Amino acid digestibility in soy protein concentrate with different particle sizes fed to weanling pigs

Soy protein concentrate is produced by aqueous ethanol extraction of water-soluble carbohydrates from soybean meal, followed by heat treatment. The ethanol extraction process removes soluble carbohydrates, leaving a product that contains at least 65% crude protein. Because soy protein concentrate contains reduced levels of oligosaccharides, trypsin inhibitors, and lectins compared with conventional soybean meal, it can be used in diets for weanling pigs.

Reducing the particle size of soybean meal can increase amino acid digestibility due to the increased surface area for enzymes to work on. However, there are no known data on the effect of particle size on amino acid digestibility in soy protein concentrate. Therefore, an experiment was conducted to determine the digestibility of crude protein and amino acids in soy protein concentrate ground to three different particle sizes and to compare these values to values for soybean meal and fish meal when fed to weanling pigs.

Materials and methods

Weanling barrows with an average initial body weight of 12.9 kg were equipped with a T-cannula in the distal ileum and allotted to one of six diets. Three sources of soy protein concentrate were used: X-SOY 80, with a particle size of 80 microns; X-SOY 200 (200 microns); and X-SOY 600, (600 microns). Five diets were formulated using one of the soy protein concentrate sources, soybean meal, or fish meal as the only source of amino acids. The final diet was a nitrogen-free diet that was used to measure the basal endogenous losses of crude protein and amino acids.

In each period, after a five day adaptation period to the diet, ileal digesta were collected and analyzed to determine the apparent ileal digestibility of crude protein and amino acids. This was then corrected for basal endogenous losses to calculate standardized ileal digestibility (SID).

Results

The SID of crude protein did not differ among the X-SOY products, and was greater (P < 0.05) in X-SOY than in fish meal and soybean meal (Table 1).

The SID of arginine was greater (P < 0.05) in X-SOY 80 and X-SOY 200 than in X-SOY 600, soybean meal or fish meal. The SID of isoleucine was the same in the X-SOY products and fish meal, but was greater (P < 0.05) in X-SOY 80 and X-SOY 200 than in soybean meal. The SID of leucine was the same in the X-SOY products and fish meal, and greater (P < 0.05) in those ingredients than in soybean meal. The SID of phenylalanine did not differ among X-SOY products, but was greater (P < 0.05) in X-SOY 80 and X-SOY 200 than in soybean meal or fish meal. The SID of tryptophan was the same in X-SOY 80, X-SOY 200, and fish meal, and greater (P < 0.05) in X-SOY 200 than in X-SOY 600 or soybean meal.

The SID of other indispensable amino acids, the mean SID of indispensable amino acids, and the mean of all amino acids did not differ among the tested ingredients. The SID of dispensable amino acids also did not differ with the exception of tyrosine, for which SID was greatest (P < 0.05) in X-SOY 80 and X-SOY 200.

Key points

  • The digestibility of crude protein and most indispensable amino acids in X-SOY 80 and X-SOY 200 was greater than in soybean meal.
  • For a few amino acids, digestibility values in X-SOY 200 were also greater than in fish meal.
  • When feeding soy protein concentrate to weanling pigs, a particle size of approximately 200 microns may maximize digestibility of indispensable amino acids.

Table 1. Standardized ileal digestibility (SID) of CP and AA in soybean meal (SBM), X-SOY 80, X-SOY 200, X-SOY 600, and fish meal by weanling pigs

Item

SBM

X-SOY 80

X-SOY 200

X-SOY 600

Fish meal

SEM

P-value

CP, %

83.87c

90.52ab

91.53a

87.45abc

85.89bc

1.83

< 0.05

Indispensable AA, %

  Arg

94.45b

97.37a

97.77a

94.81b

92.73b

1.01

< 0.01

  His

87.79

92.26

93.40

90.11

89.47

1.53

0.09

  Ile

87.11b

91.45a

92.47a

89.54ab

90.04ab

1.25

< 0.05

  Leu

86.83b

91.53a

92.56a

90.84a

91.27a

1.14

< 0.05

  Lys

85.34

90.33

92.74

89.94

91.07

1.74

0.078

  Met

89.36

92.11

91.03

88.77

90.29

1.38

0.254

  Phe

86.40c

92.59a

93.43a

90.67ab

88.70bc

1.12

< 0.01

  Thr

84.72

88.95

90.87

88.26

91.88

1.82

0.097

  Trp

87.29c

93.60ab

94.52a

89.84bc

92.94ab

1.42

< 0.05

  Val

86.15

90.46

91.49

88.52

89.64

1.49

0.118

  Mean

87.70

92.17

93.13

89.99

90.85

1.33

0.052

Dispensable AA, %

  Ala

82.73

87.78

88.81

85.96

87.52

1.85

0.174

  Asp

84.23

84.24

86.75

82.06

85.60

1.73

0.276

  Cys

75.03

79.85

81.00

72.32

83.89

4.20

0.216

  Glu

83.23

89.99

91.31

88.57

89.68

2.05

0.095

  Gly

79.25

88.69

90.93

87.90

83.08

3.57

0.183

  Pro

92.23

96.38

101.57

96.70

96.75

1.95

0.057

  Ser

89.07

93.46

94.33

91.78

89.92

1.33

0.051

  Tyr

87.72c

93.39ab

94.32a

90.74bc

89.63c

1.28

< 0.01

  Mean

84.49

89.33

90.66

86.55

88.40

2.01

0.20

All AA

85.99

90.66

91.80

88.16

89.58

1.67

0.119

a-c Within a row, means followed by the same or no superscript letter are not different (P > 0.05).

This report is based on unpublished research by Chengfei Huang and Hans H. Stein.

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