Ether extract and acid detergent fibre but not glucosinolates are determinants of the digestible and metabolizable energy of rapeseed meal in growing pigs

ABSTRACT

This study was conducted to determine the nutritional composition [acid detergent fibre (ADF), neutral detergent fibre (NDF), ether extract (EE) and crude protein (CP)], digestible energy (DE) and metabolizable energy (ME) of rapeseed meals (RSM) differing in glucosinolates (GLS) contents fed to growing pigs. One hundred and thirty-eight crossbred barrows with initial body weight (BW) of 39.0 ± 1.9 kg were allotted to 1 of 23 diets. Results showed that the content of GLS in RSM ranged from 1.72 to 62.94 mol/g DM with a coefficient of variation (CV) of 89%. The concentration of ADF ranged from 22.78 to 35.71% with a mean of 28.79% [DM (CV = 16.22%)]. The concentration of ether extract (EE) ranged from 1.42% to 14.55% with a mean of 7.78% [DM (CV = 45.16%)]. DE and ME values of the 22 RSM ranged from 10.10 to 15.42 MJ/kg DM and 9.09 to 14.94 MJ/kg DM (P < 0.05). Best-fit prediction equations were as follows: DE (MJ/kg DM) = 8.04 + 0.21 CP (%) + 0.29 EE (%) – 0.18 ADF (%) (R² = 0.67) and ME (MJ/kg DM) = 14.82 + 0.23 EE (%) – 0.16 ADF (%) (R² = 0.60). The content of GLS was not the key factor affecting DE and ME values of RSM, while EE and ADF are critical to accurately predicting the DE and ME of RSM.

KEYWORDS:

• Growing pigs
• rapeseed meal
• glucosinolates
• digestible energy
• metabolizable energy
• prediction equations

1. Introduction

Rapeseed meal (RSM) is the product remaining after oil is expeller-pressed extruded or solvent extracted from rapeseed. Globally, RSM is the second largest protein-rich ingredient after soybean meal (SBM) used in the formulation of swine diets (Carré and Pouzet 2014). In addition, the price of RSM is typically less than that of soybean meal, so RSM may be an attractive replacement for SBM in swine diets (Oil World 2012). However, the inclusion level of RSM in swine diets is restricted due to its’ high content of fibre and, more importantly, glucosinolates (GLS), which are the main antinutritional factor in RSM (Barthet and Daun 2002; Seneviratne et al. 2010). A previous study has shown that the utilization of RSM to replace SBM had a negative effect on the growth performance of piglets (Bell 1993).

In addition, as inclusion level of RSM increased in diets, the average daily gain and feed intake of weaned pigs was linearly reduced (Baidoo et al. 1987). Schöne and Opalka suggested that total GLS content in swine diet should be kept below 2 mol/g DM (Schöne et al. 1997; Opalka et al. 2001). Moreover, the digestibility of energy in RSM decreased as the content of GLS increased from 8.69 μmol/g to 15 μmol/g (Corino et al. 1991; Tripathi and Mishra 2007). However, the link between GLS and digestible energy (DE) and metabolizable energy (ME) values of RSM in swine diets is not clear.

Therefore, we hypothesized that the DE and ME in RSM fed to growing pigs would have a negative correlation with the concentration of GLS in RSM. This study was carried out to determine the DE and ME values in 22 samples of RSM with different GLS concentrations fed to growing pigs and to develop prediction equations of DE and ME in RSM using GLS and other chemical compositions as input parameters.

2. Materials and methods

All protocols in this study were approved by the Institutional Animal Care and Use Committee of China Agricultural University (Beijing, China). The experiment was conducted in FengNing Swine Research Unit of China Agricultural University (Academician Workstation in Chengdejiuyun Agricultural & Livestock Co., Ltd) (Hebei, China) Rapeseed meal used in this experiment was supplied by Institute of Oil Crops, Chinese Academy of Agricultural Sciences. A total of 22 RSM samples was collected according to the regional distribution and GLS content from 8 different provinces in China (Table 1). The chemical composition was analyzed and is presented in Table 2.

Table 1. Sources of rapeseed meal used in the experiments.

Numbers	Sources within China	GLS, μmol/g
1	Hubei	10.19
2	Shandong	19.66
3	Jiangsu	28.94
4	Jiangsu	5.87
5	Sichuan	25.09
6	Anhui	1.74
7	Hunan	3.10
8	Hunan	3.54
9	Sichuan	4.20
10	Anhui	5.54
11	Hunan	5.96
12	Hubei	6.16
13	Yunnan	10.45
14	Jiangsu	11.07
15	Jiangsu	11.67
16	Chengdu	13.88
17	Sichuan	17.54
18	Hubei	28.31
19	Henan	33.67
20	Hubei	43.10
21	Sichuan	48.13
22	Shanxi	62.94

Table 2. Chemical compositions of rapeseed meals (DM basis).

Items	GLS, μmol/g	DM, %	GE, MJ/kg	CP, %	EE, %	NDF, %	ADF, %	CF, %	Ash, %
1	10.19	89.75	19.97	41.52	3.35	46.44	26.71	17.40	8.18
2	19.66	90.32	19.91	43.36	1.94	51.96	35.71	17.50	8.48
3	28.94	89.56	19.57	40.88	2.18	39.59	24.45	15.88	9.06
4	5.87	89.20	19.82	42.26	2.10	36.45	24.04	15.95	7.52
5	25.09	89.73	18.30	42.24	1.42	41.99	25.44	14.73	8.47
6	1.74	90.86	20.80	39.08	8.98	36.47	23.16	15.89	9.19
7	3.10	91.73	21.15	36.14	10.37	38.45	22.78	16.71	6.97
8	3.54	92.73	22.33	38.71	14.55	48.50	26.17	18.25	6.83
9	4.20	90.57	21.06	41.48	6.94	48.85	30.39	18.62	7.40
10	5.54	92.17	21.51	40.07	10.44	54.12	36.13	23.24	7.81
11	5.96	92.21	20.93	39.76	7.88	52.30	32.64	19.01	8.30
12	6.16	91.59	21.06	38.13	9.01	55.38	32.00	25.79	6.80
13	10.45	92.47	21.87	39.52	11.26	49.95	32.77	22.86	7.01
14	11.07	92.17	20.76	40.13	7.02	36.70	22.42	17.23	6.91
15	11.67	91.60	21.66	38.34	9.31	54.26	33.68	22.53	7.15
16	13.88	91.19	20.98	42.90	6.77	46.47	25.95	17.15	6.66
17	17.54	92.05	21.14	41.13	8.21	57.14	36.14	27.80	4.67
18	28.31	86.69	22.87	42.08	12.25	57.37	34.43	28.58	8.27
19	33.67	91.69	21.55	38.07	11.18	42.10	25.14	18.48	7.56
20	43.10	91.36	21.04	36.04	8.54	47.49	25.01	15.81	6.22
21	48.13	91.90	21.04	35.72	9.24	48.62	27.88	23.39	7.30
22	62.94	91.77	21.10	41.32	8.28	47.24	28.39	18.56	7.68
Mean	18.21	91.06	20.92	39.94	7.78	47.17	28.79	19.60	7.47
CV	88.96	1.51	4.56	5.44	45.16	14.01	15.94	20.24	13.17

Note: TGS, total glucosinolates; DM, dry matter; GE, gross energy; CP, crude protein; EE, ether extract; NDF, neutral detergent fibre; ADF, acid detergent fibre; CF, crude fibre.

2.1. Experimental animals and diets

A total of 138 crossbred (Duroc × Landrace × Yorkshire) barrows with initial body weight (BW) of 39.0 ± 1.9 kg were selected and obtained from FengNing Swine Research Unit of China Agricultural University (Academician Workstation in Chengdejiuyun Agricultural & Livestock Co., Ltd). Because of Corn-Basal diet method was a better choice than a Corn-SBM-Basal diet method to determine the nutrient of the feedstuff when the test ingredient has a greater CP content (Liu et al. 2019). So a corn-based basal diet was formulated and fed to the pigs for 7 days before the experiment. Formulation of the diets and chemical analysis of the 22 ingredients used in this experiment were shown in Tables 3 and 4, respectively. The diets were fed to pigs at the level of 4% BW according to Adeola (2001) and was divided into two equal-sized meals provided at 0830 and 1530 h. All pigs had free access to water.

Table 3. Ingredient compositions of the experimental diets (%, as-fed basis).

Ingredients	Basal diet	Tested diets
Corn	96.90	67.83
Rapeseed meal	–	29.07
Dicalcium phosphate	1.70	1.70
Salt	0.30	0.30
Limestone	0.60	0.60
Micromineral and vitamin premix^a	0.50	0.50
Total	100.00	100.00

^aProduct of the Chemical Reagents Company (Beijing, China).

Premix provided the following per kg of the complete diet: vitamin A as retinyl acetate, 5,512 IU; vitamin D₃ as cholecalciferol, 2,200 IU; vitamin E as DL-alpha-tocopheryl acetate, 30 IU; vitamin K₃ as menadione nicotinamide bisulphite, 2.2 mg; vitamin B₁₂, 27.6 μg; riboflavin, 4 mg; pantothenic acid as DL-calcium pantothenate, 14 mg; niacin, 30 mg; choline chloride, 400 mg; folacin, 0.7 mg; thiamin as thiamine mononitrate, 1.5 mg; pyridoxine as pyridoxine hydrochloride, 3 mg; biotin, 44 μg; Mn as MnO, 40 mg; Fe as FeSO₄•H₂O, 75 mg; Zn as ZnO, 75 mg; Cu as CuSO₄•5H₂O, 100 mg; I as KI, 0.3 mg; Se as Na₂SeO₃, 0.3 mg.

Table 4. Analyzed nutrient levels of diets (DM basis).

Items	DM, %	GE, MJ/kg	CP, %	EE, %	NDF, %	ADF, %	CF, %	Ash, %	GLS, μmol/g
1	87.76	18.52	19.25	2.62	27.59	12.31	7.71	5.88	2.96
2	87.54	18.92	19.11	4.40	24.67	9.05	7.29	5.52	5.72
3	87.80	18.96	18.15	4.81	24.26	10.33	6.54	5.87	8.41
4	86.85	18.78	18.49	1.88	23.29	9.43	6.24	6.25	1.71
5	87.90	19.43	17.55	7.29	21.22	7.49	6.63	5.63	7.29
6	87.66	19.30	17.45	6.24	22.64	8.97	6.71	5.57	0.51
7	87.73	19.25	18.60	4.15	24.06	7.93	5.87	5.93	0.90
8	87.53	18.92	17.94	3.76	23.16	8.40	5.59	6.29	1.03
9	87.64	19.19	18.10	5.73	23.53	10.90	6.97	5.61	1.22
10	87.52	18.70	17.28	5.16	24.84	8.94	6.84	5.39	1.61
11	87.91	19.32	18.11	6.25	25.25	10.53	7.16	5.36	1.73
12	87.10	19.14	18.38	3.56	24.86	10.13	6.22	5.37	1.79
13	87.04	19.30	17.73	4.81	24.48	9.87	6.14	5.12	3.04
14	87.54	19.15	16.77	5.85	23.55	7.77	5.72	5.59	3.22
15	87.81	17.13	18.27	3.25	24.05	9.44	5.73	5.32	3.39
16	87.48	19.39	17.16	4.02	25.30	9.71	6.44	5.27	4.03
17	87.94	19.07	18.44	4.74	23.00	7.51	5.50	5.16	5.10
18	87.51	19.11	17.70	5.45	23.76	10.08	6.22	5.76	8.23
19	86.57	18.72	18.74	1.57	19.97	8.83	5.91	5.16	9.79
20	86.63	18.75	19.03	2.24	20.15	8.09	6.26	5.68	12.53
21	87.66	19.27	18.65	5.57	22.37	10.00	7.29	5.60	13.99
22	87.30	19.51	18.34	5.50	22.06	9.47	7.17	3.84	18.30
Basal diet	85.91	18.76	9.09	1.79	13.01	2.85	2.68	6.01	0.00

Note: DM, dry matter; GE, gross energy; CP, crude protein; EE, ether extract; NDF, neutral detergent fibre; ADF, acid detergent fibre; CF, crude fibre. GLS, glucosinolates.

2.2. Feeding management and sample collection

Pigs were placed in individual stainless-steel metabolism crates (1.4 m × 0.7 m × 0.6 m) and the room temperature was kept between 18 and 22˚C. The experiment lasted 12 d with 7 d of diet adaptation followed by 5 d of total feces and urine collection. Feces were collected into plastic bags and stored at −20˚C after collection. Total urine was collected into plastic buckets attached to funnels located under the metabolism cages at the same time as the fecal collection. Twenty mL 10% (v/v) HCl were added into plastic buckets to fix the nitrogen of urine. Urine volume was recorded daily and a subsample of 10% was collected daily and stored at −20˚C. The rooms were cleaned and rinsed twice a day to keep the environment sanitary. At the end of the experiment, the collected feces were thawed, weighed, and mixed and a subsample was taken and dried in a forced-draft oven at 65˚C for 72 h.

2.3. Chemical analysis

The RSM samples and diets were analyzed for dry matter (DM; method 930.15) (Latimer 2012). The GE of RSM, diets, feces, and urine samples were analyzed using an adiabatic oxygen bomb calorimeter (model 6400; Parr1281 Calorimeter, Moline, IL, USA). Crude protein (CP; method 984.13), ether extract (EE; Thiex et al. 2003), ash (ash; method 942.05), and crude fibre (CF; method 978.10) were also analyzed in all samples. The modified procedures of Van Soest et al. (1991), were followed to determine neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations. The concentration of NDF was analyzed using heat stable α-amylase and sodium sulphite without correction for insoluble ash using a fibre bag system (Ankom Technology, Macedon, NY, USA). The ADF fraction was analyzed in a separate sample.

2.4. Calculations

The DE and ME content of the diets as well as the 22 RSM samples were calculated using the method as described by Adeola (2001), ME values were calculated without considering CH₄:$D{E}_d=(G{E}_i-G{E}_f)/F_i$ $D{E}_{dc}=D{E}_d/0.969$ $M{E}_d=(G{E}_i-G{E}_f-G{E}_u)/F_i$ $M{E}_{dc}=M{E}_d/0.969$ $D{E}_w=[D{E}_d-(96.9\text{\%}-X\text{\%})\times D{E}_{dc}]/X\text{\%}$ $M{E}_w=[M{E}_d-(96.9\text{\%}-X\text{\%})\times M{E}_{dc}]/X\text{\%}$ $ATTD=(G{E}_i-G{E}_f)/G{E}_i$

where DE_d and ME_d are the DE and ME values in each diet (MJ of DM); GE_i is the total GE intake of each pig (MJ of DM), and F_i is the actual feed intake over the 5-d collection period; GE_f and GE_u are the GE content in feces and urine of each pig (MJ of DM) over the 5-d collection period; DE_dc and ME_dc are the corrected apparent digestible and metabolizable energy in the basal diet (MJ/Kg of DM); 0.969 is the percentage of the energy yielding ingredients in this diet; DE_w and ME_w are the DE and ME values in each RSM (MJ/kg of DM) and X is the percentage of the tested ingredients in the corresponding diets.

2.5. Statistics analysis

Data were statistically analyzed using the GLM Procedure of SAS (SAS Inst. Inc., Cary, NC). The data for the ATTD of GE, DE and ME content were analyzed using the GLM procedure (SAS Institute Inc., Cary, NC), with the pig as the experimental unit. Multiple comparisons were conducted using Student Newman Keul’s method. The relationship between DE and ME and chemical composition was determined using Proc CORR. A probability value of 0.05 was used to assess statistical significance among the means (P < 0.05). The prediction equations of DE and ME in diets and RSM were established by stepwise linear regression using chemical compositions of RSM as input parameters.

3. Results and discussion

3.1. Chemical composition of 22 RSM samples

There was significant variation (CV = 88.96%) in GLS content in the 22 RSM samples. This was indicated by a range of GLS concentrations from 1.74 to –62.94 μmol/g with a mean of 18.21 μmol/g. The CV of GLS in our study was greater than Li et al. (2015), who reported the CV of GLS in 9 RSM samples was 51.1%. This indicated that the collected samples were well representative to test our hypothesis.

The CP content of RSM averaged 39.94%, ranging from 35.72 to 43.36% (CV = 5.44%), which was similar with other reports (39.20%, 38.72%) (Li et al. 2017; Dong et al. 2019). The EE concentration in RSM ranged from 1.42 to 14.55% with a mean 7.78% (CV = 45.16%). The concentration of NDF in RSM ranged from 36.45 to 57.37% with a mean of 47.17% (CV = 14.01%). The ADF content in RSM averaged 28.79%, ranging from 22.78 to 36.14% (CV = 15.94%). The contents of NDF and ADF in the 22 RSM samples were similar compared with Maison et al. (2015). The GE in RSM ranged from 18.30 to 22.87 MJ/kg with a mean of 20.92 MJ/kg (CV = 4.56%) and this was similar to Li et al. (2015). The No. 2 RSM had greater NDF and ADF content (51.96 and 35.71%, respectively) and lower EE (1.94%) compared with other samples. The variety of rapeseed, growing conditions, impurity content, and processing conditions will all lead to the large variation in the chemical compositions of RSM (Bell 1993; Yasumoto et al. 2007; Woyengo et al. 2010).

3.2. Energy contents of 22 cultivars of RSM

Differences (P < 0.01) in DE and ME values determined in the 22 RSM samples were observed. The DE value ranged from 10.10 to 15.41 MJ/kg DM with a mean of 13.36 MJ/kg DM, and the ME averaged 12.17 MJ/kg DM, ranging from 9.09–14.94 MJ/kg DM ( Table 5). The No. 2 RSM sample had the lowest DE and ME, which is explained by greater NDF and ADF contents (51.96%, 35.71%) and lower EE (1.94%) in this sample compared with the other RSM samples.

Table 5. Digestible (DE) and metabolizable energy (ME) of rapeseed meal, and apparent total tract digestibility (ATTD) of GE in diets (DM basis) digestibility (ATTD) of GE in diets (DM basis).

Items	DE, MJ/kg	ME, MJ/kg	ME/DE	ATTD of GE, %
1	13.60^bcde	12.34^ab	0.96	81.66^abc
2	10.10^f	9.09^c	0.97	78.16^e
3	11.82^e	10.83^bc	0.97	80.97^bcd
4	13.17^cde	11.41^bc	0.95	82.91^ab
5	13.35^cde	11.76^bc	0.96	82.94^ab
6	13.91^abcd	13.48^ab	0.98	82.85^ab
7	14.56^abc	13.70^ab	0.97	83.12^ab
8	15.41^a	13.98^ab	0.96	83.16^ab
9	13.16^cde	11.69^bc	0.96	81.06^bcd
10	11.77^e	10.97^bc	0.97	78.47^ed
11	12.43^de	10.96^bc	0.96	80.36^bcde
12	13.23^cde	12.12^ab	0.97	81.18^bcd
13	13.76^abcd	11.88^bc	0.95	80.95^bcd
14	15.28^ab	14.94^a	0.98	84.34^a
15	13.56^bcde	12.62^ab	0.97	81.31^bcd
16	13.16^cde	11.11^bc	0.95	81.75^abc
17	12.64^de	11.68^bc	0.97	79.53^cde
18	14.56^abc	13.45^ab	0.97	81.22^bcd
19	14.06^abcd	12.94^ab	0.97	81.53^abc
20	12.43^de	11.38^bc	0.97	81.54^abc
21	13.45^cde	12.57^ab	0.97	80.45^bcde
22	14.59^abc	12.93^ab	0.96	82.56^abc
Max	15.41	14.94	0.98	84.34
Min	10.10	9.09	0.95	78.16
Mean	13.36	12.17	0.97	81.45
SEM	0.38	0.59	0.07	0.62
P Value	< 0.01	< 0.01	0.15	< 0.01

Note: Means in the same column bearing different superscripts differ significantly (P < 0.05).

The content of EE was positively correlated (P < 0.05) with the DE and ME of RSM, whereas the content of ADF was negatively correlated (P < 0.05) with DE and ME values of RSM (Table 6). It has been reported that EE is more easily digested by endogenous lipase in the gut and improve the digestibility of other nutrients owing to increasing the viscosity of digesta (Bruce et al. 2006). A previous study indicated that the high content of NDF reduced apparent digestibility of dietary nutrients because of increased transit rate of digesta (Noblet and Perez 1993). Therefore, the higher NDF content reduced the DE and ME of RSM. The variation of the ATTD of GE among the 22 RSM samples may be caused by differences in the heat treatment to rapeseed during oil extraction (Danicke et al. 1998; Spragg and Mailer 2007). It is higher than a previous study, which reported the average ATTD of GE was 68.6% (Li et al. 2015), but our result was consistent with previous observations of Maison et al. (2015). It was shown that replacing SBM up to 30% with expeller RSM in nutritionally balanced diets for young pigs reduced the ATTD of most nutrients and energy, which may be caused by the inferior quality of protein and amino acids in RSM than SBM (Pérez de Nanclares et al. 2018).

Table 6. Correlation coefficients between digestible and metabolizable energy and chemical compositions of rapeseed meals.

Items	DE	ME	GE	CP	EE	NDF	ADF	CF	Ash	GLS
DE	1.00
ME	0.94**	1.00
GE	0.42	0.42	1.00
CP	−0.27	−0.4	−0.35	1.00
EE	0.53*	0.55**	0.92**	−0.56**	1.00
NDF	−0.28	−0.31	0.48*	0.06	0.34	1.00
ADF	−0.45*	−0.44*	0.35	0.24	0.18	0.91**	1.00
CF	0.03	0.06	0.61**	−0.08	0.50*	0.79**	0.75**	1.00
Ash	−0.17	−0.14	−0.36	0.28	−0.35	−0.31	−0.16	−0.39	1.00
GLS	−0.01	−0.02	−0.04	−0.11	−0.03	0.05	−0.06	0.02	−0.01	1.00

Note: GLS, glucosinolates; DM, dry matter; GE, gross energy; CP, crude protein; EE, ether extract; NDF, neutral detergent fibre; ADF, acid detergent fibre; CF, crude fibre.

*, **represent P < 0.05 and P < 0.01, respectively.

3.3. Prediction equations for DE and ME

We hypothesized that a greater concentration of GLS in RSM would reduce the DE and ME contents in RSM because palatability and feed intake were reduced when the concentration of GLS exceeded 2 mol/g in the diets fed to weanling pigs (Almeida et al. 2014). Antithetical to our hypothesis, the DE and ME values in RSM were not affected by the content of GLS in this study. This result may be due to the restricted feed intake in this study. Li et al. (2015) obtained similar results on the DE of double-low rapeseed cake. Our study demonstrated that EE content had a positive correlation (P < 0.05) with DE and ME, and the ADF content had a negative correlation with DE and ME.

Several prediction equations for DE and ME of RSM were determined using stepwise regression analyses. For the prediction of DE, No.1 equations were based on a single predictor, and the estimation based on EE (R²= 0.28) ( Table 7). The accuracy of the equations was improved after including a second predictor, such as ADF (No. 2, R² = 0.59), Introducing a third variable in the equations (No.3), the predicted values of DE were closer to the determined values (R² = 0.67). In the present study, no significant correlation was found between CP or NDF and DE value, and this may be caused by the small variation in CP and NDF contents in the RSM collected for this study. Similar to the predictive equations of DE, the single predictor of ME was also based on EE (R2 = 0.30). When ADF was included as predictor, the accuracy of the equation was improved (R² = 0.60).

Table 7. Linear regression equations for prediction of energy content based on the chemical compositions of rapeseed meal fed to growing pigs.

NO	Prediction equations	R^2	RMSE^2	P value
1	DE (MJ/kg DM) = 11.96 + 0.18 EE (%)	0.28	1.16	< 0.01
2	DE (MJ/kg DM) = 15.91 + 0.22 EE (%) − 0.15 ADF (%)	0.59	0.82	< 0.01
3	DE (MJ/kg DM) = 8.04 + 0.21 CP (%) + 0.29 EE (%) − 0.18 ADF (%)	0.67	0.75	< 0.01
4	ME (MJ/kg DM) = 10.64 + 0.19 EE (%)	0.30	1.12	< 0.01
5	ME (MJ/kg DM) = 14.82 + 0.23 EE (%) − 0.16 ADF (%)	0.60	0.86	< 0.01

Regression equations were developed by stepwise regression analyses.

CP, crude protein; EE, ether extract; NDF, neutral detergent fibre; ADF, acid detergent fibre.

4. Conclusions

A large variation of DE and ME values in RSM was observed due to a large variation in chemical composition. The DE and ME contents ranged from 10.10 to 15.41 MJ/kg DM with a mean of 13.36 MJ/kg and from 9.09 to 14.94 MJ/kg DM with a mean of 13.36 MJ/kg, respectively. The best-fit prediction equations for DE and ME values in RSM were as follows: DE (MJ/kg DM) = 8.04 + 0.21 CP (%) + 0.29 EE (%) – 0.18 ADF (%) and ME (MJ/kg DM) = 14.82 + 0.23 EE (%) – 0.16 ADF (%). Antithetical to our hypothesis, GLS content in RSM was not the major factor on DE and ME values in RSM. Rather, EE and ADF should be analyzed to best predict DE and ME in RSM.

Acknowledgements

This research was financially supported by the 111 project (B16044). Rapeseed meal used in this experiment was supplied by Institute of Oil Crops, Chinese Academy of Agricultural Sciences. The authors would thank the faculty and staff in Ministry of Agriculture Feed Industry Centre and Key Research & Developmental Programme of Shandong Province (2019JZZY020308) for their support to this study. Thanks Neil Jaworski from Trouw Nutrition revision of the grammar of the manuscript. The authors declare that no competing interests on data, opinion and finance in this paper.

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Additional information

Funding

This work was supported by the 111 project [grant number B16044]; Ministry of Agriculture Feed Industry Centre and Key Research & Developmental Programme of Shandong Province [grant number 2019JZZY020308].