Effects of pelleting and extrusion on energy and nutrient digestibility in diets fed to pigs

Pelleting and extrusion are technologies that have been used in livestock feeding to improve nutrient digestibility and feed conversion. Recent research concluded that reduced performance of pigs fed diets containing high concentrations of fiber was ameliorated if the diets were pelleted. Extrusion is also of benefit in high fiber diets, because it may increase the solubility of dietary fiber. It is possible that the benefits of extrusion and pelleting are greater in high fiber diets than in low fiber diets, but this hypothesis has not been investigated. Therefore, an experiment was conducted to determine effects of extrusion and pelleting on energy and nutrient digestibility in diets containing low, medium, or high concentrations of fiber.

Experimental design

Twenty-four growing barrows were used in the experiment. Diets containing three different levels of fiber were formulated. The low fiber diet was based on corn and soybean meal, the medium-fiber diet was based on corn, soybean meal, and 25% DDGS, and the high-fiber diet was based on corn, soybean meal, 25% DDGS, and 20% soybean hulls. All ingredients were ground to an average particle size of approximately 500 microns and after mixing, each of the three diets were divided into four batches that were either fed in a mash form without further treatment, pelleted, extruded, or extruded and pelleted before feeding. Ileal digesta were collected to determine apparent ileal digestibility (AID) of energy and nutrients. Feces and urine were collected to determine apparent total tract digestibility (ATTD) of energy as well as concentrations of digestible (DE) and metabolizable (ME) energy.

Results

Pelleting increased (P < 0.01) the AID of gross energy, crude protein, and dry matter in low fiber diets, and the AID of starch in medium fiber diets (Table 1). Extrusion increased (P < 0.01) the AID of gross energy, crude protein, and dry matter in all diets, and starch in medium fiber diets. Pelleting of extruded diets did not increase the AID of energy and nutrients compared with extrusion alone.

Pelleting did not increase the mean AID of amino acids compared with meal in the low, medium, or high fiber diets. However, pelleting did increase (P < 0.01) the digestibility of some indispensable amino acids, including lysine, in the low and medium fiber diets.

The mean AID of amino acids was greater (P < 0.01) in extruded diets than in meal or pelleted diets at all levels of dietary fiber. Amino acid digestibility in extruded medium fiber diets was greater (P < 0.01) than in low fiber diets fed in meal or pelleted form, and amino acid digestibility in extruded high fiber diets was equivalent to that of low fiber diets fed in meal form. Pelleting of extruded diets did not improve amino acid digestibility compared with extrusion alone.

Pelleted low and medium fiber diets had greater (P < 0.01) ATTD of gross energy and contained more (P < 0.01) DE and ME than the same diets fed in meal form (Table 2). Extruded diets contained more (P < 0.01) DE and ME on a dry matter basis than meal diets at the high level of fiber. Regardless of fiber level, diets that were both extruded and pelleted always had greater (P < 0.05) ATTD of gross energy and contained more (P < 0.05) DE and ME than diets fed in meal form.

Key points

  • Pelleting and extrusion increase the digestibility of energy and amino acids in diets based on corn and soybean meal or corn, soybean meal and DDGS.
  • Extrusion also increases the digestibility of energy and amino acids in high fiber diets based on corn, soybean meal, DDGS, and soybean hulls.
  • Pelleting and extrusion may reduce the total costs of feed needed to produce a market pig by improving feed conversion and reducing the amount of soybean meal needed in the diets.

 

Table 1. Apparent ileal digestibility (AID) of gross energy and nutrients in experimental diets with three different levels of fiber and fed in meal, pelleted (Pel), extruded (Ext), or pelleted and extruded (Pel/Ext) form, as-fed basis

 

Low fiber

Medium fiber

High fiber

P-value

Item

Meal

Pel

Ext

Pel/Ext

Meal

Pel

Ext

Pel/Ext

Meal

Pel

Ext

Pel/Ext

 

GE, %

72.83bc

76.87a

78.56a

78.23a

68.92d

70.34cd

77.58a

73.33b

56.73f

58.09f

61.85e

61.33e

< 0.01

Starch, %

97.80bcd

98.68ab

98.94ab

99.19a

95.31f

97.95bcd

98.31ab

98.03abc

96.06ef

96.77cde

96.58def

97.84abc

< 0.01

CP, %

73.75e

76.68cd

79.99ab

79.77ab

74.65de

75.80cde

80.74a

77.42bc

68.94f

68.17f

73.00e

72.72e

< 0.01

DM, %

71.68b

74.59a

76.38a

76.04a

67.01c

68.17c

75.15a

70.57b

53.13e

54.30e

58.57d

57.22d

< 0.01

Ash, %

23.11de

26.42cd

33.31b

31.78b

31.16bc

31.12bc

42.63a

32.36b

10.70g

15.99f

21.31de

17.97ef

< 0.01

Indispensable AA

                       

  Arg

88.80bc

89.64b

92.53a

92.57a

89.36b

89.41b

92.40a

90.96ab

86.63d

86.81cd

89.78b

90.05b

< 0.01

  His

85.83ab

87.08a

87.41a

87.63a

83.56bc

86.65a

87.60a

86.24a

79.93e

81.10de

82.32cd

83.05cd

< 0.01

  Ile

80.20e

83.89bc

85.69ab

85.48ab

81.06de

82.55cd

86.27a

83.99bc

75.00g

77.57f

81.01de

81.82cde

< 0.01

  Leu

83.06ef

86.38bc

87.61ab

87.43ab

84.10de

86.11bc

88.95a

86.87b

79.51g

82.07f

84.86de

85.04cd

< 0.01

  Lys

80.99cd

83.91a

84.77a

83.40ab

79.43de

80.82bc

83.31ab

81.10bc

73.58f

74.05f

77.24e

78.19e

< 0.01

  Met

84.28d

88.11ab

88.29ab

87.76ab

83.82d

87.17bc

89.28a

87.24bc

81.74e

84.06d

85.53d

85.49cd

< 0.01

  Phe

81.98fg

85.53cd

87.72ab

87.44ab

83.40ef

85.06d

88.84a

86.98bc

78.33h

81.11g

85.22de

85.17cde

< 0.01

  Thr

71.48de

75.71abc

76.63ab

75.62bc

72.85cd

74.49bcd

78.66a

75.68bc

68.27f

69.82ef

71.92de

73.19cd

< 0.01

  Trp

80.12d

82.61bc

84.89ab

84.54ab

80.94cd

82.86bc

85.76a

85.09ab

73.11f

75.96e

78.94d

80.62cd

< 0.01

  Val

77.22d

81.30ab

82.19ab

81.81ab

78.13cd

80.02bc

83.46a

80.61b

71.57f

73.78e

75.74d

77.75cd

< 0.01

  Mean

81.74f

84.75bc

86.19ab

85.86ab

82.16ef

83.81cde

86.84a

84.86bcd

77.30g

78.71g

81.63f

82.40def

< 0.01

Dispensable AA

                       

  Ala

76.32cd

79.94b

81.81ab

81.49ab

76.93cd

79.11bc

83.58a

80.68b

71.14e

73.25e

75.53d

76.46cd

< 0.01

  Asp

79.47bc

81.91a

82.92a

81.97a

77.89cde

78.26cde

81.72ab

79.38cd

72.57g

74.30fg

76.22ef

76.83de

< 0.01

  Cys

69.93bc

74.08a

70.30abc

70.14abc

67.70cde

70.31abc

72.06ab

68.88abcd

62.52ef

61.38f

61.41f

63.88def

< 0.01

  Glu

82.81cd

86.59ab

87.80a

88.06a

81.34de

84.56bc

87.29a

85.83abc

76.43f

78.23ef

81.18d

83.24cd

< 0.01

  Gly

58.12cde

61.17bc

66.12ab

66.12ab

59.91bcd

59.72bcd

69.98a

63.08bc

49.35ef

43.55f

52.11de

52.96de

< 0.01

  Pro

55.86cde

47.48de

74.32ab

74.77ab

72.84ab

67.05abc

76.76a

78.46ab

66.90abc

46.36e

63.85abcd

59.01bcd

< 0.01

  Ser

80.06e

82.58bc

84.13ab

83.47ab

80.66cde

82.22bcd

85.52a

83.57b

76.47g

77.75fg

79.15ef

80.14de

< 0.01

  Tyr

83.55ef

87.07bcd

88.53ab

88.79ab

85.45de

87.63bc

90.10a

88.55ab

81.88f

83.91e

85.16de

85.90cd

< 0.01

  Mean

76.44bc

77.79bc

82.38a

82.31a

77.36bc

77.13bc

82.69a

79.94ab

71.69de

70.47e

74.56cd

74.97c

< 0.01

Total AA

79.08de

81.07cd

84.09ab

83.86ab

79.54de

80.31cde

84.66a

82.24bc

74.23f

74.82f

77.89e

78.55de

< 0.01

a-hMeans within a row lacking a common superscript letter differ (P < 0.05).

 

Table 2. Apparent total tract digestibility of gross energy and concentration of digestible and metabolizable energy in experimental diets, as-fed basis

 

Low fiber

Medium fiber

High fiber

P-value

Item

Meal

Pel

Ext

Pel/Ext

Meal

Pel

Ext

Pel/Ext

Meal

Pel

Ext

Pel/Ext

 

  ATTD of GE, %

89.4b

90.8a

89.8ab

90.8a

84.7d

86.4c

85.1d

86.5c

80.0f

80.7ef

81.8e

81.9e

< 0.01

  DE, kcal/kg

3502ef

3561f

3691b

3708b

3532de

3588c

3755ab

3805a

3343g

3345g

3568cdf

3428f

< 0.01

  DE, kcal/kg DM

4105cd

4184a

4117bc

4168ab

4027d

4114abc

4078cd

4136abc

3777g

3810fg

3853ef

3888e

< 0.01

  ME, kcal/kg

3300f

3361de

3490bc

3520b

3325ef

3396d

3549ab

3605a

3172g

3206g

3415f

3278ef

< 0.01

  ME, kcal/kg DM

3868cd

3949ab

3893abc

3957a

3791de

3894abc

3855bcd

3919abc

3583g

3651fg

3687f

3717ef

< 0.01

a-gMeans within a row lacking a common superscript letter differ (P < 0.05).

This report is based on unpublished research by Oscar Rojas and Hans H. Stein.

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