Bioavailability of Digestible Lysine in Heat-Damaged Soybean Meal for Chick Growth

Transcription

1 Bioavailability of Digestible Lysine in Heat-Damaged Soybean Meal for Chick Growth S. R. FERNANDEZ, and C. M. PARSONS* Department of Animal Sciences, University of Illinois, Urbana, Illinois 6181 ABSTRACT Previous experiments indicated that true digestible Lys values for soybean and cottonseed meals obtained with the precision-fed cecectomized rooster assay were accurate estimators of Lys bioavailability for chick growth. This study was conducted to determine whether the digestible Lys in overheated soybean meal (SBM) was totally bioavailable for protein synthesis. Soybean meal alone or mixed with dextrose (SBM: dextrose ratio = 3:1) was autoclaved at 114 C and 97 kpa for to 6 min. True digestibility of Lys in SBM was determined using the precision-fed cecectomized rooster assay. Bioavailability was then assessed by chick growth assay using purified crystalline amino acid diets deficient in Lys that were supplemented with varying levels of crystalline L-Lys-Cl or a SBM. Multiple regression slope-ratio methodology indicated that the digestible Lys in unautoclaved SBM was 1% bioavailable. For INTRODUCTION To efficiently formulate poultry diets, accurate composition of feed ingredients in terms of bioavailable nutrients needs to be known. One of the primary factors affecting nutrient bioavailability is the heat applied during feedstuff processing. Heating is an inherent part of processing of oilseeds such as soybeans because heating is necessary to improve nutritional quality by inactivating antinutritional factors such as trypsin inhibitors (Liener, 1994). However, excess heating reduces protein quality due to decreased amino acid availability or digestibility (Parsons et at, 1992). Amino acid availability in feedstuffs is frequently assessed using balance or digestibility assays. However, Batterham (1992) reported that ileal digestibility assays often overestimate the amounts of amino acids that are available or utilizable for protein synthesis in growing pigs, particularly for heat-damaged feed ingredients. Received for publication June 15, Accepted for publication September 19, 1995.!To whom correspondence should be addressed: 284 Animal Sciences Laboratory, 127 W. Gregory Drive, Urbana, IL SBM autoclaved for 4 or 6 min and SBM-dextrose autoclaved for 2 min, bioavailability of digestible Lys based on weight gain or carcass Lys gain was 81 to 87% and significantly less (P <.5) than 1%, whereas bioavailability values based on feed efficiency and carcass N gain did not differ (P >.5) from 1%. Bioavailability values for digestible Lys in SBM:dextrose autoclaved for 3 min ranged from 55 to 73% for all performance criteria. Partitioning the response criteria, so that only the response to the supplemental Lys source (not the basal diet) was being evaluated, increased the bioavailability values for all treatments except SBM: dextrose autoclaved for 3 min. The results of this study indicated that digestible Lys in severely heat-damaged SBM measured by the precision-fed cecectomized rooster assay was not totally bioavailable for protein synthesis. {Key words: soybean meal, lysine, amino acid digestibility, amino acid bioavailability, overprocessing) Poultry Science 75: Van Barneveld et al. (1994a,b) recently reported that ileal digestibility of Lys and bioavailability of Lys measured by slope-ratio assay were similar for unheated field peas but that Lys digestibility was much greater than Lys bioavailability for overheated field peas. Batterham (1992) proposed that the discrepancies between digestible and bioavailable values for amino acids was probably largely due to formation of early Maillard compounds during heating. Many of these carbohydrate-amino acid complexes can be absorbed in the intestine but are not utilizable for protein synthesis (Erbersdobler et al, 1981). Moreover, most of the early Maillard compounds are recovered as free amino acids during amino acid analysis (Abrams et al, 1955; Hurrell and Carpenter, 1981). Thus, early Maillard compounds would be measured as being digestible although they are not bioavailable for protein synthesis. The objective of the present study was to compare true digestibility of Lys measured by the precision-fed cecectomized rooster assay with bioavailability of Lys measured by slope-ratio chick growth assay for normal and overheated soybean meal (SBM). The SBM was also overheated in the presence of dextrose in an attempt to produce large quantities of Maillard compounds. Downloaded from by guest on 2 November 218

2 MATERIALS AND METHODS Overheating of Soybean Meal Soybean meal was overheated either alone or mixed with dextrose at a ratio 3:1 (SBM:dextrose). A thin layer (1.25 cm in depth) of SBM or SBM:dextrose (SBMDEX) was placed on metal trays, covered tightly with aluminum foil, and autoclaved at 114 C and 97 kpa in a laboratory autoclave. Autoclaving times were, 4, and 6 min for SBM alone and 2 and 3 min for the SBMDEX mixture. Analytical and Digestibility Evaluation of Ingredients Samples of the SBM or SBMDEX from the autoclaving treatments were first analyzed for dry matter and Kjeldahl nitrogen by the methods outlined by the Association of Official Analytical Chemists (AOAC, 1984). Lysine digestibility was determined using the precision-fed rooster assay (Sibbald, 1986). At 25 wk of age, Single Comb White Leghorn roosters were cecectomized as previously described (Parsons, 1985) and were not used in digestibility trials for at least 8 wk following surgery. The birds were kept in individual cages with raised wire floors in an environmentally regulated room and provided with 16 h of light daily. Feed and water were provided for ad libitum consumption before the initiation of the experiment. Following a 24-h period without feed, five roosters per SBM treatment were given 3 g of feedstuff via crop intubation. Five additional roosters were deprived of feed throughout the experimental period to measure endogenous Lys excreted. A plastic tray was placed under each cage and excreta were collected for 48 h. Excreta samples were lyophilized, weighed, and ground to pass through a 6-mesh screen. Lysine concentrations in SBM and excreta samples were analyzed by ion-exchange chromatography 2 (Spackman et al, 1958) following hydrolysis in 6N HCL for 22 h at 11 C in sealed tubes, with at least two replicates per sample. True digestibilities of Lys were calculated by the method of Sibbald (1986), with digestibility referring to the amount of dietary Lys not appearing in the feces plus urine. Chick Bioavailability Assays Experiment 1. The objective of this experiment was to determine the bioavailability of the true digestible Lys in the SBM treatments for chick growth. Female chicks resulting from the cross of New Hampshire males and Columbian Plymouth Rock females were housed in thermostatically controlled starter batteries with raised wire floors and allowed ad libitum access to water and feed. Uniform light was provided 24 h daily. The chicks 2 Amino acid analyses performed with a Beckman 63 Analyzer, Beckman Instruments Corp., Palo Alto, CA BIOAVAILABILITY OF DIGESTIBLE LYSINE 225 were fed a 24% CP corn and soybean meal pretest diet during the first 9 d posthatching. Chicks were then deprived of feed overnight, weighed, wing-banded, and allotted to dietary treatments by the procedures of Sasse and Baker (1974). All diets in the experiment were fed to four groups of five chicks from 1 to 21 d posthatching. The composition of the chemically defined basal diet (Baker et al. 1979) used is presented in Table 1. Vitamins, minerals, and all indispensable amino acids except Lys were present in amounts adequate for maximal chick growth. Two levels of L-Lys-HCl were added to the basal diet in order to establish a standard curve. The standard curve contained Lys levels from.4 to.65% to be within the linear portion of the growth curve. Likewise, the levels of SBM were added to the basal diet, replacing cornstarch, to provide estimated levels of digestible Lys that would fall within the boundaries of the standard curve. The appropriate levels of digestible Lys were estimated from the results of Parsons et al. (1992). At the beginning of the experiments four groups of five chicks were killed by saturating their atmosphere with carbon dioxide and then eviscerated (all internal organs removed except lungs and kidneys). The eviscerated bodies (carcass including feathers) were then stored frozen for further analysis. Body weight and feed intake of all other groups were measured at the termination of the experiments, and Ingredients and amino acids TABLE 1. Composition of the chemically defined basal diet 1 Cornstarch Amino acid mixture Soybean oil Solka floe Mineral mixture 2 NaHC 3 CholineCl Vitamin mixture 2 a-tocopherol acetate (2 mg/kg) Ethoxyquin (125 mg/kg) 3 Amino acid mixture L-Arginine-HCl L-HistidineHCl L-LysineHCl L-Tyrosine L-Tryptophan L-Phenylalanine L-Methionine L-Cystine L-Threonine L-Leucine L-Isoleucine L-Valine Glycine L-Proline L-Glutamate Total ibaker et al. (1979). 2 Fernandez and Parsons (1996). ssantoquin, NOVUS International, St. Louis, MO Percentage (%) to Downloaded from by guest on 2 November 218

3 226 FERNANDEZ AND PARSONS Ingredient SBM SBM SBM SBM:dextrose SBM:dextrose TABLE 2. Analyzed composition of autoclaved soybean meal (SBM) and soybean meahdextrose (3:1) mixture 1 Autoclaving time (min) Crude protein Total (%) Lysine Digestibility 2 88 ± ± 2. 9 ± ± ± 2.4!9% DM basis. 2 Mean of five cecectomized birds ± SEM. 3 Based on the Lys concentration of the unautoclaved SBM, the calculated Lys content of the SBM:dextrose is weight gain and feed efficiency (gain:feed intake ratio) were calculated. After weighing, all birds were killed and eviscerated as described earlier. The eviscerated bodies were frozen and then were ground in groups of five (one replicate at a time) in a meat grinder. A homogeneous sample was then obtained and freeze-dried. Kjeldahl N and Lys analyses were performed on the freeze-dried material as described earlier. Carcass N and Lys gain were then calculated by subtracting the amounts of N and Lys in the carcass at the beginning of the experiment from the amounts in the carcass at the end of the trial. Experiment 2. The objective of this experiment was to further investigate the poor performance obtained from the SBMDEX autoclaved for 3 min in Experiment 1. It was not known whether the poor performance was due to the low bioavailability of digestible Lys per se or at least partially due to toxic compounds formed during the autoclaving process. Procedures for housing, management, and allocation of chicks to experimental treatments were the same as for Experiment 1. The six dietary treatments consisted of the basal diet (Table 1) or the basal diet supplemented with.18% Lys, 2% SBMDEX, or SBMDEX together with three increasing levels of Lys. The.18% Lys and 2% SBMDEX treatments provided equal levels of digestible Lys. The additional treatments were designed to see whether Lys supplementation of the SBMDEX would yield performance equivalent to the.18% Lys treatment. Four replicate groups of five female chicks were fed each of six diets from 1 to 2 d of age. Statistical Analysis Bioavailability of the digestible Lys in Experiment 1 for the SBM treatments was calculated using slope-ratio methodology (Finney, 1978). Multiple regressions were computed with supplemental digestible Lys intake from L-Lys-HCl or SBM treatments as the independent variables and total body weight gain, feed efficiency, weight gain and feed efficiency on eviscerated carcass basis, or carcass N or carcass Lys gain as the dependent variable. Digestibility of crystalline Lys was assumed to be 1% (Izquierdo et al, 1988; Chung and Baker, 1992). The calculated ratio of the slope of the SBM or SBMDEX response lines to the crystalline L-Lys-HCl standard line yields the amount of bioavailable Lys expressed as a proportion of the digestible Lys. Because the dependent variable responses are a function of Lys intake from both the basal diet and from the supplemental test ingredient, bioavailable Lys values were also computed from multiple regression analyses where the chick response criteria were partitioned to reflect only the response attributable to supplemental Lys intake (Netke and Scott, 197; Hirakawa and Baker, 1986; Parsons, 1986). Prior to computing the multiple regression equations, all response lines were tested for linearity and intersection effects as described by Finney (1978). Once the multiple linear regressions were computed, the regression coefficients or slopes were tested for statistical differences as outlined by Steel and Torrie (198) and the slope-ratio values were tested for statistical differences as outlined by Finney (1978). Experiment 2 was analyzed as a completely randomized design and differences between means were determined by least significant difference method (Steel and Torrie, 198). All data were analyzed using algorithms generated by the SAS Institute (1982). RESULTS Analyzed composition of the SBM was within typical ranges for this ingredient (Table 2). Autoclaving SBM alone for 4 to 6 min yielded slight decreases in total analyzed Lys but did not affect Lys digestibility; however, autoclaving the SBMDEX mixture for 2 or 3 min decreased both total Lys and Lys digestibility. The calculated Lys concentration in the SBMDEX based on the Lys analysis of the unautoclaved SBM is 2.33% whereas the analyzed Lys in the autoclaved SBMDEX was only 1.45%. The performance responses due to Lys supplementation are summarized in Tables 3 and 4. No significant (P >.5) nonlinear or intersection effects were observed for any performance parameters. As shown in Table 3, the weight gain and feed efficiency (either total or carcass basis) and partitioned weight gain responses to supplemental digestible Lys intake were linear (P < Downloaded from by guest on 2 November 218

4 Treatment 1. Basal (B)3 2. B +.156% L-LysHCl 3. B +.312% L-LysHCl 4. B + 3% SBM 5. B + 6% SBM 6. B + 9% SBM 7. B + 5% SBM 8. B + 1% SBM 9. B + 15% SBM 1. B + 5% SBM 11. B + 1% SBM 12. B + 15% SBM 13. B + 6.7% SBM:dextrose (3:1) 14. B % SBM:dextrose (3:1) 15. B + 2.% SBM:dextrose (3:1) 16. B + 6.7% SBM:dextrose (3:1) 17. B % SBM:dextrose (3.1) 18. B + 2.% SBM:dextrose (3:1) Pooled SEM R 2 values 4 TABLE 3. Weight gain and feed efficiency of chicks fed soybean meal (SBM) autoclaved fdr varying amounts of time, E Autoclaving time (min) Supplemental digestible Lys (%) Weight gain Total body basis Partitioned gain 2 1 Values are means of four replicate groups of five female chicks from 1 to 2 d of age; average initial weight was g. 2 Values were partitioned to reflect only the chick performance due to supplemental Lys intake. The reference standard curve from regression of total intake (basal + supplemental; milligrams) for treatments 1 to 3 was: Y = X, R 2 =.99. Contained.4% lysine from L-lysineHCl. 4 R 2 for the multiple linear regression of the respective response variable regressed on supplemental digestible Lys intake. M \b> Gain: feed IfVtr} vg K g^ Downloaded from by guest on 2 November 218

5 228 FERNANDEZ AND PARSONS TABLE 4. Carcass N and lysine gain of chicks fed soybean meal (SBM) autoclaved for varying amounts of time, Experiment l 1 Treatment 1. Basal (B)3 2. B + 3. B + 4. B + 5. B + 6. B + 7. B + 8. B + 9. B + 1. B B B B B B B B B + Pooled SEM R 2 values 4.156% L-Lys-HCl.312% L-Lys-HCl 3% SBM 6% SBM 9% SBM 5% SBM 1% SBM 15% SBM 5% SBM 1% SBM 15% SBM 6.7% SBM:dextrose 13.3% SBM:dextrose (3:1) (3:1) 2.% SBM:dextrose (3:1) 6.7% SBM:dextrose (3:1) 13.3% SBM:dextrose (3:1) 2.% SBM:dextrose (3:1) Autoclaving time (min) Supplemental digestible Lys (%) Carcass N gain (g) Total , , ,23 1, ,158 1, Carcass Lys gain \ lll ts) Partitioned 2 1 Values are means of four replicate groups of five eviscerated 2-d-old female chicks. 2 Values were partitioned to reflect only the chick performance due to supplemental Lys intake. The reference standard curve from regression of total carcass Lys gain (grams) on total Lys intake (basal + supplemental; milligrams) for treatments 1 to 3 was: Y = X, R 2 =.98. ^Contained.4% lysine from L-lysine-HCl. 4 R 2 for the multiple linear regression of the respective response variable regressed on supplemental digestible Lys intake..1) for all sources of digestible Lys tested. The levels of supplemental digestible Lys for the diets containing the highest level of autoclaved SBM exceeded those of the L-Lys standard curve because higher levels of autoclaved SBM were fed in attempt to compensate for its expected low digestibility. However, the highly linear response for the autoclaved SBM indicated that the levels of digestible Lys were still in the linear portion of the response curves. The magnitude of the weight gain responses for SBMDEX autoclaved for 3 min were lower than any of the other digestible Lys sources tested. As expected, partitioned weight gain due to supplemental Lys intake for the basal diet approximated zero. The R 2 values for the multiple linear regression equations for feed efficiency were slightly lower than those for the weight gain responses. As observed for weight gain and feed efficiency, carcass N and Lys gain increased linearly (P <.1) with addition of supplemental digestible Lys from all sources tested (Table 4). As observed earlier, the responses to SBMDEX autoclaved for 3 min were the lowest of all digestible Lys sources evaluated. Partitioned Lys gain due only to supplemental Lys intake from the basal diet was zero or very close to zero. The R2 values for the multiple linear regression equations for carcass N and Lys gain exceeded.9. Bioavailability of the true digestible Lys in unautoclaved SBM was not different (P <.5) from the standard L-Lys-HCl (1%) for all response variables except feed efficiency, which exceeded 1% (Table 5). Bioavailability values for the digestible Lys in SBM autoclaved for 4 or 6 min and SBMDEX autoclaved for 2 min were generally similar. The latter bioavailability values averaged approximately 85% (different from 1%; P <.5) when based on weight gain or carcass Lys gain but were not different (P >.5) from 1% when based on feed efficiency or partitioned Lys gain. Bioavailability of digestible Lys in SBMDEX autoclaved for 3 min was much lower (55 to 73%) and significantly less than 1% (P <.5) for all eight of the variables evaluated. In Experiment 2, supplementation of the basal diet with either.22% L-Lys-HCl or SBMDEX (to provide equal amounts of digestible Lys) enhanced growth performance, but the response to the SBMDEX was lower than that from the L-Lys-HCl (Table 6). Supplementation of the SBMDEX diet with.11% L-Lys-HCl yielded growth that was similar to the.22% L-Lys-HCl treatment. Further additions of Lys to the SBMDEX also improved growth performance. DISCUSSION Autoclaving of SBM alone for up to 6 min only slightly decreased analyzed Lys concentration and had no effect on digestibility. These results were not in agreement with previous research in our laboratory (Parsons et «/., 1992), which showed that autoclaving Downloaded from by guest on 2 November 218

6 H -H l +l +l +1 +l +l t N o n o n n v +l +l l +l +1 +l BIOAVAILABILITY OF DIGESTIBLE LYSINE 229 i (N *. CO Ov SS8SSSSS to H 8 S3- -C T3 *}* *C *S.s 1 s a so (j. o (8 " ' a> < «"3 o> '2 = w ^ & SBM for 2 to 4 min decreased both total and digestible Lys concentration in SBM. The difference in results between these two studies was probably due to differences in autoclaving conditions. The SBM was autoclaved covered with aluminum foil at 114 C and 97 kpa in the current study whereas, the SBM was autoclaved uncovered at 12 C and 15 kpa in the Parsons et al. (1992) study. Thus, it seems that experimental autoclaving conditions may markedly affect protein quality of SBM. In the presence of dextrose, autoclaving SBM for only 2 min had a large negative effect on both analyzed Lys concentration and digestibility. The large effect of autoclaving on analyzed Lys concentration suggests that substantial quantities of advanced Maillard reaction products were formed during heating (Hurrell, 199). The Lys in advanced Maillard compounds is not recoverable during amino acid analysis. It was expected that large amounts of Maillard products would be formed when SBM was autoclaved with dextrose because dextrose or glucose is a reducing sugar. In addition to the effects of autoclaving SBMDEX on total Lys concentration, the reduced digestibility of the Lys remaining after autoclaving suggests the formation of substantial amounts of early Maillard reaction products or Amadori compounds. Much of the Lys in the Amadori compounds is released during acid hydrolysis and is measured by amino acid analysis, but the Lys is not utilizable for protein synthesis (Hurrell, 199). Many of the early Maillard compounds are excreted in the urine and would be measured as being undigested in the precision fed cockerel assay used herein. When considering both the effects of autoclaving on analyzed Lys and digestibility of Lys in the SBMDEX, the concentration of digestible Lys per 1 g of SBM in the SBMDEX autoclaved 2 min was 1.26 compared to 2.74 in the unautoclaved SBM, a decrease of 54%. The observation that the true digestible Lys in unautoclaved SBM measured by the precision-fed cecectomized rooster assay was 1% bioavailable for chick growth is in agreement with Fernandez and Parsons (1994, 1996). Research with swine also has shown that ileal-digestible Lys in SBM was completely bioavailable for pig growth (Batterham et al., 199). For SBM autoclaved for 4 or 6 min or SBMDEX autoclaved for 2 min, the bioavailability of true digestible Lys was only approximately 84% for weight gain and carcass Lys retention. These results suggest mat the digestible Lys in these treatments was not totally bioavailable for protein synthesis. However, the fact that bioavailability values based on feed efficiency or partitioned weight gain and partitioned carcass Lys gain did not differ from 1% suggests that the former differences between digestibility and bioavailability may have been primarily due to variation in feed intake and intake of basal diet Lys among treatments. Although no further decrease in Lys digestibility occurred when autoclaving time was increased from 2 Downloaded from by guest on 2 November 218

7 23 FERNANDEZ AND PARSONS TABLE 6. Comparative effects of lysine supplementation of diets with or without soybean meal: dextrose (SBMDEX), Experiment 2 1 Weight Feed Gain: Diet gain intake feed (g) (g/kg) 1. Basal 2 62 e 175d 355 e 2. Basal +.22% L-LysHCl 131= 251* 522= 3. Basal + 2% SBMDEX (3:1) 18d 225= 476^ 4. Basal + 2% SBMDEX (3:1) +.11% L-Lys-HCl 133= 244* 547b 5. Basal + 2% SBMDEX (3:1) +.16% L-Lys-HCl 149" 263* 564b 6. Basal + 2% SBMDEX (3:1) +.22% L-Lys-HCl 165 a 274* 64 a Pooled SEM a_e Means within a column with no common superscripts differ significantly (P <.5). Values are means of four replicate groups of five female chicks from 1 to 2 d of age; average initial weight was 12.6 g. 2 Contained.4% lysine from L-lysine-HCl. to 3 min for SBMDEX, the bioavailability of the digestible Lys was markedly reduced to approximately 6% for all parameters evaluated in this study. Thus, variation in feed intake or basal diet Lys intake among treatments did not seem to account for the low bioavailability. These results strongly suggest that large amounts of Lys were being intestinally absorbed in forms that were not utilizable for protein synthesis. Similar results have been reported by Batterham et al. (199) for cottonseed meal and van Barneveld et al. (1994a) for overheated field peas in pigs. Due to the presence of abundant reducing sugar in the SBMDEX, one would expect that most of the absorbed nonbioavailable Lys would be in the form of early Maillard compounds. However, most of the latter compounds are usually excreted in the urine (Hurrell, 199) and would be measured as undigestible in the precision-fed cecectomized rooster assay used herein. Our results suggest that substantial amounts of absorbed Maillard or other Lys compounds were somehow degraded metabolically by the bird and not excreted as analyzable Lys in the urine. Another possible reason for the low bioavailability of the digestible Lys in SBMDEX autoclaved for 3 min is that toxic compounds were formed by autoclaving. For example, some evidence exists that Maillard compounds can be toxic when fed at high levels (Johnson et al., 1977; Erbesdobler et al, 1981). Thus, the SBMDEX autoclaved for 3 min may have been toxic to the chicks and caused poor growth, which, in turn, resulted in low bioavailability values. However, the results of Experiment 2 showed that the reduced performance of chicks fed SBMDEX could be overcome by Lys supplementation, indicating that the SBMDEX response was due to its low bioavailability of Lys and not toxic compounds formed during autoclaving. REFERENCES Abrams, A., P. H. Lowy, and H. Borsook, Preparation of l-amino-deoxy-2-ketohexoses from aldohexoses and a- amino acids. J. Am. Chem. Soc. 77: Association of Official Analytical Chemists, Official Methods of Analysis. 14th ed. Association of Official Analytical Chemists, Washington, DC. Baker, D. H., K. R. Robbins, and J. S. Buck, Modification of the level of histidine and sodium bicarbonate in the Illinois crystalline amino acid diet. Poultry Sci. 58: Batterham, E. S., L. M. Andersen, D. R. Baigent, R. E. Darnell, and M. R. Taverner, 199. A comparison of the availability and ileal digestibility of lysine in cottonseed and soyabean meals for grower/ finisher pigs. Br. J. Nutr. 64: Batterham, E. S., Availability and utilization of amino acids for growing pigs. Nutr. Res. Rev. 5:1-18. Chung, T. K., and D. H. Baker, Apparent and true amino acid digestibility of a crystalline amino acid mixture and of casein: comparison of values obtained with ilealcannulated pigs and cecectomized cockerels. J. Anim. Sci. 7: Erbersdobler H. F., A. Brandt, E. Scharrer, and B. von Wangenheim, Transport and metabolism studies with fructose amino acids. Prog. Food Nutr. Sci. 5: Fernandez, S. R., and C. M. Parsons, Bioavailability of the digestible lysine and valine in cottonseed and soybean meals for chicks. Poultry Sci. 73(Suppl. 1):28. (Abstr.) Fernandez, S. R., and C. M. Parsons, Bioavailability of the digestible lysine and valine in cottonseed and soybean meals for chicks. Poultry Sci. 75: Finney, D. J., Statistical method in biological assay. 3rd ed. Charles Griffin and Co. Ltd., High Wycombe, Buckinghamshire, UK. Hirakawa, D. A., and D. H. Baker, Assessment of lysine bioavailability in an intact protein mixture: comparison of chick growth and precision-fed rooster assays. Nutr. Res. 6: Hurrell, R. F., and K. J. Carpenter, The estimation of available lysine in foodstuffs after Maillard reactions. Prog. Food Nutr. Sci. 5: Hurrell, R. F., 199. Influence of the Maillard reaction on the nutritional value of foods. Pages in: The Maillard Reaction in Food Processing, Human Nutrition and Physiology. Advances in Life Sciences. P. A. Finot, H. U. Aeschbacher, R. F. Hurrell, and R. Liardon, ed. Birkhauser Verlag, Basel, Switzerland. Izquierdo, O. A., C. M. Parsons, and D. H. Baker, Bioavailability of lysine in L-lysine-HCL. J. Anim. Sci. 66: Downloaded from by guest on 2 November 218

8 Johnson G. H., D. H. Baker, and E. G. Perkins, Nutritional implications of the maillard reaction: the availability of fructose-phenylalanine to the chick. J. Nutr. 17: Liener, I. E., Implications of antinutritional components in soybean foods. Crit. Rev. Food Sci. Nutr. 34: Netke, S. P., and H. M. Scott, 197. Estimates on the availability of amino acids in soybean oil meal as determined by chick growth assay: methodology as applied to lysine. J. Nutr. 1: Parsons, C. M., Influence of caecectomy on digestibility of amino acids by roosters fed distillers' dried grains with solubles. J. Agric. Sci. Camb. 14:469^72. Parsons, C. M., Determination of digestible and available amino acids in meat meal using conventional and caecectomized cockerels or chick growth assays. Br. J. Nutr. 56: Parsons, C. M., K. Hashimoto, K. J. Wedekend, Y. Han, and D. H. Baker, Effect of overprocessing on availability of amino acids and energy in soybean meal. Poultry Sci. 71: SAS Institute, SAS User's Guide: Statistics. Version 5 Edition. SAS Institute Inc., Cary, NC. BIOAVAILABILITY OF DIGESTIBLE LYSINE 231 Sasse, C. E., and D. H. Baker, Factors affecting sulfatesulfur utilization by the young chick. Poultry Sci. 53: Sibbald, I. R., The T.M.E. system of feed evaluation: methodology, feed composition data and bibliography. Technical Bulletin E. Agriculture Canada, Ottawa, ON, Canada. Spackman, D. H., W. H. Stein, and S. Moore, Automatic recording apparatus for use in the chromatography of amino acids. Anal. Chem. 3: Steel, R.G.D., and J. H. Torrie, 198. Principles and Procedures of Statistics. A Biometrical Approach. 2nd ed. McGraw- Hill Book Co., Inc., New York, NY. van Barneveld, R. J., E. S. Batterham, and B. W. Norton, 1994a. The effect of heat on amino acids for growing pigs 2. Utilization of ileal-digestible lysine from heat-treated field peas (Pisutn sativum cultivar Dundale). Br. J. Nutr. 72: van Barneveld, R. J., E. S. Batterham, and B. W. Norton, 1994b. The effect of heat on amino acids for growing pigs 3. The availability of lysine from heat-treated field peas (Pisutn sativum cultivar Dundale). Br. J. Nutr. 72: Downloaded from by guest on 2 November 218