Effects of different defatted rice bran sources and processing technologies on nutrient digestibility in cannulated growing pigs

Abstract

The objective of this study was to evaluate the effects of different defatted rice bran (DFRB) sources and processing technologies on nutrient digestibility in different intestinal segments of pigs. Nine barrows with T-cannula in the distal ileum were randomly allotted to nine different sources in which oil was pressed extracted for seven sources and was solvent extracted for two sources. The experiment contained 6 periods of 12 d, including 8 d for diet adaptation, 2 d for fecal collection, and 2 d for digesta collection. The apparent ileal digestibility (AID) of dry matter (DM), ash, total dietary fiber (TDF), insoluble dietary fiber (IDF), neutral detergent fiber (NDF), acid detergent fiber (ADF), and hemicellulose in different sources of DFRB was quite variable. There were no differences in the AID of dietary gross energy (GE), organic matter (OM), ether extract (EE), crude protein (CP), and soluble dietary fiber (SDF) between different sources of DFRB. There were no differences in the AID of dietary EE, TDF, IDF, and hemicellulose between different processing technologies. Pressed DFRBs have greater (P < 0.05) average AID of dietary GE, DM, ash, OM, CP, SDF, and NDF and lower (P < 0.01) ADF compared with solvent-extracted DFRBs. The apparent total tract digestibility (ATTD) of most of the dietary nutrients, except for the ATTD of dietary EE, SDF, and hemicellulose, significantly varied in different sources of DFRB (P < 0.05). In addition, pressed DFRB had greater (P < 0.05) ATTD of dietary SDF, NDF, ADF, and hemicellulose compared with solvent-extracted DFRB. The apparent hindgut digestibility (AHD) of dietary DM, SDF, NDF, and ADF significantly varied (P <0.05) in different sources of DFRB. Exception with DM, there are no differences in the AHD of nutrients digestibility between pressed DFRB and solvent-extracted DFRB. In conclusion, DFRB in different sources and processing technologies with different physicochemical properties had different effects on nutrient digestibility in the foregut and hindgut of pigs.

Introduction

Traditionally, total dietary fiber (TDF) is the sum of the dietary carbohydrates that are resistant to the endogenous enzymatic digestion in the small intestine of pigs (Devries et al., 2001). They can, however, be partially or completely fermented by bacteria in the hindgut to produce short-chain fatty acids (SCFA) that are absorbed to provide energy (Williams et al., 2001; IOM, 2006). The SCFA are considered to exert beneficial impacts on the gut health of host (Koh et al., 2016). It has been demonstrated that SCFA can improve intestinal health by modifying the gut microbiota profile and inducing responses of the immune system (Zeng et al., 2013; Liu et al., 2018). Recently, some studies have reported that dietary fiber fractions could also be fermented in the small intestine of pigs (Jha and Leterme, 2012; Lærke et al., 2015) because the fiber-degrading bacteria are present in the stomach and small intestine of pigs. In addition, previous studies have demonstrated that the nutrient digestibility of high-fiber diets is influenced by the chemical and physical properties of the fiber. (Urriola and Stein, 2010; Lyu et al., 2019).

Paddy rice is the second most commonly grown cereal grain produced worldwide after maize. The production of paddy rice is 782 million metric tons (FAO, 2018) annually. Sixty million metric tons of rice bran, a coproduct from rice milling, is produced of which the majority is utilized as animal feed or discarded directly (Orthoefer and Eastman, 2004). Rice bran is not easy to store because it contains rice oil that is approximately 41% and 34% of monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) of ether extract (EE), respectively (Juliano, 1983; Saunders, 1985, Faria et al., 2012). The high concentration of MUFA and PUFA, together with lipases and oxidases, allows the rapid oxidation of fat in rice bran if it has not stabilized after production (Saunders, 1985; Rosniyana et al., 2009). Therefore, practical processing technology of defatted rice bran (DFRB) is required to reduce rapid degradation. DFRBs are used in animal diets, primarily pressed DFRB and solvent-extracted DFRB. Pressed DFRB is the rice bran coproduct remaining after oil is removed by steam pressing, whereas solvent-extracted DFRB is produced by solvent extraction at lower temperatures. Rice bran contains a large quantity of dietary fiber (24% to 34% of total bran solids), which corresponds to changes in the content and composition of dietary fiber during germination (Kim et al., 2001; Ohtsubo et al., 2005; Mohan et al., 2010). In a previous study (Huang et al., 2018), we reported that the TDF, insoluble dietary fiber (IDF), and soluble dietary fiber (SDF) concentrations of DFRB are varied. In addition, the digestible energy, metabolizable energy, and standardized ileal digestible amino acid concentration of different DFRBs were determined to vary the geographical location of production (Huang et al., 2018). We speculated that the result of the variation may be related to the province of production and/or the processing technology. High-fiber ingredients may impose limitations in their use in diets for monogastric animals, in particular young animals, due to their bulky nature and a limited capacity to ferment fiber (Bach Knudsen et al., 2012). In order to better utilize available fiber-rich feedstuffs in the diet, their chemical and physical characteristics must be included in feed formulation (Lindberg, 2014). The objective of this study was to confirm our hypothesis that the source and processing technology influence nutrient digestibility at different intestinal locations. This work provides a reference for the use of DFRB in swine production and digestion of other fiber ingredients in pigs.

Materials and Methods

The China Agricultural University Laboratory Animal Welfare and Animal Experimental Ethical Inspection Committee (Beijing, China) reviewed and approved all protocols used in this experiment.

Animals, diets, and experimental design

Nine crossbred barrows (Duroc × Landrace × Yorkshire) were used in this experiment. And each pig was surgically equipped with a T-cannula in the distal ileum using the procedures adapted from Stein et al. (1998). Pigs were allowed a 20-d recovery period after surgery and a commercial corn–soybean meal diet was fed during this period. The chemical composition of corn–soybean meal was formulated to meet the nutrient requirements for pigs recommended by NRC (2012). The barrows were individually housed in stainless-steel metabolism crates (1.4 × 0.7 × 0.6 m) located in a temperature-controlled room (22 ± 2 °C) and were allotted to a 9 × 6 Youden square design with nine diets and six periods. Each experimental period lasted 12 d. Pig body weight (BW) was recorded at the beginning of each experimental period, and the quantity of daily feed supplied during the following period was calculated based on 4% of this weight. The daily feed allowance was divided into two equal meals that were fed at 0800 and 1700 hours. Water was available from drinking nipples at all times. DFRB numbers and sources are presented in Table 1. The chemical compositions of nine DFRBs were analyzed (Table 2). The feed ingredients and analyzed chemical compositions of the nine experimental diets are presented in Table 3 and Table 4, respectively. The initial 8 d of each period was considered an adaptation period to the diet. The nine DFRB samples were from seven different provinces, and the samples from Heilongjiang and Jiangxi have two different processing technologies. The experimental diets contained 30% DFRB as the sole source of fiber (Huang et al., 2018). All diets contained 0.3% chromic oxide as an indigestible marker. Vitamins and minerals were supplemented in all diets to meet or exceed the estimated nutrient requirements for growing pigs (NRC, 2012).

Table 1.

Sources of DFRB used in the experiment

Number	Sources within China	Processing techniques
1	Henan	Pressed
2	Jiangsu	Pressed
3	Liaoning	Pressed
4	Beijing	Pressed
5	Jilin	Pressed
6	Heilongjiang	Solvent-extracted
7	Heilongjiang	Pressed
8	Jiangxi	Solvent-extracted
9	Jiangxi	Pressed

Table 2.

The analyzed chemical compositions in DFRB (% DM basis)¹

	Method
	Pressed							Solvent-extracted
	Source No.
Items2	1	2	3	4	5	7	9	6	8
GE, MJ/kg	17.40	17.95	17.51	17.43	17.96	17.45	17.62	16.91	17.31
CP	16.50	18.31	17.77	15.87	17.74	17.38	18.48	16.48	16.72
Ash	9.99	10.62	11.15	11.78	11.21	11.68	11.01	14.34	12.01
OM	90.01	89.38	88.85	88.22	88.79	88.32	88.99	85.66	87.99
EE	1.53	0.77	0.79	0.71	1.83	0.75	0.95	0.63	0.80
NDF	21.46	27.39	28.16	31.76	26.44	27.79	23.90	35.42	27.5
ADF	7.11	11.49	11.77	14.82	10.35	11.18	8.94	16.45	11.93
Hemicellulose	14.35	15.89	16.39	16.94	16.1	16.61	14.97	18.97	15.57
TDF	24.44	34.86	32.57	31.79	30.25	30.76	30.12	38.49	30.31
SDF	3.76	4.06	3.28	3.01	1.92	3.63	4.33	2.03	2.00
IDF	20.68	30.81	29.3	28.77	28.33	27.13	25.80	36.46	28.31
Calcium	0.14	0.14	0.20	0.12	0.12	0.13	0.09	0.15	0.10
Phosphorus	1.97	2.11	2.26	1.95	2.13	2.27	1.53	1.96	2.10
Indispensable amino acids
Arginine	1.31	1.25	1.25	1.16	1.25	1.27	1.25	1.20	1.32
Histidine	0.46	0.46	0.46	0.41	0.43	0.42	0.45	0.45	0.46
Leucine	1.26	1.33	1.26	1.19	1.26	1.22	1.25	1.24	1.33
Isoleucine	0.63	0.66	0.62	0.60	0.64	0.61	0.61	0.61	0.67
Lysine	0.85	0.93	0.97	0.85	0.91	0.90	0.84	0.93	0.85
Methionine	0.38	0.36	0.38	0.35	0.37	0.35	0.43	0.35	0.43
Phenylalanine	0.79	0.81	0.77	0.73	0.78	0.74	0.78	0.75	0.81
Threonine	0.69	0.72	0.71	0.65	0.70	0.69	0.68	0.71	0.73
Tryptophan	0.21	0.18	0.19	0.18	0.19	0.20	0.19	0.19	0.19
Valine	0.99	1.01	0.98	0.91	0.96	0.95	0.95	0.99	1.02
Dispensable amino acids
Alanine	1.09	1.11	1.10	1.02	1.10	1.07	1.04	1.11	1.15
Aspartic acid	1.65	1.77	1.72	1.63	1.68	1.63	1.60	1.66	1.68
Cystine	0.35	0.37	0.36	0.33	0.36	0.36	0.39	0.34	0.34
Glutamic acid + Glutamine or Glx	2.61	2.47	2.46	2.28	2.35	2.35	2.47	2.30	2.66
Glycine	0.96	0.97	0.96	0.88	0.95	0.94	0.91	1.00	1.01
Proline	0.81	0.87	0.79	0.75	0.79	0.81	0.80	0.84	0.85
Serine	0.81	0.83	0.80	0.75	0.79	0.78	0.78	0.78	0.85
Tyrosine	0.48	0.49	0.44	0.40	0.49	0.47	0.48	0.47	0.55

¹All data are the results of chemical analysis conducted in duplicate.

²Source, effects of nine different sources of DFRB; Method, effects of oil extraction methods: pressed DFRB vs. solvent-extracted DFRB. Sources of DFRB are described in Table 1.

Table 3.

The composition (%, as-is basis) of the experimental diets

Items	DFRB1
Ingredients, %
Corn starch	37.60
Soy protein isolated	13.30
DFRB	30.00
Sucrose	15.00
Dicalcium phosphate	2.50
Cr2O3	0.30
Salt	0.40
K2CO3	0.30
MgO	0.10
Premix2	0.50
Total	100.00

¹Sources of DFRB are described in Table 1.

²Premix provided the following quantities per kilogram of the complete feed for growing pigs: vitamin A, 5,512 IU; vitamin D₃, 2,200 IU; vitamin E, 64 IU; vitamin K₃, 2.2 mg; vitamin B₁₂, 27.6 μg; riboflavin, 5.5 mg; pantothenic acid, 13.8 mg; niacin, 30.3 mg; choline chloride, 551 mg; Mn, 40 mg (MnO); Fe, 100 mg (FeSO₄∙H₂O); Zn, 100 mg (ZnO); Cu, 100 mg (CuSO₄∙5H₂O); I, 0.3 mg (CaI₂); and Se, 0.3 mg (Na₂SeO₃).

Table 4.

The analyzed chemical compositions of the experimental diets (%, as-is fed)¹

	Method
	Pressed							Solvent-extracted
	Source No.
Items2	1	2	3	4	5	7	9	6	8
GE, MJ/kg	15.94	15.77	15.87	15.97	16.03	15.93	16.00	15.96	16.09
CP	15.87	16.56	16.03	15.31	15.73	15.38	14.92	14.83	16.29
Ash	6.10	7.02	6.36	6.29	6.54	6.35	6.34	6.56	6.37
OM	85.81	84.46	85.44	85.70	85.53	85.15	85.68	85.28	85.78
EE	1.10	0.91	1.07	1.11	0.88	0.91	0.92	1.17	0.81
NDF	9.68	10.62	9.34	9.11	7.25	6.61	6.72	7.04	6.99
ADF	3.48	5.00	4.07	3.94	2.83	2.84	2.58	2.90	2.85
Hemicellulose	6.20	5.62	5.27	5.17	4.42	3.77	4.14	4.14	4.14
TDF	7.63	8.49	8.99	8.57	8.97	8.81	7.80	9.97	9.89
SDF	1.67	0.90	1.36	1.57	1.22	1.34	1.38	0.98	2.43
IDF	5.96	7.60	7.64	7.00	7.75	7.47	6.42	8.99	7.46

¹All data are the results of chemical analysis conducted in duplicate.

²Source, effects of nine different sources of DFRB; Method, effects of oil extraction methods: pressed DFRB vs. solvent-extracted DFRB. Sources of DFRB are described in Table 1.

Sample collection

The barrows were fed one of the nine diets for each period consisting of an 8-d dietary acclimation period followed by a 2-d digesta collection and a 2-d feces collection. The collection of ileal digesta lasted for 9 h daily beginning at 0800 hours using the procedures described by Stein et al. (1998). On days 9 and 10, a plastic bag was attached to the cannula barrel using a cable tie, and digesta flowing into the bag were collected. The bags were removed whenever they were filled with digesta or at least once in every 30 min and immediately stored at −20 °C to prevent bacterial degradation of amino acid (AA) (Kim et al., 2016) On days 11 and 12, fecal samples were collected via grab sampling and stored at −20 °C (Kil et al., 2010).

Chemical analyses

At the conclusion of the experiment, frozen ileal digesta samples were allowed to thaw at room temperature and then mixed and weighed. A subsample was collected, weighed, lyophilized, and weighed again. Lyophilized digesta samples, samples of all experimental diets, and dried feces were finely ground through a 1-mm screen and thoroughly mixed prior to chemical analysis and duplicate proximate analyses. Dry matter (DM) analysis of samples was performed by drying the samples in a forced-air oven at 105 °C for 6 h (method 930.15; AOAC, 2006). EEs of DFRB were obtained by an extractor (model XT15l; Ankom Technology, Macedon, NY; method 920.39; AOAC, 2006). Chromium (method 990.08; AOAC, 2006) content in diets, digesta, and feces was determined. DFRB was analyzed for Ca (atomic absorption spectrometry; method 968.08; AOAC, 2006) and P (spectrophotometry at 620 nm; method 946.06; AOAC, 2006). Ash and crude protein (CP) were analyzed using AOAC (2006) methods 942.05 and 984.13. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents were determined using fiber bags (model F57; Ankom Technology, Macedon, NY) and a fiber analyzer (ANKOM²⁰⁰ Fiber Analyzer; Ankom Technology) using the basic procedure of Van Soest et al. (1991) with heat-stable α-amylase and sodium sulfite and expressed inclusive of residual ash for DFRB. The IDF and SDF contents were determined using IDF bags and SDF bags (Dietary Fiber Analysis-IDF/SDF; Ankom Technology; AOAC 991.43). The TDF was calculated by adding the values of IDF and SDF. The gross energy (GE) of feces, diets, and DFRB was measured using an Automatic Isoperibol Oxygen Bomb Calorimeter (Parr 1281 Calorimeter; Parr Instrument Company, Moline, IL). Total starch in DFRB was measured according to the method 76-13.01 of the American Association of Cereal Chemists (1976), using a commercial Starch Assay Kit (STA20; Sigma-Aldrich Corporation, St. Louis, MO).

The AA (method 982.30) content of DFRB was analyzed according to the procedures of AOAC. Specifically, samples were hydrolyzed with 6 N HCl at 110 °C for 24 h and then analyzed for 15 AA using an Amino Acid Analyzer (Hitachi L-8900, Tokyo, Japan). Methionine and cystine were determined as methionine sulfone and cysteic acid after cold performic acid oxidation overnight and hydrolyzing with 7.5 N HCl at 110 °C for 24 h using an Amino Acid Analyzer (Hitachi L-8800, Tokyo, Japan). Tryptophan was determined after LiOH hydrolysis for 22 h at 110 °C using high performance liquid chromatography (Agilent 1200 Series, Santa Clara, CA, USA).

Calculations

The apparent ileal digestibility (AID; %) and apparent total tract digestibility (ATTD; %) of DM, GE, CP, ADF, NDF, organic matter (OM), hemicellulose, TDF, SDF, and IDF were calculated in all diets using the following equation:

$${\displaystyle \begin{array}{l}{\displaystyle \mathrm{A}{\mathrm{D}}_{\mathrm{n}\mathrm{u}\mathrm{t}\mathrm{r}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{t}}=1-\left(\mathrm{C}{\mathrm{N}}_{\mathrm{d}\mathrm{i}\mathrm{g}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{o}\mathrm{r}\mathrm{f}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}}/\mathrm{D}{\mathrm{N}}_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{t}}\right)\times \left(\mathrm{C}{\mathrm{r}}_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{t}}/\mathrm{C}{\mathrm{r}}_{\mathrm{d}\mathrm{i}\mathrm{g}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{o}\mathrm{r}\mathrm{f}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}}\right),}\end{array}}$$

where AD _nutrient is the AID or ATTD of dietary nutrients; CN _{digesta or feces} is the nutrient level in ileal digesta or feces (g/kg); and DN _diet is the nutrient level in diets (g/kg). The hindgut disappearance of the nutrients was calculated as the difference between the AID and ATTD of dietary nutrients.

Statistical analyses

Data on fiber digestibility of sources were analyzed using the MIXED procedure of SAS 9.2 (SAS, 2012) for a completely randomized design with individual pig as the experimental unit. The DFRB samples are numbers 1, 2, 3, 4, 5, 7, and 9 (from Henan, Jiangsu, Liaoning, Beijing, Jilin, Heilongjiang, and Jiangxi provinces, respectively, and all with pressed process). The UNIVARIATE procedure of SAS 9.2 (SAS Inst. Inc., Cary, NC, USA) was used to check the normality of residuals and equal variances. Outliers were identified as any value that deviated from the treatment mean by ±3 times of standard deviation. No outliers were observed in this experiment. The statistical model had DFRB source as a fixed effect and period and pig as random effects. Statistical differences among the treatments were separated by Duncan’s multiple range test. Treatment means were calculated using the LSMEANS statement, and statistical significance was declared at P < 0.05.

Data on fiber digestibility of processing technologies were analyzed using the MIXED procedure of SAS 9.2. The DFRB samples are numbers 6, 7, 8, and 9; especially, samples 6 (solvent-extracted) and 7 (pressed) are from Heilongjiang province and samples 8 (solvent-extracted) and 9 (pressed) are from Jiangxi province. Individual pig was treated as the experimental unit. The statistical model used the CONTRAST statement to compare pressed DFRB vs. solvent-extracted DFRB. Period and pig were also included in the model as random effects. The significance level was set at P < 0.05.

Result

All pigs remained healthy and readily consumed their diets. Both feces and digesta samples were successfully collected from all pigs. Pigs were weighed after the cannulation procedure (24.6 ± 4.6 kg BW) and at the end of the trial (60.4 ± 7.6 kg BW).

Effect of DFRB source and processing technology on AID of dietary chemical constituents

The AID of DM, ash, TDF, IDF, NDF, ADF, and hemicellulose from different sources of DFRB was quite variable (P < 0.01). However, there were no differences in the AID of dietary GE, OM, EE, CP, and SDF among different DFRB sources. There were no differences in the AID of dietary EE, TDF, IDF, and hemicellulose between different processing technologies (Table 5). Pressed DFRBs have greater (P < 0.05) average AID of dietary GE, DM, ash, OM, CP, SDF, and NDF and lower (P < 0.01) ADF compared with solvent-extracted DFRB.

Table 5.

Effects of defatted rice bran source and processing technology on the AID (%) of dietary nutrients¹

	Method
	Pressed							Solvent-extracted
	Source No.										P-value
Items2	1	2	3	4	5	7	9	6	8	SEM	Source	Method
GE	86.18	81.61	74.94	77.51	81.83	81.53	83.71	78.51	72.30	3.03	0.204	0.033
DM	84.33	79.08	80.34	75.96	79.43	78.52	80.92	75.09	69.76	1.729	<0.01	0.047
Ash	34.37	20.63	22.57	14.42	22.73	13.44	24.09	17.02	13.16	2.173	<0.01	<0.01
OM	87.88	83.57	78.39	80.47	83.77	83.38	85.12	80.24	72.68	2.736	0.229	0.026
EE	84.89	88.32	81.30	90.78	86.07	83.90	82.97	83.98	62.56	5.617	0.124	0.098
CP	77.78	72.59	62.60	61.48	74.28	77.83	78.91	76.15	57.76	5.299	0.065	0.023
TDF	37.77	11.79	32.26	21.63	23.73	13.10	16.72	17.18	20.86	4.432	<0.01	0.992
SDF	44.98	19.00	35.78	22.67	31.19	25.33	34.99	7.55	42.77	6.325	0.23	<0.01
IDF	30.58	14.76	31.63	18.86	22.55	11.52	12.80	16.06	13.71	3.731	0.014	0.353
NDF	55.29	18.65	46.32	33.38	27.93	8.74	19.66	19.03	7.09	2.684	<0.01	<0.01
ADF	45.23	9.42	40.04	27.44	9.37	6.93	11.17	21.20	4.09	1.581	<0.01	<0.01
Hemicellulose	63.74	24.89	40.89	37.91	40.44	11.60	26.50	21.93	23.29	5.035	<0.01	0.130

¹Data represent least-square means (n = 6), and individual pig was treated as the experimental unit.

²Source, effects of nine different sources of DFRB; Method, effects of oil extraction methods: pressed DFRB vs. solvent-extracted DFRB. Sources of DFRB are described in Table 1.

Effect of DFRB source and processing technology on ATTD of dietary chemical constituents

The ATTD of most of the dietary nutrients, except for the ATTD of EE, SDF, and hemicellulose, significantly varied for different sources of DFRB (P < 0.05). In addition, pressed DFRB had greater (P < 0.05) ATTD of dietary SDF, NDF, ADF, and hemicellulose compared with solvent-extracted DFRB (Table 6).

Table 6.

Effects of DFRB source and processing technology on the ATTD (%) of dietary nutrients¹

	Method
	Pressed							Solvent-extracted
	Source No.										P-value
Items2	1	2	3	4	5	7	9	6	8	SEM	Source	Method
GE	91.98	88.37	88.03	88.67	88.38	87.85	90.49	85.75	88.56	0.380	<0.01	0.674
DM	90.53	86.39	86.73	86.92	86.73	85.81	88.68	82.88	86.37	0.283	<0.01	0.134
Ash	46.69	37.43	41.45	35.56	39.40	31.60	41.74	25.94	31.59	1.743	<0.01	0.122
OM	93.65	90.15	90.10	90.68	90.35	89.85	92.16	87.61	90.44	0.249	<0.01	0.102
EE	59.51	66.61	56.81	60.57	47.25	55.76	58.17	35.41	36.49	8.393	0.746	0.928
CP	89.41	83.78	83.71	85.05	85.22	83.57	86.53	85.52	85.89	0.747	<0.01	<0.01
TDF	56.66	34.41	42.78	41.32	43.87	38.99	51.72	27.82	49.32	2.283	<0.01	0.233
SDF	66.42	40.85	55.31	69.54	58.31	62.58	71.94	37.44	80.46	7.436	0.136	<0.01
IDF	53.99	33.65	40.55	36.02	41.60	34.78	47.38	21.16	39.17	2.270	<0.01	0.143
NDF	67.44	33.79	52.80	45.05	45.90	27.34	47.53	30.68	27.35	2.504	<0.01	<0.01
ADF	59.53	16.66	45.83	39.19	25.57	17.79	31.88	30.40	14.69	1.451	<0.01	<0.01
Hemicellulose	68.33	46.23	48.42	49.52	46.14	34.52	57.27	36.73	34.31	6.355	0.089	<0.01

¹Data represent least square means (n = 6), and individual pig was treated as the experimental unit.

²Source, effects of nine different sources of DFRB; Method, effects of oil extraction methods: pressed DFRB vs. solvent-extracted DFRB. Sources of DFRB are described in Table 1.

Effect of DFRB source and processing technology on apparent hindgut digestibility of dietary chemical constituents

The apparent hindgut digestibility (AHD) of dietary DM, SDF, NDF, and ADF significantly varied (P < 0.05) with different sources of DFRB. Exception with DM, there are no differences in AHD of nutrients digestibility between pressed DFRB and solvent-extracted DFRB (Table 7).

Table 7.

Effects of DFRB source and processing technology on the hindgut disappearance (%) of dietary nutrients¹

	Method
	Pressed							Solvent-extracted
	Source No.										P-value
Items2	1	2	3	4	5	7	9	6	8	SEM	Source	Method
GE	5.80	6.76	13.09	11.16	6.56	6.32	6.79	7.24	16.26	2.844	0.400	0.339
DM	6.20	7.31	6.39	10.96	7.30	7.29	7.77	7.79	16.61	1.659	<0.01	0.031
Ash	12.32	16.81	18.88	21.14	16.67	18.16	16.23	8.92	18.43	2.500	0.168	0.081
OM	5.77	6.58	11.71	10.21	6.59	6.47	7.14	7.37	17.76	2.612	0.483	0.171
EE	−25.38	−21.71	−24.49	−30.21	−38.8	−28.10	−24.80	−48.57	−26.07	6.677	0.760	0.073
CP	11.64	11.18	21.11	23.57	10.94	5.75	7.61	9.37	28.13	4.976	0.073	0.934
TDF	18.89	22.62	10.52	19.68	20.15	25.89	35.00	11.90	28.47	4.935	0.064	0.172
SDF	21.94	21.85	19.52	46.88	27.12	37.24	36.95	29.89	37.69	5.978	0.037	0.707
IDF	23.41	18.89	8.92	17.16	19.05	23.26	34.58	5.10	25.46	4.587	0.068	0.224
NDF	12.15	15.13	6.47	11.67	17.96	18.59	27.88	11.65	20.26	3.600	0.012	0.609
ADF	14.30	7.24	5.78	11.75	16.2	10.86	20.71	9.20	10.60	1.992	<0.01	0.329
Hemicellulose	10.95	21.34	13.31	19.23	9.65	22.92	30.77	14.81	11.02	5.493	0.224	0.089

¹Data represent least square means (n = 6), and individual pig was treated as the experimental unit.

²Source, effects of nine different sources of DFRB; Method, effects of oil extraction methods: pressed DFRB vs. solvent-extracted DFRB. Sources of DFRB are described in Table 1.

Correlation Analysis of nutrients digestibility at the different digestive sites

Correlation coefficients (r) between the AID and the AHD of dietary nutrients of the seven DFRB samples from different sources are presented in Table 8. The AID of dietary GE (r = –0.93; P < 0.01), OM (r = –0.91; P < 0.01), ash (r = –0.85; P <0.05), and CP (r = –0.96; P <0.01) had significant correlations with them in the hindgut. The AID of dietary GE also had correlations with the hindgut dietary OM (r = –0.93; P < 0.01), CP (r = –0.76; P < 0.05), and IDF (r = 0.77; P < 0.05). The AID of OM showed negative correlations with the AHD of GE (r = –0.91; P < 0.01) and ash (r = –0.83; P < 0.05). Meanwhile, the AID of CP had negative correlations with the AHD of GE (r = –0.93; P < 0.01), OM (r = –0.91; P < 0.01), and IDF (r = 0.79; P < 0.05).

Table 8.

Correlation coefficients between the AID (%) and the hindgut digestibility (%) of dietary nutrients of the seven DFRB samples from different sources¹

Item	AID of GE	AID of DM	AID of ash	AID of OM	AID of EE	AID of NDF	AID of ADF	AID of HE	AID of IDF	AID of SDF	AID of TDF
AHD of GE	−0.93**	−0.39	−0.30	−0.91**	−0.03	0.37	0.48	0.11	0.41	−0.09	0.29
AHD of DM	−0.33	−0.78*	−0.61	−0.34	0.74	−0.22	−0.17	−0.19	−0.39	−0.56	−0.34
AHD of ash	−0.80*	−0.89**	−0.85*	−0.83*	0.24	−0.39	−0.26	−0.54	−0.36	−0.63	−0.44
AHD of OM	−0.93**	−0.41	−0.32	−0.91**	−0.06	0.33	0.43	0.06	0.37	−0.09	0.25
AHD of EE	0.03	0.30	0.18	0.03	−0.22	0.07	0.25	−0.1	−0.04	0.03	−0.07
AHD of NDF	0.57	0.04	−0.05	0.50	−0.12	−0.66	−0.71	−0.48	−0.73	−0.06	−0.58
AHD of ADF	0.63	0.27	0.30	0.61	−0.08	−0.13	−0.26	0.10	−0.26	0.38	−0.03
AHD of HE	0.12	−0.26	−0.4	0.05	−0.03	−0.69	−0.54	−0.71	−0.82	−0.37	−0.73
AHD of CP	−0.76*	−0.36	−0.14	−0.71	0.32	0.56	0.60	0.40	0.52	−0.08	0.42
AHD of IDF	0.77*	0.28	0.19	0.72	−0.11	−0.40	−0.42	−0.22	−0.57	0.18	−0.35
AHD of SDF	−0.11	−0.65	−0.64	−0.14	0.42	−0.45	−0.34	−0.41	−0.60	−0.41	−0.45
AHD of TDF	0.58	−0.01	−0.12	0.51	0.00	−0.67	−0.66	−0.52	−0.81	−0.14	−0.64

¹Sources of DFRB are described in Table 1 and all are pressed.

*The two criteria are significantly correlated (P < 0.05).

**The two criteria are significantly correlated (P < 0.01).

Discussion

A number of factors influence nutrient digestibility. The difference in digestibility can be explained by differences in chemical composition (Hughes and Choct, 1999), anti-nutritive factors such as non-starch polysaccharides (Bryden, 1996; Hughes and Choct, 1999), and processing (Marty and Chavez, 1993). Protein can modulate rice starch properties, which may indirectly affect starch digestibility (Khatun et al., 2019). Camire et al. (1990) indicated that extrusion resulted in a redistribution of insoluble to more water-soluble fiber fractions, which may be conducive to fiber digestibility.

Effect of DFRB source on fiber digestibility at different digestive sites of pigs

In the current study, the DFRB samples come from four administrative geography districts of China, including central China (Henan province), east China(Jiangsu and Jiangxi provinces), north China (Beijing city), and northeast China (Liaoning, Jilin, and Heilongjiang provinces). The eastern part of China belongs to the subtropical monsoon climate, which has high temperature in summers with lots of rain and mild winters with little rain. North and Northeast China belong to the temperate monsoon climate, which has high temperature in summers with lots of rain and cold, dry winters; the four seasons are distinctive. In addition, central China has the both above monsoon climates. The air temperature has been reported to have a negative correlation with amylose content (Asaoka et al., 1985) and was the major factor affecting protein content in rice during the period of 10 to 20 d after heading (Nakamura et al., 1989). Rice bran originated from different rice cultivars and grown environmental conditions may differ widely in chemical composition (Shi et al., 2015). In addition, different soil, years, and climatic conditions resulted in the different chemical composition of rice bran (Zhou et al., 2006). There are differences in paddy rice field cropping system and cultivar of different districts, which also affect the chemical composition of paddy rice. The AID of dietary DM, ash, TDF, IDF, NDF, ADF, and hemicellulose of different sources of DFRB was quite variable. It is highly likely that there is a direct connection between nutrient digestibility and chemical composition. The greater AID of dietary fiber digestibility in sample 1 (Henan, pressed) DFRB diet was mainly caused by a greater ash digestibility, which is relative to low ash in sample 1. One of the most important attributes used to measure DFRB quality is ash concentration (Ministry of Agriculture and Rural Affairs, PRC, 2019). The AID of dietary fiber in sample 1 DFRB diet was greatest compared with those in other sources diets in this study, which may be caused by the lowest NDF, ADF, IDF, and TDF contents in sample 1 DFRB diets. Similarly, sample 2 (Jiangsu, pressed) had the greatest TDF and IDF and the lowest dietary TDF digestibility and lower dietary IDF digestibility. In a previous study (Huang et al., 2018), we reported that the TDF of DFRB contains IDF averaging 31.92 (23.44% to 41.93%) and 28.39 (20.81% to 39.67%) and SDF averaging 3.53 (1.37% to 6.99%). The data for TDF, IDF, and SDF in this study are within the range above.

With the exception of EE, SDF, and hemicellulose, the ATTD of most of the dietary nutrients significantly varied in different sources of DFRB. The average value for ATTD of dietary GE, DM, and OM (89.23%, 87.57%, and 91.13%) in the seven samples is greater than the value of 80.92%, 80.50%, and 84.00% of dietary GE, DM, and OM reported by Casas and Stein (2017), but their reported ATTD of dietary NDF (48.96%) was in the range of our study (27.34% to 67.44%). Such discrepancies may be related to the variation in DFRB source, processing technologies, and the condition of the pigs. The lower ATTD of nutrients in sample 2 diet may be caused by its high IDF content, which is difficult to be fermented by gut bacteria and could speed up the evacuation rate of digesta in the gut of pigs (Molist et al., 2009).

There were differences in the hindgut disappearance of DM, SDF, NDF, and ADF, among pigs fed the diets containing DFRB from different sources. In addition, the AHD of TDF and IDF also tended to variable. These findings could be related to the greater fiber content that may be fermented to produce SCFA mainly in the hindgut of pigs. The result of negative values for the AHD of dietary EE was consistent with a previous study (Urriola and Stein, 2012). This is likely a consequence of fatty acids synthesis from carbohydrates in the hindgut (Williams et al., 2001).

The current study showed that the ileal dietary GE, OM, ash, and CP digestibility had significant negative correlations with them in the hindgut. The result may be that these dietary nutrients are primarily digested in the foregut. The ileal dietary GE digestibility also had correlations with the hindgut dietary OM, CP, and IDF digestibility. On the one hand, the correlations can be explained by the definition of GE, which is the energy that is released by complete combustion of OM including CP. It means that the AID of dietary GE increased as the AHD of OM and CP decreased. On the other hand, IDF was found to decrease intestinal transit time, bind organic compounds, and increase fecal bulk (Renteria-Flores, 2006) and then decrease the AID of nutrients (Dikeman and Fahey, 2006).

Effects of DFRB processing technology on fiber digestibility at different digestive sites of pigs

Pressed DFRB showed greater average AID of dietary GE, DM ash, OM, CP, SDF, and NDF digestibility but lower dietary ADF digestibility. The differences in these findings for the two processing technologies of DFRB may have resulted from the greater GE, DM, OM, CP, and SDF and lower ash contents of samples 7 (Heilongjiang, pressed) and 9 (Jiangxi, pressed). Furthermore, the two samples had lower fibrous fractions than solvent-extracted DFRB. The concentration of NDF (Bell, 1993; Noblet and Perez, 1993) is a major factor responsible for variation in the energy utilization of some ingredients. The CP, EE, and SDF contents, however, are greater in pressed DFRB than those in solvent-extracted DFRB, which possibly contributes to the dietary GE and OM digestibility variation. Dietary fiber is mainly composed of SDF and IDF, which can be partially or completely fermented by microbiota in the hindgut to produce SCFA that are absorbed for energy (Williams et al., 2001; Jha and Berrocoso, 2015). The SDF is generally more easily, rapidly, and completely fermented in either the small or large intestine than IDF (Urriola and Stein, 2010). Therefore, the influence of feed processing on the nutritional value of feed must be considered. There are two main types of technologies for defatting. One technique is pressed, and the other one of the efforts to improve the quality of rice bran is the solvent-extracted technique. These technologies are expected to decrease the crude fat so that storage time can be extended. It is interesting to note that there was no difference in the concentration of fat between pressed vs. solvent-extracted sources. It may be resulted from low EE content and endogenous fat contribution to the small intestine. The main difference between the two processing techniques is temperature. The starch granules can hydrate and swell due to absorption of water (Fellows, 2000); therefore, the higher the temperature is, the longer feedstuffs are exposed to the steam, the greater is the starch gelatinization (Hancock and Behnke, 2001; Lewis et al., 2015). Pressed DFRB had a greater (P < 0.01) average ATTD of dietary SDF, NDF, ADF, and hemicellulose compared with solvent-extracted DFRB (Table 6). These results were consistent with the above, which indicated that the average AID of SDF, NDF, and ADF in pressed DFRB is greater than in solvent-extracted DFRB. In addition, pressed DFRB had lower NDF, ADF, and hemicellulose and greater SDF concentrations than solvent-extracted DFRB. As we all known, SDF could be largely fermented to produce SCFA in the hindgut, which is considered to provide energy for pigs. There were no differences in the AHD of fiber fractions. The results are inconsistent with the data, which reported by Zhao et al. (2019). One possible explanation for the discrepancy is that the presence of non-dietary material in the gastrointestinal tract interferes with the determination of dietary fiber in the gastrointestinal contents (Nyman and Asp, 1982; Englyst and Cummings, 1986; Cervantes-Pahm et al., 2014; Montoya et al., 2015). Nondietary interfering material present in the SDF and IDF has also been determined at the ileal and fecal levels in growing pigs (Cervantes-Pahm et al., 2014). The main sources of nondietary interfering material in small intestinal digesta are mucins and bacteria, while the main source in feces is bacteria (Cabotaje et al., 1990; Monsma et al., 1992; Lien et al., 1996; Montoya et al., 2015).

Conclusions

There are differences in the foregut and hindgut nutrient digestibility of pigs fed with different sources and processing technologies of DFRB with different physicochemical properties. Therefore, it is necessary to take the processing technologies and sources into consideration when formulating DFRB diets for growing pigs.

Glossary

Abbreviations

ADF

acid detergent fiber

AID

apparent ileal digestibility

ATTD

apparent total tract digestibility

BW

body weight

CP

crude protein

DFRB

defatted rice bran

DM

dry matter

EE

ether extract

GE

gross energy

IDF

insoluble dietary fiber

MUFA

monounsaturated fatty acid

NDF

neutral detergent fiber

OM

organic matter

PUFA

polyunsaturated fatty acid

SCFA

short-chain fatty acids

SDF

soluble dietary fiber

TDF

total dietary fiber

Conflict of interest statement

The authors declare no competing interests in connection with data, opinion, and finance of this manuscript.