Amino acid digestibility in rice co-products fed to growing pigs

Global production of rice is third in terms of total tonnage after corn and wheat. Rice is grown to produce polished white rice for human consumption. However, harvested rice, called paddy rice or rough rice, needs to be dehulled, which results in production of brown rice. The outer brown bran layer of brown rice, known as rice bran, also needs to be removed before polished white rice is produced. Approximately 20% of the paddy rice is hulls and the bran fraction is 8 to 10%, so only 70% of the paddy rice will become polished rice. Rice bran is high in fiber, and also contains about 15% crude protein and 14 to 20% fat. Rice bran can be fed as full fat rice bran or defatted rice bran. During milling of the rice, some kernels may get broken and cannot be used for human consumption. These broken kernels are known as broken rice or brewers rice and may also be used in animal feeding. Broken rice is high in starch and contains little fat, fiber, or protein.

Both rice bran and broken rice may be fed to pigs, but these ingredients are poorly characterized in terms of nutritional value. An experiment was, therefore, conducted to determine the standardized ileal digestibility (SID) of crude protein and amino acids in broken rice, two sources of full fat rice bran (FFRB), and defatted rice bran (DFRB) fed to growing pigs.

Experimental design

Seven growing pigs with an average initial body weight of 70.07 kg were fed one of six diets. The control diet was based on bakery meal, which is a mixture of by-products from the bakery and confectionary industries. Bakery meal was used because it is highly palatable to pigs. Four diets were formulated by mixing bakery meal with one of four rice co-products: broken rice, two sources of FFRB, and one source of DFRB. A nitrogen-free diet that was used to determine endogenous losses of crude protein and amino acids was also formulated. Because none of the diets contained sufficient amino acids to meet the requirements for growing pigs, an amino acid mixture was fed to the pigs in the adaptation periods to the diets. The apparent ileal digestibility of amino acids in the experimental ingredients was calculated using the difference procedure, and adjusted for endogenous losses to calculate standardized ileal digestibility.

Results

The SID of crude protein and all amino acids was greatest (P <0.01) in broken rice compared with the rice bran products (Table 2). This is likely due to the lower concentration of fiber in broken rice. The SID of crude protein was greater (P <0.01) in FFRB-1 than in FFRB-2, but the average SID of indispensable amino acids and of all amino acids did not differ between the two sources of FFRB. The SID of crude protein was the same in DFRB as in FFRB-2, but the mean SID of indispensable amino acids and of all amino acids was less (P <0.01) in DFRB than in the 2 sources of FFRB.

Although digestibility of amino acids was less in DFRB than in the other rice co-products, the relatively high concentration of crude protein and amino acids in DFRB (Table 1) meant that it had the greatest (P <0.001) concentration of standardized ileal digestible amino acids of the test ingredients (Table 3). The concentration of SID crude protein and amino acids was not different between FFRB-1 and FFRB-2. Broken rice, which has a low concentration of crude protein and AA, had the least (P <0.01) SID of crude protein and amino acids despite the high digestibility of amino acids in this product.

Key points

  • The SID of crude protein and amino acids in broken rice was greater than in the rice bran products.
  • Due to its higher fat content, FFRB had greater digestibility of amino acids compared with DFRB.
  • Because of its relatively high protein content, the concentration of standardized ileal digestible crude protein and amino acids is greatest in DFRB. Broken rice contains less SID crude protein and amino acids than any of the rice bran products.

Table 1. Analyzed nutrient composition (as-fed basis) of broken rice, full fat rice bran (FFRB-1 and FFRB-2), and defatted rice bran (DFRB)

 

Ingredient

Item, %

Broken rice

FFRB-1

FFRB-2

DFRB

GE, kcal/kg

4,399

4,554

5,044

4,348

DM, %

88.13

95.11

96.20

90.96

CP, %

7.67

14.30

15.31

17.08

AEE, %

0.85

17.06

19.28

1.09

Ash, %

1.25

8.69

8.04

11.97

Starch, %

76.83

25.58

29.58

28.30

ADF, %

0.46

9.42

9.09

11.98

NDF, %

0.61

14.76

14.13

19.27

Lignin, %

0.35

3.01

3.51

4.32

Indispensable AA, %

     

   Arg

0.52

1.11

0.61

1.21

   His

0.16

0.38

0.76

0.42

   Ile

0.29

0.47

0.27

0.59

   Leu

0.59

0.94

3.22

1.18

   Lys

0.28

0.65

0.55

0.79

   Met

0.20

0.27

1.18

0.33

   Phe

0.36

0.57

0.56

0.71

   Thr

0.25

0.49

0.35

0.63

   Trp

0.07

0.16

0.15

0.18

   Val

0.40

0.72

0.79

0.91

Total

3.12

5.76

8.44

6.95

Dispensable AA, %

     

   Ala

0.40

0.82

0.87

1.03

   Asp

0.63

1.15

1.26

1.49

   Cys

0.15

0.28

0.30

0.32

   Glu

1.23

1.76

1.86

2.09

   Gly

0.32

0.73

0.78

0.89

   Pro

0.35

0.58

0.62

0.78

   Ser

0.35

0.53

0.57

0.63

   Tyr

0.16

0.35

0.40

0.47

Total

3.59

6.20

6.66

7.70

Lys:CP ratio (%)

3.65

4.54

3.59 

4.62

 

Table 2. Standardized ileal digestibility (%) of CP and AA in broken rice, two sources of full fat rice bran (FFRB-1 and FFRB-2) and defatted rice bran (DFRB)

 

Ingredient

 

Item

Broken rice

FFRB-1

FFRB-2

DFRB

SEM

P-value

  CP, %

97.2a

83.9b

79.8c

78.7c

1.25

<0.0001

Indispensable AA, %

         

    Arg

98.7a

93.8b

92.2bc

90.5c

0.81

<0.0001

    His

95.1a

88.6b

87.0c

82.7d

0.67

<0.0001

    Ile

93.2a

83.5b

82.9b

78.4c

1.01

<0.0001

    Leu

94.1a

83.0b

82.8b

77.7c

0.95

<0.0001

    Lys

94.5a

88.5b

83.1c

82.3c

1.02

<0.0001

    Met

92.9a

87.4b

87.2c

78.7d

0.60

<0.0001

    Phe

94.0a

81.0b

81.1b

78.0b

2.22

<0.0001

    Thr

95.0a

81.4b

79.8bc

77.0c

1.41

<0.0001

    Trp

94.3a

84.6b

81.4bc

79.7c

1.35

<0.0001

    Val

94.2a

84.2b

83.6b

79.0c

0.97

<0.0001

Mean

94.9a

86.2b

85.0b

81.7c

1.01

<0.0001

Dispensable AA, %

         

    Ala

94.7a

85.8b

84.4b

82.3c

1.09

<0.0001

    Asp

94.4a

83.6b

79.8c

77.4d

0.90

<0.0001

    Cys

94.2a

81.2b

78.3b

74.5c

1.33

<0.0001

    Glu

94.1a

87.5b

86.4b

81.8c

1.03

<0.0001

    Gly

103.6a

81.0b

78.1bc

78.0b

3.40

<0.0001

    Pro

185.5a

127.0b

126.1b

134.7b

19.01

<0.0001

    Ser

96.3a

83.0b

81.3b

77.9c

1.06

<0.0001

Mean1

95.0a

86.2b

85.1b

81.7c

1.30

<0.0001

All AA

95.2a

85.3b

84.2b

80.5c

1.14

<0.0001

 a-dMeans within a row lacking a common superscript letter are different (P < 0.05).

1Values for Pro were not included in the calculated mean for dispensable AA.

Table 3. Concentrations (g/kg DM) of standardized ileal digestible CP and AA in broken rice, two sources of full fat rice bran (FFRB-1 and FFRB-2) and defatted rice bran (DFRB)

 

Ingredient

 

Item

Broken rice

FFRB-1

FFRB-2

DFRB

SEM

P-value

CP, g/kg DM

84.6c

126.1b

127.16b

148.3a

2.22

<0.001

Indispensable AA, g/kg DM

         

    Arg

5.8d

10.0c

11.3b

12.1a

0.10

<0.001

    His

1.7d

3.5c

3.6b

3.9a

0.04

<0.001

    Ile

3.1d

4.1c

4.4b

5.2a

0.64

<0.001

    Leu

6.3d

8.2c

8.7b

10.1a

0.11

<0.001

    Lys

3.0d

6.0b

5.5c

7.2a

0.83

<0.001

    Met

2.1c

2.5b

2.5b

2.9a

0.04

<0.001

    Phe

3.9c

4.9b

5.0b

6.1a

0.13

<0.001

    Thr

2.7c

4.2b

4.4b

5.4a

0.09

<0.001

    Trp

0.7d

1.4b

1.2c

1.6a

0.21

<0.001

    Val

4.3d

6.4c

6.8b

8.0a

0.95

<0.001

Mean

33.6c

52.2b

53.3b

62.7a

0.70

<0.002

Dispensable AA, g/kg DM

         

    Ala

4.3d

7.4b

5.2c

9.3a

0.11

<0.001

    Asp

6.7c

10.1b

10.3b

12.8a

0.14

<0.001

    Cys

1.6c

2.4b

2.4b

2.6a

0.05

<0.001

    Glu

13.1c

16.2b

16.3b

18.8a

0.25

<0.001

    Gly

3.8c

6.2b

6.0b

7.7a

0.28

<0.001

    Pro

7.4b

7.7b

7.6b

12.1a

1.07

<0.001

    Ser

3.8c

4.6b

4.7b

5.5a

0.07

<0.001

Mean

37.2c

51.9a

49.7b

51.9a

0.97

<0.001

All AA

70.8c

104.2b

103.2b

126.1a

1.65

<0.001

a-dMeans within a row lacking a common superscript letter are different (P < 0.05).

This report is based on unpublished research by Gloria Casas-Bedoya and Hans H. Stein.

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