The Use of True Digestible Amino Acids in Diet Formulation

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In practical terms, the digestibility concept chosen for the evaluation of the individual feed ingredients will have a major impact on the ranking of these feedstuffs. For example,

Table 10.6. Comparison of true ileal protein and amino acid digestibility values (%) in selected feedstuffs.

Ingredients Barley Wheat

Crude protein NRC (1998) Rademacher etal. (1999) 80 89

Ami Pig (2000) 80 88

Rademacher et al. (1999) 76 84

AmiPig (2000) 75 81

Rademacher etal. (1999) 82 90

AmiPig (2000) 84 89

Rademacher et al. (1999) 81 89

AmiPig (2000) 84 90

Rademacher et al. (1999) 80 86

AmiPig (2000) 75 83

Rademacher etal. (1999) 77 88

AmiPig (2000) 79 88

PS3S

Rapeseed Soybean Sugarbeet meal meal pulp

74 80

76 76

70 73

73 76

81 87

75 84

71 75

71 80

87 87

90 88

86 87

86 86

87 86

46 53

50 64

50 41

apparent and true ileal lysine and threonine digestibilities in some low- and high-protein feedstuffs, are ranked in Tables 10.7 and 10.8, respectively, in relation to soybean meal as a reference. In comparison to true ileal digestibility values the corresponding apparent digestibility coefficients systematically underestimate the digestibility of both, lysine and threonine (and other amino acids), in low protein grain cereals such as wheat, barley, maize and triticale. On the other hand, the consequences of different digestibility estimates on the ranking of high-protein feedstuffs such as oilseed meals and legume seeds are much less pronounced.

It is claimed that the application of true protein and amino acid digestibility values in diet formulation for growing pigs will promote the use of alternative low-protein feedstuffs and various by-products of the food processing industry. In the following two examples, two commercially available diets, referred to as reference diets, are formulated to contain as main ingredients maize and soybean meal (Table 10.9) or barley, wheat and soybean meal (Table 10.10). These diets contained equal levels of ME (13.5 MJ kg N x 6.25 (183 g kg-1) and total lysine (10.5 g kg-1). Through complete or partial replacement of maize, barley, wheat and soybean meal in the

Table 10.7. Ranking of feed ingredients based on apparent and true ileal lysine digestibility values. (Adapted from Rademacher eta!., 1999.)

Apparent digestibility True digestibility

Table 10.7. Ranking of feed ingredients based on apparent and true ileal lysine digestibility values. (Adapted from Rademacher eta!., 1999.)

Ingredients

Absolute (%)

Relative3 (%)

Absolute (%)

Relative3 (%)

Soybean meal

88

100

89

100

Wheat

75

85

84

94

Triticale

75

85

83

93

Barley

67

76

76

85

Maize

62

70

76

85

Sunflower meal

76

86

79

89

Rapeseed meal

71

81

74

83

Peas (field)

79

90

81

91

Beans (field)

80

91

82

92

aRelative to soybean meal.

Table 10.8. Ranking of feed ingredients based on apparent and true ileal threonine digestibility values. (Adapted from Rademacher et a/.. 1999.)

Apparent digestibility True digestibility

Table 10.8. Ranking of feed ingredients based on apparent and true ileal threonine digestibility values. (Adapted from Rademacher et a/.. 1999.)

Ingredients

Absolute (%)

Relative3 (%)

Absolute (%)

Relative3 (%)

Soybean meal

83

100

86

100

Wheat

72

87

86

100

Triticale

65

78

79

92

Barley

65

78

80

93

Maize

63

76

80

93

Sunflower meal

76

92

80

93

Rapeseed meal

67

81

71

83

Peas (field)

69

83

76

88

Beans (field)

71

86

77

90

3Relative to soybean meal.

reference diets by alternative protein sources such as cottonseed meal, canola meal and peas and by-products such as wheat bran and rice bran, two types of diets were formulated, referred to as mixed diets type A and B (Tables 10.9 and 10.10).

The mixed diets type A were formulated to contain the same level of ME (13.5 MJ kg-1), N x 6.25 (183 g kg-1) and total lysine (10.5 kg-1) as the corresponding reference diets in Tables 10.9 and 10.10. However, due to the substitution of dietary components with a relatively high true ileal digestibility of lysine by those with lower digestibility coefficients, lower contents of true ileal digestible lysine in the mixed diets type A in comparison to the corresponding reference diets were obtained.

The level of true ileal digestible lysine in the mixed diets type A declined from 9.2 to 8.8 g kg-1 (Table 10.9) and from 9.4 to 8.7 g kg-1 (Table 10.10) as compared to the reference diets based on maize and soybean meal and barley, wheat and soybean meal, respectively. This decline in the content of true ileal digestible lysine would certainly have a negative effect on the growth performance of pigs, provided that these figures are below the actual lysine requirement of the pigs.

As a further example, two mixed diets type B were formulated that contained the same level of ME (13.5 MJ kg-1) and N x 6.25 (183 g kg-1) as compared to the reference diets and the mixed diets type A (Tables 10.9 and 10.10). However, to compensate

Table 10.9. The use of true ileal digestible lysine in the formulation of a maize-soybean meal-based diet and two types of mixed di

Maize-soybean meal

Mixed diet Aa

Mixed diet Bb

Ingredient (g kg 1)

Maize

543

380

356

Wheat middlings

200

170

210

Soybean meal (440 g CP kg-1)

223

149

177

Rice bran

-

200

190

Cottonseed meal

-

63

30

Tallow

-

7.4

06.8

dl-Methionine

0.8

0.7

01.0

l-Lysine-HCI

2.4

3.0

03.0

l-Threonine

0.6

0.8

00.8

Vitamins and minerals

30.2

26.1

25.4

Energy and nutrients

ME (MJ kg-1)

13.5

13.5

13.5

N X 6.25 (g kg 1)

183

183

183

Lysine (g kg 1)

10.5

10.5

108

Lysine, true ileal digestible (g kg 1)

9.2

8.8

92

Feed cost (US$ per 100 kg)0

12.56

11.46

11.45

aFormulated to contain equal levels of crude protein and total lysine as maize-soybean meal diet. bFormulated to contain equal levels of crude protein and true ileal digestible lysine as the maize-soybean meal diet.

┬░Based on US ingredient prices, February 2002.

for the lower content of true ileal digestible lysine in the mixed diets type A, the total dietary lysine level was elevated by supplemental lysine addition. As a result, there was no difference in the level of true ileal digestible lysine between the reference diets and the corresponding mixed diets type B. Consequently, no negative impact on growth performance of pigs could be expected.

Formulating more complex mixed diets according to type A, while maintaining the same level of total lysine as in the reference diets based on maize and soyabean meal or barley, wheat and soybean meal, significantly reduced feed costs by approximately 8-9% (Tables 10.9 and 10.10). However, replacements of grain cereals and soybean meal by increasing proportions of alternative protein sources and by-products resulted in a pronounced decline in the level of true ileal digestible lysine which, in turn, most likely will result in a loss of growth performance.

On the other hand, formulating more complex diets according to type B by maintaining the same levels of true ileal digestible lysine as in the reference diets decreased feed costs by approximately 9 and 3% as compared to the reference diets based on maize and soybean meal (Table 10.9) and barley, wheat and soybean meal, respectively (Table 10.10). In other words, savings in feed costs varied between 3 and 9% compared with standard diets based on cereal grains and soybean meal while maintaining the same content of true ileal digestible lysine in the diets. Therefore, the use of true ileal amino acid digestibility values in diet formulation for growing pigs offers the potential not only to improve the precision of diet formulation but also to improve the productivity in pig production through lower feed costs.

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