Fermentability of dietary fibre and metabolic impacts of including high levels of fibrous feed ingedients in maize-soyabean growing pig diets supplemented with exogenous enzymes

Abstract

The objectives of the research were to examine the effects of high dietary levels of fibrous feeds, and of supplementation with Roxazyme® G2 (RX), on the digestive metabolic and physiological responses of growing pigs fed maize-soybean diets. The nutrient and dietary fibre (DF) composition, the swelling and water-binding capacities of maize (MM), its hominy chop (HC) and cobs (MC), dehulled soybean (dSBM) and the hulls (SH), brewer’s grains (BG), lucerne hay (LH) and wheat bran (WB) were evaluated using standard procedures. Feed fibre fractions were isolated by simulating upper tract digestion in an Ankom® DaisyII Incubator, whereby each feed was digested in pepsin (porcine, 200 FIP-U/g, Merck No, 7190), followed by pancreatin (porcine, grade IV, Sigma No P-1750), with recovery of the fibrous residues. In a third step to complete the simulated pig gastro-intestinal digestion, the pepsin-pancreatin fibre extracts were digested by RX or Viscozyme L ® V2010 (VZ). Enzyme activity was measured as the coefficients of partial degradability (solubilisation) of the washed fibre extracts. The kinetics and products of fermentation of the DF were evaluated in an AnkomRF gas production system, using buffered faecal inoculum. Among the feed ingredients, dissimilar, fibre source-dependent activities between RX (0.02 to 0.12) and VZ (0.04-0.33) were observed. The lowest RX activities were observed on the maize and soybean derived fibres, with similarly low VZ activity on MC fibre. Variation in the activity of faecal microbial enzymes was similarly indicated by the variable production of fermentation gas (51.8-299.4 mL g-1 DM) and short chain fatty acids (SCFA) (2.3-6.0 mMol g-1 DM). Soy hull, dSBH, MM and HC fibres were highly fermentable, with low fermentability of BG, MC and WB fibres. The fibres differed in the composition of fermentation SCFA, whereby SH, LH and MC shifted fermentation to Ace, and BG, dSBM, WB, MM, HC favoured Pro, while MM and HC favoured But production. The same nutritional properties were similarly evaluated in complete diets which were formulated from the ingredients for growth, and metabolic trials. For the growth trial, a standard (STD) (control), 141 g total dietary fibre (TDF) kg-1 dry matter (DM) maize-soybean growing pig diet, and five iso-nutritive, 246 g TDF kg-1 DM nutritionally balanced diets were formulated. The high DF was achieved by partial replacement of the MM and dSBM in the STD diet with MC, SH, BG, LH or WB. The differences in RX and VZ activities and in the fermentation characteristics which were observed on the fibre extracts from the high fibre ingredients were reflected in the DF from the respective complete diets in which they were included. However, the fibre from the basal dietary ingredients reduced the absolute values and the variation in the activities of RX (0.03-0.06) and VZ (0.16-0.22), and similarly reduced the variation in gas (126.6-187.6 mL g-1 DM) and SCFA (4.1-5.4 mMol g-1 DM) production of the DF from the fibrous diets. Enzyme activities on the STD DF were low for RX (0.03) and high for VZ (0.25). The STD DF produced 205.3 mL gas g-1 DM, which was similar to SH DF, and higher than all the other diets. The STD DF produced 5.0-mMol SCFA g-1 DM, which was quantitatively, and not statistically higher than the other fibres. The composition of SCFA was similar across all diets, except for the high percent Ace, with low Pro by the SH DF. Compared to the STD, the high DF diets increased percent Ace, with reduced Pro and But. The STD, MC, SH, BG, LH and WB diets were each prepared in duplicate mixes, one of which was fortified with 200 mg RX kg-1 feed (as fed). Seventy-two intact Large White X Landrace, male, 32.0 ± 5.6 kg live weight (LW) pigs were allocated to the diets in two completely randomised weight blocks in a 2 (fibre source) X 2 (enzyme) factorial arrangement. The pigs were fed ad libitum for 10 weeks. Cumulative LW gain and feed intake were measured at different stages of growth, and at slaughter. Apparent total tract digestibility (ATTD) of nutrients was estimated at 65-70 kg LW, using 0.2% (as fed) chromium oxide as the indigestible marker. Ileal tissue was sampled 50 cm above the ileo-caecal valve, on which villi height and area, and crypt depth were evaluated by computerised image analysis. Blood was sampled at slaughter from the severed vena jugularis, 16 hours after feeding. Serum urea, creatinine, triglycerides, glucose, and total cholesterol were analysed chemically. The serum metabolome was further explored using Proton Nuclear Magnetic Resonance Spectroscopy (1H -NMRS). There was fibre X RX interaction for villi height, whereby the enzyme reduced the villi height in pigs on the SH, STD and WB diets, with an opposite effect on pigs on the MC, BG, LH diets. The soluble fibre content was negatively correlated with crypt depth. Chemical analysis did not detect differences in metabolite concentration between the STD and the high fibre diets. However, more serum cholesterol was observed in pigs fed the WB compared to the LH and MC diets. 1H-NMRS indicated that feeding pigs the WB diet increased serum Cys and His, while supplementation of RX increased serum formate, glucose, and urea. There was diet X enzyme interaction for fructose, glucose, Arg, Cys, Ser, and Trp, whereby RX increased the levels in pigs on MC and WB, with an opposite effect in pigs on the other diets. There was large DF source-dependent variation among diets in ATTD of DM (0.80-0.85), organic matter (OM) (0.81-0.87), gross energy (GE) (079-0.85) and CP (0.81-0.85), whereby, relative to the STD diet, high DF reduced the ATTD of DM (all diets except SH), organic matter (OM) and energy and CP (all diets except the MC). Positive correlation was observed between fermentability and the ATTD digestibility of DM, OM, energy, ADF, NDF, and fat. Negative correlation was observed between the swelling capacity and the ATTD of DM, OM, energy and protein, between DF solubility and DM, OM, protein, ADF and NDF, and between water binding capacity and ATTD of DM and OM, energy and NDF. At slaughter, there was similarly large, and DF source-dependent variation among the high fibre diets in feed intake (2.31-2.71 kg as fed day-1), live weight gain (0.75-0.86 kg day-1), and feed: gain ratio (2.73-3.00). Corresponding values for the STD diet were 2.44 kg day-1, 0.83 kg day-1and 2.86 kg day-1, respectively. Relative to the STD, LH reduced feed intake and live weight gain, and MC increased the feed: gain ratio. Predictions based on the in vitro fermentability of DF and feed intake suggested that due to poor fermentability, and or restriction of feed intake, relative to a standard fibre diet, high dietary levels of MC, WB and BG may reduce fermentation in the lower gut, while similar dietary levels of SH and LH may result in substantial increases in fermentation. At 50 kg LW, the fermentability of DF was positively correlated with feed intake and with weight gain, while water binding capacity and solubility of DF were negatively correlated with feed intake. At slaughter, the solubility of DF was negatively correlated with feed intake and feed: gain ratio. Large variation among the high fibre diets was also observed in the slaughter weight (89.2-96.8 kg), dressing % (68.6-76.4), meat colour (80.4-82.3), lean % (69.5-71.2), and fat % (10.1-12.6). In comparison, pigs on the STD diet scored 94.7 kg slaughter weight, 75.1% dressing, 81.6 cm carcass length, 82.5 meat colour, 68.4% lean, and 15.0% fat. Relative to the STD, LH reduced dressing and fat %. Lucerne hay and WB increased the lean%. For the metabolic trial, two iso-nutritive, mixed high fibre (319 g TDF kg-1 DM), nutritionally balanced diets were formulated to contain DF of high (HF) versus low (LF) fermentability. The diets had similar content of soluble DF and similar swelling and water binding capacities. Viscozyme was more active than RX on both the HF (0.20 versus 0.04) and the LF (0.17 versus 0.07) DF. The combination of RX and VZ statistically increased the enzyme activity on the HF (0.25) and quantitatively increased enzyme activity on the LF (0.18) DF, suggesting additive or synergistic effects. More gas was produced by the HF (159.5 mL g-1 DM) compared to the LF DF (96.6 mL g-1 DM). More SCFA were produced by HF (5.0 mMol g-1 DM), compared to the LF DF (3.6 mMol g-1 DM). Compared to the STD, HF DF increased percent Ace, with reduced Pro and But. The LF DF increased percent Ace, with quantitative, and not statistical reduction of Pro and But. In a metabolic trial, the HF and LF diets, and their duplicates containing 0.270 g RX kg-1 DM of feed (as fed) were fed ad libitum to eight ileum T-cannulised, intact Large White X Landrace male pigs weighing 65.0 ± 5.1 kg. The diets were allocated to the pigs in a duplicate 4 x 4 Latin Square design, in a 2 (enzyme) x 2 (fermentability) factorial arrangement. Each period consisted of two weeks of adaptation followed by five days of sampling. The ileal digesta was collected in each period and was similarly subjected to the fermentation test. Apparent ileal digestibility (AID) and ATTD were determined using 0.2% (as fed) chromium oxide as the indigestible marker. N excretion in faeces and urine were measured, and N retention was calculated. Blood was sampled by vena jugularis puncture on the last day of each period. Two blood samples were collected, the first 15 hours after removal from feed (15-hour serum), and the second 3 hours after re-introduction to feed (3-hour serum). Serum metabolites were evaluated by both chemical analyses and by 1H-NMRS, as described for the growth trial. Roxazyme did not affect the fermentation characteristics of the ileal digesta. In similar proportion to the fermentability of the PP digesta, the HF ileal digesta was more fermentable (65.4 mL gas g-1 DM and 6.1 mMol SCFA g-1 DM) than the LF ileal digesta (46.7 mL gas g-1 DM and 4.4 mMol SCFA g-1 DM SCFA). Prediction based on the in vitro fermentability of DF and feed intake suggested the HF diet could support one half times more fermentation in the lower gut compared to the LF diet. The HF diet had higher AID of DM (62.5 vs. 58.6), OM (65.6 vs. 62.1), energy (64.4 vs. 61.0), fat (85.8 vs. 81.7) and ash (41.8 vs. 32.7). The AID of HO-Pro, Met and Val were higher for the LF diet. There was diet X enzyme interaction on the AID of Met, whereby the RX reduced the AID of met in the LF diet, and not that of the HF diet. The ATTD was higher for the HF diet for DM (74.2 vs. 68.4), NDF (64.7 vs. 57.4), and ADF (35.1 vs. 21.0). There was positive correlation between the fermentability of DF and the AID DM, OM, ash, ash, fat and energy. The solubility of DF was negatively correlated with the AID of DM, OM, ash, fat, ADF and energy, and with the ATTD of DM, OM, ash, fat, energy, NDF, and ADF. Negative correlation was also observed between the swelling capacity of DF and the AID of protein, Trp and Lys. The solubility of DF was positively correlated with Ser, Ala, Val, Iso-Leu and His. There was diet X enzyme interaction for urea in the 15- hour serum, whereby RX tended to reduce the urea in the LF diet, while it increased that of the HF diet. Fermentability negatively correlated with urea in the 15- hour serum, and positively correlated with serum glucose in the 3-hour serum. In the 3-hour sample, 1H-NMRS indicated higher fucose, Pro and cholesterol in the LF diet. 1H-NMRS also indicated fermentability x RX interaction for Ser, Tyr, Lys, creatine, and possibly, glucose or fructose, glycerol or Gly and His or Arg, whereby RX increased the levels in the LF diets, with opposite effect in the HF diet. In conclusion, enzyme activities and fermentability were higly variable among different DF sources, and the effects were evident in the fibrous complete diets. The results of the in vitro studies supported the application of the methods to formulate fermentable insoluble fibre-rich, maize-soybean-mixed co-product diets. Correlation analyses suggested that DF fermentability, and solubility, swelling and water binding capacities explained significant proportions of the variances of the metabolic and physiological responses of the pigs to different feeds. Predictions based on the in vitro fermentability of DF and feed intake suggested that a strategy whereby pig diets are enriched in DF after the feedstuffs are screened on DF fermentability could substantially increase fermentation in the lower gut. Overall, the results suggested that productivity can be maintained in growing pigs fed diets containing up to twice the standard levels of DF, provided producers target co-product feeds that contain highly fermentable DF. The use of RX to improve nutrient digestion and to stimulate gut fermentation was not justified.