Effect of De-hulling on Ileal Amino Acids Digestibility of Soybean Meals Fed to Growing Pigs

A study was carried out to determine the effect of de-hulling on apparent and true ileal amino acids digestibility of soybean meals for growing pigs. Twenty barrows (Duroc×Large white×Longer white) were fitted with a simple T-cannula at the distal ilium. Digestibility of 20 experimental diets was determined, nine of them were de-hulled soybean meal diets, and nine of them were regular soybean meal diets and two low protein casein diets for determination of endogenous amino acid correction for true digestibility determination. A 5×5 Latin Squares Design was adopted in this trail. The results showed that de-hulling increased apparent ileal digestibility of isoleucine,threonine, aspartic, tyrosine and indispensable and dispensable amino acid (p<0.05) in soybean meals. Furthermore, dehulling is also increased apparent digestibility of arginine, leucine, lysine, phenylalanine, alanine, glutamic acid, serine and gross amino acids (p<0.01). However, there were no significant differences found for histidine, methionine, tryptophan, cystine and glycine (p>0.05). Similar responses were found for true ileal digestibility. In three dehulled and non-dehulled pairs soybean meals from the same respective sources, de-hulling increased apparent digestibility of lysine, methionine, threonine and cystine 1.42%, 2.06%, 2.18% and 1.40% respectively. True digestibility of lysine, methionine, threonine and cystine was increased 1.65%, 1.94%, 2.30% and 1.82% respectively. A prediction equation for true ileal amino acid digestibility (including lysine and arginine) was established by multivariate linear regression. The independent variables included relevant amino acid, organic matter, crude protein, ether extract and nitrogen free extract. The coefficient R values of lysine and agrinine were 0.596 and 0.531 respectively. According to the crude protein content, a prediction equation for lysine and arginine content in soybean meal was also established by single linear regression. The coefficient R values of lysine and agrinine were 0.636 and 0.636 respectively. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 6 : 928-938)


INTRODUCTION
Soybean meal is the most widely used as source of plant protein in swine diets due to its excellent amino acid profile, dependable supply, competitive price, and especially a high level of lysine content of about 2.83-3.02%(NRC, 1998).Many studies have been done on the digestibility of amino acids in soybean meals (Tandsley et al, 1981b;Jmarty and Cavz, 1994;Thacker, 1984;Furuya and Kaji, 1991).The effect of different batches, soybean meal particle size and different soybean processors on amino acid digestibility in swine has been reported (Vestgen et al., 2000;Robert, 2000;Kempen and Kim. 2000;Scott and Brandon, 2000;Fasing and Mahan, 2000;Gabert, 2000).De-hulling may improve the protein and energy levels in soybean meal and increase quantity of soybean oil from soybean.It is economical to use de-hulled soybean meal (Erickson, 1995;Swick, 1999).However, only limited data are available on the effect of de-hulling on the digestibility of amino acid in soybean meals.Rudolph et al. (1983) compared apparent ileal amino acid digestibility between soybean meals with crude protein of 44.0% and 48.5%.
A knowledge of de-hulling effects and the digestible amino acid content of de-hulled and regular soybean meals may lead to more accurate formulation of swine diets based on digestible amino acid, and provide the materials for establishing the digestible amino acid data of China.

Soybean meal samples and experimental diets
In this research, the effect of de-hulling on apparent and true ileal amino acid digestibility was determined in nine de-hulled soybean meals (DSBMs) and nine regular soybean meals (RSBMs) which were provided by American Soybean Association from China, America and South America.The origin, nutrient contents, urease activity (UA), protein solubility (KOH) and amino acid contents of the samples where shown in table 1 and table 2. The experimental diets (table 3 and table 4) were corn starch-based, with the soybean samples and provided 16% crude protein on an as-fed basis.The casein diet was corn starch-based with 5% casein and provided 4.4 percentage units of crude protein.One percent soybean oil was added to the diets to improve palatability.Chromic oxide was added to each diet at a level of 0.5% as an indigestible marker for determination of amino acid digestibility (Huo, 1996).

Animals and experimental design
Twenty barrows (Duroc×Large White×Longer White) were obtained from a commercial pig farm.The animals were housed individually in metabolic cases in an airconditioned room.The pigs were surgically fitted with a simple T-cannula at the distal ilium using the procedures described by Huo (1996).
After recovery from surgery, the barrows were fed the experimental diets using four what of 5×5 Latin square design with observations from five pigs for every diet.Digestibility of amino acid was determined in 18 experimental diets, of which nine were de-hulled soybean meals and nine were regular soybean meals, as well as two casein diets.The experiments were divided into three trials.In trial 1, nine experimental diets D 1 , R 1 , D 2 , R 2 , D 3 , R 3 , D 5 , D 6 , D 7 and one casein diet were evaluated, using ten barrows with initial body weight 35.9±1.6 kg in two what of 5×5 Latin square design.In trial 2, four experimental diets D 4 , D 8 , R 5 , R 5 and another Casein diet were evaluated, using five barrows with initial body weight 37.5±1.9kg, one what of 5X5 Latin square design.Using five barrows with 29.8±0.9kg initial body weight, one what of 5X5 Latin square design, for five experimental diets D 9 , R 7 , R 8 , R 9 and R 4 diets were evaluated in trial 3. The pigs remained healthy and consumed their meals throughout the experiment.
The barrows were fed twice daily, at 0800 and 1800, with equal amounts at each meal.The feeding level was initially set at 3.5% of body weight, and then increased 50-100 g at the beginning of each period.Water was provided ad libitum..
The duration of each experiment was 8 days.The barrows were allowed to adapt to each experimental diet for 4 days, and ileal digesta were collected on the final 4 days.Digesta were collected over ten hours, from 0900 to 1900 on each of the 4 days of collection.Digesta were frozen immediately after collection.The digesta samples for every period were mixed and freeze-dried.Samples were preserved at -20°C.

Sample preparation and chemical analyses
The samples of soybean meals, diets and digesta were subjected to analyses.The items included dry matter, crude protein, chromic oxide and contents of eighteen amino acid.Amino acid contents were determined with an Amino Acid Analyzer (Japan, L-8800) according to procedures described by the AOAC (1984).Acid hydrolysis (6 N HCl for 24 h with constant N 2 flushing) was used in the analyses of all amino acids except tryptophan, methionine and cystine.Tryptophan was determined following the procedure of Kohler and Palter (1967), methionine and cystine were determined by the procedure of Moore (1963).Chromic oxide in diets and digesta was determined by mixing acid (HNO 3 :HClO 4 =5:1) hydrolysis and was analyzed with an Atomic Absorption Spectroscopy (Japan, Z-5000) as described by Li (1998).

Data analysis
Ileal digestibility was calculated using the following equation: Apparent digestibility, %=(1-(Md×AAi)/(AAd×Mi)) ×100 Where, Md is chromium concentration in diet; AAd is amino acid concentration in ileal digesta; AAi is amino acid concentration in diet; Mi is chromium concentration in ileal digesta.EO=((100-AD)/100)×IDM Where, EO is endogenous output of amino acids on a g/kg dry matter intake basis; AD is apparent digestibility of amino acid from the casein diet; IDM is dry matter intake of an amino acid from the casein diet.
True digestibility, %=AD+EO×10×IDM Where, AD is apparent digestibility of amino acid from the experiment diet; EO is endogenous output of amino acids; IDM is dry matter intake of an amino acid from the experimental diet.
The data were analyzed statistically using multivariate linear regression and single linear regression with SPSS 9.0.

Effect of de-hulling on apparent ileal amino acid digestibility
Apparent ileal digestibility of indispensable and dispensable amino acids for nine DSBMs and nine RSBMs are shown in table 5 and table 6.

89.12% respectively between the different DSBMs sources.
For the soybean imported from U.S., there was a difference in the apparent digestibility of amino acid among three soybean meals in which apparent lysine digestibility were 91.91%(D 3 ), 91.80% (D 6 ) and 90.96%(D 2 ) respectively, but it was not significant (p>0.05).For Chinese local soybean meals, the apparent lysine digestibility between dehulled and non-dehulled was 89.82% (D9) and 88.41% (D 4 ), which was a significant difference (p<0.05).This may be attributed to different extent of de-hulling and other processing technology.De-hulling may remove 6-8% by weight of soybeans in America (David, 1995).
Apparent ileal digestibility for all amino acids was different in different sources of RSBMs (p<0.01), with the exception of methionine (p<0.05)(table 6).For lysine, methionine and threonine the values ranged from 84.21%-90.26%,85.47%-91.17%and 83.21%-89.11%respectively between the different RSBMs sources.In the case of three pairs of DSBMs and RSBMs from the same respective sources, de-hulling increased the apparent digestibility of histidine (p<0.05) and tyrosine (p<0.10) about 2 percentage units (Table 10).There were no differences in other amino acids (p>0.10).For key amino acids, the digestibility of lysine, methionine, threonine and cystine in DSBMs were 1.42, 2.06, 2.18 and 1.40 percentage units higher than that in RSBMs.The digestibility of arginine and glycine in DSBMs was just 0.32 and 0.35 percentage units higher than that in RSBMs.However, the digestibility of proline in DSBMs was 0.50 percentage units lower than that in RSBMs.This may be attributed to adding chromic oxide in cornstarch-soybean meal diets, which increased the amount of endogenous proline.

Effect of de-hulling on true ileal amino acid digestibility
The average amount of endogenous amino acids in two casein diets was measured: LYS 0.55; THR 0.77; MET The true digestibility of amino acids of nine DSBMs and nine RSBMs are shown in table 7 and table 8.
The results indicated that there was a difference to true ileal digestibility of most of amino acids from different sources of DSBMs.With the exception of isoleucine, leucine and methionine (p>0.10) and lysine, histidine and threonine (p<0.1),there were significant differences found for arginine, phenylalanine, valine, cysine, proline, tyrosine and indispensable and gross amino acids (p<0.01) and alanine, aspartic, glutamic acid, glycine and serine (p<0.05).The true digestibility in lysine, methionine and threonine ranged from 91.68%-94.48%,91.56%-94.72%and 89.67%-93.79%respectively between the different DSBMs sources.For soybean meals from soybeans imported from America, there were differences in true digestibility among three True ileal digestibility for all amino acids showed a difference in different sources of RSBMs.For lysine, methionine and threonine the values were found from 84. 21%-90.26%, 85.47%-91.17% and 83.21%-89.11%respectively between the different RSBMs sources.There were significant differences found for arginine, valine and proline (p<0.05) and other amino acids and the average value of indispensable and dispensable amino acids (p<0.01).This may be related to the many sources of RSBMs used in this work.Samples R 6 , R 7 , R 8 and R 9 were produced at the laboratory by mixing by several soybean meal samples respectively.R 6 mixed from Dalian oil industry, Dalian Huanong, Liaoning Pulandian, Langfang Huamei, whose soybeans came from America, Brazil and Argentina; R 7 mixed from Shanghai, Heilongjiang Zhengda, Neimeng Zhalantun, whose soybeans from America; Jilin R 8 mixed from Langfang, Jilin Guojiadian, Jinlin Jiutai, whose soybeans from America and Jilin; R 9 mixed from Sichuan Jiali and Guangzhou Dongling, whose soybeans come from America and Argentina.The weight of each of the soybean meal samples mixed was 25 kg.
The average value of true amino acid digestibility between nine DSBMs and nine RSBMs was compared by T-test.The results showed that except for histidine, methionine, tryptophan, threonine, valine and tyrosine, dehulling increased the true ileal digestibility of cysine and glutamic acid (p<0.05), and arginine，isoleucine, leucine, lysine, phenylalanine, alanine, aspartic, glycine, proline, serine and indispensable and gross amino acids (p<0.01).Thus is clear that de-hulling had a positive effect on true ileal digestibility among different sources and producers.
However, it is most important to study the effect of dehulling on soybean meals from the same sources.In three pair's soybean meals from the same respective sources, the true digestibility of four key amino acids lysine, methionine, threonine and cystine in DSBMs were 92.74%, 93.82%, 89.67% and 85.11% respectively, and which were 1.64, 1.94, 2.30 and 1.82 percentage units higher than that in RSBMs respectively.The digestibility of arginine and glycine in DSBMs were 0.32 and 0.01 percentage unit higher than that in RSBMs.However digestibility of proline in DSBMs was 0.39 % lower than that in RSBMs.For of all six of the above samples, on average the true digestibility of each amino acid in DSBMs did not differ from that in RSBMs (p>0.05), with the exception of histidine (p<0.05)(table 10).
For apparent digestibility in DBMs and RSBMs there were differences for each amino acid.This was shown in table 10, figure 1 and figure 2. In RSBMs the apparent digestibility of argnine was highest which was 93.17%;The range of digestibility of histidine, isoleucine, leucine, lysine, methionine, phenylalanine, aspartic acid, glutamic acid and  Rudolph (1983).The low apparent digestibility for proline, glycine, and threonine at the end of the small intestine probably resulted from their high concentrations in the endogenous secretions, as was discussed by Low (1979).Apparent ileal digestibility of most indispensable and dispensable amino acids in the soybean meals in this research, and of those previously cited, were higher than other values reported.Lysine digestibility averaged were 86.51% for RSBMs and 89.6% for DSBMs.Previously reported values were 83.5% for soybean meal that contain 48.5% crude protein and 85.1% for soybean meal that contain 44.0% crude protein (Rudolph, 1983), in diets with 6% added cellulose; and that of Zhong (1997) was 85.7% for DSBMs The data is shown in table 11.Numerically, the samples tested in this experiment had a higher value than the NRC data in all amino acid expect of valine and cystine.The apparent lysine digestibility of 85% in both RSBMs and DSBMs is found in NRC (1998).The NRC tables are compilations of digestibility data collected from several countries and thus is more likely to include batches of soybean meal that were produced under poor condition (Kempen et al., 2002).Kempen (2002) reported that 86.3% apparent lysine digestibility for a common soybean meal with 48% crude protein tested by five sites in America with the diets which had 17% crude protein content and 20% added sucrose.
For of all the diets, there were differences in the digestibility of lysine in the soybean meals in the present results.However, the ileal amino acid digestibility values of lysine, methionine and threonine in different soybean meal samples, ranged from 80.1% to 90.7%, 74.5% to 96.7% and 70.7% to 82.2% respectively (Sauer and Ozimek, 1986;Knable et al., 1989).Perhaps this may be attributed to the formulation of diet and the weights of the trial pigs.Differences is crude protein and amino acid content in the assay diets may explain, in part, the variation in apparent ileal amino acid digestibility values among different samples of the same feedstuff (Sauer and Ozimek, 1986).Different amounts of cellulose, sucrose, chromic oxide and crude protein were found in different cornstarch-soybean meal diets (table 11).Pigs with different ages were found to have different endogenous secretions.The use of young pigs in digestibility trials may result high endogenous secretions (Kempen, 2002).

Table 1 .
Analyzed composition and urease activity of nine de-hulled soybean meals

Table 2 .
Analyzed composition and urease activity of nine regular soybean meals

Table 4 .
Formulation (%) of the experimental diets (as-fed basis) of regular soybean meal

Table 5 .
Apparent digestibility of amino acids in nine de-hulled soybean meal samples

Table 6 .
Apparent digestibility of amino acid in nine regular soybean meal samples

Table 7 .
True amino acid digestibility of nine de-hullled soybean meals

Table 8 .
True amino acid digestibility of nine regular soybean meals

Table 9 .
Comparison of apparent and true amino acid digestibility between nine de-hulled soybean meals and nine regular soybean meals in growing pigs

Table 10 .
Comparison of apparent amino acid digestibility and true amino acid digestibility between three pairs de-hulled and regular soybean meals in growing swine

Table 11 .
Comparison with different resource data of apparent ileal amino acid digestibility