J. Anim. Sci. 2004. 82:2610-2614
© 2004 American Society of Animal Science
Bioefficacy of L-lysine sulfate compared with feed-grade L-lysine•HCl in young pigs
M. R. Smiricky-Tjardes*,
I. Mavromichalis*,1,
D. M. Albin*,
J. E. Wubben*,
M. Rademacher
,2 and
V. M. Gabert*,3
* University of Illinois, Urbana 61801; and
and
Degussa AG, Hanau-Wolfgang, Germany
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Abstract
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A pig growth assay was conducted to determine the relative biological value (RBV) of lysine from L-lysine sulfate compared with feed-grade L-lysine•HCl. One hundred nursery pigs with an average initial BW of 9.5 ± 1.5 kg were blocked by BW and gender and allotted randomly to five dietary treatments in five replicates of four pigs per pen. A corn-peanut meal diet containing 0.6% total lysine (as-fed basis) was supplemented with two levels (0.1 and 0.2%) of lysine from L-lysine•HCl or L-lysine sulfate. The RBV of L-lysine sulfate was determined using multiple regression slope-ratio methodology, with ADG and G:F as the response criteria. At the tested levels, linear responses for gain and G:F were obtained from increments of lysine from the two lysine sources. When ADG was regressed on supplemental lysine intake, the RBV of lysine in L-lysine sulfate was 99% of the RBV of lysine in L-lysine•HCl. When G:F was regressed on supplemental lysine intake, the RBV of lysine in L-lysine sulfate was 97% of the RBV of lysine in L-lysine•HCl. The t-test analysis revealed that the RBV of lysine in L-lysine sulfate was not significantly different from the RBV of lysine in L-lysine•HCl, which was assumed to be 100% bioavailable. In conclusion, L-lysine sulfate can replace L-lysine•HCl in diets for growing swine.
Key Words: L-Lysine•HCl • L-Lysine Sulfate • Pigs • Relative Bioavailability
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Introduction
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Lysine is accepted as the first-limiting AA in pig diets based on corn and soybean meal, and it has therefore become an established practice to supplement pig diets with crystalline lysine in the form of L-lysine•HCl to meet the lysine requirement of 1.35% (total basis; NRC, 1998
) in diets for pigs weighing 5 to 10 kg. Recently, a new source of L-lysine has been developed. L-Lysine sulfate also contains by-products from fermentation, and has a minimum lysine content of 47.3% compared with L-lysine•HCl, which contains a minimum of 78% lysine. Although L-lysine sulfate is a product of bacterial fermentation of carbohydrates, like L-lysine•HCl, further processing methods differ (Schutte and Pack, 1994). Although this new source of lysine is not anticipated to differ from the standard L-lysine•HCl due to the presence of by-products of fermentation (otherwise known as dried microbial cells), differences in performance may be observed. Whittemore and Moffat (1976) determined that dried microbial cells contained 4,475 kcal of DE/kg and 12% digestible N for pigs.
Ammerman (1995) defined bioavailability as the "degree to which an ingested nutrient in a particular source is absorbed in a form that can be utilized in metabolism by the animal." Izquierdo et al. (1988) determined that crystalline L-lysine•HCl is 100% bioavailable. A variety of methods are used to determine the bioavailability of AA; however, measuring AA availability via growth assays determines the ability of a protein to provide a specific limiting AA and subsequently, to promote growth (Lewis and Bayley, 1995). A commonly used approach to determine AA bioavailability is the slope-ratio technique (Batterham, 1992). Therefore, the objective of the current study was to compare the biological efficacy of L-lysine sulfate with that of L-lysine•HCl in young pigs.
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Materials and Methods
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General
The University of Illinois Laboratory Animal Care and Use Committee approved all experimental procedures (Protocol No. A8R197). Before beginning the study, pigs were weaned at 21 ± 3 d of age and were fed a 22.0% CP Phase 1 nursery diet for approximately 7 d until they reached approximately 10 kg BW. One hundred nursery pigs (line 337 sire x C15 dams; PIC, Franklin, KY) with an average initial BW of 9.5 ± 1.5 kg were then blocked by BW and gender and allotted randomly to five dietary treatments in five replicates of four pigs per pen. Pigs were removed from the study after 3 wk on test. Pigs were housed in an environmentally controlled nursery facility with raised-deck pens that had 100% expanded metal flooring and fluorescent lighting. Each pen was equipped with a five-hole feeder and one nipple waterer. Feed and water were provided ad libitum. Pigs and feeders were weighed weekly to determine ADG, feed disappearance (as-fed basis), and G:F.
The basal diet (Table 1) met or exceeded requirement estimates (NRC, 1998) for all nutrients except AA. It was fortified with crystalline AA to reach 120% of the ideal AA concentrations (Baker, 1997; NRC, 1998) with the exception of lysine. Peanut meal was used as a protein source that was relatively balanced in all essential AA, with the exception of lysine. The basal diet was then supplemented with two doses (0.1 and 0.2%) of lysine either as L-lysine•HCl or L-lysine sulfate at the expense of cornstarch. The L-lysine sulfate product (Biolys 60, Degussa AG, Hanau-Wolfgang, Germany, Table 2) contained at least 46.8% free L-lysine and an additional 0.5% lysine bound in biomass, thereby resulting in a total lysine concentration of 47.3%. L-Lysine•HCl contained 78.5% total lysine. The analyzed free lysine content of the diets was used in all calculations.
Chemical Analyses
Crude protein content in the experimental diets was determined by the combustion technique using a Leco analyzer (Leco Corp., St. Joseph, MI) and AOAC method 990.03 (AOAC, 1995). The total AA content of the diets was quantified by ion-exchange chromatography with postcolumn derivation with ninhydrin following 24-h acid hydrolysis at 105°C with 6N HCl (Llames and Fontaine, 1994). Amino acid concentrations were not corrected for incomplete recovery resulting from hydrolysis. Performic acid oxidation preceded acid hydrolysis for the determination of methionine and cystine. All AA other than lysine were determined to verify that the diets contained 120% of the ideal AA concentrations. The determination of nonprotein-bound or supplemental lysine in the experimental diets was quantified by ion-exchange chromatography with postcolumn derivation with ninhydrin after hydrolysis with dilute hydrochloric acid at room temperature using norleucine as an internal standard (Fontaine, 1995). Nonprotein-bound lysine analysis verified that the diets contained the correct amount of added lysine for either L-lysine sulfate or L-lysine•HCl.
Statistical Analyses
Pen means were analyzed as a randomized complete block design using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC), with dietary treatment and block as defined sources of variation. The means for ADG, feed intake, and G:F were separated using the PDIFF procedure of SAS. Data were considered significantly different at P < 0.05. Data were fitted in a multivariate linear regression model with the following equation:
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where a = common y-intercept of the two lines, b1 = slope of L-lysine•HCl line, b2 = slope of L-lysine sulfate line, x1 = value for L-lysine•HCl, and x2 = value for L-lysine sulfate (Littell et al., 1997). The multiple regression model consisted of two straight lines with a common intercept. The dependent variables, ADG and G:F, were regressed on supplemental lysine intake. The RBV was defined as RBV = x2/x1 x 100, where x1 = L-lysine•HCl and x2 = L-lysine sulfate. An unpaired t-test was conducted to determine if the RBV of lysine in L-lysine sulfate was different from the RBV of lysine in L-lysine•HCl (Petrie and Watson, 1999).
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Results
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Supplementation of the basal diet with lysine increased (P < 0.05) ADG and feed efficiency of pigs (Table 3). However, the source of lysine (L-lysine•HCl or L-lysine sulfate) did not affect these response variables. Feed intake was also not affected by dietary treatment. By supplementing the basal diet with 0.1% lysine, ADG increased 51% and 42% for the L-lysine•HCl and L-lysine sulfate diets, respectively. Gain:feed was improved 105% and 80% for the L-lysine•HCl- and L-lysine sulfate-based diets, respectively, compared with the basal diet. By supplementing the basal diet with 0.2% lysine, ADG increased 165% and 202% for the L-lysine•HCl- and L-lysine sulfate-based diets. Feed efficiency was improved 174% and 211% for the L-lysine•HCl- and L-lysine sulfate-based diets, respectively, compared with the basal diet. An unpaired t-test was conducted to determine whether the slopes of the lines in Figures 1 and 2 were statistically different from each other. The test demonstrated (P = 0.05) that the slopes of the lines for the L-lysine sulfate vs. L-lysine•HCl were not different.
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Figure 1. Regression of ADG against supplemental lysine intake from either L-lysine•HCl (X1) or L-lysine sulfate (X2). A total of 100 pigs (9.5 ± 1.5 kg BW) was used in five replicates in a 21-d growth assay. Relative bioavailability of lysine in L-lysine sulfate was 99% compared with lysine in feed-grade L-lysine•HCl.
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Figure 2. Regression of feed efficiency against supplemental lysine intake from either L-lysine•HCl (X1) or L-lysine sulfate (X2). A total of 100 pigs (9.5 ± 1.5 kg BW) was used in five replicates in a 21-d growth assay. Relative bioavailability of lysine in L-lysine sulfate was 97% compared with lysine in feed-grade L-lysine•HCl.
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Relative biological value (RBV) was calculated for lysine in L-lysine sulfate. Slope ratio analysis of ADG showed that the RBV of lysine in L-lysine sulfate was 99% of that in L-lysine•HCl (Figure 1
). The analysis showed that the RBV of lysine in L-lysine sulfate was 97% of that in L-lysine•HCl, based on feed efficiency (Figure 2). However, neither 99% nor 97% were different (P = 0.88) from 100% as determined by an unpaired t-test (Petrie and Watson, 1999).
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Discussion
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In typical corn-soybean meal-based diets for young pigs, lysine is the first-limiting AA (Mavromichalis et al., 1998). Therefore, lysine addition to these diets has become a common practice in the swine industry. L-Lysine•HCl is the dominant source of lysine for addition to pig diet, and it is produced by bacterial fermentation of carbohydrates and other ingredients (Nhan et al., 1976). After fermentation, cell separation occurs and the biomass is removed. The chloride ion is then added to the lysine via ion exchange, evaporation occurs, and ammonia is released. After crystallization, the hydrochloric salt product is dried to form L-lysine•HCl (Schutte and Pack, 1994), which contains about 78.5% free lysine.
L-Lysine sulfate is produced via the same fermentation process. However, after fermentation, the biomass is not separated from the fermentation broth and the product is maintained in the sulfate form. The resulting product undergoes evaporation and granulation. L-Lysine sulfate contains 15.0% sulfate and a small amount of other nutrients, such as AA other than lysine, and P. However, in this study, experimental diets were formulated to contain similar concentrations of AA, Ca, and P, so the differences in lysine source composition would not affect the outcome of the experiment.
Determination of bioavailability is important for accurate feed formulation and maximal growth. Supplementation of the basal diet with lysine resulted in an increase in both ADG and G:F (Table 3); however, the source of lysine did not affect these response parameters. This is in agreement with an earlier study conducted by Kirchgessner and Roth (1996), who reported that supplementation of the deficient basal diet with 0.1 or 0.2% lysine improved gain and feed efficiency, irrespective of lysine source. Additionally, results of a study conducted by Neme et al. (2001) reported no difference in the true digestibility of L-lysine sulfate compared with L-lysine•HCl in cecectomized roosters. These data further support the lack of difference in animal performance noted in the current study because the digestibility of the two lysine sources was not different.
The improvements in ADG and G:F can be attributed only to the supplementation with lysine because the experimental diets were formulated at 120% of the ideal AA ratio (Baker, 1997). Furthermore, the experimental diets contained 0.3% Na and 0.4% Cl, which are above the NRC (1998) requirements. Mahan et al. (1996) reported no improvement in ADG as a result of dietary supplementation above the NRC recommended levels of either Na or Cl after 14 d after weaning in starter pigs weaned at 23 ± 2 d of age. These results therefore suggest that the experimental diets in the current study were adequate in Na and Cl for growth in starter pigs, and any growth responses were the result of lysine supplementation alone.
The RBV was determined by comparing regression coefficients of the two sources for which gain was regressed on intake. Baker (1986) suggested that bioavailability studies should be regressed on absolute intake of the nutrient because, otherwise, variation in feed intake may affect bioavailability results. Additionally, the nutrient intake from the basal diet should be in the constant slope region of the growth curve or be approximately 30 to 70% of animal requirement (Baker, 1986). The test diets provided 54 and 63% of the lysine requirement. Therefore, our supplemental lysine levels are clearly deficient and fall in the linear portion of the growth curve. The RBV of lysine in L-lysine sulfate did not differ from that of L-lysine•HCl. A preliminary comparison of L-lysine•HCl and L-lysine sulfate showed no difference in their efficacy pigs (Schutte and Pack, 1994). Similar to the results of our experiment, Neme et al. (2001) reported no difference in the relative bioavailability of L-lysine sulfate compared with L-lysine•HCL in broiler chickens, and the average bioavailability of L-lysine sulfate was determined to be 100.19% of L-lysine•HCL. This lack of difference in RBV was additionally supported by the absence of differences in ADG and feed efficiency between the two lysine sources.
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Implications
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The bioavailability of lysine in L-lysine sulfate in promoting growth in young pigs is not different from the lysine supplied by L-lysine•HCl. Moreover, the relative bioavailability of lysine in L-lysine•HCl determined by slope ratio methods was not different from the relative bioavailability of lysine in L-lysine sulfate. Therefore, L-lysine sulfate can be used instead of L-lysine•HCl to fortify lysine-deficient corn-soybean meal-based swine diets.
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Footnotes
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1 Present address: NUTRAL S. A., Madrid, Spain. 
3 Present address: Unifeed, Edmonton, Alberta, Canada.
2 Correspondence: Feed Additives Division, Rodenbacher, Chausee 4, Hanau-Wolfgang, Germany (phone: +49-6181-59-3584; fax: +49-6181-59-2129; e-mail: meike.rademacher{at}degussa.com).
Received for publication July 1, 2003.
Accepted for publication May 17, 2004.
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Baker, D. H. 1997. Ideal amino acid profiles for swine and poultry and their applications in feed formulation. Pages 1–21 in Biokyowa Technical Review-9. Nutri-Quest, Inc., Chesterfield, MO.
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Abstract
Introduction
