Effects of chromium-loaded chitosan nanoparticles on growth, carcass characteristics, pork quality, and lipid metabolism in finishing pigs

Livestock Science 161 (2014) 123–129

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Effects of chromium-loaded chitosan nanoparticles on growth, carcass characteristics, pork quality, and lipid metabolism in finishing pigs M.Q. Wang a,b,n, C. Wang a,b, Y.J. Du a,b, H. Li a,b, W.J. Tao a,b, S.S. Ye a,b, Y.D. He a,b, S.Y. Chen a,b a b

College of Animal Sciences, Zhejiang University, Hangzhou 310058, China Key Laboratory of Molecular Animal Nutrition, Ministry of Education, Hangzhou 310058, China

a r t i c l e i n f o

abstract

Article history: Received 19 April 2012 Received in revised form 5 November 2013 Accepted 31 December 2013

The study was conducted to evaluate the effects of chromium-loaded chitosan nanoparticles (Cr-CNP) on growth, carcass characteristics, pork quality, and lipid metabolism in finishing pigs. A total of 160 crossbred barrows with an average initial BW of 66.10 7 1.01 kg were randomly allotted to 4 dietary treatments, with 4 pens per treatments and 10 pigs per pen. Pigs were fed the basal diet supplemented with 0, 100, 200, or 400 μg/kg of Cr from Cr-CNP. All pigs were given free access to feed and water for 35 d. Two pigs from each pen were selected to collect serum samples and slaughtered to measure carcass characteristics and pork quality and collect adipose tissue samples. The results showed that gain to feed ratio of pigs fed supplemental Cr from Cr-CNP increased (P o 0.05) compared with those fed the control diet. Dietary Cr-CNP increased the carcass lean ratio (P o 0.01) and longissimus muscle area (P o 0.05), decreased carcass fat ratio (P o 0.001), and backfat thickness (P o 0.01) linearly and quadratically. The 24 h drip loss was decreased (P o0.01) linearly and quadratically, while 45 min pH value and Hunter L, a, b values in longissimus muscle were unaffected with the dietary supplementation of CrCNP. Supplemental Cr from Cr-CNP increased serum free fatty acids (linear and quadratic, P o 0.001), lipase activity (linear and quadratic, Po 0.01), and serum insulin-like growth factor I (quadratic, P o 0.01), while decreased serum insulin (linear, Po 0.001). Dietary supplementation of Cr-CNP decreased activities of fatty acid synthase (linear and quadratic, Po 0.01) and malate dehydrogenase (linear, P o 0.01), while increased the activity of hormone-sensitive lipase (linear and quadratic, P o 0.05) in subcutaneous adipose tissue. The present results indicated that dietary supplementation of Cr as Cr-CNP had beneficial effects on growth, carcass characteristics, and pork quality, and positively affected lipid catabolism in finishing pigs. & 2014 Elsevier B.V. All rights reserved.

Keywords: Chromium Chitosan nanoparticle Carcass characteristics Pork quality Lipid metabolism Pigs

1. Introduction Chromium has been considered an essential trace element for over 50 years, and it is considered to be n Corresponding author at: College of Animal Sciences, Zhejiang University, Hangzhou 310058, China. Tel.: þ 86 571 88982112; fax: þ86 571 88982650. E-mail address: [email protected] (M.Q. Wang).

1871-1413/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.livsci.2013.12.029

associated with various enzymes and hormones in human and animals, which plays an important role in carbohydrate, fat, and protein metabolism (Anderson, 1987; Mertz, 1993). A number of experiments have been conducted to study the effects of Cr from different chemical forms, such as chromium chloride (Mooney and Cromwell, 1997; Uyanik et al., 2002), chromium picolinate (CrPic; Kim et al., 2009, 2010; Lindemann et al., 1995; Page et al., 1993), chromium nicotinate (CrNic; Kegley et al., 1996),

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chromium propionate (CrProp; Jackson et al., 2009; Shelton et al., 2003), and chromium nanocomposite (CrNano; Wang and Xu, 2004; Zha et al., 2007a, 2007b) on growth performance, carcass characteristics, pork quality, reproduction, and tissue deposition in domestic animals. Page et al. (1993) first reported that supplementation of Cr could increase carcass leanness and decrease fat deposition in pigs, which was supported by Lindemann et al. (1995, 1997), Boleman et al. (1995), Mooney and Cromwell (1995, 1997), Wang et al. (2004, 2007), Jackson et al. (2009), and Sales and Jancik (2011). However, Matthews et al. (2001) reported no responses in carcass leanness to supplemental Cr. The inconsistent response of the experiments may result from different dietary levels, pigs0 Cr status, or absorption rate of different Cr sources (Dunshea et al., 2011; White et al., 1993). The factors controlling absorption of Cr may include levels, source, and status in the gastrointestinal tract. It is well known that organic sources of Cr have a greater bioavailability than inorganic sources (NRC, 1997). Previous research indicated that Cr from nanocomposite of CrCl3 (Wang and Xu, 2004; Wang et al., 2007) was shown to produce beneficial effects on carcass characteristics, pork quality, and individual skeletal muscle weight, with an approximate 2 to 3 fold greater tissue Cr deposition in selected muscle and organs compared to the control group, which implicated greater absorption rate and bioavailability in finishing pigs. And, a substantially greater absorption and uptake of Cr from CrNano was confirmed in Caco-2 cell lines (Zha et al., 2008). Chitosan, one of the nontoxic and biodegradable carbohydrate polymers, is prepared from chitin by treatment with alkali. It is applied in various fields, including biotechnology (Hirano, 1999), pharmaceuticals (Kathryn et al., 1999), waste water treatment (Jha et al., 1988), and food science (Wang et al., 2007). Chitosan nanoparticles have been synthesized and mainly used as drug carrier as reported in previous studies (De Campos et al., 2001; Xu and Du, 2003). A new form of Cr composite [chromium (III)-loaded chitosan nanoparticles, Cr-CNP] was developed, and was patented in China (Wang et al., 2012). The objective of the present study was to evaluate the effects of Cr-CNP supplementation on growth, carcass characteristics, pork quality, and lipid metabolism in finishing pigs. 2. Materials and methods 2.1. Materials The chitosan used in the study was provided by a commercial company (Zhejiang Golden-Shell Biochemical Co. Ltd.; Zhejiang, China). The degree of deacetylation and molecular mass were about 90% and 150 kDa, respectively, as determined by elemental analysis and the viscometric method. The Cr-CNP (average size, approximate 90 nm) was constructed according to the method described by Wang et al. (2012). Briefly, chitosan was dissolved into 0.5% (v/v) acetic acid to obtain a 1% (w/v) chitosan solution and modulate its pH to 3.5 with 0.5% (v/v) acetic acid. The chitosan solution was stirred at room temperature for 1 h. Under stirring, the precipitate was added into 200 mg/L

CrCl3 solution to obtain a suspension that the ratio of chitosan to CrCl3 was 47:3. The pH of the mixture was modulated to 6.5 and stirred for 5 h. Subsequently, the precipitate, centrifuged 12,000  g for 15 min at room temperature, was purified with water to obtain Cr-CNP. 2.2. Animals and experimental design The protocol of this study was approved by the Institution Animal Care and Use Committee at Zhejiang University. And, the animal trial was conducted in accordance with the National Institutes of Health guidelines for the care and use of experimental animals. A total of 160 crossbred barrows (Duroc  Landrace  Yorkshire) with an average body weight of 66.107 1.01 kg were selected (Anji Zhengxin Breeding Farm, Zhejiang,China). The pigs were blocked by initial BW and assigned to pens with 10 pigs per pen. Pens were randomly assigned within block to 4 dietary treatments with 4 replicates per treatment. The pigs were housed in 3.25  5.25 m pens with concrete floors. Feed was provided ad libitum and water was provided by nipple waterers. The duration of the feeding trial was 35 d. The ADG, ADFI, and G:F were determined throughout the experimental period. Pigs received the basal diet (Table 1) supplemented with 0, 100, 200, or 400 μg/kg of Cr from CNP-Cr. The basal diet, which consisted primarily of corn, soybean meal, and wheat bran, was supplemented with minerals and vitamins to meet or exceed NRC (1998) requirement estimates. To minimize potential variation that can occur with multiple diet mixings, a single batch of basal diet was prepared. Approximately the first 5 and Table 1 Ingredient inclusion and chemical composition of basal diet. Item

Content

Ingredient (g/kg) Corn Soybean meal Wheat bran Alfalfa meal Rapeseed meal Limestone Monocalcium phosphate Salt Mineral and vitamin premixa

610.0 210.0 70.0 50.0 20.0 14.0 13.0 3.0 10.0

Chemical compositionb DE (MJ/kg) CP (g/kg) Crude fat (g/kg) Ca (g/kg) P (g/kg) Lys (g/kg) Met (g/kg)

13.2 179.8 27.9 7.8 6.0 10.5 4.5

a Provided per kilogram of diet: Cu, 15 mg (as CuSO4  5H2O); Zn, 105 mg (as ZnSO4.7H2O); Fe, 135 mg (as FeSO4  H2O); Mn, 40 mg (as MnSO4  5H2O); Se, 0.15 mg (as Na2SeO3  5H2O); I, 0.3 mg (as KI); vitamin A, 6200 IU; vitamin D3, 700 IU; vitamin E, 88 IU; vitamin K (as menadione sodium bisulfite complex), 4.4 mg; vitamin B2, 8.8 mg; Dpantothenic acid, 24.2 mg; niacin, 33 mg; and choline chloride, 330 mg (as 50% choline chloride premix). b Analyzed values, except for DE, which was computed from data of the ingredient energy values provided by Feed Database in China (2010).

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last 5% of the basal diet removed from the mixer was excluded in manufacturing the specific treatment diets. 2.3. Blood sampling On 35 d of the experiment, 8 pigs closest to the mean pen weight from each treatment (2 pigs per pen) were selected, and blood samples were obtained by anterior vena cava puncture using plain vacutainer tubes after 12-h fasting. The samples were then centrifuged at 1500  g for 15 min at 4 1C. Serum from each sample was collected and stored at  70 1C until needed for analysis. 2.4. Carcass measurement After blood sampling, pigs selected for blood sampling (2 pigs per pen) were transported to a meat factory (Anji, Zhejiang, China) and slaughtered by exsanguination after electrical stunning. At slaughter, the head, hair, and viscera were removed from carcass and the right and left halves of the carcasses were separated. The left carcass was dissected by separating bone, muscle, fat, and skin. Each component was weighed respectively. Measurements of backfat depth and longissmus muscle (LM) area were made from the carcass tracings taken at the 10th rib. Carcass dressing percentage was calculated by the following formula: hot carcass weight divided by final live weight  100.

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China). The assay used human INS and antibodies against human INS as the standard. Minimum detectability of INS was 0.1 μIU/mL, and the intraassay CV was 10%. Serum growth hormone (GH) was determined using a 125I RIA kit (National Hormone and Peptide Program HARBDE-UCLA Medical Center, Los Angeles, ca., US). The minimum detectable concentration of GH was 0.1 μg/L, and the intraassay CV was 10%. Serum insulin-like growth factor I (IGF-I) was analyzed using a commercially available 125I RIA kit (INCSTAR Co., Stillwater, MN, US). In the assay, recombinant human IGF-I and mouse antiIGF-I monoclonal antibody were used as the standard. Recovery rate ranged from 92.3 to 110.0%. The intraassay CV was 10%, and the minimum detectable concentration of IGF-I was 0.1 ng/mL. 2.7. Assay of enzymatic activities in subcutaneous adipose tissue After pigs were slaughtered, subcutaneous adipose tissues from 10th rib were collected for measurements of enzymatic activities. The activities of fatty acid synthase (FAS), hormone-sensitive lipase (HSL), malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G-6PDH), and isocitrate dehydrogenase (ICDH) were analyzed using the ELISA kits (Xiamen Huijia Biochemical Reagent Co., Xiamen, China) with the recommended procedures. 2.8. Statistical analysis

2.5. Pork quality evaluation Approximately 45 min after slaughter, pH were measured in the LM between the 10th and 11th ribs. The pH of LM was determined using a hand-held pH meter (Model 2000; VWR Scientific Products Co., Aurora, CO, US) fitted with a spear-tipped electrode (Cole-Parmer Instrument Co., Vernon Hills, IL, US). Two 2.5 cm (thickness) chops were collected from the 9th and 10th ribs. Immediately after collection of the chops, Hunter L (light index), a (red index) and, b (yellow index) value were obtained from 3 orientation on the 10th rib chop using a spectrophotometer (Hunter Lab ColorFlex Spectrophotometer; Hunter Associates Laboratory, Inc., Reston, VA, US). The drip loss was determined according to the method reported by Jiang et al. (2003). The 9th rib chop was used for determining 24 h drip loss using a suspension method. The chops were weighed and then suspended using a hook and line; while suspended chop was placed in a 10.8  21.6 cm Whirl-Pak sample bag and sealed. Chops were stored at 2 1C for 24 h then reweighed to determine drip loss.

The data were analyzed using GLM of SAS (SAS Inst. Inc., Cary, NC). Contrasts were used to compare the control group vs. the Cr-CNP treated group. Orthogonal polynomials were used to determine the linear and quadratic effects of the dietary Cr-CNP supplementation. Each pen was considered as an experimental unit. The alpha level used for determination of statistical significance was 0.05. 3. Results 3.1. Growth performance Effects of Cr-CNP on growth performance are shown in Table 2. The G:F of pigs fed supplemental 100, 200, 400 μg/kg of Cr from Cr-CNP was increased (3.47, 3.73, and 3.47%, respectively; Po0.05) compared with those fed the control diet, which resulted in both linear and quadratic increases in G:F as Cr-CNP supplementation increased (Po0.05). The ADG and ADFI were not affected by dietary treatments. 3.2. Carcass traits and pork quality

2.6. Analysis of serum metabolites The concentrations of serum triglyceride (TG), cholesterol (CHL), high density lipoprotein (HDL), free fatty acids (FFA), and activity of lipase (LIP) were determined by corresponding commercial kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) with the recommended procedures. The concentration of insulin (INS) was analyzed using a commercially available 125I RIA kit (Beijing North Institute of Biological Technology, Beijing,

Effects of Cr-CNP on carcass characteristics of sampled pigs are presented in Table 3. Compared with the control group, supplemental 100, 200, 400 μg/kg of Cr from Cr-CNP increased the carcass lean ratio (3.19, 3.71, and 3.71%, respectively; linear and quadratic, Po0.01), and decreased carcass fat ratio (22.48, 25.77, and 39.77%, respectively; linear and quadratic, Po0.001) and backfat thickness (5.21, 8.06, and 7.58%, respectively; linear and quadratic P o0.01). The LM area was also increased (13.50,

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Table 2 Effect of Cr-loaded chitosan nanoparticles (Cr-CNP) on growth performance in finishing pigs.a Item

Initial weight (kg) Final weight (kg) ADG (kg) ADFI (kg) Gain:feed (kg/kg)

SEMb

Cr as Cr-CNP (μg/kg) 0

100

200

400

65.65 92.88 0.778 2.91 0.267

65.88 93.45 0.788 2.85 0.276

66.45 93.65 0.777 2.80 0.278

67.05 94.13 0.774 2.80 0.276

1.26 1.63 0.015 0.05 0.027

P-valuec Control vs. Cr-CNP

Linear

Quadratic

0.753 0.814 0.503 0.761 0.011

0.435 0.295 0.666 0.447 0.015

0.876 0.891 0.362 0.753 0.014

a

Each least squares mean represents 4 pens of 10 pigs/pen. Standard error of means. c P-values are for single degree of freedom contrasts. Control vs. Cr-CNP represents the contrast between pigs fed 0 vs. 100, 200, or 400 μg/kg of Cr from Cr-CNP. b

Table 3 Effects of Cr-loaded chitosan nanoparticles (Cr-CNP) on carcass characteristics and pork quality in finishing pigs.a Item

Dressing percentage (%) Lean ratio (%) Fat ratio (%) Bone ratio (%) Skin ratio (%) Longissmus muscle area (cm2) Backfat thickness (cm) 45 min pH value 24 h drip loss (%) Hunter (L) Hunter (a) Hunter (b)

SEMb

Cr as Cr-CNP, μg/kg 0

100

200

400

71.20 64.17 13.39 10.03 7.60 41.99 2.11 6.03 7.23 37.05 11.01 7.10

71.95 66.22 10.38 10.76 7.39 47.66 2.00 6.14 6.44 37.17 11.29 7.014

71.99 66.55 9.94 10.26 7.45 48.62 1.94 6.25 6.24 35.68 10.79 6.67

71.90 66.21 9.58 10.73 7.81 46.80 1.95 6.06 6.39 36.39 10.67 7.08

0.45 0.43 0.46 0.38 0.37 1.32 0.02 0.09 0.19 0.55 0.38 0.53

P-valuec Control vs. Cr-CNP

Linear

Quadratic

0.558 0.002 o0.001 0.237 0.724 0.007 o0.001 0.306 0.003 0.327 0.679 0.931

0.371 0.008 o 0.001 0.478 0.453 0.043 o 0.001 0.907 0.008 0.846 0.372 0.961

0.300 0.003 0.001 0.120 0.483 0.004 0.003 0.068 0.006 0.459 0.824 0.576

a

Each least squares mean represents 4 pens of 2 pigs/pen. Standard error of means. c P-values are for single degree of freedom contrasts. Control vs. Cr-CNP represents the contrast between pigs fed 0 vs. 100, 200, or 400 μg/kg of Cr from Cr-CNP. b

15.79, and 11.46%, respectively; linear and quadratic, P o0.05) by dietary supplementation of the basal diet with 100, 200, 400 μg/kg of Cr from Cr-CNP. Compared with the control group, supplemental 100, 200, 400 μg/kg of Cr from Cr-CNP decreased 24 h drip loss (10.93, 13.69, and 11.62%, respectively) linearly and quadratically (P o0.01). The 45 min pH value and Hunter L, a b, values in longissimus muscle were unaffected by the dietary supplementation of Cr-CNP.

3.3. Serum metabolites The effects of Cr-CNP on serum parameters were presented in Table 4. Supplementation with 100, 200, 400 μg/kg of Cr from Cr-CNP increased serum FFA (66.67, 146.67, and 120.00%, respectively; linear and quadratic, P o0.001) and LIP activity (23.52, 27.69, and 24.33%, respectively; linear and quadratic, P o0.01). No difference was found in serum TG, CHL, and HDL between control and Cr-CNP treated groups. Supplementation with 100, 200, 400 μg/kg of Cr from Cr-CNP linearly decreased serum INS (14.85, 23.09, and 30.80%, respectively; Po0.001) and increased serum IGF-I (45.32, 25.63, and 19.76%,

respectively) quadratically (P o0.01), while serum GH was not affected with the supplementation of Cr-CNP. 3.4. Enzymatic activities in subcutaneous adipose tissue The effects of Cr-CNP on enzymatic activities in adipose tissues was presented in Table 5. Dietary supplementation with 100, 200, 400 μg/kg of Cr from Cr-CNP decreased the activity of FAS (30.19, 22.66, and 21.97%, respectively; linear and quadratic, Po0.01) and increased the activity of HSL (13.53, 17.65, and 11.76%, respectively; linear and quadratic, Po0.05) in subcutaneous adipose tissue. The activity of MDH linearly decreased (1.10, 8.60, and 7.07% for 100, 200, 400 μg Cr/kg, respectively; Po0.01), while the activities of G-6-PDH and ICDH in subcutaneous adipose tissue were unaffected by the supplementation of Cr-CNP. 4. Discussion Previous experiments have demonstrated inconsistent results on the growth rate and feed to gain ratio in pigs fed diets supplemented with Cr. Improvements in growth rate of swine as a result of supplementing diets with 200 to 500 μg Cr/kg as CrPic or 500 μg to 5 mg Cr/kg as CrCl3 were

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Table 4 Effects of Cr-loaded chitosan nanoparticles (Cr-CNP) on serum metabolites in finishing pigs.a Item

TG (mmol/L) CHL (mmol/L) FFA (mmol/L) HDL (mmol/L) LIP (U/L) INS (μIU/ml) GH (μg/L) IGF–I (ng/ml)

SEMb

Cr as Cr-CNP, μg/kg 0

100

200

400

0.33 2.23 0.15 0.79 14.88 15.42 9.65 164.2

0.37 2.34 0.25 0.91 18.38 13.13 9.46 238.7

0.36 2.34 0.37 0.86 19.00 11.86 9.30 206.3

0.34 2.28 0.33 0.87 18.50 10.67 9.82 196.79

0.02 0.07 0.02 0.04 0.69 0.61 0.53 11.9

P-valuec Control vs. Cr-CNP

Linear

Quadratic

0.320 0.590 o0.001 0.173 0.001 o0.001 0.425 0.002

0.893 0.774 o 0.001 0.343 0.003 o 0.001 0.736 0.438

0.089 0.200 o 0.001 0.151 0.002 0.078 0.651 0.004

a TG ¼triglyceride, CHL¼ cholesterol, FFA ¼free fatty acids, HDL ¼high density lipoprotein, LIP ¼lipase, INS ¼insulin, GH¼ growth hormone, and IGFI ¼insulin-like growth factor I. Each least square mean represents 4 pens of 2 pigs/pen. b Standard error of means. c P-values are for single degree of freedom contrasts. Control vs. Cr-CNP represents the contrast between pigs fed 0 vs. 100, 200, or 400 μg/kg of Cr from Cr-CNP.

Table 5 Effects of Cr-loaded chitosan nanoparticles (Cr-CNP) on enzymatic activities in adipose tissues.a Item

FAS (mIU/L) HSL (U/L) MDH (U/L) G-6-PDH (U/mL) ICDH (U/L)

SEMb

Cr as Cr-CNP, μg/kg 0

100

200

400

113.26 1.70 73.74 24.84 35.66

79.07 1.93 72.92 25.88 35.88

87.60 2.00 67.40 26.26 36.71

88.38 1.90 68.53 25.48 32.64

3.27 0.05 1.42 1.02 1.20

P-valuec Control vs. Cr-CNP

Linear

Quadratic

o 0.001 0.002 0.007 0.784 0.752

0.007 0.025 0.002 0.739 0.290

o 0.001 0.001 0.344 0.336 0.453

a FAS ¼fatty acid synthase, HSL¼ hormone-sensitive lipase, MDH¼ malate dehydrogenase, G-6-PDH ¼ glucose-6-phosphate dehydrogenase, and ICDH¼ isocitrate dehydrogenase. Each least square mean represents 4 pens of 2 pigs/pen. b Standard error of means. c P-values are for single degree of freedom contrasts. Control vs. Cr-CNP represents the contrast between pigs fed 0 vs. 100, 200, or 400 μg/kg of Cr from Cr-CNP.

reported in 11 out of 31 studies, and feed efficiency was improved by Cr supplementation of diets in 8 out of 31 studies (NRC, 1997). Page et al. (1993) first reported an increase in growth rate with the supplementation of CrPic, however, the increase in growth rate was not observed in subsequent experiments and no change in feed efficiency was detected. Lindemann et al. (1995) observed no change in growth rates but found an improvement in the feed: gain with the addition of Cr in the form of CrPic. Amoikon et al. (1995) and Boleman et al. (1995) reported that CrPic had no effect on either growth rate or feed efficiency in pigs. Shelton et al. (2003) reported that overall growth performance was not affected by addition of Cr in the form of CrPic or CrProp. The effect of Cr-CNP on growth performance reported here is partly consistent with the previous study of CrNano in finishing pigs, in which no change in growth rate but an improvement in feed efficiency was observed with the supplementation of CrNano (Wang and Xu, 2004; Wang et al., 2007). Therefore, no definite conclusion on the effect of Cr on growth performance can be drawn from those studies at the moment, and the current result of Cr-CNP on growth also remains to be confirmed. Dietary supplementation of Cr with various forms of Cr complex has been explored extensively to improve carcass characteristic by reducing fat deposition or increasing

carcass lean percentage. Page et al. (1993), Lindemann et al. (1995), Mooney and Cromwell (1995), Lindemann (1999), and Jackson et al. (2009) reported that Cr exhibited beneficial effect on carcass characteristics in finishing pigs. Chromium nanocomposite, which has higher surface area and smaller size, has been reported to exhibit high bioavailability and has attracted more attention. In the present study, dietary supplementation of Cr-CNP increased carcass lean percentage and LM area, decreased carcass fat percentage, and reduced backfat thickness, which is consistent with the reports on CrNano (Wang and Xu, 2004; Wang et al., 2007). The size of nanocomposite of CrCl3 ranges from 40 to 70 nm. The striking effect of Cr nanocomposite on carcass traits may have partially contributed to the increased absorption of Cr because of the smaller size, microparticles or nanoparticles. Nanocomposite has been proven to exhibit a high rate of absorption in the gastrointestinal tract (Desai et al., 1996; Hussain et al., 2001). The efficiency of uptake of 100 nm size particles by the intestinal tissues was 15- to 250-fold greater compared to larger size microparticles (Desai et al., 1996), and considerably greater uptake of small diameter microparticles and size dependency of uptake were confirmed in Caco-2 cell lines (Desai et al., 1997). There is limited research on the effect of Cr supplementation on pork quality. In the present study, dietary

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Cr-CNP decreased 24 h drip loss, while no effect on 45 min pH value and Hunter L, a, b values on LM was observed, which is consistent with the previous results with CrNano in finishing pigs. O0 Quinn et al. (1998) reported decreased drip loss in gilts fed diets with supplemental CrPic. Matthews et al. (2003) indicated a decrease in drip loss in chops from pigs fed CrProp. However, Boleman et al. (1995) reported no effect on drip loss when CrPic was added to swine diets. O0 Quinn et al. (1998) reported a decreased visual color score of chop from barrows and gilts and an increased Hunter a to b ratio in barrows when CrNic was supplemented in the diet. In the present study, serum FFA concentration and LIP activity were linearly increased with the supplementation of Cr from Cr-CNP, which was in agreement with the previous reports where Cr was supplemented as CrNano (Wang et al., 2007). Serum FFA is mainly generated by the hydrolysis of TG in adipose tissues, and its concentration is an important criterion related to degradation of lipid (Mersmann and MacNeil, 1985). The increased activity of LIP could inhibit lipid accumulation by inhibiting lipogenesis (Schroeder-Gloeckler et al., 2007). These results indicated that supplemental Cr-CNP could enhance degradation of lipid and reduce lipid accumulation. However, no effects of dietary supplementation of Cr-CNP on HDL, TG, and CHL concentration in serum were observed, which was partially consistent with Shelton et al. (2003) who used CrProp and Wang et al. (2007) who used CrNano. The decreases in concentrations of insulin in serum in the present study are consistent with the studies conducted with Cr from CrPic (Amoikon et al., 1995; Evans and Bowman, 1992; Lindemann et al., 1995; Page et al., 1993) and Cr from CrNano (Wang et al., 2007). It has been reported that Cr is able to increase the rate of insulin internalization and uptake of glucose into rat skeletal muscle cells (Evans and Bowman, 1992). Thus, an increase in insulin internalization would be consistent with the observed reduction in circulating concentrations of insulin (Amoikon et al., 1995). The result of increased IGF-I concentration in serum was in agreement with the studies conducted by Wang et al. (2007) with CrNano and Xi et al. (2001) with CrPic. The elevated IGF-I level measured in pigs fed the Cr-CNP supplemented diets may have played a role in the protein and fat metabolism changes because IGF-I mediates the effects of GH on protein metabolism. The lack of any effect of Cr-CNP on serum GH, however, indicates that the effect on IGF-I may have been independent of GH, though a single blood sample may not be adequate to assess treatment effects on GH because of the pulsatile nature of GH release in most mammals (Barb et al., 2002). In our previous study, serum IGF-I was increased and GH was not influenced by CrNano (Wang et al., 2007). The GH pulsatile secretion and pituitary GH mRNA expression in pigs fed 200 μg/kg of CrNano was further investigated (Wang et al., 2009). The results indicated that supplemental CrNano increased serum GH (mean level, lowest value, peak value, and peak duration), and pituitary mRNA expression of GH was also improved. The effect of Cr-CNP on GH pulsatile secretion and pituitary GH mRNA expression remains to be investigated further.

The majority of lipid in the body is derived from de novo fatty acids, which are mostly synthesized in adipose tissues (Bauman, 1976; O0 Hea and Leveille, 1969). In the current study, Cr-CNP supplementation reduced FAS activity and increased HSL activity linearly and quadratically in adipose tissues. The activity of FAS in adipose tissues was positively correlated with the weight of carcass fat (Xiong et al., 2001), and is considered as a key enzyme in fatty acid mobilization. The elevated activity of HSL could depress the accumulation of triglyceride in adipose cells (Sztalryd et al., 1995; Thompson et al., 1993). Moreover, the activity of MDH in present study was linearly decreased by supplemental Cr-CNP. The activity of MDH was positively correlated with the level of NADPH, which directly stimulates fat synthesis. The decreased activity of MDH may partially result in decreased fat deposition as lower carcass fat percentage and backfat thickness were observed with Cr-CNP supplementation in the present study. 5. Conclusion The present results indicated that dietary supplementation of Cr as Cr-CNP had beneficial effects on growth, carcass characteristics, and pork quality. In addition, the dietary Cr supplementation positively affected lipid catabolism in finishing pigs. Conflict of interest The submitted manuscript has no conflict of interest.

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