Applications of Ideal Amino Acid Ratios

Best estimates of digestible lysine requirements of male and female broiler chicks as a function of age are presented in Fig. 13.7. Requirements are expressed as g kg-1 for diets containing 13.4 MJ kg-1 metabolizable energy. Using the revised and updated ideal AA ratios shown in Tables 13.5 and 13.6 together with the regression equations presented in Fig. 13.7, one can calculate digestible AA requirements for broiler chicks at any age period. This was done for three different age periods in Table 13.6 using average ages of 10.5 days (0-21 days), 31.5 days (21-42 days) and 49 days (42-56 days) for substitution into the regression equations for

Fig. 13.7. Plot of the digestible Lys requirement (y) of male (•) and female (♦) broiler chicks as a function of age (x) for diets containing 13.4 MJ kg 1 metabolizable energy (ME). The requirement values for 0-21 days of age (average = 10.5 days) came from Han and Baker (1991, 1993), for 21-42 days of age (average = 31.5 days) from Han and Baker (1994), and for 42-56 days of age (average = 49 days) from NRC (1994).

Age (days)

Fig. 13.7. Plot of the digestible Lys requirement (y) of male (•) and female (♦) broiler chicks as a function of age (x) for diets containing 13.4 MJ kg 1 metabolizable energy (ME). The requirement values for 0-21 days of age (average = 10.5 days) came from Han and Baker (1991, 1993), for 21-42 days of age (average = 31.5 days) from Han and Baker (1994), and for 42-56 days of age (average = 49 days) from NRC (1994).

Table 13.5. Summary of true digestible requirements of male chicks fed a maize gluten meal semipurified diet during the second and third week of life: extrapolation to ideal ratios relative to lysine.

Amino acid

Assay

Broken-line requirement estimate (g kg 1) Weight gain Gain/feed

Ratio

(%)a

Lysine

1

8.46

9.64

100

Lysine

2

8.49

9.56

100

Tryptophan

3

1.59

1.57

16.6

Threonine

4

5.35

5.33

55.7

Isoleucine

5

5.89

5.81

61.4

Valine

6

7.44

7.43

77.5

Arginine

7

10.14

-

105.6

aBased on Assays 1-6, using the higher of requirement estimates for gain and gain/feed ratio. Requirement values were ratioed to the average Lys requirement for gain/feed of 9.60 g kg-1.

Table 13.6. Predicted requirements (g kg 1) for digestible amino acids in broiler chicks at three different growth periods3.

Amino acid

Ideal ratio (%)

0-21 days

21-

-42 days

42-56 days

Male

Female

Male

Female

Male

Female

Lysine

100

11.1

10.2

9.2

8.6

7.6

7.3

Methionine

36

4.0

3.7

3.3

3.1

2.7

2.6

Cystine

36

4.0

3.7

3.3

3.1

2.7

2.6

SAAb

72

8.0

7.4

6.6

6.2

5.4

5.2

Threonine

56 (58)°

6.2

5.7

5.3

5.0

4.4

4.2

Tryptophan

17

1.9

1.7

1.6

1.5

1.3

1.2

Valine

78

8.7

8.0

7.2

6.7

5.9

5.7

Isoleucine

61

6.8

6.2

5.6

5.2

4.6

4.5

Leucine

109

12.1

11.1

10.0

9.4

8.3

8.0

Arginine

105

11.7

10.7

9.7

9.0

8.0

7.7

Histidine

35

3.9

3.6

3.2

3.0

2.7

2.6

Phe + Tyr

105

11.7

10.7

9.7

9.0

8.0

7.7

aThe digestible Lys requirement for each age group was calculated based on the equations presented in Fig. 13.7, after which the ideal AA ratios were used to calculate requirements for the other amino acids. A dietary ME value of 13.4 MJ kg 1 is assumed for all age periods. bSAA, sulphur amino acids.

°Based on the report of Emmert and Baker (1997), the ideal Thr:Lys ratio is projected to be 2 percentage units higher for the 21 -42 day and 42-56 day age periods than for the 0-21 -day age period.

purposes of calculating the digestible lysine requirement.

It is noteworthy that among the AA evaluated by Baker et al. (2002), only lysine resulted in a higher requirement for feed efficiency than for weight gain. However, the SAA requirement may be similar to the lysine requirement in this regard (Schutte and Pack, 1995; Baker et al., 1996; Mack et al.,

1999). Mack et al. (1999) evaluated breast yield as well as weight gain and feed efficiency in their AA requirement studies. Among the AA studied (lysine, methionine, threonine, tryptophan, arginine, isoleucine and valine), there was little evidence that the requirements for maximal breast yield were higher than the requirements predicted for either weight gain or feed efficiency.

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