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. 2020 May 21;98(6):skaa174. doi: 10.1093/jas/skaa174

Digestibility of amino acids, energy, and minerals in roasted full-fat soybean and expelled-extruded soybean meal fed to growing pigs without or with multienzyme supplement containing fiber-degrading enzymes, protease, and phytase

Elijah G Kiarie 1,✉, Ilona A Parenteau 1,✉, Cuilan Zhu 1, Nelson E Ward 2, Aaron J Cowieson 3
PMCID: PMC7276670  PMID: 32437583

Abstract

Indigestible fiber–protein–phytate complexes reduce the feeding value of soy products. We investigated the effects of multienzyme supplement (MES, Victus) on standardized ileal digestibility (SID) of amino acids (AA) and apparent total tract digestibility (ATTD) of energy and minerals in roasted full-fat soybean (FFSB) seeds and expelled-extruded soybean meal (SBM) fed to growing pigs. The crude protein (CP) was 33.4% and 42.8% dry matter (DM) in FFSB seeds and SBM, respectively and corresponding values for crude fat were 17.4% and 11.8% DM. Semi-purified diets with 50% of either FFSB seeds or SBM as the sole source of AA were prepared without or with MES supplying phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively. Diets had TiO2 as an indigestible marker and the ratio of cornstarch to sucrose and corn oil was identical to calculate DE by the difference method. Eight ileal-cannulated barrows (22.1 ± 0.61 kg) were fed diets in a replicated 4 × 4 Latin square design to give eight replicates per diet. The period lasted for 9 d: 5 d for acclimation, 2 d for fecal, and 2 d for ileal digesta samples. There was no (P > 0.05) interaction between soy type and MES or MES effect on SID of AA; SBM had higher (P < 0.05) SID of CP, His, Leu, and Lys. There was no (P > 0.05) interaction between soy type and MES on energy digestibility. The FFSB seeds had higher ATTD of gross energy (GE, 80.2% vs. 76.6%; P < 0.01) than SBM. Pigs fed MES had higher (P < 0.05) ATTD of DM (91.3% vs. 87.7 %), GE (87.5% vs. 82.4%), CP (86.4% vs. 82.9%), crude fat (70.6% vs. 54.9%), Ca (63.2% vs. 60.2%), and P (67.5% vs. 63.2%). In conclusions, differences on AA and energy digestibility in soy products could be linked to processing and compositional differences. Although MES had no effect on SID of AA, the effects on the utilization of minerals and energy demonstrated the value of fiber-degrading enzymes, protease, and phytase in improving the nutritive value of soy products independent of processing.

Keywords: digestible energy, full-fat soybean, growing pig, multienzyme supplement, soybean meal, standardized ileal digestibility of amino acids

Introduction

Soybean is a legume that is highly adaptable, rich in protein, oil, and other functional components with wide utility in human food, animal feed, and industrial applications. Majority of soy products available for use in swine nutrition programs are in the form of soybean meal (SBM) and its derivatives (NRC, 2012). Commodity SBM typically refers to a co-product from the extraction of oil mainly through pressing and solvent extraction. For various reasons, full-fat soybeans (FFSBs) are also used in animal nutrition. Regardless, a common denominator for the production of soy products for monogastric nutrition is the application of some degree of thermal processing to denature trypsin inhibitors (TIs) and other heat-labile anti-nutritional factors (Ayoade et al., 2012; NRC, 2012; Woyengo et al., 2014; Yáñez et al., 2019).

The nutritive value of soy products varies in terms of amino acid and energy utilization (NRC, 2012). This variation has been associated with many factors such as bean genotype and growing husbandry practices as well as conditions applied during oil extraction and processing (Ravindran et al., 2014; García-Rebollar et al., 2016). An evaluation of 55 SBM samples (CP 44% to 48%) sourced from four countries (United States, Argentina, Brazil, and India) demonstrated that variation in digestibility of amino acids (AA) and energy in poultry was not correlated with processing quality checks (TIs, urease index, and potassium hydroxide [KOH] protein solubility) or concentration of CP but was highly negatively correlated with the concentration of fiber and ash (Ravindran et al., 2014). These observations suggested that the concentration of these chemical constituents and attendant complexes interferes with digestion, absorption, and utilization of nutrients in soy products (NRC, 2012; Ravindran et al., 2014).

In cognizant of the complexity of the indigestible components in soy products, researchers have attempted to apply multi-exogenous feed enzyme activities to improve the nutritive value of soy products in pigs (Ayoade et al., 2012; Woyengo et al., 2016). An enzyme product containing pectinase, cellulase, mannanase, xylanase, β-glucanase, and galactanase improved AA and energy digestibility in extruded FFSB seeds fed to finishing pigs (Ayoade et al., 2012). In contrast, a multienzyme containing xylanase, β-glucanase, cellulase, mannanase, invertase, protease, and amylase had marginal effects on AA digestibility and no effects on energy digestibility in cold-pressed soybean cake (Woyengo et al., 2016). Such discrepancies in supplemental enzymes responses may be related to soy processing regimens, enzymes to substrate ratio, among other factors. However, soy products contain a significant level of phytate that has been associated with negative effects on the utilization of AA and energy in monogastric animals (Cowieson et al., 2017; Zouaoui et al., 2018). It is plausible that the presence of phytase might augment responses of fiber degrading and protease activities. Multienzyme supplement (MES) containing fiber-degrading and debranching, protease, and phytase activities has been shown to be effective in improving the utilization of nutrients in poultry-fed SBM-based diets (Ward et al., 2014, 2015, 2020; Jasek et al., 2015). We hypothesized that an MES product containing fiber-degrading enzymes, protease, and phytase activities will increase the utilization of nutrients in soy products in pigs. Therefore, the objective of the present study was to investigate effects MES on standardized ileal digestibility (SID) of AA and apparent total tract digestibility (ATTD) of energy and minerals in SBM and roasted FFSB seeds fed to growing pigs.

Materials and Methods

Animal care and use protocols were approved by the University of Guelph Animal Care and Use Committee. Pigs were cared for in accordance with the Canadian Council on Animal Care guidelines (CCAC, 2009).

Soybean products and diets

The SBM was a product from soy oil extraction using extrusion and expelling processes (Soy-Max Protein Inc., Cartier, MB, Canada) and was previously described by Opapeju et al. (2006). Samples for FFSB seeds were procured from a local farm (James Valley Colony, MB, Canada) that uses an automatic electric-powered 32-ft long, 14-inch diameter stainless steel roaster (Dilts-Wetzel Manufacturing Co., Ithaca, MI). Briefly, the first 20 ft is surrounded by a 20-inch diameter heating chamber tube that holds up to 165 gallons of oil, electric heating elements, and 4-inch thick fiberglass to transfer heat from the oil to the beans. The beans are cooked at 190.6 °C for 1 h, then enter a steeping chamber, and continue to be cooked by steam for an additional half an hour, exiting the steeping chamber at 121 °C. Two semi-purified corn–starch-based basal diets were formulated (Table 1) with 50% inclusion of soy products as the sole source of AA. The FFSB was ground by a hammer mill prior to feed mixing. The ratio of corn starch:sucrose:oil was kept constant as main sources of energy in our previously published reference N-free (corn starch, oil, and sucrose) diet (Rho et al., 2017) to allow for the calculation of DE content of soy products by the difference method (Kiarie et al., 2016a). Minerals and vitamins were added to meet or exceed the nutrient requirements of growing pigs (NRC, 2012). Titanium dioxide (0.2% of the diet) was added as a digestibility marker. Each of the basal diets was split into two portions: one portion was designated control and the other was treated with MES. The MES supplied main activities of phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively (Victus, DSM Nutritional Products Inc., Parsippany, NJ). In addition, recent mass spectrophotometry proteomic evaluation of the MES confirmed the presence of a wide range of side activities such as arabinofuranosidase, exoarabinase, pectin lyase, pectin methylesterase, and others (Sluis et al., 2017; Ward et al., 2020), considered important in facilitating the accessibility of complex substrates to the main enzyme activities (Mohnen, 2008; Rytioja et al., 2014).

Table 1.

Composition of the basal diets, as-fed

Soy product
Ingredient FFSB seeds SBM
FFSB seeds 50.0 —
SBM — 50.0
Corn starch 42.8 42.9
Sucrose 3.08 3.08
Limestone 0.55 0.65
Monocalcium phosphate 1.20 1.09
Corn oil 1.03 1.03
Vitamin trace mineral premix1 0.60 0.60
Salt 0.50 0.50
Titanium dioxide 0.20 0.20
Calculated provisions
 Metabolizable energy, kcal/kg 3,902 3,770
 CP, % 17.4 21.0
 Crude fat, % 11.0 4.50
 Digestible P, % 0.42 0.41
 Ca, % 0.66 0.67
 Total P, % 0.55 0.56
 Na, % 0.21 0.20
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1Provided per kg of premix: vitamin A, 2,000,000 IU as retinyl acetate; vitamin D3, 200,000 IU as cholecalciferol; vitamin E, 8,000 IU as dl-α-tocopherol acetate; vitamin K, 500 mg as menadione; pantothenic acid, 3,000 mg; riboflavin, 1,000 mg; choline, 100,000 mg; folic acid, 400 mg; niacin, 5,000 mg; thiamine, 300 mg; pyridoxine, 300 mg; vitamin B12, 5,000 mcg; biotin, 40,000 mcg; Cu, 3,000 mg from CuSO4 × 5H2O; Fe, 20,000 mg from FeSO4; Mn, 4,000 mg from MnSO4; Zn, 21,000 mg from ZnO; Se, 60 mg from Na2SeO3; and I, 100 mg from KI (DSM Nutritional Products Canada Inc., Ayr, ON, Canada).

Experimental procedures

Eight barrows (BW, 22.1 ± 0.61 kg) were procured from the University of Guelph’s Arkell Swine Research Station (Guelph, ON, Canada) and housed in individual plexiglass-lined pens with tenderfoot floors in a temperature-controlled room at 20 to 22 °C for 5 d prior to surgery. Pigs were surgically fitted with a simple T-cannula at the distal ileum, followed by a 1-wk postsurgical recovery period (de Lange et al., 1998). The surgical area was cleaned every day with warm water, and zinc oxide cream was applied after the area was fully dried. The experiment was conducted according to a replicated 4 × 4 Latin Square design (n = 8). Feeding levels were based on the BW (2.8 × estimated maintenance energy requirements; NRC, 2012) adjusted for individual pigs at the beginning of each experimental period. Diets were fed as a wet mash with a water-to-feed ratio of 2:1 twice daily (0830 and 1630 hours). Water was provided ad libitum from a low-pressure drinking nipple. Each period lasted for 9 d: 5 d for acclimation, 2 d for fecal, and 2 d of ileal digesta collection. Fresh fecal samples were collected six times daily and stored at −20 °C. Ileal digesta collection bag was filled with 10 mL, 10% formic acid, and was attached to the cannula by an elastic band and was replaced as needed. Digesta were kept in the refrigerator during the collection, pooled at the end of the day, and stored at −20 °C. The pigs were euthanized after the study to assess any intestinal abnormalities from cannulation.

Sample processing and laboratory analyses

The ileal digesta and fecal samples were freeze-dried and, along with soy products and diets, finely ground for chemical analyses. All samples were analyzed for N by the combustion method 968.06 (AOAC, 2005) using a CNS-2000 carbon, N, and sulfur analyzer (LECO Corporation, St. Joseph, MI). The CP values were derived by multiplying the assayed N values by a factor of 6.25. Samples of soy products, diets, and feces were analyzed for dry matter (DM), gross energy (GE), neutral detergent fiber (NDF), acid detergent fiber (ADF), crude fat, and minerals (Ca, P, K, Mg, and Na). DM determination was carried out according to standard procedures method 930.15 (AOAC, 2005). GE was determined using a bomb calorimeter (IKA Calorimeter System C 5000; IKA Works, Wilmington, NC). The NDF and ADF contents were determined according to Van Soest et al. (1991) using α-amylase (Sigma No. A3306, Sigma Chemical Co., St. Louis, MO) and sodium sulfite and were corrected for ash concentration adapted for Ankom 200 Fiber Analyzer (Ankom Technology, Fairport, NY). using ANKOM 200 Fiber Analyzer (ANKOM Technology, Fairport, NY). Crude fat content was determined using ANKOM XT 20 Extractor (ANKOM Technology, Fairport, NY). The samples were wet acid digested with nitric and perchloric acid mixture (AOAC, 2005; method 968.08) and concentrations of minerals read on an inductively coupled plasma mass spectrometer (Varian Inc, Palo Alto, CA). Titanium content was measured on a UV spectrophotometer following the method of Myers et al. (2004). For AA analyses, samples were prepared by acid hydrolysis according to AOAC (2005, method 982.30). Briefly, about 100 mg of each sample was digested in 4 mL of 6 N HCl for 24 h at 110 °C, followed by neutralization with 4 mL of 25% (wt/vol) NaOH and cooled to room temperature. The mixture was then equalized to 50 mL volume with sodium citrate buffer (pH 2.2) and analyzed using Ultra performance liquid chromatography (UPLC, Waters Corporation, Milford, CA, USA). Samples for the analysis of sulfur-containing AA (methionine and cysteine) were subjected to performic acid oxidation prior to acid hydrolysis. Tryptophan was not determined. The soy product samples were further tested for TI, urease activity, and KOH protein solubility. TI activity, defined as the number of TI units per milligram of sample, was determined according to AOCS (2017). Urease activity and KOH protein solubility in a commercial laboratory (Midwest Laboratories Inc., Omaha, NE, USA). The enzyme recovery (phytase, protease, xylanase, and β-glucanase) was analyzed at DSM Nutritional Products laboratories (Belvidere, NJ).

Calculations and statistical analysis

Apparent ileal digestibility (AID) and SID of CP and AA were calculated according to de Lange et al. (1998). Ileal endogenous N and AA loss values were from our previous study (Rho et al., 2017). The ATTD of components in the diet were calculated according to Adeola (2001). The ATTD of GE and DE content in soy products was calculated using the difference method (Adeola, 2001) using values of N-free (corn starch, oil, and sucrose) diet (NFD) from our previous study (Rho et al., 2017). The equation used is as follows: DA = DB + (DD − DB)/PA, where DA = ATTD of GE (%) in soy product (FFSB or SB); DB = ATTD of GE in NFD; DD = ATTD of GE in test diet; and PA = proportion (decimal percentage) of soy product in test diet.

Data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model contained the fixed effects of soy product, MES and associated interactions, and the random effects of the pig and period. An alpha level of 0.05 was used to determine statistical significance, and treatments were compared using Tukey’s test.

Results and Discussion

The pigs remained healthy for the entire experiment and there was no evidence of abnormalities at necropsy at the end of the study. The chemical analyses of the soybean products and experimental diets are shown in Table 2. The concentration of CP, crude fat, GE, and AA in FFSB seeds was comparable to values reported for FFSB seeds (NRC, 2012; Woyengo et al., 2014). Derived from a combination of extrusion and expulsion, the crude fat concentration in the SBM sample was within the mean ± SD reported for expeller SBM (NRC, 2012) but slightly lower than average (9.8%) of two samples derived from the same process (Opapeju et al., 2006) or 8.9% for expeller SBM subjected to further extrusion (Woyengo et al., 2016). However, the concentrations of CP and AA in SBM were comparable to values for similarly processed SBM samples (Opapeju et al., 2006) and expeller SBM (NRC, 2012; Woyengo et al., 2016). TIs are the most important anti-nutritional factors present in raw soybeans and are typically destroyed by thermal treatment (NRC, 2012). However, heating has to be optimized to safeguard meal quality and nutritive value (Araba and Dale, 1990). Urease index (indicator of underheating) and protein solubility (indicator for overheating) tests were run on soy products used in the present study (Ravindran et al., 2014; García-Rebollar et al., 2016). Indicators of processing adequacy are often inconsistent in the literature; however, the general recommendations are that adequately heat-processed soy products for animal feeds should have TI of 1.75 to 2.50 mg/g, urease index of 0.10 pH unit change or below, and KOH protein solubility of between 78% and 85% (Van Eys, 2012). The TI was 3.00 and 2.15 mg/g, KOH protein solubility was 79.3% and 82.3%, and the urease index was 0.02 and 0.01 pH unit rise for FFSB seeds and SBM, respectively (Table 2). The data for enzyme recovery are presented in Table 3; with exception of phytase, recovery of protease, xylanase, and β-glucanase in FFSB seeds was lower than SBM. It is rather hard to explain this discrepancy; however, in terms of application and efficacy, such variation in target and recovered activities is acceptable by industry standards (Bedford, 2018).

Table 2.

Analyzed chemical composition of test ingredients and basal diets

Ingredient Diets
Item Soy: FFSB seeds SBM FFSB seeds SBM
DM, % 92.8 93.3 96.4 96.7
CP, % 33.4 42.8 16.7 20.9
Ca, % 0.24 0.25 0.69 0.70
P, % 0.60 0.67 0.60 0.59
NDF, % 12.7 9.9 5.8 4.5
ADF, % 8.4 5.6 3.8 2.3
Crude fat, % 20.1 7.00 10.6 5.6
GE, kcal/kg 5,025 4,692 4,621 4,337
AA, %
 Indispensable AA
  Arg 2.61 3.06 1.31 1.53
  His 0.93 1.31 0.50 0.66
  Ile 1.60 1.83 0.78 0.92
  Leu 2.69 3.18 1.33 1.59
  Lys 2.20 2.72 1.10 1.36
  Met 0.48 0.63 0.24 0.32
  Phe 1.79 2.08 0.91 1.04
  Thr 1.38 1.73 0.71 0.87
  Val 1.68 1.95 0.87 0.98
 Dispensable AA
  Ala 1.53 1.85 1.56 2.05
  Asp 4.04 3.53 1.88 1.59
  Cys 0.55 0.65 0.28 0.33
  Glu 6.34 7.89 3.17 3.95
  Gly 1.79 1.63 0.76 0.90
  Pro 1.77 2.18 0.95 1.05
  Ser 1.78 1.91 0.70 0.76
  Tyr 1.37 1.37 0.69 1.10
Soy quality check
 TIs, mg/g 3.00 2.15
 KOH, % 79.3 83.2 — —
 Urease activity, pH rise unit 0.02 0.01 — —
 Lys to CP ratio, % 6.59 6.36
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Table 3.

Enzyme recovery in experimental diets, as fed

FFSB seeds SBM
Item −MES +MES1 −MES +MES
Phytase, FYT/kg 318 2,596 100 2,719
Protease, PROT/kg 100 5,988 100 8,112
Xylanase, IU/kg n.d.2 327 n.d. 419
β-glucanase, IU/kg 13 84 6 101
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1The MES supplied main activities of phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively (Victus, DSM Nutritional Products Inc., Parsippany, NJ).

2n.d., not detected.

There was no (P > 0.05) interaction between soy product and MES or main effect of MES on AID (Table 4) and SID (Table 5) of CP and AA. The AID and SID of CP, His, Leu, Lys, Asp, and Tyr were higher for SBM vs. FFSB seeds. In addition, the SID of Pro was higher for SBM than FFSB seeds. The observed SID of Lys (84.4%), Met (87.2%), and Thr (85.8%) in FFSB seeds was within the mean ± SD reported for these AA in NRC (2012). However, SID values of Lys, Met, and Thr in the present study were higher than respective values reported for FFSB seeds subjected to micronization (76.4%, 67.7%, and 64.9%) (Woyengo et al., 2014) and extrusion (69.1, 57.2, and 61.2) (Ayoade et al., 2012). Woyengo et al. (2014) observed that solvent-extracted SBM have higher AA digestibility than micronized FFSB seeds in growing pigs. The concentration of TI in solvent-extracted SBM was 6.21 mg/g and values for the two samples of micronized FFSB seeds were 3.23 and 4.31 mg/g (Woyengo et al., 2014). These values of micronized FFSB seeds were comparable to TI values observed for FFSB seeds in the present study. This suggested that the superior AA digestibility observed for solvent-extracted SBM by Woyengo et al. (2014) and SBM in the present study was not related to the concentration of TI. Ravindran et al. (2014) observed poor correlation between indicators of processing adequacy (TI, urease index, and KOH) and in vivo crude protein (CP) digestibility of SBM samples from different geographical regions fed to broiler chickens. The authors opined that standardization of processing conditions (in terms of temperature and duration of heat treatment) has enabled the global industry to optimize indicators for soy products processing adequacy.

Table 4.

Apparent ileal digestibility (%) of CP and AA in roasted FFSB seeds and expeller SBM fed to growing pigs without or with MES1

Soy product MES Probabilities
Item FFSB seeds SBM − + SEM Soy MES Soy * MES
CP 77.8b 82.0a 79.3 80.5 1.168 0.017 0.473 0.628
Indispensable AA
 Arg 86.2 87.2 86.5 86.9 0.409 0.086 0.438 0.441
 His 86.9b 90.6a 87.5 90.0 1.002 0.015 0.090 0.729
 Ile 84.1 85.9 84.3 85.7 1.004 0.201 0.353 0.705
 Leu 84.6b 87.7a 85.3 87.0 0.995 0.036 0.222 0.686
 Lys 82.6b 87.8a 84.7 85.6 1.363 0.011 0.650 0.704
 Met 84.7 86.9 84.6 87.0 1.364 0.255 0.228 0.610
 Phe 78.3 81.6 79.1 80.8 2.846 0.413 0.683 0.863
 Thr 81.1 83.3 81.4 83.0 1.494 0.300 0.443 0.980
 Val 82.7 85.0 83.0 84.8 1.029 0.135 0.232 0.632
Dispensable AA
 Ala 84.2 86.6 84.0 86.9 1.377 0.239 0.150 0.526
 Asp 82.9b 87.5a 84.5 85.9 1.350 0.021 0.456 0.824
 Cys 67.1 64.5 64.2 67.4 3.365 0.590 0.505 0.940
 Glu 81.5 85.7 84.7 82.6 2.135 0.182 0.493 0.291
 Gly 95.5 90.4 92.2 93.7 2.432 0.175 0.673 0.669
 Pro 77.5 82.8 79.2 81.1 2.809 0.194 0.620 0.862
 Ser 83.7 86.8 84.4 86.1 1.263 0.088 0.369 0.960
 Tyr 83.7 86.6 84.4 85.9 1.008 0.050 0.315 0.612
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1The MES supplied main activities of phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively (Victus, DSM Nutritional Products Inc., Parsippany, NJ).

a,bLsmeans with different letters within the factor of analyses (soy product or MES) differ (P < 0.05).

Table 5.

SID (%) of CP and AA in roasted FFSB seeds and expeller SBM fed to growing pigs without or with MES1

Soy product MES Probabilities
Item FFSB seeds SBM − + SEM Soy MES Soy * MES
CP 86.9b 91.1a 88.5 89.6 1.168 0.009 0.453 0.663
Indispensable AA
 Arg 92.5 93.5 92.8 93.2 0.409 0.076 0.438 0.386
 His 89.3b 93.0a 89.9 92.3 1.002 0.012 0.083 0.681
 Ile 86.2 88.0 86.4 87.7 1.004 0.187 0.340 0.723
 Leu 86.7b 89.8a 87.4 89.2 0.995 0.030 0.209 0.706
 Lys 84.4b 89.6a 86.6 87.5 1.363 0.010 0.648 0.673
 Met 87.2 89.4 87.1 89.5 1.364 0.251 0.227 0.624
 Phe 82.8 86.0 83.6 85.2 2.846 0.358 0.620 0.876
 Thr 85.8 88.0 86.1 87.7 1.494 0.271 0.418 0.932
 Val 85.5 87.8 85.8 87.5 1.029 0.116 0.212 0.644
Dispensable AA
 Ala 84.2 86.6 84.0 86.9 1.377 0.239 0.150 0.526
 Asp 85.2b 89.8a 86.8 88.2 1.350 0.016 0.438 0.792
 Cys 78.1 75.2 75.1 78.2 3.365 0.459 0.429 0.989
 Glu 82.7 86.9 85.8 83.7 2.135 0.182 0.490 0.287
 Gly 98.3 93.2 94.1 96.3 2.432 0.175 0.673 0.669
 Pro 93.3a 97.9b 94.6 96.6 2.809 0.045 0.370 0.927
 Ser 87.1 90.2 87.9 89.4 1.263 0.071 0.347 0.912
 Tyr 83.7b 86.6a 84.4 85.9 1.008 0.050 0.315 0.612
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1The MES supplied main activities of phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively (Victus, DSM Nutritional Products Inc., Parsippany, NJ).

a,bLsmeans with different letters within the factor of analyses (soy product or MES) differ (P < 0.05).

Unlike roasting, extrusion applies high heat, high pressure, and shear force (Kim et al., 2006) that may have collectively led to further destruction of other anti-nutritional factors enabling higher utilization of AA (Fan et al., 1995). For example, it is plausible that the fiber–protein matrix in SBM may have been disrupted by the extrusion process in SBM and as such increased the release of AA. The differences in dietary CP concentration between FFSB seeds and SBM (Table 1) could have also partly influenced AA digestibility because of differing proportions of endogenous N contributions (Nyachoti et al., 1997). However, it has been indicated that ileal AA digestibilities are comparable when dietary CP contents are at least 15% (Sauer et al., 1980). Overall, it appears that the processing of soybean through the combination of thermal and mechanical processes results in superior AA utilization. The SID of AA in SBM sample tested in the present study was comparable to values for expeller-extruded SBM samples (Opapeju et al., 2006; Woyengo et al., 2016) and expeller SBM (NRC, 2012). Comparatively, the variation of SID of AA in FFSB seeds was twice that of commodity solvent-extracted SBM with or without dehulling (NRC, 2012). In general, pork producers who use FFSB seeds in their feeding programs are small-scale farmers and use different heating methods and it is, therefore, relevant to apply SID of AA values specific to the processing method of FFSBM (Van Eys, 2012).

The utility of exogenous feed enzymes in monogastric feeding program is rooted in overcoming apparent limitations of feed processing and digestive capacity (Kiarie et al., 2016b; Kiarie and Mills, 2019). Attempts have been made to determine the impact of feed enzymes on AA digestibility of SBM subjected to different processing in pigs (Ayoade et al., 2012; Woyengo et al., 2016) and poultry (Thanabalan et al., 2018). We did not observe the effects (P < 0.05) of an enzyme containing fiber-degrading, protease, and phytase on AA digestibility in the present study. In contrast, an enzyme supplement containing pectinase, cellulase, mannanase, xylanase, β-glucanase, and galactanase improved SID values of CP, Leu, Lys, Met + Cys, and Thr in extruded FFSB seeds fed to finishing pigs (Ayoade et al., 2012). In agreement with the present study, Woyengo et al. (2014) observed marginal effects of multienzyme containing xylanase, β-glucanase, cellulase, mannanase, invertase, protease, and amylase on ileal AA digestibility in cold-pressed soybean cake. As soybean contains an appreciable amount of pectic polysaccharides, based on Ayoade et al. (2012) study, it appears that pectinase and galactanase are critical for soy fiber. However, it is noteworthy that MES tended to improve the SID of HIS (+2.7%, P = 0.08) relative to non-MES. Minimal effects of exogenous enzymes on AA digestibility are usually associated with 1) inherently high digestibility in the control groups, 2) poor substrate accessibility or concentration, and 3) animal status, e.g., stress and enteric challenge (Cowieson et al., 2017; Bedford, 2018; Kiarie et al., 2019). Notably, although numerical, the percentage differences between MES and non-MES for SID of Arg, Ile, Leu, Lys, Met, Phe, Thr, and Val were 0.43%, 1.5%, 2.1%, 1.0%, 2.8%, 1.9%, 1.9%, and 2.0%, respectively. The respective differences for Ala, Asp, Cys, Glu, Gly, Pro, Ser, and Tyr were 3.5%, 1.6%, 4.1%, −2.5%, 2.3%, 2.1%, 1.7%, and 1. 8%, respectively (Table 5). These differences in SID of AA between MES and non-MES were broadly in line with reported meta-analyses indicating that microbial phytase improves ileal AA digestibility in pigs (Cowieson et al., 2017; Zouaoui et al., 2018). It may be that increased replication would have bolstered statistical power to detect significant effects of MES on SID of AA in the present study.

There was an interaction between soy type and MES on ATTD of NDF in the diet (Table 6). In this context, MES improved ATTD of NDF in SBM and not in FFSB seeds. A possible explanation of this could be related to solubilization of fiber by the extrusion process. It has been shown that the thermal processing of feedstuffs increases the susceptibility of fibrous fractions to hydrolysis by exogenous enzymes (de Vries et al., 2012; Kiarie and Mills, 2019). However, fiber solubility was not measured in the present study to ascertain this notion. The soy type and MES had independent effects (P < 0.05) on ATTD of crude fat, CP, ash, and minerals. The effects of soy type on ATTD of CP and minerals suggested that the combination of thermal and mechanical processing improved the utilization of these nutrients. The ATTD of GE and DE of ingredients determined by difference method are shown in Table 6. There was no (P > 0.05) interaction between soy type and MES on energy digestibility in soy products tested in the present study. Roasted FFSB seeds had higher ATTD of GE (80.2% vs. 76.6%; P<0.01) than SBM. In contrast, a comparison of solvent-extracted SBM and micronized regular and low oligosaccharides FFSB seeds indicated that SBM had higher energy digestibility (Woyengo et al., 2014). Because of higher GE digestibility and concentration, the DE in FFSB seeds sample was 622 kcal/kg DM higher (P < 0.01) than in SBM in the present study. The observed DE (4,511 kcal/kg DM) for FFSB seeds was within a range of 4,440 to 4,540 kcal/kg DM (NRC, 2012; Woyengo et al., 2014). However, the DE for SBM (3,889 kcal/kg DM) was lower than DE for expeller SBM (4,130 kcal/kg) (NRC, 2012). Such discrepancies in DE could be because of the concentration of energy-yielding substrates particularly the crude fat; 7.0% in present samples vs. 9.9% in the NRC database (NRC, 2012). Because the NRC database is a composite of samples, it is also plausible that further heat treatment of expeller SBM could increase the utilization of energy. For example, subjecting an expeller SBM (~7.2% crude fat content) to extrusion numerically increased DE by 46 kcal/kg DM (Woyengo et al., 2016). This was linked to increased release of oil trapped in the fibrous matrix.

Table 6.

ATTD (%) of components and energy concentration in roasted FFSB seeds and expeller SBM fed to growing pigs without or with MES1

Interaction effects Main effects
Soy product: FFSB seeds FFSB seeds SBM SBM Soy product MES Probabilities
MES: − + − + SEM FFSB seeds SBM − + SEM Soy MES Soy * MES
Diets
 DM 87.3 91.4 88.1 91.3 0.34 89.3 89.7 87.7b 91.3a 0.24 0.349 <0.01 0.263
 GE 83.6 88.2 81.3 86.8 0.42 85.9a 84.0b 82.4b 87.5a 0.30 <0.01 <0.01 0.316
 CP 80.1 85.0 85.7 87.9 0.86 82.5b 86.8a 82.9b 86.4a 0.61 <0.01 <0.01 0.124
 Crude fat 54.0 71.5 55.9 69.6 1.60 62.7 62.8 54.9b 70.6a 1.13 0.983 <0.01 0.235
 NDF 54.7b 64.6a 49.4c 66.7a 1.19 59.7 58.0 52.0b 65.7a 0.84 0.187 <0.01 0.004
 ADF 44.4 53.9 46.4 50.6 2.31 49.1 48.5 45.4b 52.2a 1.63 0.788 <0.01 0.260
 Ash 68.2 69.7 69.1 71.8 1.04 68.9b 70.4a 68.6b 70.7a 0.72 0.047 0.008 0.408
 Calcium 58.5 61.4 61.8 65.0 1.92 60.0b 63.4a 60.2b 63.2a 1.33 0.016 0.030 0.914
 Phosphorous 63.6 66.3 62.7 68.7 1.45 64.9 65.7 63.2b 67.5a 1.01 0.451 <0.01 0.123
 Potassium 82.2 83.0 87.1 90.2 2.17 82.6b 88.6a 84.6 86.6 1.51 <0.01 0.208 0.433
 Magnesium 32.4 35.7 30.6 29.6 3.07 34.0 30.1 31.5 32.6 2.13 0.078 0.591 0.322
 Sodium 87.5 90.2 93.9 94.2 3.03 88.9b 94.0a 90.7 92.2 2.10 0.022 0.490 0.561
Ingredient
 GE 75.8 84.6 71.4 81.8 0.78 80.2a 76.6b 73.6b 83.2a 0.56 <0.01 <0.01 0.316
 DE, kcal/kg, as fed 3,950 4,409 3,330 3,816 38.1 4,179a 3,573b 3,640b 4,112a 26.95 <0.01 <0.01 0.722
 DE, kcal/kg DM 4,264 4,759 3,625 4,154 41.4 4,511a 3,889b 3,944b 4,457a 29.28 <0.01 <0.01 0.685
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1The MES supplied main activities of phytase, protease, xylanase, and β-glucanase at 2,200, 8,300, 400, and 100 U/kg of feed, respectively (Victus, DSM Nutritional Products Inc., Parsippany, NJ).

a,b,c Lsmeans with different letters within the factor of analyses (soy product, MES or interactions) differ (P < 0.05).

Pigs fed MES had higher (P < 0.01) ATTD of DM (91.3% vs. 87.7 %), GE (87.5% vs. 82.4%), CP (86.4% vs. 82.9%), crude fat (70.6% vs. 54.9%), and ADF (52.2% vs. 45.4%). Digestibility of crude fat was improved to a large extent than other organic components indicating that the use of feed enzyme increased the release of more oil. This aligned with concepts of application of exogenous feed enzymes to release nutrients bound by feedstuffs components that are recalcitrant to digestive fluids. The effect of MES on ATTD of ADF and NDF was appreciable (Table 6) and suggested that the MES was capable of substantial hydrolysis of the non-starch polysaccharides in both SBM and FFSB seeds. This hydrolysis may influence fermentation patterns in the large intestine with commensurate effects on digesta pH and volatile fatty acid production. Indeed, fermentation of non-starch polysaccharides by the microbiome in the large intestine, potentiated by the MES, may have been one of the major contributors to the observed increases in DE. Further research is needed to explore the effect of this MES on gut health, the profile of the microbiome, disease resilience, and passage rate of feed in pigs. Supplemental enzyme increased ATTD of ash (70.7% vs. 68.6%; P = 0.008), Ca (63.2% vs. 60.2%; P = 0.03), and P (67.5% vs. 63.2%; P < 0.01). In essence, MES improved Ca and P digestibility by 5.0% and 6.8%, respectively extending well-established concepts that phytase increased phytate degradation in oilseeds (Kiarie et al., 2016a). In alignment with Ayoade et al. (2012), MES improved ATTD of GE and subsequently DE content in FFSB seeds and SBM. Moreover, the enzyme composite tested in the present study allowed for the sustained growth performance in nursery pigs fed diets with various nutrient and ingredient reductions (Tsai et al., 2017). The MES also increased ileal digestible energy and overcame reductions in energy, P, and AA contents of the diet based on solvent-extracted SBM and corn (Jasek et al., 2015) and significantly improved broiler growth performance (Ward et al., 2014, 2015, 2020; Jasek et al., 2015).

Three countries (Brazil, Argentina, and the United States) produce more than 80% of global soybean output, as such soybean is one of most trans-border traded commodities because some regions are either not endowed with climatic conditions for growing it and/or demand outstrips local supply. In this context, advancements in standardized thermal processing approaches have enabled the production of products with very low TIs for the global feed industry (Van Eys, 2012; Ravindran et al., 2014; García-Rebollar et al., 2016). However, variability in nutrient utilization in soy products is still a major concern in the feed industry (Ravindran et al., 2014; García-Rebollar et al., 2016; Yáñez et al., 2019; Leung and Kiarie, 2020). Processing and supplemental MES had independent effects on nutrients and energy utilization in soy products tested in the present study. Expeller SBM had better nutritive value than roasted FFSB seeds in growing pigs; this partly reflected the impact of processing and compositional differences on nutrient utilization. Although MES had minimal effects on ileal AA digestibility, increased utilization of minerals and energy indicated value of fiber-degrading enzymes, protease, and phytase in improving the nutritive value of compositional diverse soy products subjected to different processing regimens.

Acknowledgments

We would like to acknowledge the financial support provided by the Ontario Agri-Food Innovation Alliance. Animal care and sampling assistance by the current and former students and research associates of E.G.K Monogastric Nutrition Research Laboratory at University of Guelph appreciated. The enzyme supplement and analytical services were provided in-kind by DSM Nutritional Products. This paper is presented in part at the 2018 ASAS-CSAS Annual Meeting & Trade Show, July 8 to 12, 2018, Vancouver, BC.

Glossary

Abbreviations

AA

amino acids

ADF

acid detergent fiber

ATTD

apparent total tract digestibility

BW

body weight

CP

crude protein

DE

digestible energy

DM

dry matter

FFSB

full-fat soybean

GE

gross energy

MES

multi-enzyme supplement

NDF

neutral detergent fiber

NFD

N-free diet

SBM

soybean meal

SID

standardized ileal digestibility

TI

trypsin inhibitors

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. N.E.W. and A.J.C. are employees of DSM Nutritional Products.

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