Effects of Aspergillus oryzae prebiotic on dietary energy and nutrient digestibility of growing pigs

Abstract

The objective of this study was to determine the effects of Aspergillus oryzae prebiotic (AOP) on nutrient digestibility in growing pigs fed high-fiber diets. Eighteen growing barrows (initial body weight = 50.6 ± 4.9 kg) were surgically equipped with a T-cannula at the distal ileum. Corn and soybean meal-based diets were formulated with fiber from cereal grain byproducts corn (distillers dried grains with solubles, DDGS), rice (rice bran, RB), or wheat (wheat middlings, WM) to meet or exceed all nutrient requirements for 50 to 75 kg growing pigs. Three additional diets were formulated to contain 0.05% AOP supplemented at the expense of corn in the DDGS diet (DDGS + AOP), RB diet (RB + AOP), and WM diet (WM + AOP). All diets contained 0.5% of titanium dioxide as an indigestible marker. Pigs were allotted randomly to a triplicated 6 × 2 Youden square design with six diets and two successive periods. Ileal digesta and fecal samples were collected for 2 d after a 21-d adaptation period, and dry matter (DM), gross energy (GE), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF), and ash were analyzed to calculate apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD). Standardized ileal digestibility (SID) of amino acids (AA) was calculated by correcting AID with basal endogenous AA losses from the same set of pigs. Pigs fed the DDGS+AOP diet had greater (P < 0.05) AID of EE compared with those fed the DDGS diet. However, supplementation of AOP did not (P > 0.05) affect AID of GE, DM, CP, NDF, ash or SID of AA of any high-fiber diet. Supplementation of 0.05% AOP increased (P < 0.05) ATTD of DM, GE, CP, NDF, and ash in DDGS, RB, and WM diets. Diet digestible energy was 35 kcal/kg greater (P < 0.05) in pigs fed AOP supplemented diets compared with those fed diets without AOP. In conclusion, supplementation of AOP increased ATTD of nutrients and energy value in high-fiber diets containing DDGS, RB, or WM.

INTRODUCTION

Large quantities of coproducts of biofuel and food industry, such as distillers dried grains with solubles (DDGS), wheat middlings (WM), and rice bran (RB) are available to be used in swine feeds to reduce feed cost (Cromwell et al., 1999; Stein and Shurson, 2009; Casas and Stein, 2016) and increase upcycle of nutrients to produce high-value protein (Shurson, 2020). However, dietary fiber, especially from DDGS, WM, and RB, is generally not well-utilized by monogastric animals due to the lack of fiber-degrading enzymes (Agyekum and Nyachoti, 2017; Zeng et al., 2018). Therefore, effective ways are needed to enhance fundamental elements of gastrointestinal function such as the digestibility and utilization efficiency of energy and nutrients of high-fiber co-products fed to growing pigs.

Fundamental elements of gut health are better defined by the functions of the gastrointestinal tract that include nutrient digestion and absorption, absence of illness, normal microbiota, effective immune system, and effective sensing and signaling (Bischoff, 2011). Gastrointestinal functions may be modulated by pre- and post-biotics which can contain fungi cell-wall carbohydrates, enzymes, and metabolites in the fermentation media (Amirdahri et al., 2012; Mano et al., 2018). Constituents of Aspergillus oryzae and other postbiotics and prebiotic-like products may enhance diverse aspects of gastrointestinal functions by a variety of mechanism that are currently under investigation but include modulation of resident microbiota, enhancement of epithelial functions, modulation of immune responses, and modulation of signaling via nervous system (Gibson et al., 2017; Salminen et al., 2021).

Aspergillus oryzae prebiotic (AOP) has been used as a feed additive in ruminant diets to increase nutrient digestibility through enhanced fiber degradation (Newbold et al., 1991; Chang et al., 1999; Newbold, 2007). Conversely, studies on the potential benefits of supplementing AOP in swine diets are very limited. No beneficial effects on performance of lactating sows fed a corn soybean-meal diets supplemented with AOP were observed by Jackson et al. (2006), but Moeller and Hess (2016) reported that sows fed AOP supplemented diets weaned more piglets during lactation. Both studies in sows did not test effects of AOP fed high-fiber ingredients and no studies have been conducted to evaluate the effect of AOP supplementation on energy and nutrient digestibility in growing pigs fed high-fiber diets.

Corn, wheat, and rice are the common cereal grains globally produced and their byproducts contain high levels of NDF: corn distillers dried grains with solubles (30.46%), wheat middlings (34.97%), and high far rice bran (26.28%). All three byproducts have similar arabinose to xylose ratio (A:X) but the soluble arabinoxylan content in corn-DDGS, WM, and RB are different (4.80%, 45.22%, and 3.13%, respectively). The efficacy of nonstarch polysaccharide degrading enzymes was less in corn DDGS than in WM when fed to growing pigs (Zeng et al., 2018). Therefore, we hypothesized that supplementing AOP in growing pigs fed diets with fibrous ingredients will increase energy and nutrient digestibility and the magnitude of the response to AOP may depend on the fiber source. Therefore, the objective of this study was to determine the effects of supplementing AOP to growing pigs fed diets containing cereal grain based fibrous ingredients that vary in composition and characteristics of fiber on energy and nutrient digestibility.

MATERIALS AND METHODS

The animal use protocol (#1805-35983A) was reviewed and approved by the Institution Animal Care and Use Committee at University of Minnesota.

Animals and Diets

Eighteen growing barrows (initial body weight = 50.6 ± 4.9 kg) were surgically equipped with a T-cannula at the distal ileum (Stein et al., 1998). Pigs were housed individually in metabolism cages (198 cm × 84 cm × 71 cm) at the Southern Research and Outreach Center of University of Minnesota in Waseca, MN. Three corn and soybean meal-based diets were formulated to contain 29.65% corn-DDGS, 36.65% full fat RB or 24.59% WM (Tables 1 and 2) and meet or exceed all nutrient requirements for 50–75 kg growing pigs (NRC, 2012). Three additional diets were formulated to contain 0.05% AOP (the fermentation extract of a specific strain Aspergillus oryzae NRL 458 in a submerged fermentation, Amaferm, BioZyme Inc., St. Joseph, MO) following the manufacturer’s recommendation, which was supplemented at the expense of corn in the DDGS diet (DDGS+AOP), RB diet (RB+AOP), and WM diet (WM+AOP). Titanium dioxide (Sachtleben Chemie, Duisburg, Germany) was added at 0.50% to each diet as an indigestible marker. Pigs were allotted randomly to a triplicated 6 × 2 Youden square design with six diets and two successive periods. Within each period, three pigs received one of the six diets for a total of six observations per diet for the two periods. Pigs received a daily feed allowance equivalent to 3% initial BW (Supplement 1) and were fed twice daily in two equal meals at 0800 and 1700 hours. Pigs had free access to water from nipple drinkers throughout the experiment.

Table 1.

Analyzed chemical composition of test feed ingredients (as-fed basis)

Items	Corn	Soybean meal	Corn-DDGS1	Wheat middling	Full fat rice bran
Gross energy, kcal/kg	3,943	4,234	4,492	4,053	4,621
Dry matter, %	88.51	89.73	89.56	90.20	94.35
Crude protein, %	6.92	46.45	27.00	16.49	13.52
Ether extract, %	1.26	1.82	5.03	3.24	16.94
Crude fiber, %	1.65	3.80	8.00	6.80	5.71
Neutral detergent fiber, %	8.29	7.72	28.35	28.86	10.21
Ash, %	1.18	6.65	5.18	7.11	12.96
Indispensable AA
Arg	0.34	3.47	1.21	1.02	1.03
His	0.21	1.23	0.81	0.44	0.39
Ile	0.25	2.30	1.07	0.55	0.48
Leu	0.80	3.68	2.97	1.03	0.92
Lys	0.26	3.07	1.04	0.69	0.68
Met	0.14	0.64	0.53	0.24	0.26
Phe	0.34	2.45	1.23	0.67	0.58
Thr	0.25	1.85	1.06	0.52	0.49
Trp	0.04	0.56	0.17	0.20	0.16
Val
Dispensable AA
Ala	0.50	2.08	1.96	0.76	0.80
Asp	0.48	5.38	1.79	1.11	1.21
Cys	0.16	0.69	0.61	0.34	0.31
Glu	1.21	8.57	4.13	3.32	1.80
Gly	0.28	2.01	1.15	0.82	0.73
Pro	0.55	2.36	2.10	1.10	0.56
Ser	0.31	2.18	1.24	0.63	0.55
Tyr	0.21	1.70	0.95	0.44	0.43
Total AA	6.91	47.13	26.18	14.96	12.45

¹Corn-distiller’s dried grains with solubles.

Table 2.

Composition and nutrient levels of experimental diets formulated with corn-distiller’s dried grains with solubles (corn-DDGS), wheat middling, or full-fat rice bran with or without the supplementation of 0.05% Aspergillus oryzae prebiotic (AOP) (as-fed basis)

Item	Corn-DDGS		Rice bran		Wheat middling
	−AOP	+ AOP	−AOP	+ AOP	− AOP	+ AOP
Ingredient, %
Corn, yellow dent	44.91	44.86	38.86	38.81	48.52	48.47
Soybean meal	22.94	22.94	22.27	22.27	24.13	24.13
Corn DDGS	29.65	29.65	–	–	–	–
Wheat middling	–	–	–	–	24.59	24.59
Rice bran	–	–	36.65	36.65	–	–
Monocalcium phosphate	0.30	0.30	0.17	0.17	0.56	0.56
Limestone	1.20	1.20	1.05	1.05	1.20	1.20
Salt	0.25	0.25	0.25	0.25	0.25	0.25
Premix1	0.25	0.25	0.25	0.25	0.25	0.25
Titanium dioxide	0.50	0.50	0.50	0.50	0.50	0.50
AOP	–	0.05	–	0.05	–	0.05
Calculated nutrient content, %
DE, kcal/kg	3,442	3,440	3,283	3,281	3,303	3301
ME, kcal/kg	3,287	3,285	3,150	3,148	3,170	3168
NE, kcal/kg	2,374	2,372	2,339	2,337	2,319	2319
Standardized ileal digestible amino acid, %
Lys	0.85	0.85	0.85	0.85	0.85	0.85
Met	0.34	0.34	0.27	0.27	0.27	0.27
Met + Cys	0.64	0.64	0.53	0.53	0.55	0.55
Thr	0.67	0.67	0.58	0.58	0.58	0.58
Trp	0.20	0.20	0.20	0.20	0.21	0.21
Analyzed nutrient content, %
Gross energy, kcal/kg	4,061	4,118	4,116	4,152	3974	3876
Dry matter	88.98	89.90	90.99	91.51	89.76	88.66
Crude protein	21.60	21.29	18.51	18.70	19.08	18.78
Ether extract	2.09	2.41	5.95	6.26	1.41	1.11
Neutral detergent fiber	14.50	13.73	9.79	10.47	13.28	13.33
Ash	6.15	6.02	8.47	8.69	6.37	6.74

¹The premix provided the following per kilogram of complete diet: vitamin A = 12,000 IU; vitamin D3 = 2,500 IU; vitamin E = 30 IU; vitamin K3 = 3 mg; vitamin B12 = 0.012 mg; riboflavin = 4 mg; niacin = 40 mg; pantothenic acid = 15 mg; choline chloride = 400 mg; folic acid = 0.7 mg; thiamin = 1.5 mg; pyridoxine = 3 mg; biotin = 0.1 mg; Zn = 105 mg; Mn = 22 mg; Fe = 84 mg; Cu = 10 mg; I = 0.50 mg; Se = 0.35 mg.

Sample Collection

The entire experiment was conducted using two 25-d periods for a total of 50 d. To obtain stable measurements of digestibility when feeding high-fiber diets in pigs, at least 21-d are recommended to adapt pigs and their gut microflora to diets (Longland et al., 1993; Huang et al., 2018). Therefore, a 21-d adaptation period was applied for each of the two periods. After adaptation, representative fecal samples were collected twice daily from each pig on days 22 to 23 (period 1), and days 47 to 48 (period 2). Fecal samples from the 2-d collection in each period were pooled within pig and stored in a –20 °C freezer until further analysis. Ileal digesta samples were collected for 8 h starting at 0800 hours until 1600 hours on days 24 to 25 (period 1) and days 49 to 50 (period 2) using a 207-mL sealed plastic bag (Whirl-pak, Nasco, Fort Atkinson, WI) attached to the cannula barrel. Bags were removed every 30 min or whenever full. Ileal digesta samples were pooled into 1-L wide-mouth high-density polyethylene bottles (Fisher Scientific Company, Ottawa, ON) and stored at –20 °C immediately to prevent bacterial fermentation until further analysis. One pig fed the DDGS+AOP diet became ill when samples were collected in period 2 and consequently was removed from the experiment.

Chemical Analyses

At the conclusion of the experiment, frozen ileal digesta samples were thawed at room temperature and then mixed thoroughly, subsampled and lyophilized. Frozen feces were thawed and dried in a forced-air oven at 65 °C for 72 h. Ingredients, diets, dried ileal digesta, and feces were ground to pass through a 1-mm screen in a Wiley mill (Thomas Scientific, Swedesboro, NJ) prior to chemical analysis. Samples were analyzed using AOAC (2007) methods for dry matter (DM, method 934.01), crude protein (CP, method 990.03), ether exact using Soxhlet apparatus and petroleum ether (EE, method 920.39), and ash (method 942.05). Crude protein was analyzed using Kjeldahl method with a LECO FP-528 analyzer (St. Joseph, MI, USA). Neutral detergent fiber (NDF) was analyzed using filter bags and ANKOM²⁰⁰ fiber analyzer (Ankom Technology, Macedon, NY) following the procedure described by Van Soest et al. (1991) with minor modifications. The concentration of NDF was analyzed using heat stable α-amylase and sodium sulfite without correction for insoluble ash. Amino acid concentrations in ingredients, diets, and ileal digesta were analyzed with a Hitachi Amino Acid Analyzer (Model L8800; Hitachi High Technologies America Inc., Pleasanton, CA) using ninhydrin for postcolumn derivatization and norleucine as the internal standard (Method 982.30 E [a, b, c]; AOAC 2006). The gross energy (GE) content in all samples was determined using an isoperibol bomb calorimeter (model 6400; Parr Instrument Co., Moline, IL). Benzoic acid (6,318 kcal GE/kg) was used as the standard for calibration. The concentration of titanium dioxide in diets, ileal digesta, and feces was determined photometrically according to the technical procedure described by Myers et al (2004).

Calculations and Statistical Analysis

The apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of GE, DM, CP, EE, ash, and NDF were calculated based on the following equation (Stein et al., 2007):

$${\displaystyle \begin{array}{ll}& \mathrm{A}\mathrm{I}\mathrm{D}\mathrm{o}\mathrm{r}\mathrm{A}\mathrm{T}\mathrm{T}\mathrm{D},\mathrm{\%}=\\ & [1-\left(N_{\mathrm{d}\mathrm{i}\mathrm{g}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{o}\mathrm{r}\mathrm{f}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}}/N_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{t}}\right)\times \left(M_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{f}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}}/{\left(M\right)}_{\mathrm{d}\mathrm{i}\mathrm{g}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{a}}\right)]\times 100,\end{array}}$$

where N_{digesta or feces} and N_diet are the nutrient concentrations (g/kg) in digesta/feces and diet DM, respectively, and M_diet and M_{digesta/feces} are the titanium dioxide concentrations (g/kg) in diet and digesta/feces DM, respectively.

The standardized ileal digestibility (SID) of AA was calculated using the following equation (Stein et al., 2007). The basal endogenous AA losses were determined with the same set of pigs by feeding a N-free diet and described previously (Fung et al., 2019).

$${\displaystyle \begin{array}{ll}& \mathrm{S}\mathrm{I}\mathrm{D}\left(\mathrm{\%}\right)=\\ & [\mathrm{A}{\mathrm{A}}_{}\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{k}{\mathrm{e}}_{}-(\mathrm{i}\mathrm{l}\mathrm{e}\mathrm{a}\mathrm{l}\mathrm{A}\mathrm{A}\mathrm{o}\mathrm{u}\mathrm{t}\mathrm{f}\mathrm{l}\mathrm{o}\mathrm{w}-\mathrm{b}\mathrm{a}\mathrm{s}\mathrm{a}\mathrm{l}\mathrm{I}\mathrm{A}{\mathrm{A}}_{\mathrm{e}\mathrm{n}\mathrm{d}})/\mathrm{A}\mathrm{A}\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e}]\times 100\mathrm{\%},\end{array}}$$

where basal IAA_end is the basal endogenous loss of an AA (g/kg DM intake).

The hindgut fermentation of nutrients was calculated using the following equation (Chen et al., 2014):

$${\displaystyle \begin{array}{l}{\displaystyle \mathrm{H}\mathrm{i}\mathrm{n}\mathrm{d}\mathrm{g}\mathrm{u}\mathrm{t}\mathrm{f}\mathrm{e}\mathrm{r}\mathrm{m}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\left(\mathrm{\%}\right)=\mathrm{A}\mathrm{T}\mathrm{T}\mathrm{D}\mathrm{A}\mathrm{I}\mathrm{D}.}\end{array}}$$

Data were analyzed using the MIXED procedure of SAS 9.4 (SAS institute Inc., Cary, NC) with AOP, diet, AOP × diet, and period as fixed effects. Pig was considered as the random effect. The outliers were identified using interquartile range method (IQR). Values that are more than 1.5 IQR below the first quartile or more than 1.5 IQR above the third quartile are considered outliers and were therefore removed. Two negative values of ATTD of EE in WM group and one extremely low value of ATTD of EE in WM+AOP group were removed from the calculation. The experimental unit was individual pig. The LSMEANS procedure was used to calculate means and PDIFF option was used to separate least squares means with a Tukey-Kramer adjustment. A value of P < 0.05 was considered statistically significant, and P < 0.1 was considered a trend.

RESULTS AND DISCUSSION

Nutrient Content in Ingredients and Diets

A common feature of agricultural coproducts is the variability in processes that affect the nutrient composition of the resulting coproduct (Shurson et al., 2021). The NDF content in corn DDGS is in agreement with previously reported ranges of 20.1–32.9% by Stein and Shurson (2009) and 17.95–43.66% by Zeng et al., (2017), but was less than the value (33.75%) from NRC (2012). The NDF content of WM was in agreement with the values reported by Jha et al. (2012), but less than values reported by Jong et al. (2014) and Zeng et al. (2018). The RB used in the present study had a NDF content that was less than values reported in previous studies in China and North America which ranges between 17.17 and 33.90% (Casas et al., 2019; Li et al., 2018). Consistent with the NDF content in the ingredients, DDGS diets had the greatest NDF followed by WM diets, and RB diets had the lowest NDF content (Table 2). The EE and ash content in RB were the highest followed by those of corn-DDGS and WM (Table 1), which was also reflected in the diets (Table 2).

Ileal Digestibility of Nutrients

The AID of GE and DE value were greater (P < 0.05) in diets with RB compared with corn-DDGS and WM. However, the AID of GE in diets with AOP were not different from those without AOP. There were no differences in the AID of DM or CP among diets with DDGS, RB, or WM or among diets with and without AOP, but there was a significant interaction (P < 0.01) between diet type and AOP treatment for AID of EE. Pigs fed DDGS+AOP diet had greater (P < 0.05) AID of EE compared with those fed DDGS diet, there were no differences observed when RB or WB were compared with their corresponding AOP supplemented groups (Table 3).

Table 3.

Effect of Aspergillus oryzae prebiotic (AOP) on apparent ileal digestibility (AID), hindgut disappearance (HGD), and apparent total tract digestibility (ATTD) of energy (kcal/kg) and nutrients (%) in diets with corn distillers dried grains with solubles (DDGS), rice bran, and wheat middling^1,2

Items	Corn-DDGS		Rice bran		Wheat middling		SEM	P-value
	− AOP	+ AOP	− AOP	+ AOP	− AOP	+ AOP		AOP	Diet	AOP × Diet
AID
Gross energy	63.44	64.21	66.82	67.41	63.40	66.59	1.07	0.12	0.04	0.46
DE, kcal/kg	2,577	2,645	2,750	2,799	2,519	2,581	43.29	0.14	<0.01	0.97
Dry matter	60.74	61.41	62.89	62.88	60.96	64.72	1.24	0.15	0.26	0.28
Crude protein	71.96	73.10	74.11	72.91	73.43	74.54	1.35	0.74	0.58	0.62
Neutral detergent fiber	25.25a	17.80a	−7.07b	2.05b	22.79a	30.07a	3.18	0.30	<0.01	0.09
Ether exact	28.20b	56.70a	72.43a	76.72a	33.41b	23.20b	4.29	0.07	<0.01	0.007
Ash	22.25	22.57	24.60	22.51	22.69	29.69	2.63	0.44	0.45	0.29
HGD
Gross energy	18.01	17.56	13.85	13.59	17.21	15.95	1.25	0.54	0.03	0.92
DE, kcal/kg	731.74	723.43	569.93	563.89	683.86	618.41	51.03	0.54	0.04	0.82
Dry matter	21.39	21.00	15.49	15.86	20.41	18.85	1.26	0.63	<0.01	0.76
Crude protein	12.06	11.25	8.58	8.98	11.71	13.25	1.35	0.73	0.05	0.69
Neutral detergent fiber	33.81	46.61	52.32	51.14	28.09	24.71	4.77	0.48	<0.01	0.23
Ether exact	−4.67	−25.54	−5.44	−6.23	−15.06	−8.89	5.30	0.31	0.29	0.12
Ash	34.07	30.31	8.15	12.76	28.83	27.21	2.68	0.90	<0.01	0.29
ATTD
Gross energy	81.37	81.78	80.73	80.79	80.79	83.10	0.52	0.04	0.10	0.10
DE, kcal/kg	3,305	3,368	3,323	3,355	3,211	3,221	20.91	0.05	<0.01	0.44
Dry matter	82.00b	82.32b	78.39c	78.55c	81.61b	84.08a	0.49	0.02	<0.01	0.05
Crude protein	84.07b,c	84.40b,c	82.65c,d	81.72d	85.10b	88.10a	0.48	0.04	<0.01	0.003
Neutral detergent fiber	56.49a	60.98a	47.61b	54.31a,b	50.43a,b	54.39a,b	2.23	<0.01	<0.01	0.52
Ether exact	23.53b	31.09b	70.00a	70.50a	19.34b	18.48b	3.32	0.28	<0.01	0.55
Ash	56.23a	53.65a,b	32.95c	36.47c	44.80b,c	57.09a	1.94	0.02	<0.01	0.01

¹Data are shown as LS-means with pooled standard error of the mean. Means in a row with different letters significantly differ (P < 0.05).

² N = 5 for corn-DDGS+AOP; otherwise, N = 6.

The SID of AA was calculated by correcting AID with basal endogenous AA losses from the same set of pigs (Table 4). The SID of Arg, His, Ile, Lys, Asp, and Cys was greater (P < 0.05) in pigs fed RB or WM compared with those fed DDGS. The SID of Trp in pigs fed RB was greater (P < 0.05) compared with those fed DDGS or WM but did not differ between DDGS and WM diets. None of the SID of AA were affected (P > 0.05) by supplementing AOP in any of the high-fiber diets.

Table 4.

Effect of Aspergillus oryzae prebiotic (AOP) on standardized ileal digestibility of amino acids^1,2,3 (%)

Items	Corn-DDGS		Rice bran		Wheat middling		SEM	P-value
	− AOP	+ AOP	− AOP	+ AOP	− AOP	+ AOP		AOP	Diet	AOP × Diet
Indispensable AA
Arg	86.61	88.01	91.13	88.64	89.40	90.11	1.02	0.86	0.05	0.15
His	81.31	82.39	86.28	85.50	85.40	85.29	1.19	0.95	0.02	0.73
Ile	77.80	79.56	83.05	81.83	81.38	80.64	1.32	0.95	0.05	0.49
Leu	81.79	84.11	82.88	81.97	82.47	82.28	1.22	0.66	0.88	0.39
Lys	77.62b	79.58a,b	84.75a	83.65a	82.66a	82.44a	1.07	0.80	<0.01	0.37
Met	83.46	86.29	84.70	84.57	85.20	85.03	1.13	0.34	0.91	0.33
Phe	80.24	82.15	83.44	82.14	82.39	82.51	1.22	0.79	0.43	0.43
Thr	74.04b	76.05a,b	81.10a	80.06a,b	78.83a,b	79.96a,b	1.35	0.52	<0.01	0.53
Trp	84.95	84.38	89.16	88.28	85.02	84.98	1.41	0.65	0.03	0.96
Val	75.40	77.24	79.13	77.95	77.46	77.62	1.34	0.80	0.31	0.55
Dispensable AA
Ala	79.04	81.88	80.74	79.79	78.88	78.79	1.60	0.65	0.58	0.49
Asp	74.77c	76.09b,c	82.93a	81.33a,b	80.13a,b,c	80.38a,b,c	1.32	0.99	< 0.01	0.54
Cys	73.53b	75.25a,b	79.03a,b	78.66a,b	77.52a,b	80.04a	1.36	0.20	0.01	0.53
Glu	82.09	83.82	86.04	85.18	85.45	85.81	1.24	0.63	0.08	0.54
Gly	77.29	78.46	83.46	81.06	81.75	83.69	2.48	0.90	0.16	0.66
Pro	109.01	107.01	120.14	106.45	116.94	119.31	5.74	0.35	0.28	0.40
Ser	79.33	80.90	83.07	81.50	81.19	84.26	1.19	0.28	0.12	0.19
Tyr	82.68	84.57	86.09	83.90	83.64	84.93	1.12	0.69	0.50	0.18
Total AA	81.29	83.03	86.08	84.11	84.60	85.24	1.36	0.89	0.11	0.39

¹Data are shown as LS-means with pooled standard error of the mean. Means in a row with different letters significantly differ (P < 0.05).

² N = 5 for corn-DDGS with AOP; otherwise N = 6.

³Standardized ileal digestibility of amino acids were calculated using the following basal endogenous AA losses (g/kg of dry matter intake): Arg = 0.44; His = 0.18; Ile = 0.41; Leu = 0.65; Lys = 0.46; Met = 0.12; Phe = 0.41; Thr = 0.67; Trp = 0.13; Val = 0.58; Ala = 0.71; Asp = 0.92; Cys = 0.23; Glu = 1.1; Gly = 1.6; Pro = 5.08; Ser = 0.57; Tyr = 0.32; and total AA = 14.78.

Apparent Total Tract Digestibility of Nutrients

The ATTD of GE, DM, CP, NDF, and ash were greater (P < 0.05) in pigs fed diets with AOP compared with those fed diets without AOP. The greatest improvement of ATTD was observed for ash in WM+AOP diet, which was 12.29% greater compared with the WM diet. The magnitude of improvement in ATTD of GE and DM tended to be greatest (AOP × diet interaction, P < 0.10) when AOP was supplemented in WM than in RB or DDGS diets. The digestible energy content of the diets increased by 63, 32, and 10 kcal/kg in pigs fed DDGS+AOP, RB+AOP, and WM+AOP compared with those fed the corresponding diets without AOP, respectively. It should be noted that GE in WM was 98 kcal/kg less than WM+AOP, which indicates that the actual improvement of DE in pigs fed WM+AOP should be larger than observed if diets were adjusted to the same GE level. The increase in ATTD of GE and DM in WM was mainly a result of an increase in ATTD of CP, in which the magnitude of improvement was greatest (AOP × Diet interaction, P < 0.10) in diets with WM compared with RB or DDGS diets. The ATTD of EE (P > 0.05) was not affected by including AOP in the diets.

These findings suggest that AOP may be effective for improving the nutritional value of fibrous ingredients fed to swine. With feed cost representing the greatest expense of pork production, coproducts of biofuel and food industry are attractive for decreasing diet cost (Kerr and Shurson, 2013). However, most of these coproducts have relatively high concentration of fiber, which monogastric animals have very limited ability to utilize energy from these fibers (Knudsen et al., 2016). Therefore, effective feed additives that enhance the utilization efficiency of fiber and other nutrients of high-fiber ingredients in pigs are needed.

In the present study, a greater magnitude of improvement in nutrient digestibility by supplementing AOP was observed in WM diets compared with those in DDGS or RB diets. These results are in agreement with study by Zeng et al. (2018) where they observed that supplementing exogenous enzymes significantly increased in vitro digestibility of DM and GE in WM but the effects of those enzymes on corn-DDGS were negligible. Differences in the compositional complexity among these co-products and their corresponding parent grains are the most likely reason for the different responses to AOP treatment. Despite similar arabinoxylan content and arabinose to xylose ratio, corn-DDGS contains a greater fraction of insoluble arabinoxylan compared with WM (Pedersen et al., 2014). In addition, the concentration of diferulates in the insoluble dietary fiber fraction in corn is approximately 5–7 times greater than found in wheat (Bunzel et al., 2001). Compared with WM, rice byproducts have a much greater arabinose to xylose ratio and insoluble arabinoxylan fraction (Annison et al., 1995; Casas et al., 2019). In addition, the greater proportion of cellulose in fiber of corn-DDGS and RB compared with WM could also impair digestibility of fiber and other nutrients, because the apparent total tract digestibility of cellulose is much less than other components of dietary fiber in pigs (Pedersen et al., 2015). Therefore, the differential responses from adding AOP to growing pig diets are attributed mainly to composition and type (characteristic) of fiber in the corresponding ingredients.

Interestingly, supplementation of AOP increased AID of EE by 28.5% in DDGS but no similar effects were observed in RB and WM. However, caution is needed when interpreting these results because relatively large CV of AID of EE was observed in diets with relative low content of EE. The CV of AID of EE in DDGS and DDGS+AOP were 50.67% and 21.33%, respectively. Similarly, a significant increase in ATTD of minerals and numerical improvement of AID of minerals was observed in pigs fed RB diets supplemented with AOP. The reason for this increase in mineral digestibility in unknown but we speculate that it could be due to 1) breakdown of fiber matrix which release mineral from the matrix. When the fiber matrix is broken down, nutrients, including minerals, embedded in that matrix may be released and available for absorption. The breakdown of fiber matrix is indicated by greater ATTD of NDF in pigs fed AOP compared with those fed diets without AOP observed in the present study. 2) the increased solubility of minerals resulting from more acidic digesta pH. Absorption of calcium and other minerals increase with increased solubility of minerals and decreased pH in the lumen increase solubility of minerals (e.g. Ca, P, and Mg) by preventing the formation insoluble Ca-Mg-phosphate complexes (Greenwald et al., 1940); 3) increase in gut epithelial nutrient absorption from improved intestinal barrier integrity. The intestinal barrier plays important roles in not only facilitating the absorption of nutrients, electrolytes, and water but also limiting the transport of potentially harmful antigens and micro-organisms (Vancamelbeke and Vermeire, 2017). Post-biotics can enhance epithelial barrier integrity via mechanisms mediated by secreted proteins (Yan et al., 2013; Gao et al., 2019), exopolysaccharides (Schiavi et al., 2016), and short chain fatty acids (SCFAs; Ohata et al., 2005; Feng et al., 2018). Short chain fatty acids are the end-production of fiber in hindgut of pigs, including lactate, acetate, propionate, and butyrate (Lindberg, 2014). An increase in total SCFAs was reported by Newbold et al. (1991) when they tested the effects of AOP on the rumen fermentation in vitro. No previous experiments have evaluated effects of AOP on digestibility of fibrous ingredients in pigs. However, it has been observed before that supplementation of prebiotics is capable to modify the ability of microbes to degrade fiber in the hindgut of pigs (Mountzouris et al., 2006).

To the best of our knowledge, this is the first report to investigate the magnitude of change in nutrient digestibility in pigs fed AOP in various sources of dietary fiber. The realization of the effect will subsequently impulse to investigate the mechanism of action. In fact, the mechanisms of actions of prebiotics, probiotics, and postbiotics are far from being completely understood (Bermudez-Brito et al., 2012; Davani-Davari et al., 2019; Salminen et al., 2021). Therefore, it is still difficult to know the specific mechanism of action of AOP in pigs. Several postulated mechanisms of probiotics may also apply for AOP that might be useful for further investigation. Firstly, AOP may modulate the gut microbiota which results in enrichment of beneficial microbes such as Lactobacillus and Bifidobacterium. Several oligosaccharides, including fructooligosaccharides and mannoligosaccharides can be synthesized in Aspergillus oryzae fermentation (Guío et al., 2009; Amirdahri et al., 2012; Mano et al., 2018). These oligosaccharides can selectively stimulate the growth of beneficial bacteria, including Lactobacillus and Bifidobacterium in pigs (Duan et al., 2016; Liu et al., 2020), and consequently exert beneficial effects on gut health of pigs. Secondly, postbiotics can enhance epithelial barrier integrity via activities mediated by secreted proteins (Yan et al., 2013; Gao et al., 2019), exopolysaccharides (Schiavi et al., 2016), and short chain fatty acids (SCFAs; Ohata et al., 2005; Feng et al., 2018). Xu et al (2021) reported enhanced intestinal health and improved growth performance in nursery pigs fed diets with a prebiotic from Lactobacillus fermentate.

In conclusion, this experiment is the first to demonstrate that AOP improves aspects of gastrointestinal functions such as enhanced nutrient digestibility and absorption, but the magnitude of the impact of AOP is ingredient- and diet-dependent. The mode of action of AOP is not fully understood, and further studies are needed to elucidate the mechanisms by which AOP increases nutrient digestibility in pigs.

Conflict of interest

In addition to supplying the AOP, BioZyme Inc. provided partial financial support to conduct this project. At the time the research reported herein was conducted, L.W. was employed by BioZyme Inc. and I.R.I. consulted for BioZyme Inc. and received compensation. P.E.U, G.C.S., and J.Z. declare no competing interests.