Ajinomoto Bulletin 36 En

Today broiler feed formulations are not only focused on minimising costs; they also have to take into consideration environmental issues and their impact on broiler health. European Union regulations limit and reduce nitrogen pollution in the environment (directive 96/61/EC) and have banned the use of antimicrobial growth promoters. Reducing excess dietary protein is an important way of addressing these issues.

By reducing the nitrogen input to farms, reduced protein diets lower the nitrogen output to the environment. For instance in broilers, a reduction of 2 points of dietary protein content results in a 13% to 14% reduction in nitrogen excretion (Bregendahl et al., 2002; Jialin et al., 2004). In addition, health conditions can be improved by reducing the dietary protein supply. The crude protein level is reported as a predisposing factor for necrotic enteritis (Dahiya et al., 2005; Mc Devitt et al., 2006; van Immerseel et al., 2004 and Drew et al., 2004). Moreover, an excess of protein would lead to a physiological need for an increase in water consumption to achieve efficient nitrogen excretion. As a consequence, high crude protein diets lead to

higher levels of nitrogen and water excretion compared with low crude protein diets, leading to deterioration in litter quality and the birds environment (Lensing and van der Klis, 2006).

Instead of formulating on dietary crude protein levels, the broiler feed formulator can focus on each individual amino acid since crude protein is an attempt to represent amino acid supply but not the quality of this supply. When reducing crude protein, broiler performance will be limited by the indispensable amino acids that do not meet birds requirements. Amino acids which are said to be indispensable cannot be synthesized by the organism. They must therefore be provided in the feed so that they can be used in the synthesis of body proteins and thus support the process of growth. When the supply of one of the indispensable amino acids does not meet the animals requirement, it is said to be limiting. The present bulletin aims to determine which amino acids are next limiting in broiler diets after sulphur amino acids, lysine and threonine, in order to help the feed formulator reduce dietary crude protein levels and formulate broiler feeds more precisely.

Information N 36June 2010

G O TO E S S E N T I A L S

2 | Information n 36 | AJINOMOTO EUROLYSINE s.a.s.

Update on the next limiting amino acids in broiler feeds

Valine and IsoleucineReducing dietary crude protein level

I. Valineandisoleucinearethenextlimitingaminoacidsinbroilersdiets ................................................................................................................................................................................................ 3

II. Valineandisoleucinerequirementintheliterature ................................................................... 5 A. Published valine and isoleucine ratios to lysine ................................................................................................................ 5 B. Explanation of the variability in publishedVal:Lys and Ile:Lys ratios .................................................. 5

III. Valinerequirementsofbroilers ......................................................................................................................................... 8 A. TD valine requirement as ratio to lysine .................................................................................................................................... 9 B. TD valine requirement as amount of the feed .................................................................................................................. 11

IV. TDIle:Lysrequirementofbroilers ............................................................................................................................ 13

V. Practicalimplicationsforbroilerdiets ............................................................................................................. 20

Conclusions .......................................................................................................................................................................................................... 22

References .............................................................................................................................................................................................................. 23

Focus1: Classification of amino acids for broilers ...................................................................................................................... 4Focus2: Interactions between branched chain amino acids ....................................................................................... 17Focus3: Broilers leucine requirements ................................................................................................................................................. 18Focus4: Branched chain amino acid profiles in feedstuffs are not consistent ..................................... 19

AJINOMOTO EUROLYSINE s.a.s. | Information n 36 | 3

I. Valineandisoleucinearethenextlimitingaminoacidsinbroilersdiets

To reduce dietary crude protein (CP) levels in broiler feed, it is necessary to know which indispensable amino acids become limiting in diets and what the requirement of broilers is (Focus 1 p 4). Depending on the requirement assumed for each amino acid, valine, isoleucine, tryptophan and arginine are generally considered as the next limiting amino acids in broiler after sulphur amino acids, lysine and threonine.

>Feedstuffsusedinbroilerdietsinfluencethe4thlimitingaminoacidThe amino acid composition of protein differs between feedstuffs and can impact the order in which amino acids become limiting in diets.Recent work of Corzo et al. (2007) tried to predict the 4th limiting amino acid in broiler diets. The authors made simulations for the whole broiler growing period with their respective minimum nutritional requirements. The summary of the simulations is presented in Table 1.

Broiler age (days) 1-12 13-22 23-35 36-48 >49

Nutritional constraints

AME (kcal) 3050 3075 3100 3125 3150

TD* Lysine (%) 1.27 1.09 1.00 0.95 0.89

TD Sulphur amino acids (%) 0.92 0.81 0.76 0.74 0.70

TD Threonine (%) 0.80 0.70 0.65 0.63 0.60

TD Valine (%) 1.00 0.87 0.80 0.77 0.73

TD Isoleucine (%) 0.86 0.75 0.71 0.68 0.65

TD Arginine (%) 1.30 1.13 1.05 1.01 0.96

TD Tryptophan (%) 0.20 0.18 0.16 0.16 0.15

4th limitingAA depending on the main feedstuffs

Corn SBM Val Val Val Val Val

Wheat SBM Val Val Val Val Arg

Sorghum SBM Val Val Val Val Arg

Corn SBM MBM Val Val ValIle ValIle Ile

Wheat SBM MBM Val Val Ile Ile Ile

Sorghum SBM MBM Val Val ValIle ValIle Ile

Table 1: Prediction of the 4th liming amino acid in broiler diets (Corzo et al., 2007) (SBM = soybean meal; MBM = meat and bone meal; TD True Digestible).

In vegetable diets based on corn, wheat and sorghum, valine appears to be the 4th limiting amino acid. When animal by products are included in the diets, isoleucine becomes the 4th colimiting amino acid with valine.

An equivalent formulation study (Kidd and Hackenhaar, 2005) done on broiler grower diets gave the same results. Valine appears to be the 4th limiting amino acid in vegetable diets, and it is isoleucine when animal byproducts were used.

>TherankingofthelimitingaminoacidsdependsonthebroilerrequirementlevelsA study carried out by Fernandez et al. (1994) on 821 day chicks determined which amino acids were limiting in corn soybean meal based diets. Amino acid levels of the control diet were according to Baker and Chung (1992) specifications. The authors used the deletion method (amino acid supply was reduced one after another) and observed average daily gain (ADG) and gain:feed ratio (G:F) of the birds (Figure 1 shows the results for G:F; results for weight gain gave the same ranking of limiting amino acids).


Focus 1

Methionine, lysine and threonine were the 1st limiting amino acids for broiler performance

This trial confirmed that valine was the 4th limiting amino acid for broilers ahead of arginine and tryptophan in a corn soybean meal diet.

In another study carried out by Corzo et al. (2007) on 2142 day broilers, not done by amino acids deletions but by amino acids additions, confirmed this result. They fed a negative control diet (17.5% CP) based on corn and soybean meal with 1.0 kg/tonne of LValine or LIsoleucine or LArginine. Best broiler performance was achieved with the diet supplemented with LValine. This study confirmed that valine was limiting before isoleucine and arginine.

The present bulletin will focus on the valine and isoleucine requirements of broilers because they appear to be limiting before tryptophan and arginine. By knowing precisely the requirements, feed formulators will be able to reduce dietary crude protein levels and to formulate broiler diets more accurately.

Valine appears to be the 4th limiting amino acid in vegetable broiler diets after sulphur amino acids, lysine and threonine.

When animal by-products are used, isoleucine becomes co-limiting with valine.

a

d

c

b

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Control Control-L-Val

Control-L-Arg

Control-L-Trp

Gain:Feed(g/g)

Figure 1: Order of limiting amino acids in the protein of a corn soybean meal diet for chick growth (Fernandez et al., 1994). Columns with different letters are significantly different (P


II. Valineandisoleucinerequirementintheliterature

The first part of this section describes the available data on Val:Lys and Ile:Lys ratios in the literature and explains the existing variability between published data. The last part will describe the materials and methods used in this bulletin to determine valine and isoleucine requirements of broilers.

A. Publishedvalineandisoleucineratiostolysine

A literature survey was conducted to review valine and isoleucine published requirements. The ratio to lysine is a common way of expressing amino acid requirements and sixty Val:Lys and fiftyeight Ile:Lys (total and digestible) recommended ratios were found. Figure 2 presents the variability in the published recommendations.

1201101009080706050

Valine

Isoleucine

Ratios to lysine (%)

Figure 2: Compilation of available published requirements for valine and isoleucine expressed as Val:Lys and Ile:Lys ratios. Each point represents one published requirement.

Published recommended Val:Lys ratios vary between 61% and 122%. The average and median ratios are identical at 81%.

Published Ile:Lys ratios vary between 50% and 91%. The average and median ratios are identical at 70%.

B. ExplanationofthevariabilityinpublishedVal:LysandIle:Lysratios

The huge variability in the recommended broiler requirements could be attributed to different methods and modes of expression used to determine the requirement of a given amino acid. The following section describes how the design used in a study may impact the requirement that is reported by the study.

>Methodusedtodeterminetherequirementofvalineandisoleucine Published valine and isoleucine ratios could have been estimated by the following methods:

Literature survey: Authors compile available data at the time of their publications. Factorial approach: Generally several studies are done to determine maintenance and growth requirement of

birds. Authors then calculate the requirement based on animal weight (maintenance) and a hypothetical growth (production).

Deletion method: The study consists of comparing birds performance between a positive control diet (balanced in all amino acids) and other treatments where the tested amino acids are supplied one after the other below the birds requirement. A statistical method is then used to estimate the requirement for the tested amino acids.

Dose response study: This method consists of testing different concentrations of an amino acid (at least 3 levels) and then determining through statistical methods which concentration gives the best performance.


>MethodofexpressingaminoacidrequirementsAmino acid requirements can be expressed in several ways: as an amount in the feed, relative to energy, relative to weight gain or relative to lysine. They may also be expressed on a total, apparent digestible or standardised digestible basis. In addition to the different response criteria used (i.e. daily gain, feed conversion ratio, nitrogen retention, plasma urea nitrogen), different statistical models (Pesti et al., 2009) (linear plateau, curvilinear plateau, asymptotic model) are used to determine the requirement. Although all of these methods have their strengths and weaknesses, the desired mode of expression will determine the experimental design that has to be used in requirement studies.

In growing animals, the ideal protein concept is often used to express animals amino acid requirements. This concept defines the amino acid profile (as g of the tested amino acid / 100 g lysine) which exactly meets the animals requirement for protein deposition and maintenance (Fuller et al., 1989). In this profile, all amino acids are presumed to be equally limiting for all physiological functions. Lysine has traditionally been used as the reference because it is the 1st and 2nd limiting amino acid for growth respectively in pigs and broilers and is mainly used for muscle protein deposition. It is frequently assumed that the ideal protein profile does not change between different growth phases. In practical nutrition, this offers the advantage that the lysine requirement may be varied (per kg of feed or per unit of energy), but not the ideal protein profile expressed relative to lysine.

Finally, one of the most important criteria which must be taken into account when a requirement to lysine is being determined is that lysine must be the 2nd limiting amino acid in the experimental diets, after the studied amino acid. In a doseresponse study, different levels of the studied amino acid should be provided, while the lysine content in the diet should remain constant (and sublimiting) (Figure 3). A twolevel study will show if there is a response between the two levels tested but it will not be possible to determine the requirement for the tested amino acid from such a trial because no breakpoint would be demonstrated.

Tested AA:Lys

Lys < requirement

Lys requirement

ba

Respo

nse

Figure 3: Theoretical response to increasing levels of the tested AA:Lys when Lys is (or is not) the 2nd limiting amino acid after the tested one. The two arrows represent the estimated requirements. When a factor other than Lys is 2nd limiting for the response criterion, the calculated AA:Lys requirement ratio (a) will be underestimated in comparison to (b) where Lys is the 2nd limiting factor.


When lysine is 2nd limiting for performance (weight gain, feed efficiency), an increase in the tested amino acid supply will result in a increase in the response criterion up to the point that the tested amino acid supply is no longer limiting, which is indicated by the breakpoint. A further increase in the tested amino acid supply would not result in a change in the response criterion. If lysine is actually 2nd limiting, the plateau value will be determined by the lysine supply. At the breakpoint, the tested amino acid and lysine are colimiting and the ratio between the two will be the requirement of the tested amino acid (b).

When lysine is not the 2nd limiting nutrient in the tested amino acid doseresponse study, an increase in the tested amino acid supply will initially result in an increase in the response criterion. When the tested amino acid supply is further increased, another unknown factor (e.g., an amino acid other than the tested amino acid and lysine) will become limiting (indicated by the ooosymbols in Figure 3). The breakpoint of that line corresponds to the tested amino acid requirement relative to the unknown factor (a). Interpreting this breakpoint as the tested amino acid requirement relative to lysine would underestimate the actual tested amino acid requirement.

As shown in Figure 3, it is assumed that the optimal tested amino acid:lysine ratio is not affected by the lysine content in the diet when lysine is actually the secondlimiting factor (Boisen, 2003). The constraint that lysine should be the 2nd limiting amino acid only applies to experimental studies in order to express the requirement relative to lysine whereas in practical nutrition, the lysine levels are higher to ensure that the animals can fully express their growth potential.

Some studies have been carried out on amino acid requirements where lysine is not (or does not appear to be) the 2nd limiting amino acid. By itself, this does not invalidate these studies but the reported amino acid requirement should then be expressed relative to the 2nd limiting factor and not relative to lysine.

An exhaustive literature review show that there is huge variability in published requirements Val:Lys = 81% 19.7 Ile:Lys = 70% 17.0

This variability is dependent on a multitude of factors and at this stage does not allow conclusions to be reached on practical recommendations.

>DatabaseconstructionfordeterminationofvalineandisoleucinerequirementDue to the wide variation in published requirements, it is very difficult to interpret and reach conclusions about the valine and isoleucine requirements of broilers. In order to investigate this further, a database was built in which the available data on the valine and isoleucine responses and requirements of broilers were compiled. An exhaustive search was made of world literature and 28 valine and 66 isoleucine trials were collected into the database (articles or abstracts from scientific journals).

To enter a trial in the database, the following minimum information was required: Ages of the tested chickens Composition of the basal experimental diet. Nutritional values (apparent metabolisable energy and amino acid

expressed in true digestible) were recalculated with INRA tables (Sauvant et al., 2004) (where possible) so that the analysis could be based on complete amino acid profiles drawn from a common source, and to remove the variability arising from published values (expected analyzed).

Measures of growth performance: Average daily gain, average daily feed intake, gain:feed ratio. Carcass weight and yield, breast meat weight and yield were also entered when was available.


III.Valinerequirementsofbroilers

Valine is one of the branched-chain amino acids (BCAA) along with isoleucine and leucine. The way in which the requirement is expressed depends on the experimental design used in studies.

The lysine levels used in the trials (expressed on a true digestible (TD) basis) is of particular importance because: If TD lysine level is sublimiting, the valine requirement can be expressed as a ratio to lysine (Val:Lys) If TD lysine level is not limiting, the valine requirement should be expressed as a percentage of the feed (%)

The TD lysine of the 28 basal diets entered in the database were compared graphically to the TD lysine requirement at different ages of modern broiler genotypes (adapted from Ross 308 (2007) and Cobb 700 (2008) management guides) (Figure 4).

1.60

0.400 10 20 30

Age (days)40 50 60

0.60

0.80

1.00

1.20

1.40

TD Lysine (%)

Lysine requirement of modern genetics

Figure 4: Comparison of TD lysine levels in valine trials and TD lysine requirements of modern broilers.

Dietary TD lysine levels for the growth period studied were higher than the birds requirement in 4 trials (Corzo et al., 2008 exp.1, 2 and 3 and Mack et al., 1999). In these trials, lysine was probably not the 2nd limiting amino acid after valine and therefore the requirement could not be expressed as a ratio to lysine. Nevertheless, these trials used an experimental design that allowed an estimate of the valine requirement as a percentage of the feed according to the age of bird.


A. TDvalinerequirementasratiotolysine

>SelectionofthetrialsThe selection of trials based on lysine level in the feed (24 trials) must be further refined. No other amino acids must be at a level that would limit the broilers response to TD Val:Lys.TD amino acids profiles of basal diets were compared to Baker and Han (1994) to determine if any amino acids other than valine were limiting in the diet. If one or more amino acids were deficient, the study was eliminated from the review. The example of TD Arg:Lys levels is given in Figure 5. Trials where TD Arg:Lys was lower than 105% (in red in Figure 5) were eliminated from the compilation.

85

95

105

115

125

135

145

Trials

TD Arg:Lys (%)

TD Arg:Lysrecommended by

Baker and Han(1994)

Figure 5: TD Arg:Lys levels in trials entered the valine database. Red dots highlight trials where TD Arg:Lys was lower than recom-mended by Baker and Han (1994).

In addition, because a 2level study does not allow the determination of a requirement, two trials were eliminated from the compilation (Thornston et al., 2006 exp1 and Corzo et al. 2007 exp1). The selection process is summarized in Figure 6. In the end, 10 doseresponses were used to determine the TD Val:Lys requirement of broilers.

6

6

2

Lack of information

Deciency in oneor more amino acids

2-level TD Val:Lys studies

Non sub-limitinglysine levels

Sub-limitinglysine levels

28 trials

4 trials 24 trials

4 trialsfor TD Val (%)

10 trialsfor TD Val:Lys

Figure 6: Summary of reasons for selection or elimination of trials.


The experimental designs, the nutritional values of the basal feed and the growth performance of the best treatment in each of the 10 trials kept for estimating the TD Val:Lys requirement of broilers are presented in Table 3. The 10 trials differ in the broilers ages, sex, genetics and in the feeds nutritional values. This explains the differences in ADG, ADFI and G:F ratio between trials.

Allen et al.

Allen et al.

Mendonca et al.

Leclercq Bae et al.

Ekermans et al.

Corzo et al.

Thornston et al.

Thornston et al.

Corzo et al.

1972Exp 1

1972Exp 2

1989 1997 1999 2001 2004 Exp 2

2006Exp 2

2006Exp 3

2007

Age range (days) 8 14 8 14 21 42 20 40 8 22 7 21 42 56 21 42 21 42 21 42

GeneticsNew Hampshire X Columbian

Plymouth Rock ISA 220

Arbor Acres

Ross 308 Ross 508 Ross 508

Sex M M M M MF M M F M

Nutritional Values

AME (kcal) 4350 4450 3120 3140 4050 3040 3170 3115 3115 3125

CP (%) 14.3 16.6 15.2 15.6 17.3 23.8 17.3 14.6 14.6 17.3

TD Lys (%) 0.93 0.93 0.90 0.57 1.07 1.18 0.75 0.93 0.93 0.95

TD Thr:Lys (%) 69 69 74 80 73 66 98 73 73 67

TD SAA:Lys (%) 74 74 84 77 83 79 103 87 87 82

TD Ile:Lys (%) 65 65 75 91 73 76 100 74 74 74

TD Leu:Lys (%) 443 443 140 207 110 193 221 131 131 124

TD Arg:Lys (%) 128 128 124 135 114 108 126 110 110 139

TD Val:Lys (%) 38 59 54 75 69 91 107 154 20 104 89 228 79 107 63 136 63 136 62 88

Best performance

ADG (g/day) 5.2 5.0 54.1 78.1 28.6 36.4 103.6 69.6 60.0 66.2

ADFI (g/day) 11 11 113 134 43 53 246 178 174 141

G:F (g/g) 0.471 0.463 0.482 0.585 0.670 0.693 0.422 0.411 0.349 0.485

Table 3: Experimental designs, recalculated nutritional values of the basal feed and broiler performance of the best treatment in each of the 10 trials kept for the determination of the TDVal:Lys requirement of broilers. (M=Male; F=Female).

>ResultsfromthecompilationforgrowthperformanceIn order to estimate the TD Val:Lys ratio which optimises ADG and G:F ratio of broilers, the performance in the ten selected trials was represented in a curvilinear plateau model. The model took into account a trial effect by estimating a plateau for each trial separately. The results are presented graphically in Figures 7 and 8.

5575

80

85

90

95

100

105

110ADG (% of the plateau)

60 65 70 75TD Val:Lys (%)

80 85 90 95 100

Figure 7: Effect of TD Val:Lys ratio on ADG.

5575

80

85

90

95

100

105

110G:F (% of the plateau)

60 65 70 75TD Val:Lys (%)

80 85 90 95 100

Figure 8: Effect of TD Val:Lys ratio on G:F.

There is a clear response in ADG and G:F ratio to increased TD Val:Lys ratios, which validates the selection procedure. The TD Val:Lys ratio which optimises broiler growth and feed efficiency is 80%.


>ResultsfromthecompilationforcarcassparameterThere is a strong effect of TD Val:Lys ratio on weight of carcass and breast meat (Corzo et al., 2004; 2007). However, carcass yield (Thornston et al., 2006; Corzo et al., 2004; 2007) and breast meat yield were not affected (Leclerq, 1998; Thornston et al., 2006; Corzo et al., 2004; 2007). As carcass weight and breast meat weight increased together with increased Val:Lys ratios, the ratio between breast meat and carcass weight did not change. However, meeting the birds requirement for valine is of key importance in ensuring the optimal usage of lysine which is well known to increase breast meat yield (Berri et al., 2008).

>ValidationoftheaverageresponsecurveThornston et al. (2006, exp1) and Corzo et al. (2007, exp1) were eliminated from the compilation because they tested only two TD Val:Lys ratios. However, these trials can be used to estimate birds responses to valine, and to validate the average response curves in Figures 9 and 10. The improvement of performance observed in the 2step trials was very much in line with the average response curves and validates their representation of birds responses to increasing TD Val:Lys ratios.

55 60 65 70 75TD Val:Lys (%)

80 85 90 95 100

ADG (% of the plateau)

80

90

100

110

75

85

95

105

Corzo et al. (2007) +9%

Thornston et al. (2006) +8%

Figure 9: ADG response to TD Val:Lys ratio in 2-step trials.

Corzo et al. (2007) +5%

Thornston et al. (2006) +4%

55 60 65 70 75TD Val:Lys (%)

80 85 90 95 100

G:F (% of the plateau)

80

90

100

110

75

85

95

105

Figure 10: G:F response to TD Val:Lys ratio in 2-step trials.

Increasing the TD Val:Lys ratio in broiler diets improves performance until the valine requirement is met.

A TD Val:Lys of at least 80% is needed to optimize broiler performance.

B. TDvalinerequirementasamountofthefeed

Four trials allow the optimum valine requirement of broilers to be assessed as a percentage of the feed according to the age of birds. The procedure to determine the requirement as a percentage of the feed was different in each publication. In order to homogenise the results, recalculated nutritional values and a common statistical model (curvilinearplateau model) were used to determine the broiler requirement as a percentage of the feed for ADG and G:F in each trial (Table 4).

Authors Age (days)

Genetics Best ADG (g/day)

Best ADFI (g/day)

Best G:F (g/g)

TD Valine requirement(% of the feed)

ADG G:F

Mack et al., 1999 exp1 2040 ISA 220 77.9 136 0.585 0.79 0.76

Corzo et al., 2008 exp1 114 Ross 308 28.6 34 0.841 1.00 1.05



Table 4: ADG and G:F requirement as % of the feed in each trial.


The reestimated requirements are similar for ADG and feed efficiency within and between studies for the same broiler ages (Mack et al., 1999 and Corzo et al., 2008 exp3), whatever the genetic strain used.

The decrease in requirement with age is mainly explained by the increase in feed intake in older birds.

Four requirements were determined for ADG and feed efficiencies for 4 different periods. With the objective to model the TD valine requirement in relation to broiler age, it is essential to take into account the feed intake effect. This effect can be modelled through a logarithmic function.The reestimated requirements from each trial for ADG at different ages were plotted in a single graph. A logarithmic curve was then used to take into account the increase in feed intake with broiler age (Figure 11). The same method was used to determine the valine requirement of broilers for feed efficiency (Figure 12).

Corzo et al. 2008a

Corzo et al. 2008b

Corzo et al. 2008c

Mack et al. 1999

y = -0.1351ln(x) + 1.2843R2 = 0.87

0 5 10 15 20 25 30 35 400.40

0.60

0.80

1.00

1.20

1.40

1.60

0.50

0.70

0.90

1.10

1.30

1.50

Age (days)

TD Val (%)

Figure 11: TD valine requirement for ADG (% of the feed).

Corzo et al. 2008a

Corzo et al. 2008b

Corzo et al. 2008c

Mack et al. 1999

y = -0.2028ln(x) + 1.4561R2 = 0.99

0 5 10 15 20 25 30 35 400.40

0.60

0.80

1.00

1.20

1.40

1.60

0.50

0.70

0.90

1.10

1.30

1.50

Age (days)

TD Val (%)

Figure 12: TD valine requirement for G:F (% of the feed).

By using the equations modelling the valine requirement as % of the feed according to age of broiler (given in Figures 11 and 12), it is possible to calculate the TD valine requirement for a targeted age of bird (Table 5). However, these results should be used with care as the compilation regroups only 4 trials.

Age (days)TD Valine requirement (% of the feed)

ADG G:F

10 0.97 0.99

20 0.87 0.83

30 0.82 0.76

Table 5: Example of TD valine requirements % of feed depending on the age of broiler.

TD valine requirement as % of feed varies with broiler age

TD valine requirement as % of the feed may be estimated from the following equations:

For ADG: TDVal(%) = -0.1351ln(day) + 1.2843 For G:F: TDVal(%) = -0.2028ln(day) + 1.4561

These results are an indication of a minimum TD Valine level required in feed formulations since they are based on only 4 studies. The use of the valine ratio to lysine is preferred: TD Val:Lys = 80%


IV. TDIle:Lysrequirementofbroilers

As explained in previous sections, trials must be selected based on TD lysine levels to determine the method of expressing the isoleucine requirement (Figure 13).

1.60

0.400 10 20 30

Age (days)40 50 60

0.60

0.80

1.00

1.20

1.40

TD Lysine (%)

Lysine requirement of modern genetics

Figure 13: Comparison of TD lysine levels in isoleucine trials and TD lysine requirement of modern broiler genotypes.

>Selectionfor%ofthefeedSix trials used higher TD lysine levels than recommended for the studied growth period. Lysine was therefore probably not the 2nd limiting amino acid after isoleucine in these studies. The isoleucine requirement found in these trials should therefore not be expressed as a ratio to lysine but as a percentage of the feed. Five of the six eliminated trials were 2dose isoleucine trials. The sixth trial (Mack et al.,1999) was the only trial left with an experimental design that allowed the TD isoleucine requirement to be expressed as a percentage of the feed. Because there was only one, it was not possible to make a compilation of multitrial data. The isoleucine requirement, estimated by a curvilinearplateau model as was done for valine above, was found to be 0.72% for ADG and 0.60% for G:F in 2040 day old ISA 220 broilers.

>SelectionforratiotolysineSixty trials used sublimiting lysine levels and therefore potentially allowed an expression of broilers isoleucine requirement as a ratio to lysine. TD amino acid profiles of basal diets were compared to Baker and Han (1994) to determine if any other amino acids were limiting in the diet and therefore restrict the response to increasing TD Ile:Lys ratios. If one or more amino acids were found to be deficient, the study was eliminated from the compilation. Also, all the 2dose trials (Kidd et al., 2004 exp 1, 2 and 3 ; Park and Austic, 2000 exp 1, 2, 3 and 4) were eliminated for reasons described in previous sections. The selection procedure is summarized in Figure 14. In the end, only six trials were kept to determine the isoleucine requirement of broilers expressed as a TD Ile:Lys ratio.


12

35

7

Lack of information

Deciency in oneor more amino acids

2-level TD Ile:Lys studies

Non sub-limitinglysine levels

Sub-limitinglysine levels

5 2-level studies

66 trials

6 trials 60 trials

1 trialfor TD Ile (%)

6 trialsfor TD Ile:Lys

Figure 14: Summary of reasons for selection or elimination of trials.

The main characteristics of the trials selected are presented in Table 6. The 6 trials differ in the broilers ages, sex, genetics and nutritional values of the feed. This explains the differences in ADG, ADFI and G:F ratio between trials.

Corzo et al. Hale et al. Kidd et al. Kidd et al. Kidd et al. Corzo et al.

2004 2004 2004 2004 2004 2008

Age range (days) 42 56 30 42 18 30 30 42 42 56 35 54

Genetics Ross 308 Ross 508 Ross 308 Ross 308 Ross 308 Ross 708

Sex M F M M M

Nutritional values

AME (MJ) 3010 3000 3310 3030 3040 3110

CP (%) 15.6 15.7 17.7 16.2 15.1 16.7

TD Lys (%) 0.81 0.87 0.88 0.87 0.73 0.95

TD Thr:Lys (%) 90 79 79 79 88 69

TD SAA:Lys (%) 89 96 98 94 99 77

TD Val:Lys (%) 98 92 105 91 107 76

TD Arg:Lys (%) 122 114 119 115 126 100

TD Leu:Lys (%) 202 177 195 175 209 147

TD Ile:Lys (%) 65 95 48 96 57 91 54 89 57 98 65 74

Best performance

ADG (g/day) 93.8 60.4 59.1 79.4 52.8 99.0

ADFI (g/day) 226 142 104 157 177 208

G:F (g/g) 0.415 0.436 0.578 0.524 0.302 0.483

Table 6: Experimental designs, recalculated nutritional values of the basal feed and broiler performance of the best treatment in each of the 6 trials kept for the determination of the TDIle:Lys requirement of broilers.

Moreover, it is important to notice that in four trials (Hale et al., 2004 and Kidd et al., 2004 exp 1, 2 and 3) the authors used blood cells (animal product). Blood cells have a specific imbalance in their amino acid profiles; they are rich in valine and leucine and particularly poor in isoleucine (Figure 15 and Focus 4). This raw material is often used in isoleucine dose response trials because it easely creates a deficiency. Howewer, the imbalance between these three amino acids has been reported to be a factor that impacts animal response (Focus 2 p 17).


Leu

Lys

2 %

4 %

6 %

8 %

10 %

12 %

Lys

LeuThr Thr

Val ValIle Ile

% of CP % of CP

Blood cell, Kidd et al., 2004

Soybean meal 48, INRA 2004

2 %

4 %

6 %

8 %

10 %

12 %

Figure 15: Lysine, threonine, isoleucine, valine and leucine content in percentage of CP of blood cell (Kidd et al., 2004) and soybean meal 48 (INRA tables, Sauvant et al., 2004).

>ResultsofthecompilationIn order to estimate the TD Ile:Lys ratio that optimises ADG and G:F ratio in broilers, growth performance from the remaining six trials were compiled using the same method as for valine. The graphical results of the compilation of these trials are presented in Figures 16 and 17.

4565

70

75

80

85

90

95

100

105

110ADG (% of the plateau)

50 55 60 65TD IIe:Lys (%)

70 75 80 85 90

Figure 16: Effect of TD Ile:Lys ratio on ADG.

65

70

75

80

85

90

95

100

105

110G:F (% of the plateau)

TD IIe:Lys (%)45 50 55 60 65 70 75 80 85 90

Figure 17: Effect of TD Ile:Lys ratio on G:F.

There is a strong effect of TD Ile:Lys ratio on weight of carcass and breast meat (Kidd et al., 2004 trials 1 and 2). However, carcass yield (Kidd et al., 2004 trials 1 and 2; Corzo et al., 2004; 2008) and breast meat yield were not affected.


>ValidationoftheaverageresponsecurveThe trials of Kidd et al. (2004; exp 1, 2 and 3) and Park and Austic (2000; exp 1, 2, 3 and 4) were not used in the compilation because they tested only two isoleucine levels. However, these trials can be used to estimate the birds responses to isoleucine and to validate the average response curves in Figures 18 and 19.

25 35 45 55 65TD Ile:Lys (%)

75 85 95

ADG (% of the plateau)

50

70

90

100

110

40

60

80

Kidd et al. (2004) exp3



Park and Austic (2000) exp1


Average curve in g 16 and 17

25 35 45 55 65TD Ile:Lys (%)

75 85 95

G:F (% of the plateau)

50

70

90

100

110

40

60

80



Figure 18: ADG response to TD Ile:Lys ratio in 2-step trials. Figure 19: G:F response to TD Ile:Lys ratio in 2-step trials.

There is a response to isoleucine increase in all the trials but two trial populations appears through the differences in the magnitude of the response to increasing TD Ile:Lys ratio.The Kidd et al. (2004) trials showed a greater response (more than +30% for ADG and +25% for G:F) than those of Park and Austic (2000). The main differences in experimental design between these publications come from the diet composition (particularly the use of blood cells). Consequently, the TD Leu:Lys ratios are much higher in Kidd et al. (2004) (average TD Leu:Lys of 193%) than in Park and Austic (2000) (average TD Leu:Lys 147%) (Table 7).A consideration of interactions between BCAA is presented in Focus 2 p 17.

Publication Exp Blood cells Age (days) TD Lys level (%) TD Val:Lys ratio (%) TD Leu:Lys ratio (%)

Kidd et al., 2004

1 Present 1830 0.88 105 195

2 Present 3042 0.87 91 175

3 Present 4256 0.73 107 209

Park and Austic, 2000

1 Absent 214 1.12 84 129

2 Absent 214 1.12 123 164

3 Absent 214 1.12 84 129

4 Absent 214 1.12 123 164

Table 7: TD lysine, Val:Lys and Leu:Lys levels in feed with and without blood cells.

Increasing the TD Ile:Lys ratio in broiler diets improves performance until the isoleucine requirement is met.

A TD Ile:Lys dietary level of at least 67% is needed to optimize broiler performance.

The response to isoleucine is modified by specific feedstuff particulary rich in leucine.


Focus 2

Interactionsbetweenbranched-chainaminoacidsIt has been reported by several authors (DMello and Lewis, 1970ab; Burnham et al., 1992; Witalfsky et al., 2010) that there is an antagonism between the branchedchain amino acids (valine, isoleucine and leucine) in broilers. The first two steps in their catabolism are common to all three amino acids and involve the BCAA aminotransferase (BCAT) and branchedchain keto acid dehydrogenase (BCKDH). Their further metabolism employs distinct pathways to different end products (glucose and/or ketone bodies) (Figure 20).

BCAT enzyme-Ketoglutarate

Acetyl-CoAfrom Leu

Acetyl-CoA+ Propionyl-CoA

from Ile

Propionyl-CoAfrom Val

Glu

Reversibletransamination

-oxydation

Irreversible oxydativedecarboxylation BCKDH enzyme

Branched Chain Amino AcidsLeu - Ile - Val

Branched-chain -keto acids

-ketoacyl-CoA Thiesters

Figure 20: Catabolism of branched chain amino acids (valine, isoleucine, leucine).

In practical terms, any supply of one of the three BCAA leads to the activation of the common enzymes and the catabolism of all three BCAA (Harper et al., 1984; Langer and Fuller, 2000; Witalfsky et al., 2010). Moreover, the keto acid of leucine plays a particular role in the activation of the BCKDH complex (Witalfsky et al., 2010). DMello and Lewis (1970a) observed in growing broilers (721 days) that circulating levels of isoleucine and valine were lowered by an excess of leucine. They also described that valine and isoleucine requirements increased with leucine supply (DMello and Lewis, 1970b). Burnham et al. (1992) observed that dietary leucine set at 1.76 times the requirement level depressed chick growth. However an excess of valine does not seem to impact birds response to isoleucine (DMello and Lewis, 1970a). This is also confirmed by the comparison of the growth responses reported by Kidd et al. (2004, exp 1, 2, 3) and Park and Austic (2000, exp 1, 2, 3, 4) in Table 7.

The dataset used to determine the valine requirement of broilers did not show any interaction between valine and leucine, even with an extremely high level of leucine. Nevertheless, Barea et al. (2009) showed that an excess of leucine impacted the growth response in piglets but not the valine requirement level itself.

However, in contrast to valine, the data presented in the isoleucine trial compilation suggest that there is an interaction between leucine and isoleucine and raise doubts on the estimate of TD Ile:Lys requirement determined in this compilation. Most of the trials (4 out of 6) used blood cells which have a high leucine content. Moreover, the basal diet used by Corzo et al. (2004) contained corn gluten meal (Focus 3 p 18) which is a raw material extremely rich in leucine and this could have created an imbalance between isoleucine and leucine (Table 6).


Focus 3

BroilersleucinerequirementsAs for valine and isoleucine, there is a large range in the published requirements for leucine as expressed as Leu:Lys ratios (Figure 21). However, taking data only from publications since 1994, the Leu:Lys requirement varies between 92% and 123% with average and median values respectively of 107% and 108%. These levels are very much in line with the TD Leu:Lys of 105% given in AEL bulletin 27 (2004).

14413612812011210496

Leucine

Ratios to lysine (%)

Figure 21: Compilation of available published requirements for leucine expressed as Leu:Lys ratios. Each point represents one published requirement.

With the objective to determine how leucine is limiting in a practical broiler diet, different formulas of a broiler grower feed (3200 kcal AME and 1.05% TD lysine) were formulated:

In a corn based diet (corn 55%, wheat 10%, soybean meal 30% and supplemental amino acids), the TD Leu:Lys ratio was 140%.

In a wheat based diet (wheat 70%, soybean meal 25% and supplemental amino acids), the TD Leu:Lys ratio was approximately 120%.

Leucine levels in todays feed formulations are much higher than the recommended requirement level (TD Leu:Lys=105%).


Focus 4

Branched-chainaminoacidprofilesinfeedstuffsarenotconsistentBecause of the interactions between BCAA, it is interesting to compare the BCAA composition of various feedstuffs. The valine, isoleucine and leucine ratios to total BCAA (based on INRA table, Sauvant et al., 2004) of several feedstuffs have been calculated and are presented in Figure 22.

Barley Corn Sorghum Triticale Wheat Wheat gluten feed Corn gluten feed Corn gluten meal

Pea Rapeseed meal Soybean meal Sunower meal Fish meal Blood meal Feather meal Meat and bone meal

0.70

Leu:BCAA (%)

Ile:BCAA (%)

Val:BCAA (%)

0.65

0.60

0.55

0.50

0.45

0.40

0.700.10

0.150.20

0.250.30

0.150.20

0.25

0.30

0.35

0.40

Blood meal

Corn

Corn gluten meal

Sorghum

Blood meal

Corn

Corn gluten meal

Sorghum

Figure 22: Val:BCAA, Ile:BCAA and Leu:BCAA ratios of the main feedstuffs used in broiler diets (INRA Tables, Sauvant et al., 2004).

A large group of feedstuffs have a similar profile of BCAA (average of all listed feedstuffs; Ile:BCAA = 22%, Val:BCAA = 30% and Leu:BCAA = 48%)

However, corn (59% Leu:BCAA), corn gluten meal (65% Leu:BCAA), sorghum (58% Leu:BCAA), and blood meal (6% Ile:BCAA and 56% Leu:BCAA) have very imbalanced profiles.

Corn, corn gluten meal and sorghum have a very high proportion of leucine and may therefore contribute to an excess of dietary leucine.

Blood products have an extremely low proportion of isoleucine and may contribute to a branched-chain imbalanced even at moderate incorporation rates.


V. Practicalimplicationsforbroilerdiets

A sound knowledge of amino acid requirements is a pre-requisite for any investigation on the possibility of reducing dietary crude protein levels. This new review concerning the valine and isoleucine requirements of broilers allows the ideal protein proposed in AEL bulletin 27 (2004) to be updated (Table 8). Todays greater knowledge of individual indispensable amino acid requirements allows diets to be formulated not on crude protein but on each amino acid (precision protein). Feed formulators can now formulate more accurate diets and thereby help to reduce the number of health challenges that broilers have to face.

By using a minimum specification for each of these amino acids in formulations, it is possible to progressively determine the next limiting amino acid in broiler feed and to establish the extent to which it is possible to reduce dietary crude protein through supplementation with amino acids. As an example, three grower broiler diets (1428 days) were formulated to contain 3200 kcal AME and 1.05% TD lysine, using the AA profile presented in Table 8.

This exercise was done with different feed ingredients: to reflect European formulation practice, to understand the ranking of limiting amino acids, and to estimate the extent of crude protein reduction through supplementation with feeduse amino acids.

The first simulations are based on a wheatsoybean meal diet and the second ones on a cornwheatsoybean meal diet (Figure 23). The last one is based on a cornsoybean mealblood mealsunflower meal diet (Figure 24).

>Cereal-baseddietsimulations:

29.2

22.4 21.520.3

19.3

+DL-Met+L-Lys

+L-Thr+L-Val

19.0 18.918.0 17.3

10

15

20

25

30

35

M+C Lys Thr Val Arg Ile His Leu Trp

CP level (%)

10

15

20

25

30

35

M+C Lys Thr Val Arg Ile His Leu Trp

CP level (%)

28.7

21.320.2

19.018.0

+DL-Met+L-Lys

+L-Thr+L-Val

17.7 17.516.1 16.0

Wheat 72%/Soybean meal 23% Corn 56%/Wheat 10%/Soybean meal 23%

Figure 23: Dietary CP level (%) in a standard grower broiler diet (soybean meal was gradually replaced by wheat or corn). Ranking of limiting amino acids (from left to right) and lowest crude protein level achievable without supplementation with the corresponding amino acid.

Lysine 100

Sulphur amino acids 75

Threonine 65

Valine 80

Isoleucine 67

Arginine 105

Tryptophan 17

Histidine 40

Leucine 105

Phenylalanine + Tyrosine 105

Table 8: Proposed ideal protein for broilers (true digestible amino acids relative to lysine).


For clarification, with wheat and soya, the lowest CP level that could be achieved without DLMethionine supplementation was 29.2%. When methionine was added to the formulation, the next limiting amino acid was lysine and, without LLysine supplementation, the lowest CP level that could be reached was 22.4%. When LLysine was offered, the CP level dropped to 21.5% and threonine became limiting.

In both simulations, sulphur amino acids, lysine and threonine were the first limiting amino acids. LThreonine supplementation allowed a reduction of approximately 1 percentage point of CP in both diet types. In vegetable diets, valine was the next limiting amino acid before arginine and isoleucine, as already described in

section I. Supplementation of LValine allowed a further reduction of 1 percentage point of dietary CP.

>Dietcontainingbloodproduct(Corn 55%/Wheat 10%/Soybean meal 18%/Sunflower meal 34%/Blood meal 2%)

27.8

22.120.4

19.2 18.4

+DL-Met+L-Lys

+L-Thr +L-Ile

18.016.3 16.7 15.8

10

15

20

25

30

35CP level (%)

M+C Lys Thr Ile Arg Val Trp His Leu

Figure 24: Dietary CP level (%) in a standard grower broiler diet with blood meal and sunflower meal (soybean meal was gradually replaced by corn). Ranking of limiting amino acids (from left to right) and lowest crude protein level achievable without supplementation with the corresponding amino acid.

The order of the first limiting amino acids was the same as in the vegetable diets (1st sulphur amino acids,2nd lysine and 3rd threonine). LThreonine supplementation allowed a reduction of 1.2 percentage points of CP.

Isoleucine was the 4th limiting amino acid in this diet, ahead of arginine and valine. As already described in previous sections, blood meal is very low in isoleucine and rich in leucine. Even a moderate usage results in a limitation on the reduction in dietary crude protein.

The supplementation of LIsoleucine would allow a CP reduction of 0.8%, down to 18.4% CP in a grower broiler diet.

This practical formulation exercise confirmed the position of threonine as a limiting amino acid in corn and wheat based diets. L-Threonine supplementation helps achieve better formulations.

Valine at 80% TD Val:Lys is the next limiting amino acid after threonine in vegetable diets, followed by arginine and isoleucine.

Isoleucine at 67% TD Ile:Lys is the next limiting amino acid after threonine in feed containing blood meal, followed by arginine and valine.

Broiler nutritionists are now able to formulate on at least the first five limiting amino acids and to reduce dietary crude protein level through amino acid supplementation. L-Valine supplementation is a powerful tool in optimizing vegetable broiler feed formulations.


Conclusions

Valine is the 4th limiting amino acid in vegetable broiler diets basedon wheat or corn.

Isoleucine becomes the 4th limiting amino acid, when blood cellsor blood meal are used in formulations.

The TD Val:Lys and TD Ile:Lys requirements of broilersare respectively 80% and 67% to optimize performance.

Knowing the requirements of individual amino acids,feed formulators are able to reduce dietary crude protein levels.

L-Valine supplementation in combination with L-Threonineprovides the opportunity to formulate technically, economically and environmentally better broiler feed.

Amino acid profile for broiler feed

Lysine 100

Sulphur amino acids 75

Threonine 65

Valine 80

Isoleucine 67

Arginine 105

Tryptophan 17

Histidine 40

Leucine 105

Phenylalanine + Tyrosine 105

DisclaimerThe estimation of nutrient requirement is not an exact science. The company AJINOMOTO EUROLYSINE S.A.S.has taken all steps to check the authenticity and relevance of the information provided in this bulletin. However, AJINOMOTO EUROLYSINE S.A.S. declines all responsibility for any use made of this data and may not, under any circumstances,be held liable for any damage suffered by third parties.


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