Energy content of intact and heat-treated dry extruded-expelled soybean meal fed to growing pigs

Abstract

An experiment was performed to evaluate the energy content of extruded-expelled soybean meal (EESBM) and the effects of heat treatment on energy utilization in growing pigs. Eighteen growing barrows (18.03 ± 0.61 kg initial body weight) were individually housed in metabolism crates and randomly allotted to one of three dietary treatments (six replicates per treatment). The three experimental diets were the following: a corn-soybean meal-based basal diet and two test diets with simple substitution of a basal diet with intact EESBM or heat-treated EESBM (heat-EESBM) at a 7:3 ratio. Intact EESBM was autoclaved at 121 °C for 60 min to make heat-treated EESBM. Pigs were fed the experimental diets for 16 d, including 10 d for adaptation and 6 d for total collection of feces and urine. Pigs were then moved into indirect calorimetry chambers to determine 24-h heat production and 12-h fasting heat production. The energy content of EESBM was calculated using the difference method. Data were analyzed using the Mixed procedure of SAS with the individual pig as the experimental unit. Pigs fed heat-EESBM diets showed lower (P < 0.05) apparent total tract digestibility of dry matter (DM), gross energy, and nitrogen than those fed intact EESBM. A trend (P ≤ 0.10) was observed for greater heat increments in pigs fed intact EESBM than those fed heat-EESBM. This resulted in intact EESBM having greater (P < 0.05) digestible energy (DE) and metabolizable energy (ME) contents than heat-EESBM. However, no difference was observed in net energy (NE) contents between intact EESBM and heat-EESBM, showing a tendency (P ≤ 0.10) toward an increase in NE/ME efficiency in heat-EESBM, but comparable NE contents between intact and heat-EESBM. In conclusion, respective values of DE, ME, and NE are 4,591 kcal/kg, 4,099 kcal/kg, and 3,189 kcal/kg in intact EESBM on a DM basis. It is recommended to use NE values of feedstuffs that are exposed to heat for accurate diet formulation.

Introduction

Raw full-fat soybeans [Glycine max (L.)] are commonly processed to separate the oil and meal components. Although solvent extraction of soybeans is common to maximize the oil yield and protein content in the meal, the coupling of a dry extruder and expeller is an alternative way to separate them (Wang et al., 2008). The by-product from the extruded soybeans after oil extraction with an expeller is known as dry extruded-expelled soybean meal (EESBM). As soybean production increases with a limited number of solvent-extraction plants (Soy Canada, 2016; USDA, 2021), extruding-expelling processing has received great attention as part of an on-farm processing method (Wang et al., 2008; Kiarie et al., 2020). Furthermore, a growing interest in organic feed ingredients for organic meat production encourages extruding-expelling processing rather than solvent extraction that is criticized for the use of hexane, which may be harmful to the environment (Kumar et al., 2017). Despite the prospect of the increasing use of EESBM as swine feedstuff, limited information regarding its net energy (NE) content is available.

The heat generated during extrusion and expelling of soybeans due to friction deactivates heat-liable anti-nutritional factors (e.g., trypsin inhibitors and antigenic compounds), thereby increasing the nutritive value of the meal for pigs (Vagadia et al., 2017). However, excessive heat can accelerate the Maillard reaction, producing various insoluble complexes between reducing sugars and amino acids (Aljahdali and Carbonero, 2017). Thus, the investigation of amino acid digestibility in heat-treated feedstuffs has been a beneficial and important research topic. Although energy content is economically and practically important for swine diet formulation, at least as much as amino acids, no information is available on the effect of heat treatment on the NE value of feedstuffs for pigs. A recent study (Oliveira et al., 2020) found that heat damage can decrease digestible energy (DE) and metabolizable energy (ME), but NE was not determined. Therefore, we hypothesized that excessive heat treatment can decrease nitrogen (N) balance and energy content in EESBM. The objective of this study was to determine the N balance and energy content of intact-EESBM and heat-treated EESBM fed to growing pigs.

Materials and Methods

The animal use protocol used in this experiment was reviewed and approved by the University of Manitoba Animal Care Committee (AC11414), and pigs were handled according to the guideline described by the Canadian Council on Animal Care (2009).

Animals, housing, and experimental diets

Eighteen growing barrows (TN70 × TN Tempo; Topigs Norsvin, Winnipeg, MB, Canada) with an initial body weight (BW) of 18.03 ± 0.61 kg were used in the current study. Pigs were individually housed in adjustable metabolism crates (1.8 × 0.6 m) located in a temperature-controlled room (24 ± 1 °C). Each crate was equipped with a stainless-steel feeder and a nipple drinker, which allowed the pigs ad libitum access to water. One batch of EESBM obtained from a local mill (Soy-Max Protein Inc., Cartier, MB, Canada) was used in the study. Intact-EESBM was autoclaved at 121 °C (103 kPa) for 60 min to make heat-treated EESBM (heat-EESBM). A corn-solvent extracted soybean meal (SSBM) basal diet was formulated (Table 1). Two test diets were made with a simple substitution of the basal diet with intact- or heat-EESBM at a 7:3 ratio.

Table 1.

Diet composition and nutrients contents of experimental diets, % (as-fed basis)¹

Item	Basal
Ingredient
Corn	68.46
Solvent-extracted soybean meal	28.20
Vegetable oil	1.00
L-Lys∙HCl	0.10
Limestone	1.00
Monocalcium phosphate	0.70
Salt	0.40
Vitamin and mineral2	0.14
Analyzed nutrients
GE, kcal/g	3.99
CP	19.56

¹Two test diets were made with a simple substitution of a basal diet with intact dry EESBM or heat-treated EESBM (heat-EESBM) at a ratio of 7:3. Intact EESBM was autoclaved at 121 °C for 60 min to make heat-treated EESBM.

²Supplied per kilogram of diet: vitamins A, 2,855 IU; vitamin D_3, 318 IU; vitamin E, 24 IU; vitamin K, 1.1 mg; thiamine, 2.1 mg; riboflavin, 5.7 mg; niacin, 64 mg; pantothenic acid, 17 mg; vitamin B₁₂, 0.03 mg; folic acid, 0.63 mg; Cu, 8 mg as copper sulfate; I, 0.30 mg as calcium iodate; Fe, 129 mg as ferrous sulfate; Mn, 4 mg as manganese oxide; Se, 0.43 mg as sodium selenite; Zn, 129 mg as zinc oxide; biotin 0.14 mg.

Experimental Design and Procedure and Sample Collection

On the first day of experiment, pigs were randomly assigned one of three experimental diets to give six replicates per treatment. Pigs were fed their experimental diets for 16 d, including 10 d for adaptation and 6 d for total collection of feces and urine. Daily feed allowance was set at 550 kcal ME/kg BW^0.60 on the basis of BW on days 1 and 10, to give the amount close to ad libitum (Noblet et al., 1994). Experimental diets were provided to pigs once daily at 0800 h and pigs were trained to consume their daily feed allowance within 1 h after feeding. Total feces and urine were separately collected every morning from days 11 to 15. To mark the beginning and the end of fecal collection, 6 g of ferric oxide (product number, 310050; Sigma-Aldrich, St. Louis, MO) was fed as indigestible marker. The feces were collected once daily in the morning, weighed, and stored at −20 °C. Urine was collected in a plastic container containing 20 mL of 3 N HCl to minimize N losses. The collected urine was weighed, and a 5% aliquot was stored at −20 °C. At the end of the collection period, urine samples were thawed and thoroughly mixed, and a subsample (approximately 15 mL) was obtained by filtering with glass wool to remove impurities.

The accuracy of the indirect calorimetry chambers was tested by burning ethanol using a lamp inside the chambers and making determinations based on the stoichiometric equation of ethanol combustion. The theoretical respiratory quotient, a ratio of CO₂ production to O₂ consumption, of ethanol combustion is 0.667 (Benedict and Tompkins, 1916). A respiratory quotient value between 0.640 and 0.690 was considered acceptable. On day 16, three pigs (one pig per treatment) were transferred from the metabolism crates to the indirect calorimetry chambers (1.22 × 0.61 × 0.91 m) (Columbus Instruments, Columbus, OH) within 1 h of consuming their daily feed allowance. Respiratory gaseous exchange was continuously measured over the first 24 h to calculate fed-state heat production (HP) and over the following 12 h to calculate fasting heat production (FHP). Excreted urine was collected separately for HP and FHP through a valve underneath the chamber; the urine was then weighed and stored at −20 °C. The next sets of three pigs (one pig per treatment) were moved to the indirect calorimetry chambers every 2 d. Pigs had ad libitum access to water via a nipple drinker in the chambers. The temperature inside the chamber was maintained at 22 °C using a built-in air conditioner.

Sample preparation and chemical analyses

Fecal samples were dried in a forced-air drying oven at 60 °C for 4 d, then pooled within each pig, and finely ground before chemical analysis with a grain miller (50 to 200 μm of fineness) (HC-700, Boshi Electronic Instrument, Guangzhou, China). Urine samples were thawed, filtered through glass wool, and transferred into a plastic vial for gross energy (GE) and N analysis. Samples of diet and test ingredients (intact-EESBM, heat-EESBM) were finely ground with a grain miller (HC-700). Diet, ingredients, and fecal samples were analyzed for dry matter (DM), N, and GE. Ingredients were further analyzed for ether extract (EE), starch, neutral detergent fiber (NDF), acid detergent fiber (ADF), and non-starch polysaccharides (NSP).

The DM (method 934.01) and EE (method 902.39A) were determined according to the methods of the Association of Official Analytical Chemists (AOAC, 2006). The N content was determined using a combustion analyzer (method 984.13A-D) (model CNC-2000; Leco Corporation, St. Joseph, MI) and was used to calculate the crude protein (CP) concentration (N × 6.25). The GE was determined using an isoperibol bomb calorimeter (Parr Instrument Co., Moline, IL), which had been calibrated using benzoic acid as a standard. The starch content was measured using an assay kit (Megazyme Total Starch assay kit; Megazyme International Ltd., Wicklow, Ireland). The NSP content was analyzed as described by Englyst and Cummings (1988) with some modifications (Slominski and Campbell, 1990), using gas-liquid chromatography (Varian CP-3380, Carian Medical Systems Inc., Palo Alto, CA) for neutral sugar components and colorimetry for uronic acids (Biochrom Ultrospec 50, Biochrom Ltd., Cambridge, UK). The ADF and NDF contents were analyzed according to the method of Goering and van Soest (1970) using an ANKOM 200 Fiber Analyzer (A200, ANKOM Technology, Macedon, NY) with sodium sulfite and α-amylase (product number, A3306; Sigma-Aldrich). The GE of urine was determined using the difference method. In brief, 0.5 g of cellulose was dried at 100 °C for 24 h, and 2 mL of urine sample was sprayed over it. The urine-cellulose mixture was dried at 50 °C for 24 h and then weighed to estimate the urine DM. The GE of the mixture and pure cellulose were determined and the GE of urine calculated using the difference method.

Calculations

The apparent total tract digestibility (ATTD) of DM, GE, and CP and energy and nutrient retention (%) were determined by the total collection method using the equations described by Kong and Adeola (2014). The HP and FHP, retained energy (RE), and energy contents (Noblet et al., 1994) were calculated using the following equations:

HP = 3.866 × O₂ + 1.200 × CO₂ – 1.431 × urinary N excretion,

where HP is in kilocalories per day, O₂ is oxygen consumption in liters, CO₂ is carbon dioxide production in liters, and urinary N excretion is total urinary N excretion in grams. The same equation was used for FHP.

RE = ME – HP,

where RE, ME, and HP are in kilocalories per day.

The RE as protein was calculated from the N retention by the pigs (N × 6.25 × 5.68, kcal/g). The RE as lipid was calculated as the difference between RE and RE as protein (Labussiere et al., 2009).

DE = (GE_i − GE_f)/DMI,

ME = (GE_i − GE_f − GE_u)/DMI,

NE = (RE + FHP)/DMI,

where DE, ME, NE are the contents of a diet in kcal/kg of DM. The GE_i, GE_f, and GE_u are the total GE intake, total fecal GE output, and total urinary GE output in kilocalories, respectively. The RE and FHP are in kilocalories per day, and DMI is DM intake in kilograms.

The DE, ME, and NE of the test ingredients were calculated by subtracting the energy contribution of the basal diet from the energy content of the corresponding experimental diets as follows:

Energy content of EESBM (kcal/kg DM) = NE_{Basal diet} – [(NE_{Basal diet} – NE_{Diet containing EESBM})/0.3].

Statistical analysis

All data were analyzed using the MIXED procedure of SAS, and an individual pig was considered the experimental unit. The LSMEANS procedure was used to calculate mean values and the PDIFF option with the Tukey’s adjustment was used to separate means for each treatment. Results were considered significant at P < 0.05, and tendencies were observed at 0.05 < P ≤ 0.10.

Results and Discussion

The dry extrusion process can deactivate anti-nutritional factors by friction heat at approximately 135 °C and rupture the oil sacs for efficient extraction with the expeller in a subsequent process (Bargale et al., 1999). The EESBM is characterized by relatively high protein and fat content, suggesting it is a valuable source of amino acids, as well as energy. The EESBM used in this study contained 7% EE and 42% CP (Table 2), which is within the range of typical contents in EESBM (Webster et al., 2003; Wang et al., 2008; Kiarie et al., 2020). Given that the component sugar profile of EESBM resembles that of SSBM, dietary fiber profiles in EESBM may be similar to that in EESBM, containing arabinans, arabinogalactans, galactans, galactomannans, and pectic polysaccharides as the major constituents of dietary fiber (Slominski, 2017).

Table 2.

Analyzed nutrient composition of dry EESBM and autoclaved EESBM (heat-EESBM), % (as-fed basis)

	EESBM	heat-EESBM1
DM	95.4	94.9
GE, kcal/kg	4,754	4,769
CP, %	42.13	42.19
EE, %	7.41	6.55
Starch, %	1.88	1.85
NDF, %	16.1	24.9
ADF, %	8.7	8.5
NSP, mg/g
Arabinose	22.1	21.6
Xylose	12.9	13.5
Mannose	8.0	8.2
Galactose	40.7	41.8
Glucose	50.0	52.1
Uronic acid	42.5	41.5
Total	176.1	178.6

¹EESBM was autoclaved at 121 °C for 60 min.

The DE, ME, and NE contents of intact EESBM determined in the present study were 4,591, 4,222, and 3,189 kcal/kg (DM basis), respectively (Table 5). These values are comparable with those reported by Woodworth et al. (2001) where DE and ME were determined at 4,352 kcal/kg and 4,105 kcal/kg on a DM basis, respectively. However, Baker and Stein (2009) and Velayudhan et al. (2015) reported DE values of 3,384 to 3,827 and 3,324 to 3,620 kcal/kg, using the total collection method. This discrepancy may be attributed to differences in nutrient composition in EESBM, particularly fat content, the presence of hulls, and processing conditions. The energy content of protein-rich ingredients is often overestimated when expressed on a DE and ME bases because of protein having a lower energy efficiency than starch and fat (van Milgen et al., 2001). Although EESBM is rich in protein, NE density (3,242 kcal/kg) and energetic efficiency of GE to NE in EESBM (0.79) are higher compared with tabulated NE content in cereal grains (0.59 to 0.68) and SSBM (0.49) (NRC, 2012). This may be due to the higher fat content in EESBM than in cereal grains whose energy is largely derived from starch. Our finding of the lack of difference in the rate of N retention between the basal diet and EESBM diets implies that EESBM can be a promising source of protein and energy to replace corn, SSBM, and supplemental oil in pig diets.

Table 5.

Energy contents of dry EESBM and heat-treated EESBM, kcal/kg (DM basis)

Item	EESBM	Heat-EESBM1	SE	P-value
Energy content
DE	4,591	4,222	65.8	0.003
ME	4,099	3,692	123.9	0.043
NE	3,189	3,234	179.8	0.861
Energy efficiency
DE:GE	0.92	0.84	0.013	0.002
ME:DE	0.89	0.87	0.019	0.529
NE:DE	0.69	0.76	0.036	0.196
NE:ME	0.78	0.88	0.038	0.097

¹Heat-EESBM, EESBM was autoclaved at 121 °C for 60 min.

Autoclaving has been commonly used to mimic the heat damage of feedstuff during processing (González-Vega et al., 2011; Almeida et al., 2014a, 2014b; Oliveira et al., 2020). The autoclaving temperature (120 to 150 °C) is usually reached in the processing of oil extraction during desolventization, toasting, steam injection, or extrusion (Bargale et al., 1999; Vagadia et al., 2017). Furthermore, because autoclaving conveys heat via high-pressure steam, feedstuff processed with autoclaving are more subject to the Maillard reaction than those with convectional thermal heat in an oven (González-Vega et al., 2011). Therefore, in the present study, to mimic and maximize the heat damage during the soybean processing, intact-EESBM was autoclaved at 121 °C (103 kPa) for 60 min.

Autoclaving generates high temperatures and moist environments where heat-catalyzed glycation or the Maillard reaction is accelerated (Eklund et al., 2015). The reaction is initiated with the covalent attachment of the carbonyl group of reducing sugars to the ε-amino group of amino acids, producing glycosylamine. The initial product then isomerizes into a more stable form, ketosamine, which is called the Amadori rearrangement. The Amadori products are reactive and cross-link with other amino groups, forming polymeric aggregates and brown pigments (Tuohy et al., 2006). The chemical structure of the polymerized protein resembles that of lignin, so they are usually detected as a fraction of dietary fiber (Slominski, 2017). This explains the numerically higher levels of NDF (24.9%) in heat-EESBM than in intact-EESBM (16.1%). Similar results were reported in previous studies (Almeida et al., 2014a, 2014b), where NDF content in soybean meal, canola meal, and distiller-dried grains with solubles increased after autoclaving at 125 °C or 130 °C for 20 to 60 min. However, the change in ADF content in EESBM was not noticeable in the present study, which is consistent with Almeida et al. (2014a) who tested SSBM. Similarly, the quantities of the component sugars were comparable between intact- and heat-EESBM. In contrast, the ADF content in canola meal and distillers’ dried grains with solubles (Almeida et al., 2014b) substantially increased after autoclaving, which was in line with NDF content. This may suggest that the types and chemical properties of products from the Maillard reaction are ingredient-specific.

Amino acid-associated polymers as a consequence of the Maillard reaction are insoluble and resistant to digestive enzymes (Aljahdali and Carbonero, 2017). There is consensus that the digestibility of amino acids in heat-damaged ingredients is lower than in their intact counterparts in pigs (González-Vega et al., 2011; Messerschmidt et al., 2012; Almeida et al., 2014b; Oliveira et al., 2020). In the present study, the ATTD of N was lower (P < 0.01) in pigs fed a heat-EESBM diet than in those fed an intact-EESBM diet (Table 3). However, there was no difference in retained N/digested N (%) between pigs fed intact-EESBM and pigs fed heat-EESBM. This suggests that the absorbed N is equally metabolized in the body whether it originated from intact- or heat-EESBM. Thus, the trend (P ≤ 0.10) for a lower N retention rate seems to be mainly attributed to lower N digestibility in pigs fed heat-EESBM compared with pigs fed intact-EESBM. This is partially supported by Faist and Erbersdobler (2001) who reported that administered melanoidins, a high molecular polymer product of the Maillard reaction, were excreted through feces to a greater extent (87% to 93%) than urine (1% to 4%) based on the isotope tracer technique. In contrast, van Barneveld et al. (1994) reported that the absorbed amino acids from heat-damaged proteins were less efficiently utilized by pigs, leading to the increase in urinary N excretion. Thus, the extent of metabolic efficiency of dietary N in heat-damaged feedstuff may be associated with the type of amino acids containing N and the extent of heat damage, which warrants further research.

Table 3.

ATTD and N balance of experimental diets fed to growing pigs¹

Item	Basal	EESBM	Heat-EESBM	SEM	P-value
ATTD, %
DM	87.6xy	88.7x	86.4y	0.39	< 0.01
Nitrogen	85.7y	89.8x	85.3y	0.59	< 0.01
GE	86.7xy	88.0x	85.8y	0.42	0.008
N balance
N intake, g/day	29.3y	34.9x	37.9x	0.83	< 0.01
Fecal excretion, g/day	4.2y	3.6y	5.6x	0.23	< 0.01
Urinary excretion, g/day	8.4y	12.5xy	15.3x	1.17	0.003
Retained N/Digested N, %	66.4	59.9	52.8	3.76	0.066
N retained, g/day	16.7	18.9	17.0	1.25	0.414
N retained, %	56.9	53.8	45.1	3.21	0.052

¹EESBM, dry extruded-expelled soybean meal; Heat-EESBM, EESBM autoclaved at 121 °C for 60 min.

^x,yValues within a row with different superscripts differ significantly at P < 0.05.

Lower N digestibility contributed to a lower (P < 0.01) ATTD of DM and GE in pigs fed the intact-EESBM diet than those fed the heat-EESBM diet. Apart from N utilization, sugars that were associated with the Maillard reaction were likely to be resistant to digestive enzymes, lowering energy digestibility (Oliveira et al., 2020). Furthermore, there is evidence that Maillard reaction products could reduce digestive enzyme activities, such as amylase and amyloglucosidase (Chung et al., 2012), possibly lowering energy digestibility. The lower GE digestibility resulted in lower (P < 0.05) DE and ME content in heat-EESBM than in intact-EESBM. This is supported by a recent study (Oliveira et al., 2020) in which autoclaving at 150 °C for 3 to 18 min decreased DE and ME contents in SSBM by 15% and 18%, respectively. However, there was no difference in the ME:DE between intact- and heat-EESBM in the present study, which is in line with the observation on urinary N excretion. Thus, the difference in ME between intact- and heat-EESBM was attributed to the GE digestibility and not energy retention. This is contrary to Oliveira et al. (2020) who reported that the conversion efficiency from DE to ME was significantly lower in heat-treated than in intact SSBM. The intensity of heat treatment (e.g., temperature and time) and protein content may be associated with this discrepancy. To the best of our knowledge, this is the first report on the effect of heat damage on NE content of a feedstuff and pig diet. Interestingly, no difference was observed in NE content of intact- and heat-EESBM in contrast to DE and ME contents. Rather, there was a tendency (P ≤ 0.10) toward a decline in the heat increment in pigs fed the heat-EESBM diet compared with pigs fed the intact-EESBM diet (Tables 4 and 5). This resulted in a trend (P ≤ 0.10) for higher NE:ME in heat-EESBM than in intact-EESBM. Approximately 16% of ME in the intact-EESBM diet was dissipated through heat increments whereas 13% was dissipated in the heat-EESBM diet. It is unclear why the heat-damaged feedstuff showed higher energy efficiency from ME to NE. There could have been more heat increment in pigs fed intact-EESBM because of heat generated from more metabolizable protein and carbohydrates, compared with heat-EESBM-fed pigs. However, this cannot adequately explain the substantial difference. There is evidence that Maillard reaction products are associated with gut microbiota composition, microbial fermentation patterns, and physiological status, which possibly modify the energy efficiency (Tuohy et al., 2006; Aljahdali and Carbonero, 2017). Although heat can damage the nutrients, beneficial modifications of the chemical structure of nutrients are also commonly found. For example, starch is gelatinized by heat, respectively, which allow digestive enzymes to access the nutrient more efficiently (Wang and Copeland, 2013). There is also a report that autoclaving can alter the structure and solubility of dietary fiber in soybean meal (Oliveira et al., 2020). Based on our results, this benefit of heat treatment did not override the disadvantage of heat damage in terms of DE. However, the heat treatment may have altered the digestion site of energy in the EESBM from the hindgut to the foregut, decreasing the heat increment (e.g., heat of digestion and fermentation) and increasing the efficiency of ME (Just et al., 1983). Further studies are warranted to investigate heat-treated feedstuff in relation with components of heat increment, including heat of digestion, assimilation, tissue formation, fermentation, and waste formation (NRC, 2012).

Table 4.

Energy balance in growing pigs and energy values of experimental diets¹

Item	Basal	EESBM	Heat-EESBM	SEM	P-value
Energy balance, kcal/d
GE intake	3,730xy	3,464y	3,814x	82.9	0.024
Fecal GE excretion	496x	415y	540x	18.3	0.001
Urinary GE excretion	173y	220xy	256x	20.0	0.034
Energy retention, %	82.0x	81.6xy	79.1y	0.77	0.038
Energy value, kcal/kg DM
DE	3,939z	4,148x	4,030y	19.6	< 0.001
ME	3,727	3,846	3,716	36.1	0.040
HP2	1,653	1,790	1,698	181.9	0.864
HP, kcal/kg BW0.6	190	199	190	18.2	0.921
RQ, fed-state	1.07	1.01	0.99	0.134	0.898
Total RE3	2,073	2,056	2,017	172.4	0.972
As protein	592	704	603	45.1	0.171
As lipid	1,482	1,385	1,414	187.3	0.932
FHP4	1,154	1,159	1,213	175.2	0.966
FHP, kcal/kg BW0.6	132	128	135	18.1	0.965
RQ, fasting-state	0.79	0.78	0.74	0.115	0.936
Heat increment	497	612	488	36.4	0.052
NE7	3,230	3,234	3,228	44.7	0.995
Energy efficiency
ME:DE	0.95x	0.93xy	0.92y	0.007	0.046
NE:DE	0.82x	0.78y	0.80xy	0.010	0.034
NE:ME	0.87	0.84	0.87	0.009	0.098

¹Heat-EESBM, EESBM autoclaved at 121 °C for 60 min; RQ, respiratory quotient.

²Heat production (kcal/kg DM) = (3.87 × O₂ + 1.20 × CO₂ – 1.43 × urinary N)/DM intake

³Retained energy = (ME intake – HP)/DM intake; Retained energy as protein was calculated as N retention (g) × 6.25 × 5.68 (kcal/g) (Ewan 2001). Retained energy as lipid was calculated as the difference between total retained energy and retained energy as protein.

⁴Fasting heat production = (3.87 × O₂ + 1.20 × CO₂ – 1.43 × urinary N)/DM intake.

⁵Net energy = (RE + FHP)/DM intake.

^x,y,zValues within a row with different superscripts differ significantly at P < 0.05.

Conclusion

The DE, ME, and NE contents in intact EESBM on a DM basis were determined to be 4,591, 4,099, and 3,189 kcal/kg, respectively. The energy content of heat-EESBM was underestimated when expressed on a DE and ME basis. Therefore, it is recommended to formulate diets on an NE basis when EESBM is included in a diet, regardless of whether it is heat-treated or not. Further studies are needed to elucidate the relationship between heat-damaged feedstuff and heat increment.

Glossary

Abbreviations

ADF

acid detergent fiber

ATTD

apparent total tract digestibility

BW

body weight

CP

crude protein

DE

digestible energy

DM

dry matter

EE

ether extract

EESBM

dry extruded-expelled soybean meal

FHP

fasting heat production

GE

gross energy

HP

heat production

ME

metabolizable energy

N

nitrogen

NDF

neutral detergent fiber

NE

net energy

NSP

non-starch polysaccharides

RE

retained energy

RQ

respiratory quotient

SSBM

solvent-extracted soybean meal

Conflict of interest statement

The authors declare no real or perceived conflicts of interest.