Nutritional Evaluation of Lectin-Free Soybeans for Poultry

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1 Nutritional Evaluation of Lectin-Free Soybeans for Poultry MICHELE W. DOUGLAS,* CARL M. PARSONS,*,1 and THEODORE HYMOWITZ *Department of Animal Sciences, and Department of Crop Sciences, University of Illinois, Urbana, Illinois ABSTRACT This study evaluated the nutritional value of raw lectin-free soybeans in comparison with raw Kunitz trypsin inhibitor-free soybeans, raw conventional soybeans, and commercial heat processed soybean meal (SBM). Analyzed lectin values (milligrams per kilogram) were 7.2, 7.1, and < for the Kunitzfree, conventional, and lectin-free soybeans, respectively. Three experiments were conducted using New Hampshire Columbian male chicks fed 23% CP dextrosesoybean diets from 8 to 17 d of age. Growth performance of chicks fed lectin-free soybeans was greater (P < 0.05) than that of chicks fed raw conventional soybeans in all three experiments. However, performance of chicks fed lectin-free soybeans was lower than that of chicks fed Kunitz-free soybeans or SBM. The SBM yielded weight s and feed efficiencies that were much higher than those observed from any of the raw soybeans. True amino acid digestibility and TME n of the lectin-free and conventional soybeans were determined using the precision-fed cecectomized rooster assay. Seven roosters were crop-intubated with 30 g of soybeans and excreta were collected for 48 h. Digestibility coefficients of most amino acids for lectin-free soybeans were 5 to 8 percentage units higher than those for conventional soybeans, but the differences were not significant (P > 0.05). Likewise, the TME n for lectin-free soybeans was 11% higher than that for raw conventional soybeans (3.577 vs kcal/g DM) but the difference was not significant (P > 0.05). The results of this study indicate that the nutritional value of raw lectin-free soybeans is greater than raw conventional soybeans but is less than raw Kunitz-free soybeans and SBM, suggesting that trypsin inhibitor is a greater antinutritional factor than lectins. (Key words: soybean, trypsin inhibitor, lectin, digestibility, chick) 1999 Poultry Science 78:91 95 INTRODUCTION Lectin is a component of soybeans that is believed to be an antinutritional factor (Schulze et al., 1995). Lectins are glycoproteins that have the ability to bind to cellular surfaces via specific oligosaccharides or glycopeptides (Oliveira et al., 1989) and have a relatively high binding affinity to small intestinal epithelium (Pusztai, 1991). Furthermore, lectins can produce structural changes in the intestinal epithelium and resist gut proteolysis (Pusztai et al., 1990). These changes can result in impairment of brush border continuity and ulceration of villi (Oliveira et al., 1989), which may result in increased endogenous nitrogen losses (Oliveira and Sgarbierri, 1986; Schulze et al., 1995) and depressed growth rate in young animals (Pusztai et al., 1990). Thus, the growthdepressant effect of lectins is believed to be due primarily to their damaging impact on intestinal enterocytes (Pusztai, et al., 1979; Lorenzsonn and Olsen, 1982) Received for publication January 9, Accepted for publication August 3, To whom correspondence should be addressed: 284 Animal Sciences Laboratory, 1207 West Gregory Drive, Urbana, IL 61801, poultry@uiuc.edu and through appetite depression (Liener, 1986). Research has shown that the detrimental effects of lectins may be lessened with proper heat processing of conventional soybeans (Higuchi et al., 1984). The lectins in soybeans are tetrameric glycoproteins that have a specific affinity to terminal N-acetyl-Dglucosamine and D-galactose (Schulze et al., 1995). These lectins were originally referred to as hemagglutinating factor or soyin, and it was estimated that they accounted for one-half of the growth inhibition produced by raw soybeans fed to rats (Liener, 1953). To our knowledge, no research has been conducted to determine the effects of soybean lectins on growth and nutrient utilization of poultry. Moreover, most or all previous research on soybean lectins with animals has involved use of extracted or purified lectins (Schulze et al., 1995), which may have effects on growth performance and digestion that are different than those of the native lectins in soybeans. A new lectin-free soybean variant (L ) has been developed in the Department of Crop Sciences at the University of Illinois (Bernard and Nelson, 1996) Abbreviation Key: CSB = conventional soybeans; KFSB = Kunitz trypsin inhibitor-free soybeans; LFSB = lectin-free soybeans; SBM = soybean meal. 91

2 92 DOUGLAS ET AL. TABLE 1. Composition of diets in the chick growth assays 1 Commercial Conventional Kunitz-free Lectin-free dehulled Ingredients soybeans soybeans soybeans soybean meal (%) Conventional soybeans Kunitz-free soybeans Lectin-free soybeans Soybean meal Dextrose Soybean oil Cellulose Dicalcium phosphate Ground limestone Iodized salt DL-methionine Vitamin mix Trace minerals mix Choline-Cl (60%) Calculated analysis 4 CP Ca Nonphytate P The conventional soybeans, Kunitz-free soybeans, lectin-free soybeans, and dehulled soybean meal contained 35.7, 35.7, 35.7, and 45.4% protein on an air-dry basis. 2Provided per kilogram of diet: vitamin A (as retinyl A acetate), 4,400 IU; cholecalciferol (as activated animal sterol), 1,000 IU; vitamin E (as DL-a-tocopheryl acetate), 11 IU; vitamin B 12, 0.01 mg; riboflavin, 4.41 mg; d- pantothenic acid, 10 mg; niacin, 22 mg; menadione sodium bisulfite, 2.33 mg. 3Provided as milligrams per kilogram of diet: manganese, 75 from manganese oxide; iron, 75 from iron sulfate; zinc, 75 from zinc oxide; copper, 5 from copper sulfate; iodine, 0.35 from ethylene diamine dihydroiodide; selenium, 0.2 from sodium selenite. 4The CP values are analytical values and the Ca and nonphytate values are based on NRC (1994) table values. that is isogenic to the commercial Williams 82 cultivar except that it contains no lectin. Thus, the primary objective of this study was to compare the nutritional value of the raw lectin-free soybeans (LFSB)2 to the conventional Williams 82 soybeans (CSB)2 for poultry. In addition, the nutritional value of the LFSB and CSB were compared to raw Kunitz trypsin inhibitor-free soybeans (KFSB),2 a soybean variant that is also isogenic to Williams 82 soybeans except that it contains no functional Kunitz trypsin inhibitor allele (Bernard and Hymowitz, 1986), and commercial soybean meal (SBM) to assess the relative antinutritional importance of lectin vs trypsin inhibitor in soybeans. MATERIALS AND METHODS Raw, full-fat CSB (Williams-82), raw KFSB, raw LFSB, and commercial solvent-extracted dehulled SBM2 were ground to a similar particle size. All samples were analyzed for DM and CP according to the procedures of the Association of Official Analytical Chemists (1980). 2The CSB and KFSB were obtained from Illinois Foundation Seeds, Inc., Champaign, IL 61821, the LFSB was obtained from the Department of Crop Sciences, University of Illinois, Urbana, IL 61801, and the SBM was obtained from Archer Daniels Midland, Inc., Decatur, IL Determined by TNO Nutrition and Food Research Institute, Ultrechseweg 48, P.O. Box 360, 3700 AJ Zeist, The Netherlands. Amino acid concentrations were determined using ionexchange chromatography following hydrolysis in 6 N HCl for 22 h at 110 C (Spackman et al., 1958). Analyses of methionine and cystine were conducted following performic acid oxidation by the method of Moore (1963) except that samples were diluted with water and lyophilized to remove excess performic acid. Lectin, Kunitz trypsin inhibitor, and Bowman-Birk trypsin inhibitor levels in the CSB, KFSB, and LFSB were determined using ELISA (Schulze et al., 1995).3 Chick Assays Two replicate chick assays with identical treatments were conducted to evaluate the comparative nutritional value of CSB, KFSB, LFSB, and SBM. A third chick assay was conducted to further validate the comparative nutritional value of CSB and LFSB. One-week-old male chicks resulting from the cross of New Hampshire males and Columbian Plymouth Rock females were used in all chick assays. Chicks were housed in thermostatically controlled starter batteries with raised wire floors in an environmentally regulated room. and water were supplied for ad libitum consumption and light was provided 24 h daily. The chicks were fed a 24% CP cornsoybean meal pretest diet during the first 7 d Following an overnight period without feed, the chicks were weighed, wing-banded, and allotted to dietary treatments as described by Sasse and Baker (1973).

3 LECTIN-FREE SOYBEANS 93 TABLE 2. Protease inhibitor and lectin content of the different soybeans 1 Bowman-Birk Kunitz trypsin trypsin/ chymotrypsin Soybean inhibitor inhibitor Lectin (mg/g) Conventional Kunitz-free Lectin-free < Values are presented on a dry matter basis. The four dietary treatments in the first two chick assays consisted of feeding the soybeans or SBM as the sole source of dietary protein in a 23% CP dextrose and soybean diet (Table 1) formulated to meet all NRC (1994) nutrient requirements. Soybean oil and cellulose were added to the dextrose-sbm diet to approximate the digestible oil and fiber content of the soybean diets. The third chick assay contained two dietary treatments in which CSB and LFSB were compared. Each diet was fed to four groups of six male chicks from 8 to 17 d posthatching in all chick assays. True Digestibility Assay This experiment was conducted to determine the true digestibilities of amino acids and TME n of LFSB and CSB. The precision-fed rooster assay of Sibbald (1986) was used and the Single Comb White Leghorn roosters were 60 wk of age. The roosters were cecectomized when they were 25 wk of age (Parsons, 1985). The birds were housed in an environmentally controlled room and kept in individual cages with raised wire floors. Photoperiod consisted of 16 h light and 8 h dark daily. Following a 24-h period without feed, seven roosters were given 30 g of a soybean via crop intubation and excreta were collected for 48 h after intubation. Excreta samples were lyophilized, weighed, and ground to pass through a 60-mesh screen. The N and amino acid analyses were determined on individual samples of excreta as described previously. Gross energy was determined using a bomb calorimeter. True digestibilities of amino acids were calculated according to the method of Sibbald (1979), and TME n was calculated by the method of Parsons et al. (1982). Endogenous corrections for amino acids and energy were made using roosters that were deprived of feed for 48 h. Statistical Analyses Data from all assays were subjected to ANOVA for completely randomized designs (Steel and Torrie, 1980; SAS Institute, 1985). Statistical significance of differences among treatments were assessed using the least significant difference test (Steel and Torrie, 1980). RESULTS AND DISCUSSION The CP was approximately 36% for the three raw soybean samples and was 45% for the SBM. The levels TABLE 3. Crude protein and amino acid composition of lectin-free and conventional soybeans 1 Soybean type Component Lectin-free Conventional (%) Moisture Crude protein Amino acids Asp Thr Ser Glu Pro Gly Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg Expressed on air-dry basis. of Kunitz trypsin inhibitor in the CSB and LFSB were similar, with the KFSB being almost devoid of Kunitz trypsin inhibitor (Table 2). The levels of Bowman-Birk trypsin/chymotrypsin inhibitor were generally similar among the soybeans. Lectin contents of the CSB and KFSB were similar and the LFSB contained no measurable lectin. The amino acid compositions of the LFSB and CSB are shown in Table 3. On an air-dry or as-fed basis, the levels of amino acids in the two soybeans were generally similar. On a dry matter basis, the levels of amino acids in the LFSB were approximately 5% higher than the CSB. The results of the three chick growth assays were generally consistent and are shown in Tables 4 to 6. Chicks fed the SBM diet had greater weight s and :feed ratios than chicks fed any of the raw SBM diets in the first two trials. Growth performance of chicks fed Dietary treatments 2 TABLE 4. Growth performance of chicks fed different soybeans in chick Assay Conventional soybeans 75 d 281 b d 2. Kunitz-free soybeans 134 b 338 a b 3. Lectin-free soybeans 93 c 274 b c 4. Soybean meal 199 a 281 b a Pooled SEM a dmeans within a column with no common superscript differ

4 94 DOUGLAS ET AL. Dietary treatments 2 TABLE 5. Growth performance of chicks fed different soybeans in chick Assay Conventional soybeans 128 d 336 a d 2. Kunitz-free soybeans 156 b 335 a b 3. Lectin-free soybeans 142 c 350 a c 4. Soybean meal 228 a 305 b a Pooled SEM a dmeans within a column with no common superscript differ the KFSB diet was superior to performance of chicks fed either the CSB or LFSB in both of the first two chick trials. The inferior chick performance from raw KFSB compared to SBM has been observed previously in chicks (Anderson-Hafermann et al., 1992) and in rats (Friedman et al., 1991) and is probably due primarily to the Bowman-Birk inhibitors and lectin in the KFSB. Chicks fed the LFSB had higher weight s and feed efficiency than did those fed CSB in all three trials, with the mean difference being 15% (ranged from 10 to 20% among trials). These results indicate that the lectins in soybeans are, indeed, an antinutritional factor and that the nutritional value of raw LFSB is superior to raw CSB. However, the much lower relative growth performance of chicks fed the LFSB compared to KFSB and SBM indicates that the trypsin inhibitors in soybeans are a more important antinutritional factor than are the lectins. The importance of lectins as an antinutritional factor in the current study is less than earlier estimated by Leiner (1953). In the latter study, it was estimated that lectins (referred to as hemagglutinating factor or soyin at that time) accounted for approximately 50% of the growth-inhibiting effect of raw soybean meal in rats. Our results indicate that lectins accounted for approximately 15% of the growth depression from raw soybeans in chicks. The differences in results between our study and Liener (1953) may be due to type of TABLE 6. Growth performance of chicks fed conventional or lectin-free soybeans in chick Assay 3 1 Dietary treatments 1. Conventional soybeans 107 b 323 a b 2. Lectin-free soybeans 124 a 312 a a Pooled SEM a,bmeans within a column with no common superscript differ TABLE 7. The TME n and true digestibility of amino acids in lectin-free and conventional soybeans 1 Soybean type Variable Lectin-free Conventional Pooled SEM TME n, kcal/g DM Asp, % Thr, % Ser, % Glu, % Pro, % Ala, % Cys, % Val, % Met, % Ile, % Leu, % Tyr, % Phe, % His, % Lys, % Arg, % Mean Data are means of seven cecectomized roosters. species (rats vs chickens) or because Liener (1953) used extracted or purified lectins, whereas we used soybean genetic lines differing in lectin and, thus, were evaluating native lectins in soybeans. The TME n and digestibility of 16 measured amino acids in LFSB and CSB are presented in Table 7. Mean TME n (kilocalories per gram of DM) was and for LFSB and CSB, respectively. Whereas the TME n value and amino acid digestibility coefficients for LFSB tended to be consistently higher than for CSB, the differences were not significant (P > 0.05). ACKNOWLEDGMENT Appreciation is expressed to Finn s International Ltd., Marlborough, Wiltshire, U.K. for their support of this study. REFERENCES Anderson-Hafermann, J. C., Y. Zhang, and C. M. Parsons, Effect of heating on nutritional quality of conventional and Kunitz trypsin inhibitor-free soybeans. Poultry Sci. 71: Association of Official Analytical Chemists, Official Methods of Analysis. 13th ed. Association of Official Analytical Chemists, Washington, DC. Bernard, R. L., and T. Hymowitz, Registration of L , L and L soybean germplasm lines lacking the Kunitz trypsin inhibitor. Crop Sci. 26: Bernard, R. L., and R. L. Nelson, additions to the isoline collection of the USDA soybean genetic collection. Soybean Genet. Newsletter 23: Friedman, M., D. L. Brandon, A. H. Bates, and T. Hymowitz, Comparison of a commercial soybean cultivar and an isoline lacking the Kunitz trypsin inhibitor: composi-

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