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Asian-Australasian Journal of Animal Sciences logoLink to Asian-Australasian Journal of Animal Sciences
. 2019 Mar 7;32(11):1745–1752. doi: 10.5713/ajas.19.0037

Amino acid digestibility in plant protein sources fed to growing pigs

Ah Reum Son 1,2, Chan Sol Park 1, Kyu Ree Park 1, Beob Gyun Kim 1,2,*
PMCID: PMC6817785  PMID: 31010993

Abstract

Objective

The objective was to determine standardized ileal digestibility (SID) of amino acids (AA) in 11 plant protein sources fed to growing pigs.

Methods

Eleven feed ingredients used were sesame meal, two sources of soybean meal (SBM) produced in the Republic of Korea, a source of SBM produced in India, high-protein distillers dried grains (HPDDG), perilla meal, canola meal, copra meal, corn germ meal, palm kernel expeller, and tapioca distillers dried grains (TDDG). Experimental diets were prepared to contain each test ingredient as a sole source of AA, and a nitrogen-free diet was also prepared to estimate the basal ileal endogenous losses of AA. Twelve barrows surgically fitted with T-cannulas at the distal ileum with an initial body weight of 29.0 kg (standard deviation = 3.0) were individually housed in metabolism crates equipped with a feeder and a nipple drinker. A 12×9 incomplete Latin square design was employed with 12 experimental diets, 12 animals, and 9 periods. After a 5-d adaptation period, ileal digesta were collected on d 6 and 7 in each experimental period.

Results

Values for apparent ileal digestibility of most indispensable AA in three sources of SBM were greater compared with other test ingredients except HPDDG and canola meal (p<0.05). Pigs fed diets containing SBM sources had also greater SID of most indispensable AA compared with those fed diets containing other test ingredients (p<0.05) except for HPDDG and canola meal. There was no difference in the apparent ileal digestibility and SID of AA among sources of SBM. The TDDG had the least value for the SID of methionine among test ingredients (p<0.05).

Conclusion

The SID of most AA in SBM, HPDDG, and canola meal were greater than those in sesame meal, perilla meal, copra meal, and TDDG.

Keywords: Feedstuff, Protein Supplements, Standardized Ileal Digestibility, Swine

INTRODUCTION

Dietary supplementation of protein and amino acids (AA) is important to promote normal and optimal growth for pigs [1]. Soybean meal (SBM) is one of the most commonly used protein sources in swine diets. However, researchers and feed formulators have tried to find alternative feed ingredients to replace SBM due to its relatively high price [2]. Many plant protein sources produced from oil-extraction and distillation processes have been considered as alternative feed ingredients because crude protein (CP) and AA contents in grains, oilseeds, or fruit byproducts were concentrated after processing [3].

To use an alternative feed ingredient in swine diets, nutritional values of the ingredient should be considered [4]. The concentration of biologically available AA in a protein supplement is one of the most important factors in deciding the use of the protein supplement in swine diets. The bioavailability of AA for the pigs is generally expressed as a standardized ileal digestibility (SID) [5]. However, information on the SID of AA in some plant protein sources is very limited. Therefore, this experiment was conducted to determine the SID of AA in nine plant protein sources produced from the oil-extraction process and two plant protein sources produced from distillation process fed to growing pigs.

MATERIALS AND METHODS

Animal care

The experimental procedure was approved by the Institutional Animal Care and Use Committee at Konkuk University (KU12090).

Ingredients and diets

Eleven plant protein sources used in the present study were identical to the ingredients reported by Son et al [6]. Test ingredients were sesame meal, two sources of dehulled SBM from Korea (SBM-KD 1 and SBM-KD 2), SBM from India (SBM-I), high-protein distillers dried grains produced from corn in the USA (HPDDG), perilla meal, canola meal (CM) from Indonesia, copra meal from the Philippines, corn germ meal (CGM), palm kernel expellers from Malaysia, and tapioca distillers dried grains from China (TDDG; Table 1). The copra and palm kernel byproducts were classified as meal and expellers, respectively, based on the concentration of ether extract in each ingredient [7].

Table 1.

Energy and nutrient composition of test ingredients (as-is basis)

Item1) Ingredient
Sesame meal Soybean meal-dehulled-Korea 1 Soybean meal-dehulled-Korea 2 Soybean meal-India High-protein distillers dried grains Perilla meal Canola meal Copra meal Corn germ meal Palm kernel expellers Tapioca distillers dried grains
Indispensable amino acid (%)
 Arginine 3.79 3.46 3.51 2.97 1.32 3.87 2.40 1.65 1.42 1.62 0.66
 Histidine 1.17 1.23 1.29 1.07 1.10 1.09 0.99 0.43 0.69 0.31 0.38
 Isoleucine 1.74 2.18 2.26 1.78 1.60 1.56 1.31 0.66 0.76 0.52 0.88
 Leucine 3.32 3.79 3.88 3.19 5.70 2.88 2.48 1.37 1.74 1.05 1.37
 Lysine 1.02 3.15 3.30 2.68 1.23 1.15 1.76 0.51 1.00 0.48 0.96
 Methionine 1.05 0.31 0.48 0.34 0.52 0.54 0.47 0.16 0.23 0.18 0.14
 Phenylalanine 2.50 2.42 2.49 2.23 2.39 2.48 1.51 1.09 1.03 0.82 0.82
 Threonine 1.39 2.00 2.01 1.67 1.45 1.35 1.50 0.69 0.90 0.53 0.80
 Tryptophan 0.63 0.49 0.51 0.42 0.22 0.43 0.41 0.14 0.19 0.09 0.13
 Valine 2.01 2.10 2.16 1.75 1.79 1.85 1.61 0.95 1.08 0.74 0.98
Dispensable amino acid (%)
 Alanine 2.38 2.10 2.14 1.77 3.05 2.02 1.61 0.92 1.29 0.69 1.00
 Aspartic acid 3.38 5.54 5.61 4.53 2.42 3.21 2.42 1.63 1.67 1.27 1.57
 Cysteine 0.21 0.61 0.79 0.56 0.52 0.26 0.97 0.29 0.34 0.19 0.14
 Glutamic acid 8.81 8.61 8.70 7.48 7.22 7.70 6.59 3.84 3.25 2.96 1.87
 Glycine 2.35 2.05 2.09 1.71 1.29 2.02 1.85 0.92 1.18 0.74 0.79
 Proline 1.06 1.82 1.76 1.60 3.11 0.80 1.64 0.49 0.99 0.35 0.55
 Serine 1.29 2.40 2.40 2.06 1.85 1.51 1.53 0.84 1.05 0.68 0.75
 Tyrosine 1.77 1.66 1.47 1.48 1.60 1.53 1.04 0.54 0.68 0.46 0.50
Dry matter (%) 97.0 90.2 90.2 90.1 91.5 90.3 91.4 90.2 94.1 89.6 93.3
Gross energy (kcal/kg) 4,688 4,299 4,332 4,221 4,924 4,240 4,235 4,095 4,699 4,407 3,875
Crude protein (%) 50.0 47.1 47.4 39.6 38.0 43.2 37.5 21.8 21.4 15.3 18.4
Ether extract (%) 6.05 2.46 0.74 0.84 5.24 1.08 1.85 1.76 8.27 6.97 3.12
Crude fiber (%) 9.3 4.6 5.7 5.1 7.3 18.8 9.6 13.6 10.4 17.0 22.7
Ash (%) 11.0 6.2 6.3 6.3 1.4 9.0 9.5 6.7 2.4 4.7 14.9
Neutral detergent fiber (%) 28.1 7.4 8.7 9.6 39.0 44.7 24.7 55.1 43.4 61.4 56.2
Acid detergent fiber (%) 17.5 7.2 9.1 8.2 20.1 25.9 18.1 32.2 14.6 36.8 47.3
Calcium (%) 2.15 0.64 0.67 0.70 0.13 1.71 1.01 0.62 0.13 0.43 0.77
Phosphorus (%) 1.32 0.64 0.62 0.53 0.25 1.25 0.95 0.54 0.53 0.55 0.22
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1)

The analyzed energy and nutrient compositions except amino acids are adapted from Son et al [6].

Experimental diets were formulated to contain their respective test ingredients as a sole source of nitrogen (Tables 2, 3). A nitrogen-free diet was also prepared to estimate the basal ileal endogenous losses of AA. A 0.5% of chromic oxide was included in all experimental diets as an indigestible index. All experimental diets were formulated to contain adequate vitamins and minerals to meet or exceed the requirement estimates reported by the NRC [5].

Table 2.

Ingredient and chemical composition of experimental diets (as-fed basis)

Items Diet
Sesame meal Soybean meal-dehulled-Korea 1 Soybean meal-dehulled-Korea 2 Soybean meal-India High-protein distillers dried grains Perilla meal Canola meal Copra meal Corn germ meal Palm kernel expellers Tapioca distillers dried grains Nitrogen-free
Ingredient (%)
 Corn starch 48.6 44.2 42.2 43.3 36.7 38.6 38.3 37.0 36.8 37.3 37.0 68.4
 Sucrose 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0
 Sesame meal 30.0 - - - - - - - - - - -
 Soybean meal-dehulled-Korea 1 - 33.0 - - - - - - - - - -
 Soybean meal-dehulled-Korea 2 - - 35.0 - - - - - - - - -
 Soybean meal-India - - - 34.0 - - - - - - - -
 High-protein distillers dried grains - - - - 40.0 - - - - - - -
 Perilla meal - - - - - 40.0 - - - - - -
 Canola meal - - - - - - 40.0 - - - - -
 Copra meal - - - - - - - 40.0 - - - -
 Corn germ meal - - - - - - - - 40.0 - - -
 Palm kernel expellers - - - - - - - - - 40.0 - -
 Tapioca distillers dried grains - - - - - - - - - - 40.0 -
 Soybean oil - - - - - - - - - - - 4.00
 Cellulose - - - - - - - - - - - 4.00
 Potassium carbonate - - - - - - - - - - - 0.40
 Magnesium oxide - - - - - - - - - - - 0.10
 Limestone - 0.35 0.35 0.10 0.30 - 0.05 0.50 0.45 0.20 - 0.75
 Dicalcium phosphate - 1.10 1.10 1.25 1.65 - 0.25 1.15 1.35 1.15 1.60 1.00
 Salt 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40
 Vitamin-mineral premix1) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
 Chromic oxide 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
Analyzed composition (%)
 Dry matter 93.7 91.2 90.9 91.5 92.1 91.3 91.9 91.5 92.7 91.0 92.5 92.0
 Crude protein 16.0 19.0 18.7 13.6 14.2 18.1 14.7 8.28 8.13 6.10 7.71 0.27
 Ether extract 1.73 0.46 0.55 0.53 1.49 0.31 0.76 0.84 3.34 2.61 0.48 2.10
 Ash 4.30 4.45 4.62 4.50 3.72 5.04 5.29 4.96 3.27 4.08 9.08 3.07
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1)

Provided the following quantities per kg of complete diet: vitamin A, 25,000 IU; vitamin D3, 4,000 IU; vitamin E, 50 IU; vitamin K, 5.0 mg; thiamin, 4.9 mg; riboflavin, 10.0 mg; pyridoxine, 4.9 mg; vitamin B12, 0.06 mg; pantothenic acid, 37.5 mg; folic acid, 1.10 mg; niacin, 62 mg; biotin, 0.06 mg; Cu, 25 mg as copper sulfate; Fe, 268 mg as iron sulfate; I, 5.0 mg as potassium iodate; Mn, 125 mg as manganese sulfate; Se, 0.38 mg as sodium selenite; Zn, 313 mg as zinc oxide; and butylated hydroxytoluene, 50 mg.

Table 3.

Amino acids (AA) concentration of experimental diets (%, as-fed basis)

Items Diet
Sesame meal Soybean meal-dehulled-Korea 1 Soybean meal-dehulled-Korea 2 Soybean meal-India High-protein distillers dried grains Perilla meal Canola meal Copra meal Corn germ meal Palm kernel expellers Tapioca distillers dried grains
Indispensable AA
 Arginine 0.95 1.23 0.94 1.09 0.55 0.52 1.00 0.64 0.53 0.76 0.18
 Histidine 0.31 0.39 0.38 0.35 0.45 0.43 0.43 0.18 0.28 0.14 0.11
 Isoleucine 0.49 0.63 0.68 0.55 0.68 0.64 0.61 0.29 0.31 0.26 0.24
 Leucine 0.90 1.16 1.16 1.02 2.37 2.25 1.09 0.59 0.68 0.50 0.37
 Lysine 0.23 0.30 0.92 0.27 0.47 0.44 0.72 0.21 0.36 0.22 0.28
 Methionine 0.38 0.37 0.20 0.18 0.36 0.35 0.24 0.09 0.14 0.11 0.07
 Phenylalanine 0.64 0.82 0.76 0.73 0.91 0.86 0.65 0.44 0.40 0.38 0.24
 Threonine 0.36 0.46 0.57 0.41 0.60 0.57 0.60 0.29 0.34 0.25 0.23
 Tryptophan 0.15 0.25 0.15 0.10 0.09 0.18 0.16 0.06 0.07 0.04 0.04
 Valine 0.59 0.75 0.66 0.67 0.77 0.73 0.72 0.44 0.48 0.39 0.30
Dispensable AA
 Alanine 0.64 0.83 0.63 0.73 1.27 1.21 0.67 0.40 0.51 0.33 0.29
 Aspartic acid 0.91 1.16 1.61 1.03 1.00 0.95 1.01 0.69 0.64 0.61 0.45
 Cysteine 0.11 0.05 0.29 0.21 0.39 0.19 0.41 0.15 0.17 0.11 0.07
 Glutamic acid 2.42 3.07 2.55 2.71 2.97 2.82 2.74 1.67 1.27 1.43 0.55
 Glycine 0.63 0.81 0.61 0.72 0.55 0.52 0.77 0.40 0.47 0.34 0.23
 Proline 0.30 0.37 0.53 0.33 1.30 1.23 0.73 0.21 0.36 0.16 0.14
 Serine 0.32 0.40 0.68 0.36 0.74 0.71 0.59 0.34 0.38 0.30 0.23
 Tyrosine 0.36 0.52 0.37 0.46 0.57 0.54 0.40 0.16 0.20 0.17 0.12
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Animal, feeding, and sample collection

Twelve crossbred barrows with a mean initial body weight (BW) of 29.0±2.0 kg were surgically fitted with T-cannulas at the distal ileum based on the procedure described by Stein et al [8], and were individually placed in metabolism crates equipped with a feeder and a nipple drinker. The animals were allotted to a 12×9 incomplete Latin square design with 12 dietary treatments and 9 periods using a spreadsheet-based program to prevent potential carryover effects [9]. Based on the BW of each pig and metabolizable energy concentration of the experimental diets, daily feed allowance for each pig was calculated at the beginning of each experimental period as 2.7 times the estimated energy requirement for maintenance (i.e., 106 kcal of metabolizable energy per kg BW0.75). The amount of feed allowance was divided into two equal meals, and the feed was fed to pigs at 0800 and 1600 h. Water was available all the time. The BW of pigs was individually measured at the beginning of each period.

An experimental period consisted of a 5-d adaptation period and a 2-d collection period. The ileal digesta were collected from 0830 to 1600 h on d 6 and 7. For collecting the ileal digesta, a plastic bag was tied on the T-cannula using a wire, and the bag was changed every 30 min. The collected ileal digesta samples were immediately stored at −20°C.

Chemical analysis

Ileal digesta samples were freeze-dried and finely ground before analyses. The AA concentrations in the ingredients, diets, and ileal digesta were analyzed using acid hydrolysis method (method 994.12) except for sulfur-containing AA (method 985.28) and tryptophan (method 988.15) [10]. For analyzing chromium concentration in the diet and ileal digesta, an ultraviolet-visible spectrophotometry (Optizen 2120UV, Mecasys Inc., Daejeon, Korea) was used.

Calculation and statistical analysis

Values for apparent ileal digestibility (AID) and SID of AA were calculated based on the equations reported by a previous study [11]. Data were analyzed using MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, USA). The model included dietary treatment as a fixed variable and animal and period as random variables [12]. Least squares means of each treatment were calculated and the difference among the least squares means was tested using the PDIFF option of SAS with the Tukey’s adjustment. The experimental unit was a pig, and the statistical significance was set at a p-value less than 0.05.

RESULTS

All animals were maintained healthy and consumed provided experimental diets well. Values for the AID of most indispensable AA in three sources of SBM were greater compared with other test ingredients except HPDDG and CM (p<0.05; Table 4). There was no difference in the AID of AA among the sources of SBM. Pigs fed diets containing SBM-KD 1 and SBM-I had greater AID of lysine compared with other test ingredients (p<0.05) except for SBM-KD 2, which were not different from values in HPDDG and CM. Values for the AID of methionine in SBM-KD 2 and HPDDG were greater than in other test ingredients (p<0.05) except for SBM-KD 1, SBM-I, CM, and CGM. The AID of threonine and valine in SBM-KD 1 was greater than other test ingredients (p<0.05) but was not different from values in SBM-KD 2, SBM-I, and HPDDG. Pigs fed diets containing SBM sources and HPDDG had greater AID of isoleucine, leucine, and phenylalanine (p<0.05) except for those fed diet containing CM. Values for the AID of arginine, methionine, and phenylalanine in TDDG was the least among test ingredients (p<0.05).

Table 4.

Apparent ileal digestibility (%) of amino acids (AA) in 11 sources of plant protein sources fed to pigs

Items Diet SEM p-value
Sesame meal Soybean meal-dehulled-Korea 1 Soybean meal-dehulled-Korea 2 Soybean meal-India High-protein distillers dried grains Perilla meal Canola meal Copra meal Corn germ meal Palm kernel expellers Tapioca distillers dried grains
No. of observation 7 8 7 8 7 8 7 8 6 6 6 - -
Indispensable AA
 Arginine 59.5de 90.4a 85.7ab 86.6ab 70.4cd 65.5cd 73.5bc 48.7e 69.2cd 61.9cde 24.3f 3.2 <0.001
 Histidine 45.7cd 85.5a 80.9ab 82.6a 74.8ab 48.2cd 72.6ab 40.7d 64.3bc 45.9cd 30.7d 4.0 <0.001
 Isoleucine 37.3c 79.9a 76.3a 76.7a 74.2a 40.5c 65.1ab 36.8c 44.9c 48.6bc 29.0c 4.0 <0.001
 Leucine 46.5c 81.6a 77.8a 78.7a 84.5a 46.1c 69.8ab 45.5cd 58.4bc 53.9c 30.7d 3.4 <0.001
 Lysine 7.0ef 84.1a 78.0ab 82.1a 59.8bc 26.4de 57.5bc 7.4f 43.6cd 32.7d 35.7d 4.8 <0.001
 Methionine 61.7bc 79.0ab 86.9a 77.9ab 89.0a 34.0d 72.8ab 45.1cd 66.9abc 59.1bc 4.5e 5.5 <0.001
Phenylalanine 51.8c 82.3a 79.3a 81.3a 79.5a 55.2c 69.8ab 52.8c 57.7bc 57.3bc 31.5d 3.1 <0.001
 Threonine 17.9d 73.8a 65.0ab 69.0ab 63.9ab 27.8d 52.0bc 20.1d 31.6cd 30.0d 11.4d 4.8 <0.001
 Tryptophan 66.6abc 82.4a 79.6a 82.3a 71.6ab 55.8bc 62.2abc 45.0cd 58.8abc 41.3cd 23.2d 5.9 <0.001
 Valine 31.1de 73.9a 69.2ab 68.9ab 68.8ab 34.9de 58.6bc 38.1d 47.4cd 46.1cd 19.4e 3.8 <0.001
Dispensable AA
 Alanine 33.6de 72.5ab 66.1abc 67.7ab 78.1a 30.4de 58.0bc 30.2de 46.6cd 37.1de 20.9e 4.6 <0.001
 Aspartic acid 16.6d 79.7a 72.6ab 77.5a 63.9ab 24.1d 51.1bc 27.3d 30.7cd 33.9cd 17.2d 5.3 <0.001
 Cysteine −81.4d 63.1a 68.3a 60.2a 70.6a −32.1c 61.7a 11.4b 35.6ab 19.9b −54.6cd 8.0 <0.001
 Glutamic acid 39.8b 84.9a 79.2a 81.6a 79.5a 43.0b 76.0a 43.1b 57.0b 49.8b 20.3c 4.3 <0.001
 Glycine −5.0de 63.6a 50.8a 46.6ab 38.8abc 10.8cd 37.5abc −3.0de 12.9bcde −19.1de −24.8e 7.9 <0.001
 Proline −248.7bc 39.7a −2.0ab −36.6abc 38.2a −241.6bc −25.9abc −280.0c −146.3abc −631.9d −208.1abc 62.0 <0.001
 Serine 21.1de 79.8a 71.5ab 75.8ab 72.9ab 37.8cd 62.0b 31.7cd 41.2c 38.7cd 8.2e 4.5 <0.001
 Tyrosine 55.7cde 83.4a 72.1abc 81.9ab 78.6ab 54.2de 65.5bcd 29.7f 38.4ef 42.9ef 35.2f 3.8 <0.001
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SEM, standard error of the mean.

a–f

Means within a row without a common superscript differ (p<0.05).

Values for the SID of lysine in SBM-KD 1 and SBM-I were greater than other test ingredients (p<0.05) except for SBM-KD 2 and HPDDG, which were not different from values in CM (Table 5). Values for the SID of methionine in SBM-KD 1, SBM-KD 2, and HPDDG were greater than in sesame meal, perilla meal, copra meal, and TDDG (p<0.05) but were not different from values in SBM-I, CM, CGM, and palm kernel expellers. The TDDG had the lowest value for the SID of methionine among the test ingredients (p<0.05). Pigs fed diets containing SBM-KD1 had greater SID of threonine and valine compared with those fed diets containing other test ingredients (p<0.05) except for SBM-KD2, SBM-I, and HPDDG. Values for the SID of tryptophan in SBM-KD 1 and SBM-I were greater than perilla meal, copra meal, palm kernel expellers, and TDDG (p<0.05) but were not different from other test ingredients. Pigs fed diets containing SBM sources and HPDDG had greater SID of isoleucine, leucine, and phenylalanine compared with other test ingredients (p<0.05) except for those fed diet containing CM.

Table 5.

Standardized ileal digestibility (%) of amino acids (AA) in 11 sources of plant protein sources fed to pigs [1]

Items Diet SEM p-value
Sesame meal Soybean meal-dehulled-Korea 1 Soybean meal-dehulled-Korea 2 Soybean meal-India High-protein distillers dried grains Perilla meal Canola meal Copra meal Corn germ meal Palm kernel expellers Tapioca distillers dried grains
No. of observation 7 8 7 8 7 8 7 8 6 6 6 - -
Indispensable AA
 Arginine 64.3d 95.2a 91.5ab 92.0ab 80.4bc 69.1cd 79.0bc 57.3de 79.6bc 69.1cd 45.1e 3.2 <0.001
 Histidine 49.9d 89.2a 84.7ab 86.6ab 78.1ab 51.6cd 76.0ab 48.9d 69.6bc 56.4cd 40.4d 4.0 <0.001
 Isoleucine 41.8cd 83.1a 79.8a 80.6a 77.7a 44.3cd 68.9ab 44.8cd 52.4bcd 57.6bc 35.7d 4.0 <0.001
 Leucine 50.2cd 84.6a 81.1a 82.2a 86.1a 49.4cd 73.3ab 51.9cd 63.9bc 61.4bc 37.5d 3.4 <0.001
 Lysine 16.6g 86.9a 81.2abc 85.3ab 66.1bcd 32.8fg 61.6cde 21.4g 51.8def 46.0def 43.3ef 4.8 <0.001
 Methionine 64.6bc 87.9a 91.5a 85.8ab 91.5a 38.3de 76.6abc 55.2cd 73.4abc 67.4abc 20.8e 5.5 <0.001
 Phenylalanine 55.4c 85.7a 82.8a 84.9a 82.4a 57.9c 73.9ab 58.9c 64.4bc 64.4bc 39.6d 3.1 <0.001
 Threonine 29.2de 80.9a 73.3ab 77.3ab 71.7ab 36.5de 59.8bc 36.3de 45.5cde 48.9cd 26.1e 4.8 <0.001
 Tryptophan 70.8abc 87.3a 84.9ab 87.9a 80.4abc 60.4cd 67.1abc 58.1cd 70.1abc 61.1bcd 38.4d 5.9 <0.001
 Valine 38.8fg 80.5a 76.2ab 76.7ab 74.8ab 41.1efg 65.0bc 48.6def 57.0cde 57.9cd 31.2g 3.8 <0.001
Dispensable AA
 Alanine 40.8de 79.9a 74.3ab 76.2a 82.1a 36.8e 65.7abc 43.0de 56.6bcd 52.7cde 33.7e 4.6 <0.001
 Aspartic acid 22.9d 83.1a 76.6ab 81.6a 70.2ab 29.0d 57.4bc 36.5cd 40.6cd 44.3cd 27.3d 5.3 <0.001
 Cysteine −46.8e 74.0ab 75.8a 71.7ab 76.2a −11.1d 67.0ab 26.0c 48.4abc 39.7bc −15.7de 8.0 <0.001
 Glutamic acid 42.6de 87.6a 82.2a 84.6a 82.0a 45.5cde 78.8ab 47.6cde 62.9bc 55.1cd 30.4e 4.3 <0.001
 Glycine 14.9e 84.4a 73.8ab 70.8ab 64.4abc 28.2de 55.7abcd 32.2cde 42.9bcde 22.3de 19.7de 7.9 <0.001
 Proline −64.1ab 137.4a 108.8a 71.4a 83.4a −58.2ab 54.5a −0.5ab 16.7ab −265.0b 58.8a 62.0 <0.001
 Serine 33.4de 85.8a 78.5a 82.6a 79.3a 45.7cd 70.1ab 45.7cd 53.7bc 54.6bc 24.1e 4.5 <0.001
 Tyrosine 59.1cd 86.7a 77.0ab 85.5ab 81.7ab 57.1cd 70.1bc 41.0e 47.4de 53.6cde 44.3de 3.8 <0.001
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SEM, standard error of the mean.

1)

Values for the standardized ileal digestibility of amino acids were calculated by correcting the apparent ileal digestibility for basal endogenous losses. The basal endogenous losses (g/kg dry matter intake) were determined from pigs fed an nitrogen-free diet: arginine, 0.60; histidine, 0.16; isoleucine, 0.25; leucine, 0.41; lysine, 0.32; methionine, 0.10; phenylalanine, 0.29; threonine, 0.51; tryptophan, 0.09; valine, 0.50; alanine, 0.56; aspartic acid, 0.69; cysteine, 0.24; glutamic acid, 0.82; glycine, 1.53; proline, 6.38; serine, 0.52; tyrosine, 0.20.

a–g

Means within a row without a common superscript differ (p<0.05).

DISCUSSION

The basal ileal endogenous losses of indispensable AA determined in the present study were within a range reported in the literature [13]. The concentration of CP and AA in sesame meal was within range of previous studies [5,14–16]. However, values for the SID of indispensable AA, especially lysine, in sesame meal were less than values in previous studies [5, 15,16]. The reason for this result may be due to different oil-extraction processes and conditions [16]. In addition, fiber concentration in the sesame meal used in the present study and Son et al [6] was greater compared with those in the previous studies [5,15,16]. Although the SID of most indispensable AA in sesame meal was less than in SBM sources used in the present study, sesame meal had greater concentrations of methionine and tryptophan compared with SBM and other test ingredients. Based on the present results, therefore, sesame meal can be used as a good source of methionine and tryptophan in swine diets in agreement with a previous work [16].

The AA composition in the three sources of SBM agreed with the tabular values in the literature [5,14]. However, the SID values of AA in the three SBM sources were a bit less than those in the literature [5,14]. The SID values of AA in SBM reported in other previous studies [17,18] were similar to those in the present work. During SBM production process, soybean is dehulled, and then soyhulls are often added to the dehulled SBM after oil-extraction process resulting in SBM with hulls [19]. The concentration of CP in SBM is affected by the inclusion rate of hulls, and the AA concentration is highly correlated with the CP concentration [19]. In the present work, the SBM-KD 1 and 2 had greater concentrations of CP and most AA compared with SBM-I that contained hulls. The AA digestibility can be decreased as the inclusion rate of hulls or the dietary fiber content increases [20,21]. However, we failed to find the differences in the SID of AA among the three SBM sources used in the present study, in agreement with Park et al [22] who reported no difference in the SID of AA between two SBM sources with varying soy hull inclusion rates. A potential reason for this discrepancy is that the three SBM sources used in this work had similar fiber concentrations [6] regardless of hull inclusion rates.

The CP and most AA concentrations of HPDDG used in the present work were within the range of previously reported values [5,23–25]. However, there was a relatively large variability in CP and AA concentrations in the literature. The variability perhaps is attributed to different dehulling, degerming, or both processes before fermentation for ethanol production. Values for the SID of most AA in HPDDG determined in the present study were within the range of previous values [5,23–25]. Among the test ingredients in this study, HPDDG had most comparable values for the AA digestibility with SBM sources. Due to the low lysine and tryptophan concentrations in HPDDG, however, the value and the potential inclusion rate of HPDDG in swine diets would be limited.

The AA concentration in CM used in this study agreed with previously reported values [5,26,27]. The SID of most AA in CM used in this study was less than those in the literature. The fiber concentrations in CM used in the present work did not deviate much from the literature [5,26–28]. A previous study comparing the AA digestibility among seven sources of CM reported that the differences of 5% to 10% units were observed among the CM sources. This difference may have resulted from different genotypes of seeds and oil-extraction conditions [27,28].

The CP and AA concentrations in perilla meal, copra meal, CGM, and palm kernel expellers used in the present study agreed with values in the literature [5,11,29–31]. However, values for the SID of most indispensable AA in the test ingredients were less compared with those in the literature [5, 11,29–31]. It remains unclear why the SID of AA determined in this study were less than in the previously reported values. However, it has been reported that the digestibility of AA in the feed ingredients produced from the oil-extraction process can be affected by several factors including drying condition, heat damage, regional origins of grains or oilseeds, and species [27,31,32]. To our knowledge, the digestibility of AA in TDDG fed to the pigs has not been reported. The TDDG had less digestibility of most AA compared with other test ingredients used in this study. The reason for this result may be due to the high concentration of neutral detergent fiber and acid detergent fiber in TDDG [6,11].

In the present study, the AA digestibility of lysine was less than other indispensable AA in most test ingredients. In the oil-extraction and distillation processes, heating and drying are essential steps, and thus, byproducts can be damaged by heat. It has been reported that lysine is the most influenced by heat damage associated with Maillard reaction during the thermal processing [32]. In addition, anti-nutritional factors such as trypsin inhibitors, glucosinolates, and β-mannans in the plant protein sources may negatively affect AA digestibility [26,33]. The lack of analysis for anti-nutritional factors in the test ingredients is a limitation of the present study. Further research is warranted to quantify the influence of anti-nutritional factors on AA digestibility.

In conclusion, sources of SBM used in the present study had greater values for the SID of most AAs compared with other test ingredients. Although the HPDDG used in this study had high AA digestibility values comparable to the AA digestibility of SBM, digestible lysine and tryptophan concentrations in the HPDDG with solubles were less than those in SBM. Swine feed producers can use the data provided in the present work with combination with other nutrient concentrations and prices in determining the value of each ingredient.

ACKNOWLEDGMENTS

This work was supported by the Rural Development Administration (Republic of Korea; PJ907038). This paper was supported by Konkuk University Researcher Fund in 2017.

Footnotes

CONFLICT OF INTEREST

We certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.

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