. The RPT system was adopted to investigate AE between different sources of starch (cornstarch and wheatstarch) and NDF from rice straw, Chinese wild rye and alfalfa. Six series of mixtures were made according to a 3 X 2 factorial design. The ratios of cornstarch in every series sample were 0, 10.0, 20.0, 25.0, 33.3, 50.0, 55.6, 62.5, 71.4, 83.3 and 100 %, respectively. The GP was recorded at 0, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h. The cellulolytic bacteria and methanogens in the fermented end-products of starch, NDF and the mixture that presented the greatest AE were quantified using real-time PCR. The VFAs and methane production were determined. Similar to AE between rice straw NDF and cornstarch, significant AE were observed in all samples. The sources of NDF, starch and the interaction of NDF and starch affected the AE significantly. Low-quality NDF presented the maximal response (17.9%), but needed high content of starch (33.3%) supplement. Positive AEs were observed when evaluated by the cellulase activity, quantities of cellulolytic bacteria, total VFAs and methane production. It is indicated that the efficiencies of DE changed to ME and ME changed to NE decreased. The increased activity of cellulolytic bacteria is one of the mechanisms for the positive AE between fibrous and starchy feeds.In summary, the relationship established in this research provided theoretical support to choose suitable in vitro gas production system. Ratio of NDF to starch was the main effect on AE between concentration and roughage, and the characteristices were described. The increased activitie of cellulolytic bacteria was demonstrated to be one of the mechanisms for the positive AE between fibrous and starchy feeds and AEs evaluated from digestion and metabolism might be different.