RESEARCH ARTICLE

Effects of dietary energy and crude protein levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs

Lin Hu Fang1https://orcid.org/0000-0002-3617-7583, Ying Hai Jin2https://orcid.org/0000-0002-6925-3183, Sung Ho Do1https://orcid.org/0000-0002-5465-8292, Jin Su Hong1https://orcid.org/0000-0002-3401-3024, Byung Ock Kim1https://orcid.org/0000-0001-8952-617X, Tae Hee Han1https://orcid.org/0000-0001-5950-7103, Yoo Yong Kim1,*https://orcid.org/0000-0001-8121-3291
Author Information & Copyright
1School of Agricultural Biotechnology, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
2Department of Animal Science, Yanbian University, Yan Ji, Ji Lin 133000, China
*Corresponding author: Yoo Yong Kim, School of Agricultural Biotechnology, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea. Tel: +82-2-880-4801, E-mail: yooykim@snu.ac.kr

© Copyright 2019 Korean Society of Animal Science and Technology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: May 14, 2019 ; Revised: Jun 11, 2019 ; Accepted: Jun 11, 2019

Published Online: Jul 31, 2019

Abstract

This experiment was conducted to evaluate the effect of dietary energy and crude protein (CP) levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs. A total of 180 crossbred pigs ([Yorkshire × Landrace] × Duroc) with an average body weight of 30.96 ± 3.068 kg were used for a 12-week feeding trial. Experimental pigs were allotted to a 2 × 3 factorial arrangement using a randomized complete block (RCB) design. The first factor was two levels of dietary metabolizable energy (ME) density (13.40 MJ/kg or 13.82 MJ/kg), and the second factor was three dietary CP levels based on subdivision of growing-finishing phases (high: 18%/16.3%/16.3%/13.2% middle: 17%/15.3%/15.3%/12.2% and low: 16%/14.3%/14.3%/11.2%). Average daily gain (ADG) and gain-feed ratio (G:F ratio) decreased as dietary CP level was decreased linearly (linear, p < 0.05; p < 0.05, respectively) in the early growing period, and G:F ration also decreased as dietary CP level was decreased linearly (linearly, p < 0.05) over the whole growing phase. Over the entire experimental period, G:F ratio decreased as dietary ME level decreased (p = 0.01). Blood urea nitrogen (BUN) concentration was increased as dietary energy level decreased in growing period (p < 0.01). During finishing period, total protein concentration was decreased by lower dietary energy level (p < 0.05). In this study, there were no significant differences in proximate factors, physiochemical properties, muscle TBARS assay results, pH changes, or color of pork by dietary treatments. However, saturated fatty acid (SFA) increased (p < 0.01) and polyunsaturated fatty acid (PUFA) decreased (p < 0.05) when ME was decreased by 0.42 MJ/kg in growing-finishing pig diets. In addition, monounsaturated fatty acid (MUFA) tended to increase when CP level was decreased in growing-finishing pig diets (p = 0.06). A growing-finishing diet of 13.82 MJ/kg diet of ME with the high CP level can improve growth performance and show better fatty acids composition of pork.

Keywords: Energy; Crude protein; Growth performance; Blood profiles; Carcass traits; Growing-finishing pigs

Background

Supplying adequate nutrients has been noted as the most important factor in pig production in the swine industry. Several studies have reported that insufficient nutrients can limit the growth potential of animals, while excessive nutrients can increase economic profitability but cause environmental pollution [13]. Nieto et al. [4] demonstrated that growth was based on the deposition of proteins and lipids in pigs. Therefore, dietary energy and crude protein (CP) levels play a major role in growth performance.

Nutrient requirements defined by the NRC were revised from 1998 to 2012 [5,6], especially protein. NRC 2012 recommends a lower CP level (CP calculated from N by multiplying by 100/16 or 6.25) than NRC 1998 in growing-finishing pigs (NRC 1998: 18%–13.2%; NRC 2012: 15.7%–10.4%).

Insufficient nutrients or excessive nutrients may reduce growth production in swine [710]. Pigs fed a low-energy diet had decreased total energy intake and growth performance [1113] while excessive intake of CP increased N excretion [79]. Using low-CP diets can reduce feed costs, N excretion, and plasma urea N in swine [14,15].

Whittemore [16] showed that the pigs had the highest weight gain in the growing period, and fat deposition was greater than protein deposition in the finishing period. The most important factor to maximize muscle development in growing pigs is to provide optimal protein and amino acid levels [17]. However, finishing feeds need to be formulated keeping fat deposition in mind, as this can affect carcass fatness and pork quality [18].

This experiment was conducted to evaluate the effects of subdivision of the growing-finishing phases with different dietary protein levels and different dietary energy densities on growth performance, blood profiles, and pork quality.

Materials and Method

Experimental animals and management

All experimental procedures involving animals were conducted in accordance with the Animal Experimental Guidelines provided by the Seoul National University Institutional Animal Care and Use Committee (SNUIACUC; SNU-160819-9). A total of 180 crossbred pigs ([Yorkshire × Landrace] × Duroc) with an average body weight (BW) of 30.96 ± 3.068 kg were used for a 12-week feeding trial. Pigs were reared at the Seoul National University experimental farm. Three male pigs and three female pigs were assigned to each pen of a growing facility based on BW, and pigs in each pen were maintained until the end of experiment. Pigs were randomly allotted to their respective treatments by an experimental animal allotment program [19]. Pigs were reared in growing-finishing (2.60 × 2.84 m) facilities for 12 weeks. Feed and water were provided ad libitum during the entire experimental period by a 6-hole stainless feeder and two nipples installed in each pen.

Experimental design and diet

Experimental pigs were allotted to a 2 × 3 factorial arrangement in randomized complete block (RCB) design. The first factor was two levels of dietary metabolizable energy (ME) density (13.40 MJ/kg or 13.82 MJ/kg) and the second factor was three dietary CP levels based on subdivision of growing-finishing phases (high: 18%/16.3%/16.3%/13.2% middle: 17%/15.3%/15.3%/12.2% and low: 16%/14.3%/14.3%/11.2%).

Experimental diets were formulated for four phases: the early growing phase (0–3 weeks), the late growing phase (4–6 weeks), the early finishing phase (7–9 weeks), and the late finishing phase (10–12 weeks). All nutrients in the experimental diets except ME and CP were met or exceeded the nutrient requirements of the NRC [5]. Formula and chemical compositions of the experimental diets are provided in Tables 1, 2, 3, and 4.

Table 1. Formula and chemical compositions of diets in early growing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg
CP (%) High Middle Low High Middle Low
Total 100.00 100.00 100.00 100.00 100.00 100.00
Ingredient (%)
 Corn 66.55 69.27 71.85 63.53 66.59 69.60
 Soybean meal 23.10 20.30 17.53 23.50 20.74 18.02
 Wheat bran 3.99 4.01 4.02 3.99 3.96 3.98
 Palm kernel meal 3.04 3.05 3.04 3.07 3.03 3.04
 Tallow 1.18 1.11 1.05 3.50 3.44 3.37
 Mono-dicalcium phosphate 2.50 2.52 2.56 2.50 2.55 2.55
 Limestone 0.31 0.30 0.29 0.30 0.30 0.31
 L-Lysine-HCl (78%) 0.03 0.12 0.21 0.02 0.11 0.20
 DL-Methionine (99%) 0.01 0.02 0.03 0.01 0.02 0.03
 Vit. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Min. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Salt 0.30 0.30 0.30 0.30 0.30 0.30
Chemical composition
 Metabolizable energy (MJ/kg) 13.40 13.40 13.40 13.82 13.82 13.82
 Crude protein (%) 16.30 15.30 14.30 16.30 15.30 14.30
 Total lysine (%) 0.95 0.95 0.95 0.95 0.95 0.95
 Total methionine (%) 0.27 0.27 0.27 0.27 0.27 0.27
 Calcium (%) 0.66 0.66 0.66 0.66 0.66 0.66
 Total phosphorus (%) 0.56 0.56 0.56 0.56 0.56 0.56

1) Provided per kg of diet. Vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D3, 1,800 IU; vitamin E, 60 IU; vitamin K3, 2 mg; thiamine, 2.00 mg; riboflavin, 7.0 mg; pantothenic acid, 25 mg; niacin, 27 mg; pyridoxine, 3 mg; d-biotin, 0.2 mg; folic acid, 1 mg; vitamin B12, 0.03 mg.

2) Provided per kg of diet. Minerals per kg of complete diet: Se, 0.3 mg; I, 1 mg; Mn, 51.6 mg; Cu, 105 mg; Fe, 150 mg; Zn, 72 mg; Co, 0.5 mg.

3) Calculated value.

CP, crude protein; ME, metabolizable energy.

Download Excel Table
Table 2. Formula and chemical compositions of the diets of late growing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg
CP (%) High Middle Low High Middle Low
Total 100.00 100.00 100.00 100.00 100.00 100.00
Ingredient (%)
 Corn 66.09 68.86 71.62 63.37 66.11 68.92
 Soybean meal 22.74 20.00 17.24 23.17 20.42 17.63
 Wheat bran 3.97 3.99 4.03 4.00 4.00 3.98
 Palm kernel meal 3.11 2.99 2.89 3.06 3.01 2.95
 Tallow 0.83 0.76 0.69 3.15 3.08 3.00
 Mono-dicalcium phosphate 2.30 2.35 2.39 2.32 2.35 2.38
 Limestone 0.24 0.23 0.22 0.22 0.22 0.22
 L-Lysine-HCl (78%) 0.19 0.28 0.37 0.18 0.27 0.37
 DL-Methionine (99%) 0.03 0.04 0.05 0.03 0.04 0.05
 Vit. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Min. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Salt 0.30 0.30 0.30 0.30 0.30 0.30
Chemical composition
 Metabolizable energy (MJ/kg) 13.40 13.40 13.40 13.82 13.82 13.82
 Crude protein (%) 16.30 15.30 14.30 16.30 15.30 14.30
 Total lysine (%) 0.95 0.95 0.95 0.95 0.95 0.95
 Total methionine (%) 0.27 0.27 0.27 0.27 0.27 0.27
 Calcium (%) 0.59 0.59 0.59 0.59 0.59 0.59
 Total phosphorus (%) 0.52 0.52 0.52 0.52 0.52 0.52

1) Provided per kg of diet. Vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D3, 1,800 IU; vitamin E, 60 IU; vitamin K3, 2 mg; thiamine, 2.00 mg; riboflavin, 7.0 mg; pantothenic acid, 25 mg; niacin, 27 mg; pyridoxine, 3 mg; d-biotin, 0.2 mg; folic acid, 1 mg; vitamin B12, 0.03 mg.

2) Provided per kg of diet. Minerals per kg of complete diet: Se, 0.3 mg; I, 1 mg; Mn, 51.6 mg; Cu, 105 mg; Fe, 150 mg; Zn, 72 mg; Co, 0.5 mg.

3) Calculated value.

CP, crude protein; ME, metabolizable energy.

Download Excel Table
Table 3. Formula and chemical compositions of the diets of early finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg
CP (%) High Middle Low High Middle Low
Total 100.00 100.00 100.00 100.00 100.00 100.00
Ingredient (%)
 Corn 69.15 71.87 74.45 66.13 69.19 72.20
 Soybean meal 20.50 17.70 14.93 20.90 18.14 15.42
 Wheat bran 3.99 3.97 4.22 3.99 3.95 3.90
 Palm kernel meal 3.03 3.05 2.86 3.29 3.01 2.73
 Tallow 0.62 0.55 0.53 2.99 2.86 2.75
 Mono-dicalcium phosphate 2.05 2.05 2.10 2.05 2.05 2.10
 Limestone 0.15 0.18 0.18 0.15 0.18 0.18
 L-Lysine-HCl (78%) 0.01 0.11 0.20 0.00 0.10 0.19
 DL-Methionine (99%) 0.00 0.02 0.03 0.00 0.02 0.03
 Vit. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Min. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Salt 0.30 0.30 0.30 0.30 0.30 0.30
Chemical composition
 Metabolizable energy (MJ/kg) 13.40 13.40 13.40 13.82 13.82 13.82
 Crude protein (%) 15.30 14.30 13.30 15.30 14.30 13.30
 Total lysine (%) 0.82 0.82 0.82 0.82 0.82 0.82
 Total methionine (%) 0.25 0.25 0.25 0.25 0.25 0.25
 Calcium (%) 0.52 0.52 0.52 0.52 0.52 0.52
 Total phosphorus (%) 0.47 0.47 0.47 0.47 0.47 0.47

1) Provided per kg of diet. Vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D3, 1,800 IU; vitamin E, 60 IU; vitamin K3, 2 mg; thiamine, 2.00 mg; riboflavin, 7.0 mg; pantothenic acid, 25 mg; niacin, 27 mg; pyridoxine, 3 mg; d-biotin, 0.2 mg; folic acid, 1 mg; vitamin B12, 0.03 mg.

2) Provided per kg of diet. Minerals per kg of complete diet: Se, 0.15 mg; I, 0.3 mg; Mn, 37 mg; Cu, 11 mg; Fe, 150 mg; Zn, 85 mg; Co, 2 mg.

3) Calculated value.

CP, crude protein; ME, metabolizable energy.

Download Excel Table
Table 4. Formula and chemical compositions of the diets of late finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg
CP (%) High Middle Low High Middle Low
Total 100.00 100.00 100.00 100.00 100.00 100.00
Ingredient (%)
 Corn 75.13 77.74 80.44 72.13 75.06 78.12
 Soybean meal 15.10 12.33 9.56 15.50 12.77 10.03
 Wheat bran 3.97 4.00 4.02 3.92 3.99 4.04
 Palm kernel meal 3.02 3.02 3.03 3.30 2.97 2.63
 Tallow 0.28 0.24 0.18 2.65 2.56 2.42
 Mono-dicalcium phosphate 1.85 1.90 1.90 1.85 1.90 1.90
 Limestone 0.14 0.15 0.16 0.15 0.15 0.15
 L-Lysine-HCl (78%) 0.01 0.10 0.19 0.00 0.09 0.18
 DL-Methionine (99%) 0.00 0.01 0.02 0.00 0.01 0.03
 Vit. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Min. Mix 0.10 0.10 0.10 0.10 0.10 0.10
 Salt 0.30 0.30 0.30 0.30 0.30 0.30
Chemical composition
 Metabolizable energy (MJ/kg) 13.40 13.40 13.40 13.82 13.82 13.82
 Crude protein (%) 13.20 12.20 11.20 13.20 12.20 11.20
 Total lysine (%) 0.60 0.60 0.60 0.60 0.60 0.60
 Total methionine (%) 0.21 0.21 0.21 0.21 0.21 0.21
 Calcium (%) 0.46 0.46 0.46 0.46 0.46 0.46
 Total phosphorus (%) 0.43 0.43 0.43 0.43 0.43 0.43

1) Provided per kg of diet. Vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D3, 1,800 IU; vitamin E, 60 IU; vitamin K3, 2 mg; thiamine, 2.00 mg; riboflavin, 7.0 mg; pantothenic acid, 25 mg; niacin, 27 mg; pyridoxine, 3 mg; d-biotin, 0.2 mg; folic acid, 1 mg; vitamin B12, 0.03 mg.

2) Provided per kg of diet. Minerals per kg of complete diet: Se, 0.15 mg; I, 0.3 mg; Mn, 37 mg; Cu, 11 mg; Fe, 150 mg; Zn, 85 mg; Co, 2 mg.

3) Calculated value.

CP, crude protein; ME, metabolizable energy.

Download Excel Table
Growth performance

Body weight and feed consumption were recorded at 0, 3, 6, 9, and 12 weeks to calculate average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F ratio).

Blood analysis

Blood samples were taken from the jugular vein of six randomly selected pigs in each treatment to measure blood urea nitrogen (BUN), glucose, and total protein during growing and finishing phages. All blood samples were collected in serum tubes (SST™ II Advance, BD Vacutainer®, Becton Dickinson, Plymouth, UK). Collected blood samples were centrifuged for 15 min at 6,048 × g at 4°C (5810R, Eppendorf, Hamburg, Germany). Serum was carefully transferred to 1.5 mL plastic tubes and stored at −20°C until analysis. BUN (kinetic UV assay, Roche, Germany) and glucose (enzymatic kinetic assay, Roche, Germany) concentrations were analyzed using a blood analyzer. Total protein concentration was measured by a kinetic colorimetry assay using a blood analyzer (Modular analytics, PE, Roche, Germany).

Carcass traits

At the end of experiment, four pigs from each treatment group were selected and slaughtered at average 113.42kg ± 1.307 for carcass analysis. Pork samples were collected nearby the 10th rib on the right side of the carcass. After chilling, 30 minutes after slaughter was regarded as the initial time. The pH was measured at 0, 3, 6, 12, and 24 hours and the color of the longissimus muscle was measured at the initial time and 24 hours later. The pork samples were always stored in the freezer (4°C). The pH was measured using a pH meter (Model 720, Thermo Orion, Fullerton, CA, USA) and pork color was measured by CIE color L*, a*, and b* values using a CR300 (Minolta Camera Co., Osaka, Japan). Chemical analysis of pork samples was conducted using the AOAC method [20].

Water holding capacity of pork was measured by the centrifuge method. Longissimus muscles were ground and sampled in a filter tube, then heated in water bath at 80°C for 20 min and centrifuged for 10 min at 2,688 × g at 10°C (5810R, Eppendorf, Hamburg, Germany). To calculate cooking loss, longissimus muscles were packed in a polyethylene bag that was then heated in a water bath until the core temperature reached 72°C and weighed before and after cooking. After heating, samples were cored (0.5 inch in diameter) parallel to the muscle fiber and the cores were used to measure shear force using a salter (Warner Barzler Shear, Norwood, MA, USA). Cooking loss, shear force, and water holding capacity of pork were analyzed by the Animal Origin Food Science laboratory, Seoul National University.

Lipids in pork samples were extracted from duplicate 10 g samples with chloroform: methanol (2.1, v/v) [21] on a shaking incubator (25°C, 8.064 × g) for 24 hours. Extracted lipids were filtered with filter paper (Whatman TM No.4, Buckinghamshire, UK). Twenty-five milliliters of 0.88% NaCl was added to the filtered sample, which was then centrifuged at 2,090 × g for 10 min (Continent 512R, Hanil Co., Ltd., Incheon, Korea). The supernatant was separated and pork lipids were concentrated using N2 gas at 45°C. After concentrating the lipids, 0.1 g of lipids was transferred to a 15 mL tube with 1 mL of internal standard (1 mg of undecanoic acid in 1 mL of iso-octane) and 1.5 mL of 0.5 N methanolic NaOH. Samples were heated in a water bath at 85°C for 10 min and cooled to room temperature. After cooling, 2 mL of 14% BF3-methanol was added and then the heating process was repeated one more time. Then, 2 mL of iso-octane and 1 mL saturated NaCl were added, and the sample was centrifuged at 4,200 × g for 3 min (Continent 512R, Hanil Co., Ltd., Incheon, Korea). Upper layer containing fatty acid methyl esters (FAMEs) was dehydrated with anhydrous sodium sulfate and transferred to a vial. The sample in the vial was analyzed using a gas chromatograph (HP 7890, Agilent Technologies, Santa Clara, CA, USA) with a split ratio of 50:1. A capillary column (DB-23, 60 m × 250 μm × 0.25 μm, Agilent, Santa Clara, CA, USA) was used. The injector and detector temperatures were maintained at 250°C and 280°C, respectively. Column oven temperature was varied as follows: 50°C for 1 min, increased to 130°C at 25°C/min, 170°C at 8°C /min, then held at 215°C after increasing to this this temperature at 1.5°C/min. Nitrogen was used as a carrier gas at linear flow of 4 mL/min. Individual FAMEs were identified by comparison of relative retention times of peaks from samples with those of external standards (37 FAME mix and CLA mix, Supelco, Bellefonte, PA, USA) calculated based on the Korean Food Standards Codex (MFDS, 2017).

Statistical analysis

Data for the various groups were compared by least squares mean comparisons and evaluated using general linear models (GLMs) in SAS (SAS Institute Inc., Cary, NC, USA). Every pen was used as one unit in the feeding trial, and individual pigs were considered experimental units with regard to analysis of blood profiles and carcass qualities. Orthogonal polynomial contrasts were used to detect linear and quadratic responses to CP levels when the significance of the CP effect was evaluated. The treatment effect was considered to be significant if p < 0.01 or p <0.05 while 0.05 < p and p < 0.10 was considered to indicated a trend in the treatment effect.

Results and Discussion

Growth performance

The effect of dietary energy and CP levels on growth performance are presented in Table 5. Average daily gain and G:F ratio decreased linearly as dietary CP level was decreased (linear, p < 0.05; p < 0.05, respectively) in the early growing phase, and G:F ratio decreased linearly as dietary CP level was decreased (linear, p < 0.05) over the entire growing phase. In the growing period, pigs showed the highest weight gain due to muscle development [16]. Dietary CP and amino acid levels affect protein deposition [16,22]. Several studies have demonstrated that ADG and G:F ratio decreased as CP level increased in the growing phase [10,23]. In this study, dietary energy density did not have any significant effect on growth performance during the growing period, consistent with the study of Kil and colleagues [24].

Table 5. Effects of dietary energy and crude protein levels on growth performance in growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
Body weight (kg)
 Initial 30.97 30.95 30.97 30.95 30.95 30.95 0.854 - - -
 3 wks 42.86 40.59 41.17 43.48 42.73 40.37 1.012 0.77 0.66 0.86
 6 wks 63.03 62.26 62.64 66.92 63.66 59.77 1.369 0.78 0.57 0.63
 9 wks 80.78 83.03 82.56 87.06 84.65 78.87 1.553 0.67 0.66 0.47
 12 wks 100.19 104.10 102.78 108.17 106.05 99.62 1.602 0.50 0.61 0.40
ADG (g)
 0–3 wks 567 459 486 597 561 448 19.4 0.38 0.04 0.29
 4–6 wks 960 1,032 1,023 1,116 997 924 32.2 0.91 0.73 0.28
 0–6 wks 763 745 754 857 779 686 18.7 0.59 0.14 0.19
 7–9 wks 845 989 948 959 1,000 910 30.9 0.66 0.50 0.62
 10–12 wks 924 1,003 963 1,005 1,019 988 16.9 0.26 0.53 0.71
 7–12 wks 885 996 956 982 1,009 949 16.1 0.27 0.19 0.37
 0–12 wks 824 871 855 919 894 818 12.2 0.24 0.23 0.07
ADFI (g)
 0–3 wks 1,462 1,366 1,434 1,390 1,450 1,340 40.1 0.75 0.93 0.66
 4–6 wks 2,280 2,304 2,490 2,350 2,378 2,164 12.3 0.51 0.97 0.15
 0–6 wks 1,872 1,834 1,960 1,872 1,912 1,752 39.2 0.60 0.98 0.35
 7–9 wks 2.674 2,770 3,032 2,786 2,798 2,620 60.2 0.46 0.81 0.19
 10–12 wks 3,522 3,580 3,748 3,512 3,662 3,204 72.8 0.29 0.70 0.18
 7–12 wks 3,100 3,176 3,390 3,150 3,230 2,910 63.8 0.33 0.88 0.17
 0–12 wks 2,486 2,506 2,674 2,512 2,570 2,334 49.6 0.42 0.94 0.22
G:F ratio
 0–3 wks 0.390 0.340 0.340 0.434 0.388 0.338 0.0118 0.18 0.03 0.58
 4–6 wks 0.426 0.448 0.408 0.478 0.422 0.422 0.0112 0.56 0.42 0.39
 0–6 wks 0.416 0.406 0.382 0.456 0.408 0.390 0.0083 0.18 0.02 0.52
 7–9 wks 0.316 0.362 0.314 0.344 0.358 0.350 0.0094 0.31 0.38 0.67
 10–12 wks 0.266 0.280 0.256 0.290 0.278 0.328 0.0973 0.12 0.80 0.30
 7–12 wks 0.286 0.314 0.284 0.312 0.312 0.336 0.0073 0.09 0.71 0.33
 0–12 wks 0.334 0.350 0.322 0.368 0.348 0.356 0.0046 0.01 0.43 0.13

L Linear response (p < 0.05) to dietary CP levels when a significant CP effect was detected.

a–c means with different superscripts in the same row differ significantly (p < 0.05).

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean; ADG, average daily gain; ADFI, average daily feed intake.

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Dietary energy and protein levels did not differ significantly among groups in the finishing period. Similar to our findings, Kerr et al. [10] represented that a 0.42 MJ decrease in NE/kg and 4% CP in 88.3 –109.7 kg pigs did not significantly affect growth performance. Kil et al. [24] reported that a 1.26 MJ/kg decrease in ME in the finishing pig diet had no effect on growth performance.

However, G:F ratio decreased when dietary ME level was decreased (p = 0.01). Furthermore, BW and ADG showed significant differences over the course of the experiment (p < 0.05), and 13.82 MJ/kg and the high CP level resulted in the highest BW and ADG among the six treatments.

Blood profiles

The effects of dietary energy and CP levels on blood profiles are presented in Table 6. There were no significant differences in glucose and total protein concentrations when pigs were fed different dietary ME and CP levels during the growing period, but BUN concentration increased with a decrease in dietary ME (p < 0.01). In the finishing period, total protein concentration decreased when pigs were fed lower dietary ME concentrations (p < 0.05).

Table 6. Effects of dietary energy and crude protein levels on blood profiles in growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
Blood urea nitrogen (BUN) (mmol/L)
 6 wks 4.61 4.17 4.11 3.36 3.29 4.03 0.144 < 0.01 0.71 0.31
 12 wks 4.92 4.03 3.83 4.41 4.81 3.46 0.187 0.93 0.07 0.28
Glucose (mmol/L)
 6 wks 46.26 45.12 48.48 50.33 46.18 42.28 0.662 0.37 0.27 0.26
 12 wks 42.28 46.45 45.24 45.89 46.17 48.94 0.547 0.54 0.84 0.16
Total protein (g/L)
 6 wks 67.51 67.30 65.32 69.18 67.31 63.71 0.743 1.00 0.10 0.65
 12 wks 67.02 65.50 67.31 70.02 69.24 68.48 0.601 0.04 0.73 0.68

L Linear response (p < 0.05) to dietary CP levels when a significant CP effect was detected.

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean; BUN, blood urea nitrogen.

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Ammonia is produced by the body after eating protein and the liver produces urea as a waste product of protein digestion. Urea nitrogen is a waste product that is released by the liver and then filtered out of the blood by the kidneys [25,26]. Therefore, BUN is used as a standard index for evaluating protein quality or excessive protein intake [27,28]. Fuller et al. [29] demonstrated that feeding animals carbohydrates could increase protein deposition. BUN level is affected by N intake [30], and has a negative correlations with ADG and G:F ratio [26]. In this study, BUN concentration decreased because pigs were fed more energy, which likely improved protein deposition and utilization.

Suboptimal protein intake can decrease the levels of blood total protein [31]. Matthews et al. [32] represented that total protein concentration increased when protein utilization by pigs was improved. In this experiment showed that total protein concentration decreased as ME level in the diet was decreased during the finishing period. This is consistent with the decrease in the G:F ratio with a decrease in dietary ME.

Carcass traits

The effect of dietary energy and CP levels on carcass traits are presented in Table 7. In this study, there were no significant differences in moisture, CP, crude fat, or crude ash according to diet. Other studies have reported similar results; Kil et al. [33] showed there was no significant difference in CP and crude fat in pork when pigs were fed diets with different GE (18.34–16.20 MJ/kg). Stewart et al. [34] showed that adding soybean hulls and wheat middling to 30% could improve CP levels in growing-finishing pigs (growing diets: 17.83%–20.30%; finishing diets: 12.44%–15.21%) but this had no significant effects on moisture, CP, crude fat, or crude ash in the resulting pork.

Table 7. Effect of dietary energy and crude protein levels on proximate analysis of longissimus muscles in growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
Proximate analysis (%)
 Moisture 74.73 73.81 74.21 72.97 74.07 73.18 0.247 0.10 0.91 0.25
 Crude ash 1.19 1.29 1.15 1.07 0.95 1.21 0.720 0.16 0.99 0.15
 Crude protein 23.37 23.36 22.84 23.10 23.35 23.50 0.231 0.82 0.96 0.74
 Crude fat 2.40 4.03 3.12 3.46 1.63 1.74 0.352 0.20 0.82 0.13

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean.

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The effect of dietary energy and CP levels on physiochemical properties of the meat are presented in Table 8. Variations in diet had no detrimental effects on cooking loss, shear force, or water holding capacity. These results are consistent with those of Apple et al. [18] who demonstrated that cooking loss was not affected by different levels of ME (14.57–13.82 MJ/kg). Madeira et al. [35] represented that decreasing CP level in the finishing diet (16%–13%) had no effect on cooking loss. Additionally, Widmer et al. [36] reported that decreasing CP in the growing-finishing period by 4% had no effect on cooking loss. Meng et al. [37] demonstrated that decreasing energy (ME: 14.65–14.24 MJ/kg) and CP levels (growing period: 18%–17% and finishing period: 16%–15%) had no effects on water holding capacity or cooking loss. Widmer et al. [36] represented that decreasing energy (growing period: 1.68 MJ/kg of ME and finishing period: 0.82 MJ/kg of ME) and CP level (growing period: 21.3%–15.34%; early finishing period: 18.76%–15.34% and late finishing period: 13.64%–11.24%) had no effects on cooking loss and shear force.

Table 8. Effect of dietary energy and crude protein levels on physiochemical properties of longissimus muscles from growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
Physiochemical property
 WHC (%) 68.89 67.48 68.94 69.23 70.57 71.69 0.592 0.10 0.61 0.59
 Shear force (kg/0.5 inch) 7.59 7.23 7.45 7.64 6.94 7.34 0.261 0.84 0.75 0.97
 Cooking loss (%) 31.85 31.07 31.36 31.23 30.83 30.22 0.293 0.30 0.59 0.83

1) Water holding capacity.

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean.

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Table 9 shows the effect of energy and CP levels on muscle. TBARS is an index of fat oxidation. Madsen et al. [38] found that the process of fat oxidation could be accelerated in the logissimus by the intake of crude fat. In this study, a decrease in ME of 0.42 MJ/kg and in CP of 2% had no significant effect on muscle TBARS assay. Other studies have also reported that a decrease in ME and CP levels had no effects on TBARS assay [35,37].

Table 9. Effect of dietary energy and crude protein levels on TBARS assay of longissimus muscles from growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
TBARS (mgMA/kg)
 Day 0 0.23 0.22 0.23 0.24 0.23 0.22 0.004 0.70 0.56 0.69
 Day 5 0.24 0.22 0.21 0.21 0.22 0.21 0.004 0.21 0.44 0.53
 Day 7 0.57 0.56 0.57 0.56 0.55 0.55 0.007 0.50 0.97 0.93

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean.

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Table 10 shows the effects of energy and CP levels on fatty acid composition in growing-finishing pig diets. Saturated fatty acid (SFA) increased (p < 0.01) and polyunsaturated fatty acid (PUFA) decreased (p < 0.05) as ME was decreased by 0.42 MJ/kg in growing-finishing pig diets. In addition, monounsaturated fatty acid (MUFA) content tended to increase when CP level was decreased in growing-finishing pig diets (p = 0.06). European Food Safe Authority (EFSA) recommend that for food to be considered healthy, it should have a low content of SFA [39]. Feed ingredients and nutrition composition can also affect fatty acid composition in pork [40,41]. Nemechek et al. [42] and Davis et al. [43] demonstrated that SFA content could be decreased and PUFA content could be increased by decreasing tallow levels or decreasing ME by 0.42 MJ/kg (13.82–13.40 MJ/kg) in growing-finishing diets. Bessa et al. [44] and Madeira et al. [35] represented no significant differences in MUFA as CP levels were decreased by 3%–4% in growing-finishing pig diets. The discrepancy between this study and previous studies may due to the high CP level in our study. In summary, this experiment showed that 13.82 MJ/kg of ME in a growing-finishing pig diet can improve fatty acids composition of pork.

Table 10. Effect of dietary energy and crude protein levels on fatty acid composition of longissimus muscles from growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
Fatty acid composition (%)
 SFA 39.08 40.69 39.67 37.75 37.24 37.39 0.427 < 0.01 0.82 0.53
 MUFA 41.37 39.14 42.23 40.86 40.46 41.77 0.366 0.86 0.06 0.47
 PUFA 19.56 20.17 18.10 21.40 22.30 20.84 0.512 0.03 0.35 0.93

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean; SFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids.

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The change in pH after slaughter is a very important factor affecting the freshness, tenderness, color, texture, and storage of pork. In this study, there were no significant differences in pH at 0 and 24 hours after slaughter (Table 11). This result is in accordance with Apple et al. [18], Widmer et al. [36], Prandini et al. [45], and Madeira et al. [35] who reported that the pH at 0 and 24 hours after slaughter were not affected by ME (14.57–13.82 MJ/kg and 15.49–13.82 J/kg) or CP level (17.7%–14.5% and 16%–13%).

Table 11. Effect of dietary energy and crude protein levels on the pH of longissimus muscles from growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
pH
 0 hours 6.05 6.05 6.11 6.14 6.07 5.84 0.040 0.21 0.45 0.16
 3 hours 5.64 5.75 5.68 5.70 5.66 5.51 0.030 0.22 0.31 0.27
 6 hours 5.58 5.64 5.58 5.56 5.54 5.51 0.016 0.08 0.49 0.59
 12 hours 5.62 5.62 5.62 5.62 5.58 5.62 0.019 0.72 0.87 0.90
 24 hours 5.60 5.64 5.60 5.63 5.59 5.66 0.016 0.74 0.93 0.42

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean.

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Meat color results are shown in Table 12. There were no significant differences in L*, a*, or b* values as ME level was decreased by 0.42 MJ/kg or CP concentration was decreased by 2%. Apple et al. [18] and Hinson et al. [47] also demonstrated that decreasing energy level in the diet did not affect meat color (14.57–13.82 MJ/kg ME and 14.65–13.40 MJ/kg ME, respectively). In addition, Prandini et al. [45] and Madeira et al. [35] represented that decreasing CP level in diet did not affect meat color (17.7%–14.5% and 16%–13%, respectively).

Table 12. Effect of dietary energy and crude protein levels on color of longissimus muscles from growing-finishing pigs
Energy ME 13.40 MJ/kg ME 13.82 MJ/kg SEM p-value
CP (%) High Middle Low High Middle Low ME CP M × C
CIE value, L*
 0 hours 39.34 38.93 38.88 40.72 39.21 39.61 0.356 0.30 0.55 0.84
 3 hours 39.53 40.19 39.97 39.69 38.43 40.11 0.392 0.86 0.95 0.38
 6 hours 40.73 40.38 40.07 41.07 40.86 42.14 0.515 0.40 0.94 0.78
 12 hours 43.97 41.76 43.02 43.38 43.39 44.34 0.434 0.40 0.53 0.57
 24 hours 44.89 45.82 45.11 46.08 45.53 44.54 0.367 0.89 0.66 0.63
CIE value, a*
 0 hours 1.83 1.22 1.73 1.54 1.93 1.87 0.101 0.35 0.66 0.15
 3 hours 1.87 1.89 2.48 2.41 2.18 2.40 0.120 0.31 0.39 0.58
 6 hours 2.06 2.18 2.86 2.78 2.43 2.70 0.123 0.28 0.26 0.35
 12 hours 3.14 2.56 3.42 3.23 3.01 3.21 0.105 0.60 0.11 0.43
 24 hours 4.11 3.73 4.26 4.20 4.37 4.13 0.132 0.49 0.92 0.53
CIE value, b*
 0 hours 4.30 3.66 3.90 4.12 4.17 4.02 0.083 0.36 0.29 0.24
 3 hours 4.36 4.55 4.54 4.72 4.29 4.54 0.095 0.89 0.86 0.47
 6 hours 4.64 4.57 4.93 5.22 4.70 5.10 0.127 0.28 0.48 0.74
 12 hours 5.60 5.15 5.76 5.65 5.48 5.93 0.103 0.38 0.14 0.86
 24 hours 6.34 6.12 6.59 6.71 6.70 6.37 0.121 0.42 0.98 0.51

CP, crude protein; ME, metabolizable energy; SEM, standard error of the mean.

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Conclusions

An ME of 13.82 MJ/kg in growing-finishing pig diets increased the G:F ratio over the entire experimental period, SFA concentration in the longissimus muscles and blood total protein level in the finishing period, while decreasing BUN concentration during the growing period.

When CP level was decreased in growing-finishing pig diets, blood total protein during the growing phase and BUN during the finishing period were decreased, but MUFA level tended to increase.

In summary, a growing-finishing diet of 13.82 MJ/kg ME with the high CP level (18%/16.3%/15.3%/13.2%) can improve growth performance and show better fatty acids composition of pork.

Competing interests

No potential conflict of interest relevant to this article was reported.

Funding sources

This work was carried out with the support of the Cooperative Research Program for Agriculture Science & Technology Development (Project No. PJ011617), Rural Development Administration, Korea.

Acknowledgements

Not applicable.

Availability of data and material

Upon reasonable request, the datasets of this study can be available from the corresponding author.

Authors’ contributions

Conceptualization: Kim YY.

Data curation: Fang LH, Han TH.

Formal analysis: Fang LH, Kim BO.

Methodology: Han TH, Jin YH.

Software: Kim BO, Do SH.

Validation: Jin YH, Hong JS.

Investigation: Kim YY, Hong JS.

Writing- original draft: Fang LH, Do SH.

Writing- review & deiting: Kim YY, Hong JS.

Ethics approval and consent to participate

All experimental procedures involving animals were conducted in accordance with the Animal Experimental Guidelines provided by the Seoul National University Institutional Animal Care and Use Committee (SNUIACUC; SNU-160819-9).

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