ajinomoto bulletin 34

INFORMATION N°34July 2009

EDITO

Tryptophan (Trp) is an essential and an indispensable amino acid for

piglets. Fourth limiting amino acid in European piglet diets and not

synthesized by the animal, it has to be supplied through the feed.

Besides its role in protein deposition, Trp has other important

functions. Involved in appetite regulation (Henry et al., 1996; Zhang et

al., 2007), immune response and health maintenance, Trp allows

enhancing piglet feed intake and limiting the impact of unfavorable

health environment (Le Floc’h et al., 2007; Trevisi et al., 2008). Despite

the high number of published trials wich aim at determining the

optimum SID Trp:Lys ratio, the Tryptophan requirement for piglets is still

debated.

The numerous publications on this subject show a high variability in

published requirements. Since trial results are dependant on the

specific experimental conditions, the question of representativeness

and applicability of the results arises. Therefore the trials are often

repeated by different research teams in different countries to verify

the repeatability of the results. Thus, there is a need to synthesize all

these results in order to establish a general law applicable to the piglet

population. Meta-analysis method described by Sauvant et al. (2005)

appears to be the best tool to reach such objective.

This bulletin presents the different meta-analytic steps applied to the

quantification of the SID Tryptophan to Lysine ratio (SID Trp:Lys) which

results in the best piglet growth performance.

Y = A (L’ + V(R’ - x) 2 )

SID Trp:Lys requirementfor piglets determinedby meta-analysis

AJINOMOTO EUROLYSINE S.A.S.

A J I N O M O T O A N I M A L N U T R I T I O N G O T O E S S E N T I A L S

Meta-analysis method

1. Meta-analysis of the Trp requirement for piglets: characteristics and selection of the trials 3

1.1 Construction and description of the database 31.2 Trials selection to determine a requirement as a ratio to lysine 61.3 Statistical models and piglet response to dietary Trp 9

2. Modeling the piglet response and determining the SID Trp:Lys requirement 11

2.1 Statistical results 112.2 Piglet response between 16.5% and 22% SID Trp:Lys ratio 122.3 Statistical validation of the curvilinear model 12

General conclusion 14

Reference List 15

Meta-analysis method has precisely the objective to integrate all the information contained in different trials andquantify the effect studied. Such a rigorous method, based on statistics, is necessary because “the limitation of thehuman brain to integrate different results becomes very apparent once the number of publications involved exceeds 12 to 15 studies” (Sauvant et al., 2008).

The first meta-analyses were published in the fields of psychology, social sciences and medicine while the emergenceof this method in animal nutrition is more recent. Meta-analyses have been used in animal nutrition, for instance, toquantify physiological response of ruminants to different level of nitrogen supplementation (Rico-Gomez and Faverdin,2001), starch (Offner and Sauvant, 2004) or to different types of dietary fats (Schmidely et al., 2008). In swine nutrition, Schulin-Zeuthen et al. (2007) had published a meta-analysis aiming to estimate biological determinants ofphosphorus (P) utilization, maintenance requirement and efficiency of dietary P for growing pigs.

The main steps of meta-analyses arepresented by Figure 1.

Once objectives are clearly defined, adatabase is built thanks to differenttrials. Data may come from articles and abstracts published in scientific journals,or from referenced trial reports. Theselection of trials useful to answer theobjectives has to be done thanks to agraphical analysis. The latest also allowsidentifying factors which seem to be involved in the studied effect and givesan idea about the mathematical modelwhich could be tested. This model musttake into account a trial effect which isthe main strength of the meta-analysisapproach.

After the statistical step, a post-analysis evaluation is used for validating the model which explains the most the data.Then, results of the meta-analysis can be used for practical purposes.

Table of contents

OBJECTIVES

USERS

SELECTION OFEXPERIMENTS& DATA ENTRY

CONCEPTUALBasis

Literature search.Experiments

Survey

" Adjustments"

GRAPHICALANALYSIS

DETERMINATIONOF META-DESIGN

SELECTION OFSTATISTICAL MODEL

POST-ANALYSISEVALUATION

★ Figure 1: Schematic representation of the meta-analytic process(Sauvant et al., 2008)

Meta-analysis method

1. Meta-analysis of the Trp requirement for piglets: characteristics and selection of the trials

This part defines the precise objectives of this meta-analysis and the description of the database. With the aim to express the Trp requirement as a ratio to Lys, the selection of trials has to be selective in regards to the experimental design, in particular the dietary composition.

� The first objective of this meta-analysis is to determine the SID Trp:Lys ratio which maximizes growth performance of piglets: Average Daily Gain (ADG), Average Daily Feed Intake (ADFI) and Gain to Feed ratio (G:F).

� The second objective is to identify the factors of variation of the piglet response to dietary Trp supply.

1.1. Construction and description of the database

Numerous trials involving Trp in pigs have been conducted during the last 50 years. According to the first objective,a database has been built and is described in the following section.

With the aim of exhaustiveness, 155 publications (articles or abstracts from scientific journals) and trial reports fromresearch institutes (research collaboration with AEL) have been collected. These trials had to:

1) study the effect of Trp on piglet performance, 2) test a basal diet fortified with several levels of synthetic forms of Trp.

To enter a trial in the database, a minimum of information must be known:

� Information about experimental design to measure the statistical power of the trials:• Number of repetitions by treatment,• Number of animals by repetition.

� Information about weight of the piglets.

� Composition of the basal experimental diet:Nutritional values (Net Energy and amino acids expressed in SID) were indeed re-calculated with EvaPig® (Noblet et al., 2008 using INRA tables [Sauvant et al., 2004]) to level the variability due to published values (expected ≠ analyzed) and to work with the complete amino acids profile on a common basis.

� Measures of growth performance: ADG, ADFI and/or G:F.

Finally 130 trials which study the piglet phase defined between 7 and 25 kg LW, were entered in thedatabase.

In order to facilitate the graphical analysis, a discriminant analysis has been done with four predictors to determine threedifferent weight categories of piglets (Figure 2).

★ Figure 2: Predictors used to define weight categories of piglets and number of trials for each category

AJINOMOTO EUROLYSINE S.A.S. Information N°34 - 3

Four predictors

Age of animals (d) Duration of the experiment (d) Initial average weight (kg)Final average weight (kg)

Weight categories

Prestarter (P): 7.2 ± 1.5 - 10.3 ± 2.5 kg

Starter (S): 11.3 ± 1.8 - 24.2 ± 4.4 kg

Prestarter-starter (P-S): 7.3 ± 1.1 - 22.0 ± 4.8 kg

Number of trials

25

53

52➧

4 - AJINOMOTO EUROLYSINE S.A.S. Information N°34

1.1.2. General overview of the data

One important role of the preliminary graphical analysis is to validate the coherence and homogeneity of data. Thisstep allows having an overview of the data, noticing aberrant ones and studying the nature of inter- and intra-studyrelationships.

Inter-study response represents a global response of the population, whereas intra-study responserepresents the particular response of each trial.

� regression between published and re-calculated nutritional values

As mentioned before, nutritional values (Net Energy and amino acids expressed in SID) were re-calculated with EvaPig®. Regressions between re-calculated and published data, which have been done to verify the homogeneity ofdata, are strong. The two highest R2 are for Lys (95.8%) and Trp (94.2%); certainly due to the fact that Lys and Trpcontent are often analyzed in trials whereas other amino acids are just “expected value”.

Re-calculated data are not only more homogenous than published ones but also represent well datafrom publications. Moreover, re-calculating nutritional values allows having the full amino acids profiles for each trial. The meta-analysis is therefore exclusively conducted on the basis of these re-calculated nutritional values.

EUotherUSA

Num

ber

of t

rial

s

2422201816141210

86420

1970 1975 1980 1985 1990 1995 2000 2005 2010

Date

Mean 17.1St Dev 4.3

45

40

35

30

25

20

15

10

5

04 6 8 10 12 14 16 18 20 22 24 26

SID Trp:Lys ratios (%)

1.1.1. Trials description

Among the 130 trials, 58% are from Europe,33% from USA and 9% from other countries (Australia, Canada and Taiwan). Thesetrials are from 1971 to 2008 with most of themsince 2000 (Figure 3).

Figure 3 also highlights that European trialsare more recent than American ones.

Figure 4 points up that the distribution of theSID Trp:Lys ratios tested in the 130 trials followsa normal law with a mean about 17%. The moststudied ratios are between 14% and 22%. The effect of SID Trp:Lys ratio on pigletperformance will therefore be estimated moreprecisely in this range where trial frequency ishigher.

★ Figure 3: Histogram of dates with geographical distribution

★ Figure 4: Distribution of SID Trp:Lys ratios tested

� piglet response to Trp

To study the inter- and intra-study piglet response to Trp, ADG is expressed as a function of SID Trp:Lys ratio (Figure 6). A huge inter-study variability of response appears with ADG varying from 50 to 900 g/d. This way of expression does not consider piglets feed intake which may explain this variability. To reduce it and have a better overview of piglets’ response to Trp, ADG is expressed as a function of ingested Trp (SID Trp % * ADFI g/d) in Figure 7.

★ Figure 6: ADG as a function of SID Trp:Lys ratios for each trial

✔ Since there is both inter- and intra-study response, the goal is to quantify the inter-study response, i.e. to find the common response of the different trials. In statistical words, it is to establish a general law of the piglet response to Trp and determine the SID Trp:Lys ratio which maximizes growth performance of piglets.

In order to check the coherence of selecteddata, ADG has been expressed as a function ofADFI (Figure 5). When ADFI is increasing, ADGis improved meaning that the data are coherent.

Figure 5 also highlights two populations of piglets, which differ in their feed efficiency.On the basis of this dataset, neither the threedifferent weight categories, nor the different origin (European, American and other coun-tries) explain this difference in feed efficiency.Actually an effect of time appears: oldest trials(mainly American according to Figure 3) show alower feed efficiency which may be explained by the evolution since then of the genetic improvement and knowledge in animal nutrition.

� regression between ADG and ADFI


★ Figure 7: ADG as a function of ingested SID Trp foreach trial

AD

G (

g/d)

900

800

700

600

500

400

300

200

100

0

0 200 400 600 800 1000 1200 1400ADFI (g/d)

70’s80’s90’s

2000’s

AD

G (

g/d)

900800700600500400300200100

0

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

SID Trp:Lys ratios (%)

AD

G (

g/d)

900

800

700

600

500

400

300

200

100

0

0 500 1000 1500 2000 2500 3000

Ingested SID Trp (mg/d)

★ Figure 5: ADG as function of ADFI for different trial’s dates

1.2. Trials selection to determine a requirement as a ratio to lysine

The experimental design is the first factor of variation of the published requirements.

With the aim to determine a Trp requirement as a ratio to Lys, several conditions in relation to dietary compositionmust be respected (Boisen et al., 2003; Barea et al., 2009; Corrent and Primot, 2009):

1) lysine supply must be sub-limiting,2) the other indispensable amino acids must be at least at the requirement.

1.2.1. Thanks to a sub-limiting lysine, limiting factors are under control

In dose-response trials, Lysine (Lys) must be the second limiting amino acid after Trp which is the studied amino acid.

If Lys is oversupplied, all the Trp will be used but not all the Lys; Lys becomes a wrong reference and the optimal Trp:Lysratio will be underestimated. Moreover, by controlling the first limiting factors (Trp and Lys), none of the other nutrientsmay limit the expected response, particularly the energy content (NE) must be sufficient relatively to Lys.

Figures 8 and 9 present the mean (see symbol ⊕) and the range of respectively SID Lys and NE content for eachweight category. Some aberrant values (see symbol ** : values outside the range of mean ± 2 standard deviations)allow to clearly identify trials in which Lys and NE are over or under supplied.

★ Figure 8: Means of Lysine content (% of the diet)for each weight category

(P. Prestarter ; S. Starter ; P-S. Prestarter-Starter)

In addition, two references have been used to determine if Lys might be sub-limiting or not for each trial:

� NRC (1998) recommends a SID Lys supply (% diet) which varies according to the weight of piglets (from 1.01 to 1.34 % diet for 3-20 kg piglets),

� Whittemore et al. (2003) recommends 1.2-1.4 % diet of SID Lys for 6-15 kg piglets and 1.12 % diet SID Lys for 10-30 kg piglets.


★ Figure 9: Means of NE content (MJ/kg diet)for each weight category

(P. Prestarter ; S. Starter ; P-S. Prestarter-Starter)

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

1.050.99

1.07

P S P-S

**

*****************************

++

+

SID

Lys

ine

(% o

f the

die

t)

Weight category

12.0

11.5

11.0

10.5

10.0

9.5

9.0

8.5

8.0

P S P-S

10.48 10.36 10.25

****

+ + +

Weight category

NE

(MJ/k

g)


Figure 10 presents the SID lysine content (% diet) for each trial and the two references are represented thanks to lines(orange for NRC, 1998 and blue for Whittemore et al., 2003). Trials in red arethose which have a SID Lys content lowerthan the two references while trials in greenare those greater than these references. Trialsin green have certainly not a sub-limiting Lys(examples of trials 198, 199 and 200 in figure 10).

As seen before, the sub-limiting Lys is one ofthe conditions which must be respected. Thus,this type of trials can not be kept to determine a requirement expressed as a ratioto Lys and have been removed from themeta-analysis.

★ Figure 10: SID Lys (% diet) for each trial (starter piglets 11-24 kg LW)

1.50

1.25

1.00

0.75

0.50

0 20 40 60 80 100 120 140 160 180 200 220 240

� NRC, 1998� Whittemore et al., 2003� 200: trial referenced number

� < the 2 references� Between the 2 references� > the 2 references

Figure 11 presents the SID Thr:Lys ratios usedin each trial and the two references are represented by lines (orange for NRC, 1998and blue for Whittemore et al., 2003). Trials inred are those which have a SID Thr:Lys ratio bellow the two references. In these trials, Thris therefore a limiting factor and probably before Trp and Lys. Even if there is a responseto SID Trp:Lys, it must be limited by the lack of Thr.

Since, these trials can not be used for the determination of the SID Trp:Lys requirement,they have been removed from the meta-analysis.

This method was performed for all indispensable amino acids.

★ Figure 11: SID Thr:Lys ratios (%) for each trial(starter piglets 11-24 kg LW)

75

70

65

60

55

50

450 20 40 60 80 100 120 140 160 180 200 220 240

1.2.2. None of the other amino acids must be limiting

For trials with sub-limiting Lys, the amino acids profile (as a ratio to SID Lys) is studied to spot the limiting ones thanksto two references (NRC, 1998 and Whittemore et al., 2003).

This part presents the example of threonine (Thr). Thr is indeed an essential amino acid and is generally the secondlimiting amino acid in practical formulas. Whittemore et al., (2003) recommends a minimum of 65% SID Thr:Lys forpiglets requirement and NRC (1998) a minimum of 62.5% SID Thr:Lys.

SID

lysi

ne c

onte

nt (

% d

iet)

SID

Thr

:Lys

rat

ios

(%)

Trial number

Trial number

� NRC, 1998� Whittemore et al., 2003� 200: trial referenced number

� < the 2 references� Between the 2 references� > the 2 references

1.2.3. Final selection: 69% of trials eliminated due to the experimental design

After the selection based on the amino acid dietary composition, 41 trials among the 130 (31%) are kept for the meta-analysis (Figure 12). 89 trials were eliminated because the experimental design and diets were not adapted. Figure 13 shows similar pattern of trials selection between those obtained or not through AEL research collaboration.

★ Figure 12: ADG as a function of SID Trp:Lys ratiosfor each selected trial

Among the 41 trials kept for the meta-analysis, 51% are from Europe, 34% from USA and 15% from other countries.This distribution is similar to those of the 130 initial trials (see 1.1.1) meaning that the selected trials represent wellthe whole piglets’ population.

The first reason of elimination is a non sub-limiting Lys with 19 trials eliminated (Figure 14). The mean of SID Lyscontent in these 19 trials is 1.3%.

★ Figure 14: Reasons for trials elimination

The main limiting amino acids are Thr and Val with 12 trials eliminated for each reason (Figure 14). The mean of SIDThr:Lys in trials eliminated for this reason is 61% and the mean of SID Val:Lys in trials eliminated because of a limitingvaline is 64%. These means are both far too low compared to latest reference (respectively 65% and 70%).


★ Figure 13: Distribution of AEL trials in each category (kept or eliminated trials)

20

18

16

14

12

10

8

6

4

2

01 2 3 4 5 6 7 8 9 10 11 12 13 14

1918

14

12 12

32 2 2

1 1 1 1 1

Num

ber

of t

rial

sA

DG

(g/

d)

700

600

500

400

300

200

100

04 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

1. No sub Lys1

2. Two-levels2

3. AA imbalance3

4. Thr4

5. Val4

6. Ile4, Val4

7. Val4, Leu4

8. M+C4

9. Aberrant value LNAA5

10. Leu4

11. Thr4, M+C4

12. Leu4, His4

13. Aberrant value NE6

14. Diet7

1 No sub Lys: non sub-limiting lysine2 Two-levels: two-levels trials which are not on a linear part (slope or plateau) of an a priori model

3 AA imbalance: trials eliminated because of more than three limiting amino acids

4 Deficient amino acid 5 LNAA = Large Neutral Amino Acid6 NE = Net Energy7 Diet: a difference > 2 points between two treatments for analyzed CP values

�Ajinomoto�Other

SID Trp:Lys (%)

Kept Eliminated

34.1%

65.9% 65.2%

34.8%

Figure 15 summarizes the steps used to select trials which can be used to determine the SID Trp:Lys requirement forpiglets.

★ Figure 15: Steps for trials selection


✔ Once trials usable to determine the SID Trp:Lys requirement for piglets have been selected, a statistical step is necessary to validate the model which best represents the data from these trials.

1.3. Statistical models and piglet response to dietary Trp

1.3.1. Three different tested models

Since a meta-analysis aims to summarize and quantify results from a lot of different trials, a statistical model had to beused. In animal nutrition, the effect of a nutrient is often represented thanks to three types of non linear models (Figure 16).

★ Figure 16: Graphical and mathematical representations of the three models tested

Increased levels of a nutrient



Perf

orm

ance

Perf

orm

ance

Perf

orm

ance

With:•Y: ADG, ADFI, G:F• X: SID Trp:Lys• U, V: origins of ordinate• R, R’: inflexion points• a,b: function parameters• A: multiplicative trial effect

Broken-line model:Y=A (1 + U(R - x)) if x < RY=A if x ≥ R

Curvilinear model:Y=A (1 + V(R’ - x)2) if x < R’Y=A if x ≥ R’

Asymptotic model:Y=A (1 - a.e )

155 collected trials130 trials entered in

the database

41 trials selected to determinethe SID Trp:Lys requirement

for piglets

Presence ofspecific information

Respect of specificexperimental design

➞� ➞�

-bx


The strength of a meta-analysis lies in taking into account the trial effect (Figure 16): each point is not an isolated pointbut belongs to a dose-response. Thus, each trial is used as a unit (intra-study response) to determine the SID Trp:Lysrequirement for piglets (inter-study response). The trial effect is multiplicative to take into account the both inter- andintra-study variability.

The consideration of the inter-study variability directly in the model facilitates the analysis without being obliged toexpress performance in percentage of the maximal performance.

1.3.2. The curvilinear model is more pertinent for such analysis

The three models presented in figure 16 had been tested because they are often used by scientists to represent theeffect of a nutrient dose-response, but only the curvilinear model is adapted for the determination of a requirementfor a population of animals.

Broken-line and curvilinear models, both fit the data well and have a clear definition of what the requirement is (whenthe plateau is reached), contrary to asymptotic model (the plateau is never reached). Therefore the latter is put asideof the present discussion.

� mathematical considerations

The broken-line model is represented thanks to two linear parts (the slope and the plateau) whose the intersectionforms an angle; as for the curvilinear model, it shows a plateau with a part before which is not linear but quadratic (Figure 16). The existence of this curve can be proved by calculating the “input” for which the first derivative is equalto zero (inflexion point) whereas there is no way to prove the existence of an angle.

� biological considerations

Within a population, animals vary in their maintenance requirements (intercepts) and production potentials (plateaus).Thus the broken-line model should only be used in case of individual measurements but studying the effect of an increased amount of a nutrient on only one animal is technically impossible. Consequently, the only case of use for abroken-line model should be for a criteria expressed as a function of time. Moreover, in a group of animals, plateausare reached at different levels for each individu. The curvilinear model is therefore the most adapted to describe thisprogressive achievement of the maximum performance of the whole population.

� economic considerations

By diminishing progressively marginal productivity until the level of the requirement is reached, the curvilinear modelis again more adapted. The broken-line model indeed depicts a constant marginal productivity (slope part) whichstops suddenly (Pesti et al., 2009). Thus the curvilinear model better fits economic considerations.

✔ With the aim to determine the SID Trp:Lys requirement for piglets, 41 trials have been selected from an exhaustive database of 130 experiments.

✔ Three statistical models have been discussed and will be used to depict the general piglets’ response to Trp and to determine the SID Trp:Lys requirement for piglets.


2. Modeling the piglet response and determining the SID Trp:Lys requirement

2.1. Statistical results

The requirements values for each performance parameters are different according to the model (Table I and Figure 17). The meta-analysis results illustrate well the fact that the model used is an important factor of variation of published requirements.

★ Table 1: SID Trp:Lys ratios which maximize ADG, ADFI and G:F ± standard deviation for the three tested models

★ Figure 17: Graphical results of the meta-analysis of ADG for the three tested models

As mentioned before the asymptotic model has not a clear definition of what the requirement is (here 95% of theplateau has been arbitrary chosen) and the broken-line one is not adapted for such an analysis. Moreover, the broken-line model did not converge for ADFI, i.e. this model does not fit the data (Table I).

A good case for the curvilinear model is the coherence of the results: they highlight the role of Trp in ADFI improvement. SID Trp:Lys ratio needed to maximize ADFI is indeed higher than those to maximize ADG (Table I).

✔ Among the three models tested, the curvilinear is the best-adapted.

✔ The SID Trp:Lys requirement for piglets (7-25 kg LW) is 22%.

500

400

300

200

100

0

4 6 8 10 12 14 16 18 20 22 24 26 28

AD

G (

g/d)

SID Trp:Lys (%)

ADG

ADFI

G:F

Broken-line 1

16.7 (0.3)

/

16.2 (0.4)

Curvilinear 1

21.6 (0.8)

22.1 (1.1)

20.3 (0.9)

Asymptotic 2

26.7 (2.9)

24.7 (3.5)

20.7 (2.2)

1. The SID Trp:Lys level needed to reach the plateau

2. The SID Trp:Lys level needed to reach 95% of the plateau


2.2. Piglet response between 16.5% and 22% SID Trp:Lys ratio

The broken-line model predicts a SID Trp:Lys requirement at 16.5% in average (Table I) whereas, the curvilinear model predicts an improvement of ADG of +9% for SID Trp:Lys ratios increased from 16.5% to 22%. Figure 18 presents theincrease of ADG for the trials which compare two Trp levels. This graph illustrates well that there is a response forSID Trp:Lys ratios greater than 16.5%. The average increase of ADG between 16.5% and 22% SID Trp:Lys is +9% aspredicted by the curvilinear model. Conversely the broken-line model prediction values are not coherent with quantitative data of these trials.

✔ Using the broken-line model results, 9% improvement of the growth performance is lost.

★ Figure 18: ADG as a function of SID Trp:Lys ratios for each two-level trial (complete references available on request)

2.3. Statistical validation of the curvilinear model

To validate if a statistical model correctly depicts the data, the residuals must be studied. They indeed measure the difference between values predicted by the model and observed values. In the non-linear models presented in Figure16page 9, the residuals are supposed to:

� be identically distributed around a mean of zero,� follow a normal law,� be independent.

The normality and the mean of the residuals equals to zero had been tested for each of the three zootechnical parameters (Table 2).

The position test (Table 2) is used to verify if the residuals are around a mean of zero. The hypothesis tested is “themean equals to zero”. Table 2 shows p-values greater than 0.05 so the tested hypothesis is not rejected. The meansof the residuals are equal to zero for ADG, ADFI and G:F.

Normality tests (example of Shapiro-Wilk; Table 2) are used to verify if the residuals follow a normal law. The hypothesis tested is “the residuals do not follow a normal law”. Table 2 shows p-values lower than 0.05 so thetested hypothesis is rejected. The residuals follow a normal law for ADG, ADFI and G:F.

AD

G (

% b

est

perf

orm

ance

)

SID Trp:Lys (%)

1.00

0.95

0.90

0.85

0.80

0.75

14 16 18 20 22 24 26

Anguita et al., 2008Daza et al., 1999aDaza et al., 1999bHsia, 2005Laurinen et al., 2002Le Floc’h et al., 2005aLe Floc’h et al., 2005bLiu, 2000Piñeiro et al., 2007aPiñeiro et al., 2007bRenaudau and Gourdine, 2008Sève and Le Floc’h, 1998


Finally, the curvilinear model is not only biologically but also statistically validated. Figure 19 represents piglets performance (ADG and ADFI) which have been predicted by the curvilinear model as a function of SID Trp:Lys ratios. The residuals for each trial have been represented in grey on the same graph to highlight the taking into account of the inter-study variability (in comparison with Figure 12 page 8).

★ Figure 19: ADG (a) and ADFI (b), predicted thanks to the curvilinear model, as a function of SID Trp:Lys ratios (the residuals for each trial are represented in grey)

★ Table 2: P-Values of the normality and the position tests for the three parameters studied, ADG, ADFI and G:F

Thanks to the modeling of piglet response to increased levels of SID Trp:Lys, the requirement can be defined as theplateau-value (see 1.3.2 and Table I).

✔ The meta-analysis with more than 40 trials confirms that a SID Trp:Lys ratio at 22% is required to maximize growth performance for piglets (7-25 kg LW).

AD

G (

g/d)

500

400

300

200

100

04 6 8 10 12 14 16 18 20 24 26 2822

SID Trp:Lys (%)

a

AD

FI (

g/d)

800

700

600

500

400

3004 6 8 10 12 14 16 18 20 24 26 2822

SID Trp:Lys (%)

b

Hypothesis tested

Rejection of the hypothesis tested

CONCLUSION

Mean of residuals equals to zero

0.7981

0.8677

0.9615

NO (p > 0.05)

Mean of residuals equals to zero

The residuals do not follow a normal law

< 0.0001

0.0009

< 0.0001

YES (p < 0.05)

The residuals follow a normal law

Position test Normality test (Shapiro-Wilk)

ADG

ADFI

G:F

P-Value


General conclusionSID Trp:Lys requirement for piglets determined by meta-analysis

✔ The explanation for no response to Trp often lies in the experimentaldesign itself:�NE and SID Lys contents: if the requirement is expressed in ratio to Lys, Lys must be asub-limiting amino acid, i.e. SID Lys:NE ratio must be correctly monitored,

� amino acids profile: all amino acids must be correctly supplied, except Trp which must be the first limiting amino acid and Lys which must be the second one.

✔ The main factors explaining the high variability of published Trp requirements are:� the experimental design: amino acids other than Trp are not correctly supplied,� the model used: requirement is determined with a non-adapted model or even without any model.

✔ Thanks to the rigorous method of meta-analysis, the huge variability in published data is taken into account in the statisticalmodel and the outcome of the present study confirms thatthe SID Trp:Lys requirement to optimize growth performance is22% for piglets of 7 to 25 kg LW.

The authors are grateful to Professor Daniel Sauvant and Doctor Jaap van Milgen for their help in themeta-analytic process and the statistical analysis.

Reference list

Barea, R., L. Brossard, N. Le Floc’h, Y. Primot, D. Melchior, and J. van Milgen. 2009. The standardized ileal digestible valine-to-lysine requirement ratio is at least seventy percent in postweaned piglets. J. Anim. Sci. 87:935-947.

Boisen, S. 2003. Ideal dietary amino acid profiles for pigs. In: J. P. F. D’Mello (Ed.) Amino Acids in Animal Nutrition. pp 157-168. CABI.

Corrent, E., and Y. Primot. 2009. L-Valine: Release the potential of your feed! An indispensable amino acid for pigletgrowth. AJINOMOTO EUROLYSINE S.A.S. technical information 33.

Henry, Y.,B. Sève, A. Mounier, and P. Ganier. 1996. Growth performance and brain neurotransmitters in pigs as affected by tryptophan, protein and sex. J. Anim. Sci. 74:2700-2710.

Le Floc’h, N., D. Melchior, L. Le Bellego, J.J. Matte, and B. Sève. 2007. Le statut sanitaire affecte-t-il le besoin en tryptophane pour la croissance des porcelets après sevrage ? 39èmes Journées de la Recherche Porcine. 39:125-132.

National Research Council. 1998. Nutrient Requirements of Swine. National Academy Press, Washington, DC.

Noblet, J., A. Valancogne, G. Tran, and AJINOMOTO EUROLYSINE S.A.S. EvaPig®. [1.0.1.4]. 2008. Computer program.

Offner, A., and D. Sauvant. 2004. Prediction of in vivo starch digestion in cattle from in situ data. Animal Feed Scienceand Technology. 111:41-56.

Pesti, G.M., D. Vedenov, J.A. Cason, and L. Billard. 2009. A comparison of methods to estimate nutritional requirementsfrom experimental data. Br. Poult. Sci. 50:16-32.

Rico-Gomez, M., and P. Faverdin. 2001. La nutrition protéique modifie l’ingestion des vaches laitières: analyse bibliographique. Rencontres Recherches Ruminants. 8:285-288.

SAS. 2003. SAS/STAT User’s Guide (Release 9). SAS Inst. Inc., Cary, NC.

Sauvant, D., J. M. Perez, and G. Tran. 2004. Tables of composition and nutritional value of feed materials. WageningenAcademic Publishers, INRA Editions and AFZ, Paris.

Sauvant, D., P. Schmidely, J.J. Daudin. 2005. Les méta-analyses des données expérimentales : applications en nutrition animale. INRA Prod. Anim. 18(1):63-73.

Sauvant, D., P. Schmidely, J.J. Daudin, and N.R. St-Pierre. 2008. Meta-analyses of experimental data in animal nutrition.Animal. 2:8, pp 1203-1214.

Schmidely, P. F. Glasser, M. Doreau, and D. Sauvant. 2008. Digestion of fatty acids in ruminants: a meta-analysis of flowsand variation factors. 1. Total Fatty Acids. Animal. 2:677-690.

Schulin-Zeuthen, M., E. Kebreab, W.J.J. Gerrits, S. Lopez, M.Z. Fan, R.S. Dias, and J. France. 2007. Meta-analysis of phosphorus balance data from growing pigs. J. Anim. Sci. 85:1953-1961.

Trevisi, P., D. Melchior, M. Mazzoni, L. Casini, S. d. Filippi, L. Minieri, G. Lalatta-Costerbosa, and G. Bosi. 2008. A tryptophan-enriched diet improves feed intake and growth performance of susceptible weanling pigs orally challenged with K88 E. coli. J Anim Sci 87:148-156.

Whittemore, C. T., M. J. Hazzledine, and W. H. Close. 2003. Nutrient requirement standards for pigs. In: British Societyof Animal Science (Ed.) pp. 1-30. BSAS PO Box 3 Penicuik, Midlothian, Scotland, UK.

Zhang, H., Y. Jingdong, L. Defa, Z. Xuan, and L. Xilong. 2007. Tryptophan enhances ghrelin expression and secretion associated with increased food intake and weight gain in weanling pigs. Domestic Animal Endocrinology. 33:47-61.

The reference list of the 130 trials is available on request.


Already issued:

INFORMATION N°34 - July 2009SID Trp:Lys requirement for piglets determined by meta-analysis

INFORMATION N°33 - May 2009L-VALINE: Release the potential of your feed !

INFORMATION N°32 - November 2008AJINOMOTO EUROLYSINE S.A.S. Formulator’s HandbookMeasuring and predicting amino acids contents in feedingstuffs

INFORMATION N°31 - June 2008Threonine in pigs and broilers: a crucial amino acid for growth and gut function

INFORMATION N°30 - March 2008Tryptophan in young pigs: an essential nutrient with numerous biological functions

INFORMATION N°29 - June 2006Impact of the withdrawal of antimicrobial growth promoters and health statuson the amino acid requirement of the pig

INFORMATION N°28 - June 2005Tryptophan in young pigs: a key nutrient for growth and feed intake

INFORMATION N°27 - June 2004Amino acid nutrition of the broiler chicken - Update on lysine, threonine and other amino acids

INFORMATION N°26 - September 2002Threonine requirement in pigs - Benefits of L-Threonine supplementation

INFORMATION N°25 - March 2002Low protein diets for piglets

INFORMATION N°24 - May 2001Managing growth and carcass quality of growing pigs fed low protein diets

INFORMATION N°23 - September 2000L-Tryptophan supplementation to enhance piglet growth

INFORMATION N°22 - June 2000Prevention of nitrogen pollution from pig husbandry through feeding measures

By Aude SIMONGIOVANNI, Etienne CORRENT and Yvan PRIMOT July 2009

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