Jaroslav Heger*
TID 1 TID 2 AID 2
is great interest in the evaluation of real digestibilities from a scientific point of view (e.g. De Lange et al., 1990; Mosenthin et al., 1993). However, the use of these values in practical diet formulation for pigs is limited since any variation of the endogenous fraction related to the feedstuff itself as one of its spe- cific attributes is completely eliminated from the digestibility values.
True ileal protein and amino acid digestibility has the advantage over both apparent and real digestibility in that it repre- sents a fundamental property of the individual feedstuff. In other words, true digestibility val- ues include any variation of the endogenous fraction related to the feedstuff itself. Figure 10.3 shows that true digestibility values are not affected by the level of amino acid intake or amino acid content of the assay diet, whereas the corresponding apparent digestibility values increase exponentially with higher levels of intake because the non-spe- cific amino acid recoveries, as percentage of total recovery, decrease proportionally.
There is growing evidence that non-spe- cific endogenous amino acid losses are likely to interfere with additivity of apparent amino acid digestibilities in mixtures of feed ingredi- ents (Imbeah et al., 1988; Fan et al., 1995;
Nyachoti et al., 1997a,b). For example, Nyachoti et al. (1997b) concluded from the results of their study that there may be a lack
of additivity in apparent ileal amino acid digestibilities when low-protein feedstuffs such as barley are combined with high-pro- tein feed ingredients such as canola meal (Table 10.4). The correction of apparent ileal amino acid digestibilities for non-specific amino acid losses that are assumed not to be affected by differences in diet composition, will eliminate these effects. The resulting true amino acid digestibilities are more likely to be additive than the corresponding apparent digestibility values (Mariscal-Landin, 1992;
Jondreville et al., 1995; Boisen and Moughan, 1996; NRC, 1998; Rademacher et al., 1999). Additivity of amino acid digestibility values in the diet formulation for pigs by least-cost formulation programmes is essential since these programmes use individ- ual digestibility coefficients for each feedstuff to fulfil the amino acid specifications. True digestibility values allow feed ingredients to be accurately compared and contribute to the precision of diet formulation.
The key issue for the quantification of true ileal protein and amino acid digestibilities is the quantification of the non-specific pro- tein and amino acid recoveries in ileal digesta.
The data presented in Table 10.5 reveal con- siderable variation between estimates of non- specific protein and amino acid recoveries in the literature. Surprisingly, even when the same methodological approach was used for
176 R. Mosenthin and M. Rademacher
Digestibility (%)
TID 1 = TID 2
estimating non-specific protein and amino acid recoveries, these estimates exhibited a large variation between laboratories (AmiPig, 2000). Boisen and Moughan (1996) concluded from a literature review that differences in methods, including ana- lytical procedures to estimate these losses, and between animal variation are major fac- tors contributing to the considerable varia- tion between estimates for non-specific protein and amino acid recoveries. For example, more conventional approaches are based on the feeding of protein-free diets, the use of the regression analysis method or the feeding of diets containing protein sources (e.g. casein) with an assumed 100%
ileal protein digestibility. Other methods include the peptide alimentation ultrafiltra- tion method, also referred to as the enzy- matically hydrolysed casein (EHC) method, the homoarginine method and calculation methods based on the difference between the in vitro and in vivo digestibility of pro- tein and amino acids. Comprehensive descriptions and evaluations of these meth- ods were provided by Tamminga et al.
(1995), Boisen and Moughan (1996) and Nyachoti et al. (1997a). According to Nyachoti et al. (1997a) estimates of endogenous protein and amino acid recov- eries in ileal digesta are not only affected by animal and dietary factors but also differ for Amino Acids in Diet Formulation for Pigs 177
Table 10.4. Observed and calculated apparent and true ileal digestibilities for selected amino acids in barley, canola meal and a mixture of barley and canola meal. (Adapted from Nyachoti et al., 1997b.)
Canola Mixture of barley and canola meal
Item Barley meal Observed Calculateda Differenceb
Apparent ileal digestibility (%)
Lys 53.5 62.6 63.6 59.0 4.6
Thr 63.7 62.4 67.7 62.9 4.8
Ile 65.3 73.2 78.6 70.6 8.0
Val 67.6 69.5 72.1 65.7 6.4
True ileal digestibilityc(%)
Lys 87.1 84.6 85.8 85.8 0.0
Thr 97.0 97.8 96.6 97.5 -0.9
Ile 95.1 99.7 100.2 97.4 2.8
Val 89.1 97.4 96.4 93.1 3.3
aCalculated from observed digestibilities in the pure ingredients and their contents in the mixture of barley and canola meal.
bCalculated as observed minus calculated values.
cDetermined with the homoarginine method.
Table 10.5. Comparison of non-specific endogenous protein and amino acid recoveries in ileal digesta of growing pigs (g kg1dry matter intake).
AmiPig (2000)
Rademacher
Item LabaA Lab B Lab C et al.(1999)
N 6.25 8.66 7.22 9.67 11.82
Lys 0.29 0.24 0.41 0.40
Met 0.08 0.05 0.13 0.11
Met + Cys 0.22 0.22 0.30 0.32
Thr 0.33 0.27 0.39 0.61
Trp 0.09 0.09 0.17 0.14
aLaboratory.
Amino Acids - Chap 10 12/3/03 12:25 pm Page 177
various methods. For example, Boisen and Moughan (1996) reported that the non-spe- cific endogenous protein recoveries varied between 10 and 15 g kg1dry matter intake when protein-free diets were fed. However, under more physiologically normal conditions (i.e. when protein-containing diets were given), the non-specific recoveries accounted for about 20 g kg1 dry matter intake. Nyachoti et al. (1997a) concluded that estimates of endogenous protein and amino acid recoveries obtained with the regression method as well as by feeding protein-free diets should be referred to as the minimum values that are not related to the protein and amino acid content of the diet.
Different estimates for the correction of non-specific protein and amino acid losses are currently used in feed tables in which true ileal protein and amino acid digestibilities are summarized (Jondreville et al., 1995; CVB, 1998; NRC, 1998; Rademacher et al., 1999; AmiPig, 2000). For example, in AmiPig (2000), promoted by AFZ, Ajinomoto Eurolysine, Aventis Animal Nutrition, Institut National de la Recherche Agronomique (INRA) and Institut Technique des Céréales et des Fourrages (ITCF), the cal- culations for the correction of non-specific endogenous ileal protein and amino acid recoveries are based on data that were obtained by feeding protein-free diets to growing pigs. On the other hand, Rademacher et al. (1999) transformed values of apparent ileal protein and amino acid digestibility into values of true digestibility by using existing literature data on endogenous recoveries of protein and amino acids in ileal digesta. These authors selected 33 experi- ments from the literature that were based on different experimental approaches. These included conventional methods such as feed- ing protein-free diets without (n=16) or with parenteral infusion of amino acids (n=1) (e.g.
De Lange et al., 1989a,b), the regression method (n=3) (e.g. Fan et al., 1995) and the feeding of highly digestible protein sources such as wheat gluten or casein (n=11) (e.g.
Chung and Baker, 1992). In addition, the corrections for non-specific protein and amino acid recoveries in ileal digesta were based on the EHC method (n=2) (e.g. Butts
et al., 1993). It was claimed that the diets in the experiments selected by Rademacher et al. (1999) contained no specific anti-nutri- tional factors and not more than 8% cellulose or purified neutral detergent fibre (NDF). The data from these experiments were pooled and mean values for non-specific losses of protein and amino acid recoveries were cal- culated. As discussed by De Lange and Fuller (2000), extreme care should be taken in com- bining true digestibility values from different feed tables since differences in the methods used to estimate the non-specific endogenous protein and amino acid losses may affect the relationship between dietary amino acid lev- els and corrected amino acid digestibilities across studies and within ingredient.
The feeding of protein-free diets as pro- posed by AmiPig (2000) gives generally lower estimates of non-specific endogenous protein and amino acid recoveries as com- pared to estimates by Rademacher et al.
(1999) which were based on different exper- imental approaches. The data presented in Table 10.5 reveal that these differences were considerably higher for threonine which is present in relatively large concen- trations in endogenous protein (Holmes et al., 1974; De Lange et al., 1989a;
Mosenthin et al., 1994).
As can be expected, the method used for correction of apparent digestibility values has little effect on true digestibility estimates in high-protein feedstuffs with a relatively high apparent digestibility of amino acids and pro- tein such as soybean meal (Table 10.6).
Differences in true digestibility values in rela- tion to the method used for estimating non- specific protein and amino acid recoveries are more pronounced in feed ingredients with lower apparent protein and amino acid digestibilities, in particular with respect to threonine and tryptophan.
The Use of True Digestible Amino Acids in Diet Formulation
In practical terms, the digestibility concept chosen for the evaluation of the individual feed ingredients will have a major impact on the ranking of these feedstuffs. For example,
178 R. Mosenthin and M. Rademacher
Amino Acids - Chap 10 12/3/03 12:25 pm Page 178
apparent and true ileal lysine and threonine digestibilities in some low- and high-protein feedstuffs, are ranked in Tables 10.7 and 10.8, respectively, in relation to soybean meal as a reference. In comparison to true ileal digestibility values the corresponding apparent digestibility coefficients systemati- cally underestimate the digestibility of both, lysine and threonine (and other amino acids), in low protein grain cereals such as wheat, barley, maize and triticale. On the other hand, the consequences of different digestibil- ity estimates on the ranking of high-protein feedstuffs such as oilseed meals and legume seeds are much less pronounced.
It is claimed that the application of true protein and amino acid digestibility values in diet formulation for growing pigs will promote the use of alternative low-protein feedstuffs and various by-products of the food process- ing industry. In the following two examples, two commercially available diets, referred to as reference diets, are formulated to contain as main ingredients maize and soybean meal (Table 10.9) or barley, wheat and soybean meal (Table 10.10). These diets contained equal levels of ME (13.5 MJ kg1), N 6.25 (183 g kg1) and total lysine (10.5 g kg1).
Through complete or partial replacement of maize, barley, wheat and soybean meal in the Amino Acids in Diet Formulation for Pigs 179
Table 10.6. Comparison of true ileal protein and amino acid digestibility values (%) in selected feedstuffs.
Rapeseed Soybean Sugarbeet
Ingredients Barley Wheat Peas meal meal pulp
Crude protein
NRC (1998) – – – – – –
Rademacher
et al.(1999) 80 89 79 73 87 46
AmiPig (2000) 80 88 80 76 87 53
Lys
NRC (1998) 79 81 88 78 89 51
Rademacher
et al.(1999) 76 84 81 74 89 55
AmiPig (2000) 75 81 83 75 89 50
Met
NRC (1998) 86 90 84 86 91 64
Rademacher
et al.(1999) 82 90 74 81 90 59
AmiPig (2000) 84 89 80 87 88 61
Met + Cys
NRC (1998) 86 90 83 84 87 44
Rademacher
et al.(1999) 81 89 70 75 86 53
AmiPig (2000) 84 90 75 84 87 43
Thr
NRC (1998) 81 84 83 76 85 30
Rademacher
et al.(1999) 80 86 76 71 86 28
AmiPig (2000) 75 83 76 75 86 31
Trp
NRC (1998) 80 90 81 75 87 41
Rademacher
et al.(1999) 77 88 70 71 87 50
AmiPig (2000) 79 88 73 80 86 41
Amino Acids - Chap 10 12/3/03 12:25 pm Page 179
reference diets by alternative protein sources such as cottonseed meal, canola meal and peas and by-products such as wheat bran and rice bran, two types of diets were formulated, referred to as mixed diets type A and B (Tables 10.9 and 10.10).
The mixed diets type A were formulated to contain the same level of ME (13.5 MJ kg1), N 6.25 (183 g kg1) and total lysine (10.5 kg1) as the corresponding reference diets in Tables 10.9 and 10.10. However, due to the substitution of dietary components with a relatively high true ileal digestibility of lysine by those with lower digestibility coefficients, lower contents of true ileal digestible lysine in the mixed diets type A in comparison to the corresponding reference diets were obtained.
The level of true ileal digestible lysine in the mixed diets type A declined from 9.2 to 8.8 g kg1(Table 10.9) and from 9.4 to 8.7 g kg1 (Table 10.10) as compared to the reference diets based on maize and soybean meal and barley, wheat and soybean meal, respectively.
This decline in the content of true ileal digestible lysine would certainly have a nega- tive effect on the growth performance of pigs, provided that these figures are below the actual lysine requirement of the pigs.
As a further example, two mixed diets type B were formulated that contained the same level of ME (13.5 MJ kg1) and N 6.25 (183 g kg1) as compared to the refer- ence diets and the mixed diets type A (Tables 10.9 and 10.10). However, to compensate
180 R. Mosenthin and M. Rademacher
Table 10.7. Ranking of feed ingredients based on apparent and true ileal lysine digestibility values.
(Adapted from Rademacher et al., 1999.)
Apparent digestibility True digestibility Ingredients Absolute (%) Relativea(%) Absolute (%) Relativea(%)
Soybean meal 88 100 89 100
Wheat 75 85 84 94
Triticale 75 85 83 93
Barley 67 76 76 85
Maize 62 70 76 85
Sunflower meal 76 86 79 89
Rapeseed meal 71 81 74 83
Peas (field) 79 90 81 91
Beans (field) 80 91 82 92
aRelative to soybean meal.
Table 10.8. Ranking of feed ingredients based on apparent and true ileal threonine digestibility values.
(Adapted from Rademacher et al., 1999.)
Apparent digestibility True digestibility Ingredients Absolute (%) Relativea(%) Absolute (%) Relativea(%)
Soybean meal 83 100 86 100
Wheat 72 87 86 100
Triticale 65 78 79 92
Barley 65 78 80 93
Maize 63 76 80 93
Sunflower meal 76 92 80 93
Rapeseed meal 67 81 71 83
Peas (field) 69 83 76 88
Beans (field) 71 86 77 90
aRelative to soybean meal.
Amino Acids - Chap 10 12/3/03 12:25 pm Page 180
for the lower content of true ileal digestible lysine in the mixed diets type A, the total dietary lysine level was elevated by supple- mental lysine addition. As a result, there was no difference in the level of true ileal digestible lysine between the reference diets and the corresponding mixed diets type B.
Consequently, no negative impact on growth performance of pigs could be expected.
Formulating more complex mixed diets according to type A, while maintaining the same level of total lysine as in the reference diets based on maize and soyabean meal or barley, wheat and soybean meal, significantly reduced feed costs by approximately 8–9%
(Tables 10.9 and 10.10). However, replace- ments of grain cereals and soybean meal by increasing proportions of alternative protein sources and by-products resulted in a pro- nounced decline in the level of true ileal digestible lysine which, in turn, most likely will result in a loss of growth performance.
On the other hand, formulating more complex diets according to type B by main- taining the same levels of true ileal digestible
lysine as in the reference diets decreased feed costs by approximately 9 and 3% as compared to the reference diets based on maize and soybean meal (Table 10.9) and barley, wheat and soybean meal, respec- tively (Table 10.10). In other words, savings in feed costs varied between 3 and 9% com- pared with standard diets based on cereal grains and soybean meal while maintaining the same content of true ileal digestible lysine in the diets. Therefore, the use of true ileal amino acid digestibility values in diet formulation for growing pigs offers the potential not only to improve the precision of diet formulation but also to improve the productivity in pig production through lower feed costs.
Conclusions
It has been recognized that differences in dietary amino acids level are likely to be the largest single contributor to the variation in apparent ileal amino acid digestibility values Amino Acids in Diet Formulation for Pigs 181
Table 10.9. The use of true ileal digestible lysine in the formulation of a maize–soybean meal-based diet and two types of mixed diets.
Maize–soybean
meal Mixed diet Aa Mixed diet Bb Ingredient (g kg1)
Maize 543 380 356
Wheat middlings 200 170 210
Soybean meal (440 g CP kg1) 223 149 177
Rice bran – 200 190
Cottonseed meal – 63 30
Tallow – 7.4 06.8
DL-Methionine 0.8 0.7 01.0
L-Lysine•HCl 2.4 3.0 03.0
L-Threonine 0.6 0.8 00.8
Vitamins and minerals 30.2 26.1 25.4
Energy and nutrients
ME (MJ kg1) 13.5 13.5 13.5
N 6.25 (g kg1) 183 183 183
Lysine (g kg1) 10.5 10.5 108
Lysine, true ileal digestible (g kg1) 9.2 8.8 92
Feed cost (US$ per 100 kg)c 12.56 11.46 11.45
aFormulated to contain equal levels of crude protein and total lysine as maize–soybean meal diet.
bFormulated to contain equal levels of crude protein and true ileal digestible lysine as the maize–soybean meal diet.
cBased on US ingredient prices, February 2002.
Amino Acids - Chap 10 12/3/03 12:25 pm Page 181
within the same feed ingredient. For a given amino acid, the apparent digestibility increases curvilinearly with the ingested quan- tity since the non-specific endogenous losses, as a proportion of total endogenous losses, decreases proportionally. The transformation of apparent into true ileal amino acid digestibility values is based on estimates for the correction of non-specific amino acid losses. True ileal amino acid digestibility coef- ficients are independent of the amino acid level in the assay diet and reflect a fundamen- tal property of the feedstuff itself, not being influenced by differences in dietary condi- tions. Consequently, true amino acid digestibility values can be used in diet formu- lation for growing pigs to quantify the amino acids available for maintenance and tissue accretion at least for a wide range of com- monly used feed ingredients which have not been subjected to high temperature treatment during feed processing.
The use of true ileal digestible amino acids in diet formulation will contribute to (i) a more accurate evaluation of the cost/benefit value of ingredients; (ii) an improved additiv- ity of digestibility values in least cost formula- tion programmes; (iii) a more efficient use of alternative feedstuffs; (iv) an improved utiliza- tion of protein (nitrogen) and amino acids for maintenance and protein deposition; (v) a better prediction of growth performance of pigs; and finally (vi) a more cost-effective pig production.
However, there is considerable variation between estimates of non-specific amino acid losses at the ileal level. Consequently, differ- ent estimates are used in various tables in which true ileal amino acid digestibility values are summarized. Since the results from dif- ferent feed tables are not compatible when being used in diet formulation for growing pigs, there is a need to standardize the esti- mates used for correction of apparent
182 R. Mosenthin and M. Rademacher
Table 10.10. The use of true ileal digestible lysine in the formulation of a wheat–barley–soybean meal- based diet and two types of mixed diets.
Wheat–barley–
soybean meal Mixed diet Aa Mixed diet Bb Ingredient (g kg1)
Barley 288 – –
Wheat 450 153 300
Soybean meal (440 g CP kg1) 194 93 195
Rye – 300 250
Canola meal – 189
Triticale 200 117
Wheat bran – – 80
Tallow 31.6 35.0 23.5
DL-Methionine 1.0 0.5 1.0
L-Lysine•HCl 3.0 2.1 2.8
L-Threonine 1.0 0.3 1.1
Vitamins and minerals 31.4 27.1 29.6
Energy and nutrients
ME (MJ kg1) 13.5 13.5 13.5
N 6.25 (g kg1) 183 183 183
Lysine (g kg1) 10.5 10.5 10.6
Lysine, true ileal digestible (g kg1) 9.4 8.7 9.4
Feed cost (Euros per 100 kg)c 16.24 14.99 15.84
aFormulated to contain equal levels of crude protein and total lysine as wheat–barley–soybean meal diet.
bFormulated to contain equal levels of crude protein and true ileal digestible lysine as the wheat–barley–soybean meal diet.
cBased on European ingredient prices, February 2002.
Amino Acids - Chap 10 12/3/03 12:25 pm Page 182
digestibility values. Finally, the expression of true ileal amino acid digestibility and their use in diet formulation requires the assess- ment of the animal’s requirement on digestible amino acids. In other words, the
non-specific endogenous amino acid losses have to be taken into account when express- ing amino acid requirements according to the concept of ideal protein which is dis- cussed elsewhere.
Amino Acids in Diet Formulation for Pigs 183
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