Directory UMM :Data Elmu:jurnal:L:Livestock Production Science:Vol64.Issue2-3.Jun2000:

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www.elsevier.com / locate / livprodsci

The concept of digestible amino acids in diet formulation for

pigs

a ,

_*

b c d e

R. Mosenthin

, W.C. Sauer , R. Blank , J. Huisman , M.Z. Fan

Hohenheim University, Institute of Animal Nutrition, D-70593 Stuttgart, Germany

University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, Alberta, Canada T6G 2P5

University of Kiel, Institute of Animal Nutrition, Physiology and Metabolism, D-24098 Kiel, Germany

TNO –Nutrition and Food Research Institute, P.O. Box 15, NL-6700 AA Wageningen, The Netherlands

University of Guelph, Department of Animal and Poultry Science, Guelph, Ontario, Canada N1G 2 W1 Received 23 March 1999; received in revised form 4 August 1999; accepted 5 August 1999

Abstract

There is sufficient evidence that ileal rather than fecal amino acid digestibility values provide a more reliable estimate of protein digestion and amino acid absorption. In addition to differences in ileal amino acid digestibility values between feedstuffs there are large differences in ileal amino acid digestibility values within the same feedstuff. Furthermore, in addition to different processing conditions and inherent differences among samples of the same feedstuff, a large proportion of this variation can be attributed to different methodological approaches. In order to reduce the within variation associated with different methods for determination, methods specifically suitable for different feedstuffs are recommended. Differences in dietary amino acid levels are likely to be the largest single contributor to the variation in ileal amino acid digestibility values. Therefore, it is suggested to determine their plateau values, also referred to as dietary threshold levels, after which apparent digestibility values become independent of the dietary amino acid levels. The correction for non-specific endogenous protein and amino acid recoveries in ileal digesta allow for the transformation of apparent digestibility to standardised ileal digestibility values. The non-specific recoveries are related to the dry matter intake but independent of the type of feedstuff. In principle, standardised digestibility values should be the preferred approach in protein evaluation because these values reflect a fundamental property of the feedstuffs being independent of experimental conditions. However, estimates of endogenous recoveries are still confounded by the method used for determination, and further research is warranted in this area.  2000 Elsevier Science B.V. All rights reserved.

Keywords: Pigs; Amino acids; Endogenous protein; Standardised ileal digestibility

1. Introduction

The concept of digestible amino acids for pigs has received a lot of attention and research effort. The

*Corresponding author. Tel.: 149-711-459-2414; fax: 1

49-nutritive value of protein for monogastrics is not

711-459-2421.

E-mail address: [email protected] (R. Mosenthin) only determined by the amino acid composition but

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also by the digestibility of amino acids, in particular amino acid per assay (Austic, 1983; Sibbald, 1987). the amino acids likely to be limiting. Pigs require a Furthermore, the results obtained may be confounded diet with a balanced pattern of different indispens- by the influence of ingredients other than the test able amino acids for optimum performance in which amino acid such as starch, fibre, energy and protein the protein supplements usually represent 20% of the (Austic, 1983). Since this assay is obviously not diet but make up approximately up to 35% of the practical and applicable for all amino acids in all cost of the diet. One means to lower the cost of feedstuffs, assessing amino acid digestibility may be protein is to reduce the concentration of amino acids a more reasonable alternative from a practical point in the diets or to reduce the quantity of amino acids of view. According to Williams (1995), the use of possibly provided in excess of the actual require- apparent ileal amino acid digestibilities will still ment, i.e. to reduce the margin of safety. However, improve the accuracy of diet formulation, and offers this cannot be done efficiently without affecting a compromise between total amino acid values in optimum performance unless the quantity of avail- feedstuffs and amino acid availability.

able amino acids in the diet and the quantity required The objective of this review is to evaluate the ileal

by the pig are known. amino acid digestibility concept and to identify its

At this point it is important to distinguish between strengths and weaknesses. This evaluation will in-the concepts of digestible and available amino acids. clude physiological aspects by comparing apparent By definition, apparent amino acid digestibility is fecal and ileal amino acid digestibilities values. calculated as the percentage of amino acid intake that Furthermore, methodological sources of variation in does not appear in digesta or feces. Using the term apparent ileal amino acid digestibility values includ-‘‘apparent’’ implies that no correction for endogen- ing the effects of methods for determination and ous amino acid losses has been made. On the other dietary amino acid level will be addressed. Finally, hand, availability is defined as the proportion of the the transformation of apparent ileal digestibility amino acid in the diet that is absorbed in a form values into standardised ileal digestibility values by suitable for utilisation (Sauer et al., 1989). Batterham correction for non-specific endogenous amino acid et al. (1979) introduced the slope-ratio technique for recoveries will be discussed.

measuring the availability of amino acids for tissue synthesis. This animal growth assay provides a

combined estimation of digestibility and post-absorp- 2. The ileal versus the fecal analysis method

tive utilisation of amino acids at the tissue level.

Batterham (1992) concluded from the results of After being consumed, dietary protein becomes different studies that there is likely to be a dis- mixed with endogenous protein, and the combination crepancy between digestibility and availability values is subjected to digestion and absorption in the small when heat-treated or heat-damaged meals such as intestine. Free amino acids and small peptides which cottonseed meal and meat and bone meal were are released by the digestive enzymes are usually assayed. The differences were significant for lysine, absorbed before entering the large intestine. How-methionine, threonine and tryptophan but not for the ever, there will be a certain amount of protein which branched-chained amino acids. The aforementioned has not been digested and peptides and free amino amino acids are susceptible to the effect of heat, they acids that have not been absorbed in the small may be partly damaged and, if modified by the intestine. These along with other undigested dietary Maillard-reaction, absorbed in a form which renders components will pass into the large intestine and the these unavailable for protein synthesis (Hurrell and total is subjected to fermentation by the microflora. Finot, 1985). Batterham (1992) concluded that par- The disappearance of amino acids from the large ticularly for cereals ileal digestibility values were the intestine would not be necessarily a problem if the most appropriate as these account for losses in disappearance represented absorption of amino acids digestibility. In addition, assessing amino acid avail- from the large intestine. However, several studies ability is expensive and time-consuming because it clearly showed that protein digestion in the large provides an estimate of the availability of only one intestine makes little or no contribution to the protein

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Table 1

status of the pig (Zebrowska, 1973; Wunsche et al.,

Apparent ileal and fecal amino acid digestibility values of the

1982; Mosenthin et al., 1992). This can be attributed a

indispensable amino acids in raw and heated soy flakes

to the fact that the microflora in the large intestine

Digestibility, % Difference, %

have the capacity to deaminate amino acids and to

use the carbon skeletons for energy. The amino Fecal Ileal Raw Heated

nitrogen can be absorbed from the large intestine, _Raw _Heated _Raw _Heated mainly in the form of ammonia, which will be

Histidine 80 90 48 82 32 8

transported to the liver, converted to urea and _Isoleucine ₆₈ ₈₄ ₄₃ ₇₈ ₂₅ ₆

excreted in the urine. Thus, the amino acids have Leucine 68 87 37 80 31 7

disappeared from feces and are assumed to have Lysine 72 87 44 85 28 2

Methionine 61 83 47 82 14 1

been digested by the pig. In this case, apparent

Threonine 65 83 32 72 33 11

amino acid digestibilities obtained by the fecal

Tryptophan 75 87 25 72 50 15

analysis method are higher than those determined by _Valine ₆₄ ₈₅ ₃₅ ₇₈ ₂₉ ₇

the ileal analysis method. Cystine, threonine and a

Vandergrift et al. (1983).

tryptophan usually disappear to a large extent in the b

Difference between fecal and ileal digestibility values.

large intestine (Zebrowska et al., 1978; Sauer et al., 1982; Mosenthin et al., 1994). On the other hand microbial net synthesis for methionine and

some-times for lysine has been reported in some studies averaged 30% whereas the corresponding difference resulting in lower fecal than ileal digestibility values in heated soy flakes was approximately 7%. Al-(Sauer et al., 1982; Tanksley and Knabe, 1982; Sauer though fecal digestibilities indicated that heated soy et al., 1991). An indication of the significance of the flakes were a better nutrient source than raw soy anabolic capacities of the intestinal microflora is that, flakes the magnitude of this difference was substan-depending on diet composition, between 50 to 90% tially underestimated (Vandergrift et al., 1983). of the total nitrogen in feces is of bacterial origin It is obvious that apparent ileal amino acid di-(Poppe et al., 1983; Kreuzer et al., 1989; Sauer et al., gestibilities are a more sensitive approach to describe

1991). the nutritive value of feedstuffs than fecal

diges-In conclusion, due to microbial metabolism of tibilities. The poorer the protein quality of feed, the nitrogenous material in the large intestine, only a more important ileal digestibility values are com-relatively small proportion of the amino acid excre- pared to fecal digestibility values. Convincing evi-tion in feces is directly related to the amino acids dence that ileal rather than fecal digestibility values recovered at the distal ileum. Thus, depending on the should be used in practical diet formulation for amino acid and on the feedstuff, digestibility values growing pigs was provided by Dierick et al. (1988). obtained by the fecal analysis method overestimate In this study the performance of pigs was related to (which is usually the case) or underestimate those digestibility measurements. There was a higher cor-obtained by the ileal analysis method. Therefore, it is relation between average daily gain and ileal rather now recognised that the ileal analysis method should than fecal protein digestibility (r50.76 vs. r5

be considered as an improvement over the fecal 0.34). In the same order, for feed efficiency (kg analysis method which was originally developed by feed / kg carcass gain) the correlation coefficients Kuiken and Lyman (1948) for rats and which were 20.87 and 20.65, respectively. In agreement thereafter has been used extensively in studies with with these findings, apparent ileal lysine digestibility pigs (Dammers, 1964; Eggum, 1973). coefficients were found to accurately indicate the A comparison of apparent fecal and ileal amino amount of dietary lysine available for growth acid digestibilities in raw and heated soy flakes (Moughan and Smith, 1985; Rademacher et al., illustrates the inadequacy of the fecal analysis meth- 1995). These results provide sufficient evidence that od for measuring amino acid digestibility values nitrogen absorbed in the large intestine does not (Table 1). The difference between fecal and ileal contribute significantly to protein synthesis in grow-digestibility values of amino acids in raw soy flakes ing pigs.

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3. Variation in apparent ileal protein and amino of legume seeds were compiled from a literature

acid digestibilities review by Mosenthin et al. (1997) and are summa-rised in Table 2.

The apparent ileal digestibilities of protein and There are substantial differences in apparent ileal amino acids have been determined in a large number protein and amino acid digestibility values among of samples from the most common feedstuffs used in samples of the same cereal grain as reflected by large pig nutrition. It is obvious that there are large standard deviations. For protein and the indispens-differences in ileal protein and amino acid diges- able amino acids the differences were largest in tibility values between feedstuffs. The main factors barley, ranging from 45–80%, 38–79%, 67–88% responsible for these differences including methods and 44–76% for protein, lysine, methionine and for digesta collection, processing conditions and threonine, respectively. Some of the differences in inherent dietary factors were previously discussed apparent ileal protein and amino acid digestibilities (Sauer and Ozimek, 1986; Knabe et al., 1989; may be attributed to differences in processing con-Knabe, 1991; Mosenthin and Sauer, 1992; Mosenthin ditions and such factors as variety of grain, fertiliser et al., 1997). In addition, there are also large application and environmental conditions which were differences in ileal amino acid digestibilities among discussed in detail by Sauer and Ozimek (1986) and different samples of the same feedstuff (Sauer et al., Mosenthin et al. (1997). However, as shown in Table 1990). The extent of this variation depends on the 2, there were relatively small differences in the type of feedstuff (Sauer and Ozimek, 1986; Mosen- average apparent ileal protein and amino acid di-thin et al., 1997). The apparent ileal protein and gestibility values between different cereal grains amino acid digestibilities of various cereal grains, compared with differences within the same cereal protein supplements of plant and animal origin and grain. The digestibility coefficients for wheat, barley,

Table 2

Apparent ileal digestibilities (%) of crude protein and indispensable amino acids in cereal grains, protein supplements and legume seeds

Ingredients n Crude protein Lysine Methionine Threonine

c c d

DC Range SD DC Range SD DC Range SD DC Range SD

Cereal grains

Wheat 22 81 71–86 4.2 73 62–84 6.5 85 79–92 3.5 72 51–78 6.7

Barley 20 70 45–80 8.2 [19] 66 38–79 10.1 78 67–88 6.0 [18] 64 44–76 8.6

Corn 8 70 49–82 11.7 [7] 68 50–82 5.9 85 79–92 4.3 65 53–79 9.6

Triticale 6 78 76–82 3.0 [4] 72 62–81 6.7 82 77–85 3.1 62 46–74 11.1

Protein supplements

Soybean meal 30 80 72–89 3.7 84 76–91 3.4 86 77–97 4.3 [27] 75 68–83 3.9 Canola meal 14 69 64–73 2.5 73 69–81 3.1 82 76–93 4.7 [11] 67 60–74 3.7 Cottonseed meal 12 75 67–86 5.7 66 42–87 11.5 77 65–87 8.6 [11] 66 55–79 7.7 Meat and bone meal 16 67 57–82 6.8 70 56–85 8.5 77 66–85 6.6 [7] 64 50–81 9.2

Fishmeal 7 76 72–82 3.9 83 77–89 5.0 88 82–94 5.2 [4] 78 73–84 3.6

Legume seeds

Peas 9 73 69–76 2.7 81 73–84 3.6 73 68–76 2.5 65 60–74 4.1

Faba beans 6 74 69–77 2.8 80 77–87 3.6 67 61–77 7.1 [4] 73 57–84 11.5

Compiled from Mosenthin et al. (1997).

Number of observations.

Digestibility coefficient, mean values and range of values.

Standard deviation.

Values in parentheses following protein and methionine digestibility values indicate the number of samples in which the protein and methionine digestibility was determined.

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corn and triticale ranged from 70 to 81%, 66 to 73%, and Sauvant (1983) for ruminants and recently by 78 to 85% and 62 to 72% for protein, lysine, Fan and Sauer (1995a,b) for pigs.

methionine and threonine, respectively. The large

within rather than between variation in cereal grains _{4.1.1. Direct method}

indicates that methodological rather than other fac- _{Using this method the assay diet is formulated in} tors may be responsible for a large proportion of this _{such a manner that the assay ingredient provides the}

variation. _{sole dietary nutrient in question. Therefore, the}

A similar conclusion can be drawn for protein _{nutrient digestibility in the assay feed ingredient is} supplements and legume seeds. Once again, there _{equal to the corresponding value in the assay diet.} were large differences in apparent ileal protein and

amino acid digestibility values among samples of the _{4.1.2. Difference method}

same feedstuff, with relatively larger variations in _{This method involves the formulation of both a} cottonseed meal, meat and bone meal, fishmeal and _{basal and an assay diet. In this approach the basal} faba beans and smaller in soybean meal, canola meal _{diet contains the basal feed ingredient which} pro-and peas (Table 2). With respect to the protein _{vides the sole assay nutrient in the diet, whereas the} supplements and legume seeds, there seems to be _{assay diet consists of a mixture of the basal and} less variation as compared to the cereal grains, with _{assay feed ingredient. Provided that there is no} the exception of methionine which may be related to _{interaction in nutrient digestibility between the basal} the analytical procedure (Sauer and Ozimek, 1986). _{feed ingredients and the assay feed ingredient, the} However, similar to cereal grains, there were in most _{digestibility of the nutrient in question of the assay} cases relatively small differences in the average _{diet can be calculated by difference.}

apparent ileal protein and amino acid digestibility values between different protein supplements and

4.1.3. Regression method legume seeds compared with differences within the

In this method the basal and the assay feed same feedstuff.

ingredient are evaluated simultaneously. Under the In addition to different processing conditions and

condition that the basal and the assay feed ingredient inherent factors among samples of the same feedstuff

provide the sole assay nutrient in the assay diets, and (e.g. fibre levels, anti-nutritional factors, variety of

provided that there is no interaction between the two grain, fertiliser application, environmental

condi-feed ingredients, the ingredients can be mixed at tions), a large proportion of this variation can be

various graded levels. As a result more than two attributed to different methodological approaches.

assay diets are formulated for digestibility measure-The major responsible methodological factors, those

ments. The relationship between the nutrient di-including methods of determination and dietary

gestibility in the assay diets and the contribution protein and amino acid levels, will be addressed.

levels of the nutrient from the basal and assay feed ingredient to the assay diets can be expressed according to the following equation:

4. Evaluation of methodological sources of

variation in apparent ileal protein and amino _D ₅_D ₃_C ₁_D ₃_C

Di B Bi A Ai

acid digestibilities

where DDi5apparent digestibility of a nutrient in the 4.1. The effect of methods for determination assay diet (%); DA5apparent digestibility of a nutrient in the assay feed ingredient (%); DB5

There are three methods for measurements of apparent digestibility of a nutrient in the basal feed nutrient digestibility in assay diets and assay feed ingredient (%); CAi5contribution level (%) of a ingredients. These methods are the direct, the differ- nutrient from the assay feed ingredient to the assay ence and the regression method. The principles of diet; CBi5contribution level (%) of a nutrient from these methods were previously described by Giger the basal feed ingredient to the assay diet.

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The direct method has been applied especially to diets 2, 3, and 4 barley and canola meal were the many of the cereal grains, in part, because most only amino acid sources and included at three levels, cereals are very palatable. However, as will be 67.5, 45.0 and 22.5%, respectively for barley and discussed in Section 4.2, the ileal digestibility values 24.4, 30.5 and 36.5% respectively for canola meal. of amino acids in cereal grains determined with the Except for diet 1 all diets were formulated to contain direct method are influenced by their amino acid 16% crude protein. The digestibility values for content in the assay diet. In addition to cereal grains protein and amino acids in barley are compared in the direct method may apply to the formulation of a Table 3. For some of these amino acids ileal semi-purified diet, usually based on corn starch, in digestibility coefficients could not be estimated by which the assay ingredient provides the sole dietary the regression method. This was due to the fact that amino acids. With respect to protein supplements and the differences in ileal digestibility values for these legume seeds, most measurements of apparent ileal amino acids between the assay and the basal feed digestibilities were carried out with the direct meth- ingredient were not large enough to create linear

od. responses.

However, in case of some protein supplements or Ileal digestibility coefficients in barley estimated legume seeds, some of which are of poor palatability by the regression method were not different (P.

(e.g. blood meal) and / or have a high content of 0.05) from values determined by the difference anti-nutritional factors (e.g. faba beans), the differ- method when barley was included in the diet at a ence method was chosen for the determination of level of 67.5% (diet 2). However, at lower inclusion apparent ileal amino acid digestibility values. Ac- levels (22.5 and 45.0%) the ileal digestibility values cording to previous studies no effect of level of of protein and amino acids in barley were under-inclusion of soybean meal in the diet on apparent estimated (results not shown). This indicates that the ileal amino acid digestibilities was obtained (Van difference method is only reliable at relatively high Leeuwen et al., 1987). Similarly, studies by Imbeah inclusion levels of the assay amino acids from the et al. (1988) showed with the exception of lysine and test feedstuff in the diets. In addition, the ileal phenylalanine no differences (P.0.05) between digestibility values of protein and amino acids apparent ileal amino acid digestibilities in soybean determined by the direct method were usually lower meal and canola meal determined with the direct and (P,0.05 or 0.10) than those determined by the difference method, respectively. It should be men- difference or regression method. Fan and Sauer tioned, however, that the studies by Imbeah et al. (1995a) concluded that the direct method is not a (1988) indicate the presence of associative effects, valid approach for the determination of protein and albeit of small magnitude, for some amino acids amino acid digestibilities in feedstuffs with a low

from barley and canola meal. protein content.

Recently, comprehensive studies were carried out On the other hand, for some low-protein feedstuffs by Fan and Sauer (1995a,b) in which the effect of of poor palatability such as rye, wheat bran and the direct, the difference and the regression method forage plants, the difference rather than the direct on apparent ileal protein and amino acid digestibility method has been used. For example, Kreienbring et values was determined. In these studies feed ingredi- al. (1988) reported that the apparent ileal digestibili-ents with a low, medium and high protein content ty values of amino acids in forage plants determined such as barley, peas and canola meal, respectively, by the difference method varied considerably, indi-were tested as representative feed ingredients for cated by large standard deviations. Since the amino cereal grains, legume seeds and protein supplements. acid contents in these forage plants were low and due Fan and Sauer (1995a) formulated 5 diets which to a poor palatability the inclusion levels in the assay were fed to 5 barrows with an initial body weight of diets were also low, the large variation likely re-35 kg according to a 535 Latin square design. Diet sulted from the magnifying effect induced by the 1 contained 90% barley providing the sole source of calculation process of the difference method. In amino acids whereas diet 5 contained 42.6% canola conclusion, the difference method may not be suit-meal as the sole source of amino acids in the diet. In able for these low-protein feedstuffs and the

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regres-Table 3

Comparison of the apparent ileal crude protein and amino acid digestibility values (%) in barley with the direct, the difference and the

a,b

regression methods

Items Methods of determination

Direct method Difference method Regression method

Number of observations 5 5 20

Crude protein 56.661.88 58.963.36 57.762.83

Amino acids Indispensable

Arginine 64.761.93 69.863.15 68.462.39

Histidine 69.562.68 71.963.56 70.562.27

Isoleucine 61.163.29 66.964.80 –

Leucine 66.662.80 70.363.79 –

Lysine 54.164.18 61.364.93 59.364.65

Phenylalanine 69.663.41 72.164.28 –

e f

Threonine 53.363.12 62.463.90 –

Valine 62.662.96 67.263.94 –

Dispensable

e f f

Alanine 48.862.96 57.363.39 53.962.81

e f

Aspartic acid 50.563.83 62.164.68 –

Glutamic acid 75.162.52 73.962.10 72.262.89

e f f

Glycine 31.763.41 48.165.64 34.565.08

e f

Serine 58.463.19 64.862.67 –

Tyrosine 51.563.88 61.265.62 58.263.43

Fan and Sauer (1995a).

Mean and standard error of the mean.

Digestibility values calculated from diet 2 (67.5% inclusion level of barley).

Means in the same row show a trend to increase (P,0.10, by one-tailed Student’s t-test).

e,f

Means in the same row with different superscript letters differ (P,0.05).

sion method should be preferred (Fan and Sauer, (30.5 and 36.5%). However, these values were

1995a). usually lower than those determined by the

differ-The apparent ileal protein and amino acid di- ence method when the assay ingredient (canola meal) gestibility values in canola meal determined by the was included at a relatively low level (24.4%) in the direct, the difference and the regression methods are diet (results not shown). With respect to the differ-presented in Table 4. Similar to barley (Table 3), for ence method, the apparent ileal digestibility values of some amino acids ileal digestibility values could not amino acids in high-protein feedstuffs such as canola be calculated by the regression method since the meal were overestimated (P,0.05 or 0.10) when a differences in digestibilities for these amino acids low-protein feedstuff such as barley was the basal between the assay (canola meal) and the basal feed feed ingredient and when the inclusion level of the ingredient (barley) were not large enough to create assay feed ingredient (canola meal) was relatively

linear responses. low in the assay diet. Therefore, it was recommended

As shown in Table 4, the apparent ileal diges- by Fan and Sauer (1995a) that a protein supplement tibilities of crude protein and amino acids in canola rather than a low-protein feedstuff (e.g. cereal grains) meal estimated by the regression method were not should be the basal feed ingredient when the differ-different (P.0.05) from those determined by the ence method is used.

direct method, and were very close (P.0.05) to the On the other hand, for protein supplements of poor values determined by the difference method at the palatability such as blood meal the apparent ileal higher inclusion levels of canola meal in the diet digestibility values of amino acids should be

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de-Table 4

Comparison of the apparent ileal crude protein and amino acid digestibility values (%) in canola meal with the direct, the difference and the

a,b

regressions methods

Items Methods of determination

Direct method Difference method Regression method

Number of observations 5 5 20

Crude protein 66.060.85 62.561.44 64.361.46

Amino acids Indispensable

Arginine 80.861.19 79.461.14 79.560.95

Histidine 80.060.78 77.461.19 78.761.09

Isoleucine 69.360.77 65.361.58 –

Leucine 70.861.15 67.761.68 –

Lysine 73.760.79 70.761.10 71.861.38

Phenylalanine 70.861.18 67.961.90 –

Threonine 63.160.88 60.761.64 –

Valine 67.560.84 63.861.72 –

Dispensable

Alanine 68.960.60 65.261.95 66.661.55

Aspartic acid 64.161.04 61.261.65 –

Glutamic acid 80.361.17 75.861.42 79.661.19

Glycine 63.461.95 63.761.28 62.061.89

Serine 65.060.64 62.061.65 –

Tyrosine 66.060.81 64.561.53 64.561.49

Fan and Sauer (1995a).

Mean and standard error of the mean.

Digestibility values calculated from diet 4 (36.6% inclusion level of canola meal).

termined by the regression rather than the difference the basal and the assay feed ingredient should be method. This can be attributed to the fact that due to paired in such a way that differences in apparent ileal the low level of inclusion of these protein supple- digestibility values of amino acids between the two ments in the assay diet, the ileal digestibility co- feed ingredients are large enough to create linear efficients may not be reliable. For example, Knabe et responses. With respect to the difference method, it is al. (1989) reported that the ileal digestibility values recommended that a protein supplement rather than a of isoleucine calculated by the difference method for low-protein feedstuff (e.g. cereal grains) is the basal three samples of blood meal were 60, 70 and 80%, feed ingredient and that, in addition, the inclusion respectively. However, as was pointed out by the level of the test protein supplement is relatively high authors, these values do not represent the variation in in the assay diet.

apparent ileal digestibility values of isoleucine but These recommendations for the determination of are a reflection of experimental error since blood apparent ileal protein and amino acid digestibilities meal provided only 15% of the isoleucine content in in high-protein feedstuffs were confirmed in further

the assay diet. studies with peas (Fan and Sauer, 1995b). Peas

Fan and Sauer (1995a) concluded that the regres- represent feed ingredients with a medium protein sion method is, in principle the most accurate content compared to protein supplements (e.g. approach for determining ileal digestibility values in oilseed products) with a relatively high and cereal protein supplements, in particular for protein supple- grains with a relatively low protein content. Provided ments with a low level of inclusion in the assay diet that the consumption of the assay diets is not limited due to poor palatability. In order to apply the due to poor palatability of the test feedstuff, the regression method successfully for all amino acids, direct method may be also suitable to determine

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apparent ileal protein and amino acid digestibility gestibility values according to a segmented quadratic

values in legume seeds. with plateau model resulted in quadratic relationships

between the apparent ileal amino acid digestibility 4.2. The effect of dietary protein and amino acid values and the amino acid content in the assay diet.

levels These relationships are illustrated in Fig. 1 for

leucine, lysine, methionine and threonine; a similar With increasing levels of dietary protein from pattern was observed for the other amino acids. At soybean meal the apparent fecal protein digestibility lower dietary levels the apparent ileal amino acid increased curvilinearly as was originally shown by digestibility values increased sharply; thereafter the Eggum (1973) in studies with rats. A similar rela- increases became smaller and reached their indi-tionship was established by Furuya and Kaji (1989) vidual plateau values after which there were no in pigs who reported differences in apparent ileal further increases which means that the digestibility digestibility values of protein and amino acids in coefficients became independent of the dietary amino relation to their dietary contents. Therefore, values acid levels. In this model the lower endpoints of 95% for apparent ileal amino acid digestibility are only confidence intervals of the plateau digestibility val-valid under standardised conditions with respect to ues are defined to be the initial plateau digestibility the protein and / or amino acid content of the assay values. By definition, the dietary protein and amino diet. However, an examination of the literature acid contents, corresponding to the initial plateau reveals that in most cases the determination of digestibility values, are referred to as the dietary apparent ileal amino acid digestibility values was threshold levels.

carried out at different dietary amino acid levels as It should be emphasised, however, that the appar-indicated by differences in dietary protein content. ent ileal protein and amino acid digestibility values For example, the crude protein contents in corn do not reach their initial plateau values simultaneous-starch-based soybean meal diets were 21, 14 and ly at the same dietary crude protein content (Fig. 2). 12%, in studies by Holmes et al. (1974), Jørgensen The studies by Fan et al. (1994) clearly show that the et al. (1984) and Knabe et al. (1989), respectively. dietary amino acid contents affect apparent ileal From a literature review Sauer and Ozimek (1986) amino acid digestibility values, irrespective of the and more recently Mosenthin et al. (1997) concluded level of protein in the diet. The authors suggested that differences in protein and amino acid content in that the level of inclusion of a feedstuff in the assay the assay diets may explain, in part, the variation in diet should be such that the amino acid contents in apparent ileal digestibility values of protein and the assay diet are equal to or exceed the expected amino acids among different samples of the same threshold levels in order to obtain the plateau values.

feedstuff. Despite the fact that dietary factors such as fibre and

As there is a scarcity of information about the anti-nutritional compounds may alter the ratio of effect of dietary protein and amino acid content on exogenous to endogenous amino acids, thereby af-the corresponding apparent ileal digestibility values, fecting the dietary threshold levels of protein and Fan et al. (1994) initiated a comprehensive study in amino acids, these values are valuable for reference. which 6 corn starch-based diets with graded levels of Fan et al. (1994) concluded from the literature that crude protein from soybean meal (4, 8, 12, 16, 20 the total contents of crude protein and most amino and 24%) were fed to growing pigs according to a acids in cereal grains are usually far below the 636 Latin square design. As expected, there were threshold levels that were established in their study. large increases (P,0.01) in apparent ileal digestibili- As a result, small differences in dietary contents of ty coefficients for protein and all amino acids with crude protein and amino acids below the corre-increasing levels of dietary protein. These increases sponding threshold levels will result in relatively were greatest at the lower protein levels; they large variations in the digestibility coefficients of became negligible at the higher levels as endogenous amino acids, as dietary amino acid levels quadrati-protein accounts for a smaller proportion of total cally affect ileal amino acid digestibilities. Especially protein in ileal digesta. The analysis of the di- those amino acids present at low levels in cereal

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Fig. 1. The quadratic with plateau relationships between the apparent ileal amino acid digestibility values and the dietary amino acid contents (as-fed basis) (Fan et al., 1994).

grains (lysine, threonine and tryptophan) and / or 5. Standardised ileal amino acid digestibility

amino acids of which the ileal endogenous recovery values

is relatively high (e.g. threonine) will be affected. In

general, this applies also to protein supplements and If one accepts that the determination of amino acid legume seeds, especially for the limiting amino digestibility values should be based on the ileal acids. The relatively large variation in the apparent analysis method, one should recognise that ileal ileal digestibility of methionine within samples of digesta contains variable amounts of endogenous soybean meal and in methionine, cystine and protein originating mainly from digestive secretions, tryptophan within samples of peas, can be attributed sloughed-off epithelial cells and mucins.

to the relatively low levels of these amino acids in Adjustments for endogenous protein and amino the assay diets (Fan et al., 1994). In addition to the acid recoveries, which may be extra stimulated by previously discussed effect of methods for determi- the presence of anti-nutritional factors such as lec-nation, differences in dietary protein and amino acids tins, trypsin inhibitors and tannins in the diet, allow contents are likely to be the most important single for the determination of true ileal protein and amino factor for the variation in ileal amino acid digestibili- acid digestibility values. In principle, true amino acid ty values within samples of the same feedstuff. digestibility values should be the preferred approach

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because it reflects a fundamental property of the feedstuff being independent of experimental and dietary conditions.

Endogenous protein and amino acid recoveries in ileal digesta can be divided in a non-specific and a specific fraction. The non-specific recovery – also referred to as basal recovery – is related to the dry matter intake but independent of the type of feedstuff or diet. In contrast, the specific recovery – also referred to as extra recovery – is related to the composition of the feedstuff or diet (e.g. presence of inherent factors such as lectins, trypsin inhibitors and tannins).

Due to the non-specific recovery, values of appar-ent digestibility are influenced by the protein and amino acid levels in the assay diet. For a given amino acid, the apparent digestibility values increase exponentially with higher levels of intake because endogenous recoveries, as a percent of total re-covery, decrease proportionally. By contrast, true

Fig. 2. The quadratic with plateau relationships between the

apparent ileal crude protein and amino acid digestibility values amino acid digestibility values are not affected by

and the dietary crude protein content (as-fed basis) (Fan et al., _{the level of intake or amino acid content of the assay} 1994).

diet as illustrated in Fig. 3. True digestibility values

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allow accurate comparisons between different feed- also differ for various methods. For example, Boisen stuffs, even if these are fed in different quantities. and Moughan (1996b) reported that the non-specific Furthermore, true digestibility values are likely to be endogenous protein recoveries varied between 10 more additive between feed ingredients than apparent and 15 g / kg dry matter intake when protein-free values (Mariscal–Landin, 1992). diets were fed. However, under more physiologically It is therefore suggested that for use in feed normal conditions (i.e. when protein-containing diets evaluation values of apparent digestibility should be were given), the non-specific recoveries accounted

transformed into values of true digestibility (Seve, for about 20 g / kg dry matter intake. Nyachoti et al. 1994; Boisen and Moughan, 1996a; Boisen, 1998). (1997) concluded that estimates of endogenous Therefore, the term ‘‘standardised ileal digestibility’’ protein and amino acid recoveries obtained with the was introduced by Mariscal-Landin (1992). It de- regression method as well as with feeding protein-scribes the transformation of apparent amino acid free-diets should be referred to as the minimum digestibility values into values of standardised di- values that are not related to the protein and amino gestibilities by correction for non-specific amino acid acid content of the diet.

recoveries in ileal digesta according to the following For the calculation of standardised digestibility

equation: coefficients two different approaches were

intro-duced in practice. Jondreville et al. (1995), in

SID (%)5AID (%)

association with Eurolysine and the Technical

Insti-Non-specific endogenous amino acid recoveries (g / kg DMI)

tute for Cereals and Forages (ITCF), based their

]]]]]]]]]]]]

1 3100

Dietary amino acid content (g / kg DM)

calculations for the correction of non-specific endog-where SID5standardised ileal digestibility values; enous ileal protein and amino acid recoveries on data AID5apparent ileal digestibility values; DMI5dry that were obtained by feeding protein-free diets to

matter intake. growing pigs. On the other hand, Rademacher et al.

Standardised ileal digestibility values of protein (1999) transformed values of apparent ileal protein and amino acids in feedstuffs for pigs were published and amino acid digestibility to values of standardised by Jondreville et al. (1995), CVB (1998) and digestibility by using existing literature data on Degussa (1998). The calculation of standardised ileal endogenous recoveries of protein and amino acids in protein and amino acid digestibilities requires an ileal digesta. These authors selected 33 experiments estimate of the amount of non-specific endogenous from the literature including experiments carried out protein and amino acid recoveries in ileal digesta. at the TNO Nutrition and Food Research Institute, Several methods have been developed and applied to Department of Animal Nutrition and Physiology quantify these recoveries. These include convention- (ILOB) in Wageningen, The Netherlands. The de-al methods such as feeding protein-free diets, the termination of average values for the non-specific regression method and feeding diets containing endogenous protein and amino acid recoveries in protein sources (e.g. casein) with an assumed 100% ileal digesta was based on different experimental digestibility. Other methods include the peptide approaches. These included conventional methods alimentation ultrafiltration method, also referred to as such as feeding protein-free diets without (n516) or the enzymatically hydrolysed casein (EHC) method, with parenteral infusion of amino acids (n51) (e.g. the homoarginine method, isotope dilution tech- De Lange et al., 1989a,b), the regression method niques and calculation methods based on the differ- (n53) (e.g. Fan et al., 1995c) and the feeding of ence between the in vitro and in vivo digestibility of highly digestible protein sources such as wheat protein and amino acids. Comprehensive descriptions gluten or casein (n511) (e.g. Chung and Baker, and evaluations of these methods were provided by 1992). In addition, the corrections for non-specific Tamminga et al. (1995), Boisen and Moughan protein and amino acid recoveries in ileal digesta (1996b) and Nyachoti et al. (1997). According to were based on the EHC method (n52) (e.g. Butts et Nyachoti et al. (1997) estimates of endogenous al., 1993). It should be mentioned that the diets in protein and amino acid recoveries in ileal digesta are the experiments selected by Rademacher et al. not only affected by animal and dietary factors but (1999) contained no specific anti-nutritional factors

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and not more than 8% cellulose or purified neutral because of the higher proportion of endogenous to detergent fibre (NDF). The data of these experiments exogenous (dietary) recoveries of protein and amino were pooled and mean values for non-specific losses acids in ileal digesta. In addition, the standardised of protein and amino acid recoveries were calculated. ileal protein and amino acid digestibilities differ The feeding of protein-free diets as described by considerably between the methods used for correc-Jondreville et al. (1995) gives lower estimates of tion of non-specific endogenous recoveries. For non-specific endogenous and amino acid recoveries example, the large differences in standardised ileal as compared to estimates by Rademacher et al. threonine digestibility values for barley and in (1999) which were based on different experimental particular for sugar-beet pulp are a reflection of the approaches as outlined in Table 5. These differences different values (0.25 vs. 0.61 g / kg DMI) for non-were highest for threonine which is present in specific endogenous ileal recoveries of threonine relatively large concentrations in endogenous protein obtained by Jondreville et al. (1995) and (Holmes et al., 1974; De Lange et al., 1989a; Sauer Rademacher et al. (1999), respectively.

et al., 1991; Mosenthin et al., 1994). As a result, these sources of variation decrease the Standardised ileal digestibility coefficients for sensitivity and liability of standardised ileal amino crude protein and amino acids were compared by acid digestibility values between different feedstuffs. correcting the corresponding apparent digestibility In addition, this variation may misrepresent the real values for non-specific crude protein and amino acid variation among samples of the same feedstuff. recoveries according to the approach by Jondreville

et al. (1995) and Rademacher et al. (1999),

respec-tively (Table 6). The effect of transforming apparent 6. Conclusions

into standardised digestibility values is of small

magnitude in high-protein feedstuffs such as soybean The ileal rather than fecal analysis method should meal. Furthermore, the values are not affected by the be used for determining amino acid digestibility. experimental approach used for corrections. How- Values determined with this method reflect the ever, this effect is much more pronounced in low- digestive utilisation of amino acids in feed ingredi-protein feedstuffs such as barley and sugar-beet pulp ents by pigs. Ileal amino acid digestibility values

Table 5

Comparison of non-specific endogenous crude protein and amino acid recoveries in ileal digesta with different experimental techniques (g / kg DMI)

a b

Method Protein-free diet Other methods Difference (%)

Observations n520 (including protein-free diet method) Protein-free diet5100

c n533

Crude protein 7.15 11.82 165

Arginine 0.20 0.39 195

Cystine 0.10 0.21 210

Histidine 0.09 0.19 211

Isoleucine 0.19 0.38 200

Leucine 0.30 0.49 163

Lysine 0.27 0.40 148

Methionine 0.09 0.11 122

Phenylalanine 0.23 0.34 148

Threonine 0.25 0.61 244

Tryptophan 0.08 0.14 175

Valine 0.24 0.54 225

Jondreville et al. (1995).

Rademacher et al. (1999).

Protein-free diet method (n516); Protein-free diet method with parenteral infusion of amino acids (n51); Regression method (n53); Diets with casein or wheat gluten (n511); Enzyme hydrolysed casein (EHC) method (n52).

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Table 6 _{plateau apparent ileal amino acid digestibility values} Comparison of apparent and standardised ileal crude protein and _{should be determined.}

amino acid digestibility values in soybean meal, barley and

sugar-Finally, methods for determination can also result

beet pulp

in differences in ileal amino acid digestibility values

Ingredients Soybean Barley Sugar-beet

within the same feedstuff. In order to eliminate this

meal pulp

variation, methods of determination specifically

Crude protein _{suited for different feedstuffs are recommended. For}

g / kg DM 512 130 119

b,c cereal grains, the regression and the difference

AID 85 78 48

d method rather than the direct method should be used.

SID 86 84 54

SID 87 87 58 In protein supplements, the direct, the difference and

the regression method are all suited for the

de-Lysine

termination. However, for feedstuffs including some

g / kg DM 30.8 4.7 3.6

AID 89 72 44 protein supplements and byproducts that can only be

SID 90 78 52 _{included at low levels in the assay diets, the}

regres-SID 90 81 55

sion rather than the direct or the difference method

Methionine _{should be used.}

g / kg DM 7.5 2.3 1.4 _{Further research is warranted to identify, to}

quan-AID 90 84 57

tify and finally to eliminate potential methodological

SID 91 88 63

sources of variation in the determination of

non-SID 91 89 65

specific endogenous ileal protein and amino acid

Threonine

recoveries in order to obtain reliable estimates for the

g / kg DM 19.5 4.3 3.3

transformation of apparent digestibility values into

AID 84 73 22

SID 85 79 30 values of standardised digestibilities.

SID 87 87 40

a,b

Compiled from Jondreville et al. (1995).

Apparent ileal digestibility values. _References

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` ´

(1)

because it reflects a fundamental property of the

feedstuff being independent of experimental and

dietary conditions.

Endogenous protein and amino acid recoveries in

ileal digesta can be divided in a non-specific and a

specific fraction. The non-specific recovery – also

referred to as basal recovery – is related to the dry

matter intake but independent of the type of feedstuff

or diet. In contrast, the specific recovery – also

referred to as extra recovery – is related to the

composition of the feedstuff or diet (e.g. presence of

inherent factors such as lectins, trypsin inhibitors and

tannins).

Due to the non-specific recovery, values of

appar-ent digestibility are influenced by the protein and

amino acid levels in the assay diet. For a given

amino acid, the apparent digestibility values increase

exponentially with higher levels of intake because

endogenous recoveries, as a percent of total

re-covery, decrease proportionally. By contrast, true

Fig. 2. The quadratic with plateau relationships between the

apparent ileal crude protein and amino acid digestibility values

amino acid digestibility values are not affected by

and the dietary crude protein content (as-fed basis) (Fan et al.,

_{the level of intake or amino acid content of the assay}

1994).

diet as illustrated in Fig. 3. True digestibility values

(2)

allow accurate comparisons between different feed-

also differ for various methods. For example, Boisen

stuffs, even if these are fed in different quantities.

and Moughan (1996b) reported that the non-specific

Furthermore, true digestibility values are likely to be

endogenous protein recoveries varied between 10

more additive between feed ingredients than apparent

and 15 g / kg dry matter intake when protein-free

values (Mariscal–Landin, 1992).

diets were fed. However, under more physiologically

It is therefore suggested that for use in feed

normal conditions (i.e. when protein-containing diets

evaluation values of apparent digestibility should be

were given), the non-specific recoveries accounted

`

transformed into values of true digestibility (Seve,

for about 20 g / kg dry matter intake. Nyachoti et al.

1994; Boisen and Moughan, 1996a; Boisen, 1998).

(1997) concluded that estimates of endogenous

Therefore, the term ‘‘standardised ileal digestibility’’

protein and amino acid recoveries obtained with the

was introduced by Mariscal-Landin (1992). It de-

regression method as well as with feeding

protein-scribes the transformation of apparent amino acid

free-diets should be referred to as the minimum

digestibility values into values of standardised di-

values that are not related to the protein and amino

gestibilities by correction for non-specific amino acid

acid content of the diet.

recoveries in ileal digesta according to the following

For the calculation of standardised digestibility

equation:

coefficients two different approaches were

intro-duced in practice. Jondreville et al. (1995), in

SID (%)5AID (%)

association with Eurolysine and the Technical

Insti-Non-specific endogenous amino acid recoveries (g / kg DMI)

tute for Cereals and Forages (ITCF), based their

]]]]]]]]]]]]

1 3100

Dietary amino acid content (g / kg DM)

calculations for the correction of non-specific

endog-where SID

5 standardised ileal digestibility values;

enous ileal protein and amino acid recoveries on data

AID

5 apparent ileal digestibility values; DMI

5 dry

that were obtained by feeding protein-free diets to

matter intake.

growing pigs. On the other hand, Rademacher et al.

Standardised ileal digestibility values of protein

(1999) transformed values of apparent ileal protein

and amino acids in feedstuffs for pigs were published

and amino acid digestibility to values of standardised

by Jondreville et al. (1995), CVB (1998) and

digestibility by using existing literature data on

Degussa (1998). The calculation of standardised ileal

endogenous recoveries of protein and amino acids in

protein and amino acid digestibilities requires an

ileal digesta. These authors selected 33 experiments

estimate of the amount of non-specific endogenous

from the literature including experiments carried out

protein and amino acid recoveries in ileal digesta.

at the TNO Nutrition and Food Research Institute,

Several methods have been developed and applied to

Department of Animal Nutrition and Physiology

quantify these recoveries. These include convention-

(ILOB) in Wageningen, The Netherlands. The

de-al methods such as feeding protein-free diets, the

termination of average values for the non-specific

regression method and feeding diets containing

endogenous protein and amino acid recoveries in

protein sources (e.g. casein) with an assumed 100%

ileal digesta was based on different experimental

digestibility. Other methods include the peptide

approaches. These included conventional methods

alimentation ultrafiltration method, also referred to as

such as feeding protein-free diets without (n

5 16) or

the enzymatically hydrolysed casein (EHC) method,

with parenteral infusion of amino acids (n

5 1) (e.g.

the homoarginine method, isotope dilution tech-

De Lange et al., 1989a,b), the regression method

niques and calculation methods based on the differ-

(n

5 3) (e.g. Fan et al., 1995c) and the feeding of

ence between the in vitro and in vivo digestibility of

highly digestible protein sources such as wheat

protein and amino acids. Comprehensive descriptions

gluten or casein (n

5 11) (e.g. Chung and Baker,

and evaluations of these methods were provided by

1992). In addition, the corrections for non-specific

Tamminga et al. (1995), Boisen and Moughan

protein and amino acid recoveries in ileal digesta

(1996b) and Nyachoti et al. (1997). According to

were based on the EHC method (n

5 2) (e.g. Butts et

Nyachoti et al. (1997) estimates of endogenous

al., 1993). It should be mentioned that the diets in

protein and amino acid recoveries in ileal digesta are

the experiments selected by Rademacher et al.

not only affected by animal and dietary factors but

(1999) contained no specific anti-nutritional factors

(3)

and not more than 8% cellulose or purified neutral

because of the higher proportion of endogenous to

detergent fibre (NDF). The data of these experiments

exogenous (dietary) recoveries of protein and amino

were pooled and mean values for non-specific losses

acids in ileal digesta. In addition, the standardised

of protein and amino acid recoveries were calculated.

ileal protein and amino acid digestibilities differ

The feeding of protein-free diets as described by

considerably between the methods used for

correc-Jondreville et al. (1995) gives lower estimates of

tion of non-specific endogenous recoveries. For

non-specific endogenous and amino acid recoveries

example, the large differences in standardised ileal

as compared to estimates by Rademacher et al.

threonine digestibility values for barley and in

(1999) which were based on different experimental

particular for sugar-beet pulp are a reflection of the

approaches as outlined in Table 5. These differences

different values (0.25 vs. 0.61 g / kg DMI) for

non-were highest for threonine which is present in

specific endogenous ileal recoveries of threonine

relatively large concentrations in endogenous protein

obtained

by

Jondreville

et

al.

(1995)

and

(Holmes et al., 1974; De Lange et al., 1989a; Sauer

Rademacher et al. (1999), respectively.

et al., 1991; Mosenthin et al., 1994).

As a result, these sources of variation decrease the

Standardised ileal digestibility coefficients for

sensitivity and liability of standardised ileal amino

crude protein and amino acids were compared by

acid digestibility values between different feedstuffs.

correcting the corresponding apparent digestibility

In addition, this variation may misrepresent the real

values for non-specific crude protein and amino acid

variation among samples of the same feedstuff.

recoveries according to the approach by Jondreville

et al. (1995) and Rademacher et al. (1999),

respec-tively (Table 6). The effect of transforming apparent

6. Conclusions

into standardised digestibility values is of small

magnitude in high-protein feedstuffs such as soybean

The ileal rather than fecal analysis method should

meal. Furthermore, the values are not affected by the

be used for determining amino acid digestibility.

experimental approach used for corrections. How-

Values determined with this method reflect the

ever, this effect is much more pronounced in low-

digestive utilisation of amino acids in feed

ingredi-protein feedstuffs such as barley and sugar-beet pulp

ents by pigs. Ileal amino acid digestibility values

Table 5

Comparison of non-specific endogenous crude protein and amino acid recoveries in ileal digesta with different experimental techniques (g / kg DMI)

a b

Method Protein-free diet Other methods Difference (%)

Observations n520 (including protein-free diet method) Protein-free diet5100 c

n533

Crude protein 7.15 11.82 165

Arginine 0.20 0.39 195

Cystine 0.10 0.21 210

Histidine 0.09 0.19 211

Isoleucine 0.19 0.38 200

Leucine 0.30 0.49 163

Lysine 0.27 0.40 148

Methionine 0.09 0.11 122

Phenylalanine 0.23 0.34 148

Threonine 0.25 0.61 244

Tryptophan 0.08 0.14 175

Valine 0.24 0.54 225

Jondreville et al. (1995). b

Rademacher et al. (1999). c

(4)

Table 6

_{plateau apparent ileal amino acid digestibility values}

Comparison of apparent and standardised ileal crude protein and

_{should be determined.}

amino acid digestibility values in soybean meal, barley and

sugar-Finally, methods for determination can also result

beet pulp

in differences in ileal amino acid digestibility values

Ingredients Soybean Barley Sugar-beet

within the same feedstuff. In order to eliminate this

meal pulp

variation, methods of determination specifically

Crude protein

_{suited for different feedstuffs are recommended. For}

g / kg DM 512 130 119

b,c

cereal grains, the regression and the difference

AID 85 78 48

method rather than the direct method should be used.

SID 86 84 54

SID 87 87 58

In protein supplements, the direct, the difference and

the regression method are all suited for the

de-Lysine

termination. However, for feedstuffs including some

g / kg DM 30.8 4.7 3.6

AID 89 72 44

protein supplements and byproducts that can only be

SID 90 78 52

_{included at low levels in the assay diets, the}

regres-SID 90 81 55

sion rather than the direct or the difference method

Methionine

_{should be used.}

g / kg DM 7.5 2.3 1.4

_{Further research is warranted to identify, to}

quan-AID 90 84 57

tify and finally to eliminate potential methodological

SID 91 88 63

sources of variation in the determination of

non-SID 91 89 65

specific endogenous ileal protein and amino acid

Threonine

recoveries in order to obtain reliable estimates for the

g / kg DM 19.5 4.3 3.3

transformation of apparent digestibility values into

AID 84 73 22

SID 85 79 30

values of standardised digestibilities.

SID 87 87 40

a,b

Compiled from Jondreville et al. (1995). c

Apparent ileal digestibility values.

_References

Standardised ileal digestibility values according to Jondreville et al. (1995). (Refer to Table 5).

e Austic, R.E., 1983. The availability of amino acids as an attribute Standardised ileal digestibility values according to

of feeds. In: Robards, G.E., Packham, R.G. (Eds.), Feed Rademacher et al. (1999). (Refer to Table 5).

Information and Animal Production – Proceedings of the 2nd Symposium of the International Network of Feed Information Centres, Commonwealth Agricultural Bureau, Slough, UK, pp. 175–189.

provide an estimate of amino acid availability values

Batterham, E.S., 1992. Availability and utilization of amino acids for growing pigs. Nutr. Res. Rev. 5, 1–18.

and should be used in feed evaluation.

Batterham, E.S., Murison, R.D., Lewis, C.E., 1979. Availability of

Apparent ileal amino acid digestibility values from

lysine in protein concentrates as determined by the slope-ratio

the literature, determined with ileal analysis method,

_{assay with growing pigs and rats and by chemical techniques.}

showed considerable variation among different sam-

Br. J. Nutr. 41, 383–391.

ples of the same feedstuff. In addition to different

Boisen, S., 1998. A new protein evaluation system for pig feeds and its practical application. Acta Agric. Scand., Sect. A,