Evaluation of extruded or unextruded double-low rapeseed meal and multienzymes preparation in pigs nutrition during the finishing phase of production

Abstract

The aim of this study was to compare the effects of extruded or non-extruded double-low rapeseed meal (DL-RSM) and multienzyme preparation on performance, nutrient digestibility, immune function and antioxidant status of the finishing pigs. Forty-eight pigs (Duroc×Landrace×Yorkshire) with an average weight of 62 kg were randomly divided into four groups with three replicates according to gender. Four diets were formulated to meet NRC (1998) nutrient requirements. Diet 1, based on the corn and soybean meal (SBM), was used as control. Diet 2 used 13% DL-RSM instead of the 11% SBM used in the Diet 1. Diet 3 used 13% extruded double-low rapeseed meal (E-DL-RSM) instead of 11% SBM, and Diet 4 0.03% multienzyme preparation was supplemented in Diet 3. The results showed that replacement of 11% SBM by 13% DL-RSM had no negative effects on performance and nutrient digestibility for finishing pigs. Extrusion and multienzyme preparation also had no beneficial effects on pig performance. However, the concentration of immunoglobulin G (IgG) in serum of DL-RSM treatment was lower (P<0.05) than that of the control, but it increased to the level of control in the treatment of extrusion combined with multienzyme preparation. The diet containing E-DL-RSM combined with multienzyme preparation significantly decreased the malondialdehyde (MDA) content (P<0.05) in serum. It was concluded that DL-RSM was an acceptable alternative to SBM as part of a protein supplement for finishing pig diets. In addition, extrusion and multienzymes preparation were not economically applied in the current study because of their extra cost.

Keywords:

• Finishing pig
• Double-low rapeseed meal
• Extrusion
• Multienzyme preparation
• Performance.

Introduction

Rapeseed meal with approximately 35% crude protein and a good amino acid profile (Bell et al., 1991, 1998) has been considered an important alternative resource for supplementary protein for livestock. Over the last twenty years in China, the content of anti-nutritional factors in rapeseed, such as glucosinolates and erucic acid, has been greatly reduced by the introduction of double low rapeseed. It has been proved that the protein biological value of double low rapeseed meal (DL-RSM) is comparable to that of soybean meal (SBM) (Campbell et al., 1981; Nasi, 1991). Previous studies on poultry (Hickling, 2001; Taylor et al., 2004), swine (Baidoo et al., 1987; Siljander-Rasi et al., 1996) and fish (Davies et al., 1990) have shown that DL-RSM was a feasible protein source substitute for SBM. However, results from studies on pig diets using DL-RSM vary considerably. This may be due to the different content of anti-nutritional factors, meal processing, and the age and weight of the pigs used in the experiments.

Extrusion involves heat treatment, pressure and shear force, which has been found to have beneficial effects on the nutritional value of rapeseed meal and other feedstuffs (Pongmaneerat and Watanabe, 1993; Burel et al., 2000; Allan and Booth, 2004). It has been reported that diets with less than 9% extruded rapeseed meal instead of SBM have no negative effect on the feed intake or weight gain of weaning piglets, and 5% extruded rapeseed meal can even improve the productive performance of growing pigs (Yang et al., 2004a, 2004b). Furthermore, adding commercial enzymes is one of the methods used to improve the nutritional quality of rapeseed meal. Exogenous commercial enzymes have been shown to improve the nutritional value of feedstuffs in animals (Bedford, 1995; Classen, 1996; Gdala et al., 1997).

To our knowledge, there is still some controversy concerning the effect of extrusion and enzyme supplementation on the dietary quality of DL-RSM for finishing pigs. Therefore, the aim of this study was to make a comprehensive evaluation of the effects of extruded DL-RSM and multienzyme preparation in the diets of finishing pigs on growth performance, nutrient digestibility, serum thyroid hormone level, immune function, antioxidant status and conventional biochemical index.

Materials and methods

Experimental design and feeding management

The experiment was conducted in accordance with the Chinese guidelines for animal welfare and was approved by the animal welfare committee of the Animal Science College, Zhejiang University.

Extruded and non-extruded double-low rapeseed meal and multienzymes preparation (cellulase 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) were all provided by Zhejiang Xinxin Feed Co., Ltd. in China. The physical conditions for extrusion are: diameter of die nozzle 14 mm, temperature 115°C, steam pressure 0.3 MPa, screw speed 55 r/min. The chemical composition of double-low rapeseed meal and extruded double-low rapeseed meal is shown in Table 1.

Table 1 Chemical composition of double-low rapeseed meal and extruded double-low rapeseed meal.

	Double-low rapeseed meal	Extruded double-low rapeseed meal
Dry matter, %	91.93	91.21
Crude protein, %	35.62	35.44
Ether extract, %	4.37	3.58
Crude fibre, %	5.69	5.42
ADF, %	13.06	12.53
NDF, %	20.34	19.47
Ash, %	6.87	6.68
Amino acids
Aspartic acid, %	2.57	2.50
Threonine, %	1.57	1.60
Serine, %	1.62	1.66
Glutamic acid, %	8.33	8.27
Proline, %	1.90	1.97
Glycine, %	1.81	1.80
Alanine, %	1.47	1.62
Cystine, %	0.34	0.36
Valine, %	1.56	1.57
Methionine, %	0.51	0.57
Isoleucine, %	1.23	1.27
Leucine, %	2.37	2.57
Tyrosine, %	0.95	0.95
Phenylalanine, %	1.60	1.62
Lysine, %	2.20	2.13
Histidine, %	0.92	0.93
Arginine, %	1.70	1.69
Total amino acids	32.65	33.08
Calcium, %	0.62	0.59
Total phosphorus, %	1.53	1.62
Glucosinolate, mol/g	25.67	24.04
Erucic acid, %	2.15	1.86
Tannin, %	1.29	1.03

ADF, acid detergent fibre; NDF, neutral detergent fibre. All components were measured wet.

Forty-eight healthy fattening pigs (Duroc×Landrace×Yorkshire), 110 days of age, were randomly divided into four groups according to gender. Each group had three replicates with 4 pigs (2 males and 2 females) per replicate, and each replicate was kept in its own pen. Average initial weight of the pigs was approximately 62 kg. Basal diets with different dietary treatments were formulated in equal energy and digestible amino acids to meet NRC (1998) nutrient requirements (Table 2). Diet 1, based on corn and soybean meal (SBM), was used as control, Diet 2 (DL-RSM group) used 13% DL-RSM instead of the 11% SBM in the control diet, Diet 3 (E-DL-RSM group) used 13% extruded double-low rapeseed meal (E-DL-RSM) to replace 11% soybean meal, and Diet 4 (E-DL-RSM+ enzyme group) contained 0.03% multienzyme preparation on the basis of the E-DL-RSM group diet. The entire study lasted 37 days; a 7-day acclimation and a 30-day experimental period. According to the average price of ingredients in the diet in the first six months of 2011 on the local market (Zhejiang province, China), costs of the diets studied were as follows. Diet 1: 2728 yuan/t; Diet 2: 2607 yuan/t; Diet 3: 2636 yuan/t; Diet 4: 2667 yuan/t.

Table 2 Ingredients and nutrient composition of diets.

	Control group	Test group
Ingredients
Corn, %	68.0	68.0
Soybean meal, %	21.5	10.5
Wheat, %	5	5
DL-RSM, %	13
CaHPO4, %	0.5	0.4
Limestone, %	1.0	1.0
NaCl, %	0.3	0.3
Rice bran, %	1.5
Zeolite powder, %	1.2	0.8
Premix°, %	1.0	1.0
Calculated content#
DE, MJ/kg	13.56	13.23
CP, %	15.72	15.66
Ca, %	0.56	0.58
P, %	0.46	0.47
Digestible Lys, %	0.67	0.65
Digestible Met+Cys, %	0.46	0.48
Digestible Thr, %	0.47	0.46

DL-RSM, double-low rapeseed meal;

° provided per kg of diet: vitamin A, 6000 U; vitamin D₃ 1200 U; vitamin E, 20 U; vitamin K₃, 1.5 mg; vitamin B₁, 1.5 mg; vitamin B₂, 3 mg; vitamin B₆, 1.6 mg; pantothenic acid, 15 mg; nicotinic acid, 8 mg; manganese, 5 mg; iron, 84 mg; zinc, 56 mg; copper, 100 mg; iodine, 0.15 mg; cobalt, 0.15 mg; selenium, 0.15 mg.

# Calculated values expressed as dry matter.

DE, digestible energy; CP, crude protein; Ca, calcium; P, phosphorus; Lys, lysine; Met, methionine; Cys, cystine; Thr, threonine.

The feeding trial was carried out at the Zhejiang Xinxin Breeding Co., Ltd. in China. Pigs were provided with feed and water ad libitum, and individually weighed at the beginning and the end of the study. Feed intake was recorded daily for each pen. Average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were calculated from these data.

Sampling and biochemical analyses

Faeces were collected from each pen at three time points (06:00 h, 13:00 h and 20:00 h) on Days 35, 36 and 37. All faeces samples were freeze-dried (−20°C) and finely ground before analysis. At the end of the trial, 2 pigs (one male and one female) from each replicate were held in a supine position and blood samples were obtained by anterior vena cava puncture using heparinized and plain vacutainer tubes after 12-h fasting. The samples were then centrifuged at 2000 g for 15 min at 4°C, serum was stored at −80°C until hormone levels, immune and antioxidant parameters, and other biochemical indexes were measured.

Serum thyroxine (T₄), free thyroxine (FT₄), triiodothyronine (T₃) and free triiodothyronine (FT₃) were measured on a microplate reader (SpectraMax M5, Molecular Devices, Sunnyvale, CA, USA) using sandwich ELISA assay kits (ICN Pharmaceuticals, Orangeburg, NY, USA) according to the manufacturer’s instructions. The concentration of thyroid hormone level in serum was expressed as nanomole per liter (nmol/L). Levels of immunoglobins (IgA, IgG, IgM) and complements (C3, C4) were analyzed by indirect enzyme-linked immunosorbent assays (Tiemann et al., 2006), and were all expressed as gram per litre (g/L). The GSH-Px, superoxide dismutase (SOD), and malondialdehyde (MDA), were determined using the method of Lawrence and Burk (1976), Panckenko et al. (1975), and Placer et al., (1966), respectively. The total antioxidant capability (T-AOC) and urea nitrogen (UN) concentration was examined by assay kits purchased from Nanjing Jiancheng Institute of Bioengineering (Nanjing, Jiangsu, China) according to approved procedures. The total antioxidant capability (T-AOC) and activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) in serum were all expressed as units per milliliter (U/mL), and the concentration of malondialdehyde (MDA) was expressed as nanomole per milliliter (nmol/mL) in serum. Blood urea nitrogen (BUN) was expressed as millimole per liter (mmol/L) in serum. Levels of calcium (Ca) and phosphorus (P) in serum were analyzed spectrophotometrically (UV-2000, Unico Instruments Co. Ltd., Shanghai, China) using diagnostic kits obtained from the same institute in Nanjing. DL-RSM, E-DL-RSM, and faeces samples were ground to pass a 1-mm screen. Dry matter (DM), crude protein (CP), ether extract (EE), acid detergent fibre (ADF), crude fibre (CF) and ash were determined according to methods 925.09, 988.05, 920.39, 973.18, 978.10 and 942.05, respectively, of the AOAC (1990). Neutral detergent fibre (NDF) was analyzed by the method of Holst (1973). Quintuple samples were digested with a wet ash procedure (968.08; AOAC, 1990). Digests were analyzed for the concentration of total phosphorus (TP) by the colorimetric molybdovanadate method (T6 new century, Beijing Purkinje general instrument Co., Ltd., Beijing, China) and for the concentration of Ca by atomic absorption spectrophotometry (AA320CRT, Shanghai Precision Instruments Co., Ltd., Shanghai, China). To determine amino acids, samples were hydrolyzed with 6 M HCl at 110 for 24 h, and the amino acid composition of hydrolysates was analyzed by HPLC (Hitachi L-8900 Amino Acid Analyzer, Tokyo, Japan). The content of glucosinolate, erucic acid and tannin was determined by the palladium chloride (Thies, 1982), measuring iron pectmphotometric (Latta and Eskin, 1980), and Folin-Denis (Folin and Denis, 1912) methods, respectively.

Digestibility trial

The nutrient digestibility was determined by the endogenous marker method. After four weeks of the feeding experiment, the faeces samples in the four groups were collected each day for three days. We added 20 mL 10% of hydrochloric acid solution and a few drops of toluene to every 100 g faeces sample. This was mixed equally, and then immediately stored at 4°C at once. The content of nutrients and hydrochloric acid insoluble ash (AIA) in diets and feces samples were measured to calculate digestibility. Apparent digestibility (AD) of nutrients was calculated using the following formula: (1)

where

DAIA is the concentrations of indicator in diet

FAIA is the concentrations of indicator in feces

FN is the nutrient concentrations in feces

DN is the nutrient concentrations in diet

Statistical analysis

All data were subjected to one-way ANOVA using the SPSS 16.0 software (SPSS Inc., Chicago, IL, USA). Data are expressed as mean ±SEM. If significant differences were indicated at P=0.05, then the Duncan Multiple Range test was used to identify significant differences among the treatments.

Results and discussion

The chemical composition of DL-RSM and E-DL-RSM is shown in Table 1. As expected, extrusion had no negative effect on nutritive value of DL-RSM. There was no significant change in DM, CP, EE, CF Ash, the amino acids, Ca and P in E-DL-RSM, but the values of some nutritive parameters, CP (35.44%), Lys (2.13%), Met (0.57%), Arg (1.69%), Ile (1.27%) and Val (1.57%) in E-DL-RSM were lower than the values reported by Woyengo et al. (2010) and Seneviratne et al. (2010), which may be due to the different strain and processing condition of rapeseed meal. Glucosinolate, erucic acid and tannin were decreased by 6.35%, 13.49% and 20.16%, respectively, due to extrusion. In the current study, replacing 11% SBM with 13% DL-RSM had no negative effect on the ADG, ADFI and FCR of finishing pigs during the entire experimental period (Table 3), and the digestibility of CP, EE, Ash, CF and TP was also not significantly affected (P>0.05) (Table 4). These findings are in agreement with previous reports (Lee et al., 1983; Thacker and Qiao, 2002; Landero et al., 2012). Extrusion and adding exogenous enzymes could be effective ways to improve the nutritional quality and reduce the activity of anti-nutritional factors in feedstuffs (Bedford and Clasen, 1992; Choct, 1999; Friesen et al., 1993). However, in this study, extrusion and extrusion combined with multienzyme preparation in diets did not significantly increase the performance or nutrient digestibility in finishing pigs (P>0.05). Previous experiments often gave inconsistent results. The performance of pigs fed DL-RSM has been shown to be improved as result of extrusion (Froseth and Peters, 1981), and starch digestibility is increased (Bengala Freiere et al., 1991), but no beneficial effect was reported by Thacker and Qiao (2002). The reason for this variation may be due to the different content of anti-nutritional factors, meal processing and the substitute proportion. However, results from this study indicated that double-low rapeseed meal could be an alternative protein resource to soybean meal for finishing pigs.

Table 3 Effects of different treatment diets on the growth performance of finishing pigs.

	Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
IW, kg	62.70	62.12	62.50	62.77	2.23
FW, kg	86.60	85.93	85.96	87.40	4.04
ADG, g	797	794	782	821	69
ADFI, kg	2.22	2.13	2.15	2.24	0.63
FCR	2.79	2.68	2.77	2.72	0.21

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet. Data were not statistically significant (P>0.05).

IW, initial weight; FW, final weight; ADG, average daily gain; ADFI, average daily feed intake; FCR, feed conversion ratio. Values are expressed as individual data.

Table 4 Effects of different treatment diets on the apparent nutrient digestibility of finishing pigs.

Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
CP	78.30	76.91	77.21	78.36	1.70
EE	72.51	70.52	70.95	72.92	0.93
Ash	48.11	46.51	46.82	47.97	1.67
CF	46.79	45.85	44.40	47.08	1.30
Ca	56.00	53.72	56.50	58.33	2.27
P	46.00	43.39	44.08	46.08	1.42

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet. Data were not statistically significant (P>0.05).

CP, crude protein; EE, ether extract; CF, crude fibre; Ca, calcium; P, phosphorus. Values are expressed per pen.

There was no significant change in hormones, T3, T4, FT3, and FT4, secreted by pig thyroid gland in serum (P>0.05) with the different dietary treatments (Table 5). There were also no significant differences between the DL-RSM group and the E-DL-RSM group (P>0.05). It has been shown that degradation of glucosinolates, isothiocyanate and oxazolidine, can induce hypertrophy of liver, kidney and thyroid and cause iodine deficiency (Schöne et al., 1997; Tripathi et al., 2001). Iodine is necessary for the synthesis of the thyroid hormones, T4 and T3, which regulate energy metabolism. Schöne et al. (2001, 2002) found that 15% rapeseed meal in diet can cause reduced feed intake and reduced weight gain in pigs (live weight range 24 to 104 kg), while the weight of thyroid gland and liver increased and the serum T4 concentration decreased. The present study has shown that diets containing 13% of DL-RSM did not significantly reduce the serum T4 concentration, so thyroid gland function may be not impaired. This suggests that the higher weight of pigs used in the present experiment probably (approx. 62 kg) can support a high proportion of rapeseed meal. Therefore, replacement of 11% SBM by 13% DL-RSM is appropriate for pigs during the finishing phase of production, and offers economic benefits.

Table 5 Effects of different treatment diets on the serum thyroid hormone level of finishing pigs.

Items	Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
T3(nmol/L)	1.65	1.75	1.69	1.66	0.17
T4(nmol/L)	43.07	41.54	42.24	42.42	0.81
FT3(nmol/L)	0.13	0.14	0.14	0.13	0.01
FT4(nmol/L)	0.77	0.81	0.78	0.75	0.06

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet. Data were not statistically significant (P>0.05).

T3, triiodothyronine; T4, thyroxine; FT3, free triiodothyronine; FT4, free thyroxine.

Results showed that the levels of IgA, IgM, C3 and C4 in serum had not been significantly affected by different dietary treatments (P>0.05), while the level of IgG was decreased significantly by 6.62% (P<0.05) in the DL-RSM group and it returned to the level of control in E-DL-RSM + enzymes group (Table 6). So far, there has been little research examining the effects of rapeseed meal on immunoglobulin concentration in the serum of pigs. Xu et al. (2011) found that replacement of soybean meal by fermented rapeseed meal in the diet of duck could increase the level of IgG and IgM in serum; this differs from our results. The addition of rapeseed meal may have different effects on the immune system in different animals and the underlying mechanisms need to be studied further. Extrusion and adding multienzyme preparation can make IgG concentration return to the control level (Table 6) and such treatments could possibly cancel out the factors that induce changes in immunoglobulin concentration in pig serum.

Table 6 Effects of different treatment diets on the immunity of finishing pigs.

Items	Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
IgA, g/L	1.18	1.18	1.18	1.21	1.34×10-2
IgG, g/L	5.43^ab	5.07^c	5.21^bc	5.65^a	0.13
IgM, g/L	1.05	0.99	0.97	1.05	0.22
C3, g/L	0.65	0.65	0.65	0.67	1.30×10-2
C4, g/L	0.18	0.17	0.18	0.18	3.20×10-3

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet.

IgA, immunoglobulin A; IgG, immunoglobulin G; IgM, immunoglobulin M; C3, complement 3; C4, complement 4.

a—c Data in the same row with different letter mean significant difference (P<0.05), while with the same and no small letter superscripts mean no significant difference (P>0.05).

Little is known about the effects of DL-RSM on the antioxidant status in livestock. The present study has clearly shown that the T-AOC and enzyme activity of GSH-Px and SOD were not significantly affected (P>0.05) by different treatment diets (Table 7). But the concentration of MDA was significantly decreased (P<0.05) in the E-DL-RSM + enzymes group. Since the DL-RSM and E- DL-RSM diets did not change the oxidative state parameters in comparison with control (soybean meal), 13% RSM in the diet may not have a significant toxic or anti-nutritional effect such as to harm the antioxidant capability of finishing pigs. However, similar to immune parameters, whether extrusion and enzyme preparation are beneficial to the whole antioxidant system of pigs still needs further investigation.

Table 7 Effects of different treatment diets on serum antioxidant status of finishing pigs.

Items	Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
T-AOC, U/mL	3.54	3.62	3.67	3.76	0.50
GSH-Px, U/mL	513.61	518.14	524.19	535.12	49.16
SOD, U/mL	91.28	89.71	91.24	93.83	5.17
MDA, nmol/mL	3.62^a	3.35^a	3.32^a	2.79^b	0.25

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet.

T-AOC, total antioxidant capability; GSH-Px, glutathione peroxidase; SOD, superoxide dismutase; MDA, malondialdehyde.

a—b Data in the same row with different letter mean significant difference (P<0.05), while with the same and no small letter superscripts mean no significant difference (P>0.05).

Improving the utilization ratio of nitrogen in diets is an effective way to reduce the cost of protein resources. So, the decrease in urea nitrogen concentration in serum indicates that protein retention was increased in the body (Fukawa et al., 1982). It was reported that extruded SBM had an obvious tendency to improve nitrogen digestibility and retention in weaned pigs (Friesen et al., 1993; Sun et al., 2007). Adding non-starch polysaccharide enzymes in diets also significantly improved nitrogen retention in Japanese seabass (Lateolabrax japonicus) (Ai et al., 2007). In the present study, BUN was not influenced by the dietary treatments (Table 8) that suggests that extrusion and enzyme preparation can not improve the nitrogen utilization of pigs during the finishing phase of production on the condition that 11% soybean meal was replaced by 13% double-low rapeseed meal in the diet.

Table 8 Effects of different treatment diets on conventional biochemical index of finishing pigs.

Items	Diet°				SEM
	Control	DL-RSM	E-DL-RSM	E-DL-RSM+ enzymes
Ca, mmol/L	1.10	1.06	1.08	1.14	0.13
P, mmol/L	2.56	2.37	2.42	2.66	0.16
BUN, mmol/L	18.36	16.50	15.83	15.13	3.26

° Control diet, based on corn and soybean meal; DL-RSM (double-low rapeseed meal), used 13% double-low rapeseed meal instead of 11% soybean meal in the control diet; E-DL-RSM, used 13% extruded double-low rapeseed meal to replace 11% soybean meal; E-DL-RSM+ enzymes, contained 0.03% multienzymes preparation (cellulose enzyme 10,000 U/g, xylanase 6000 U/g, β-glucanase 5000 U/g, protease 12,000 U/g) on the basis of E-DL-RSM group diet.

Ca, calcium; P, phosphorus; BUN, blood urea nitrogen. Data were not statistically significant (P>0.05).

Conclusions

In summary, replacement of 11% soybean meal by 13% double-low rapeseed meal in finishing pig diets had no negative effects on growth performance, nutrient digestibility and biochemical indexes except IgG concentration in serum. Although extrusion and multienzyme preparation were beneficial to IgG concentration and can decrease MDA in the serum, adding DL-RSM supplements directly in the diet was still the best choice given the extra cost of extrusion and of enzyme preparation.

Acknowledgments:

this research was supported by the earmarked fund for the Modern Agro-Industry Technology Research System.