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ANIMAL NUTRITION |
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* Novus International Inc., St. Louis, MO 63304;
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Animal Science Research Center, University of Missouri, Columbia 65211
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: DL-methionine • growth • 2-hydroxy-4-(methylthio)butanoic acid • methionine bioefficacy • pig • sulfur amino acid
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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; Knight et al., 1998; Jansman and de Jong, 1999). Comparable growth responses (Urbanczyk et al., 1981; Reifsnyder et al., 1984) and N retention (Romer and Abel, 1999) have also been reported for nursery and growing pigs when there was no difference between DL-Met and HMTBA on a molar basis to satisfy the SAA requirement or maintain N retention. However, not all reports have shown similar responses between Met sources, and some have indicated a greater bioefficacy of DL-Met than HMTBA (Schmidt et al., 1998; Schindler et al., 2000; Kim et al., 2005).
The TID Lys requirement of modern lean-genotype nursery pigs (11- to 26-kg) has been reported to be greater than current NRC (1998) recommendations (Gaines et al., 2003; Hill et al., 2005). Previously reported work evaluating the SAA requirement of nursery pigs used either DL-Met (Chung and Baker, 1992c; Owen et al., 1995a; Matthews et al., 2001) or HMTBA (Owen et al., 1995b) as the Met source with some differences in the estimates for the weight ranges as compared with the current NRC (1998). There are limited data estimating the TID SAA requirement of modern lean-genotype nursery pigs except the recent work of Shoveller et al. (2003), Schneider et al. (2004), and Moehn et al. (2005). Thus, the objectives of this research were to determine concurrently the TID Lys and SAA requirement of modern lean-genotype pigs at 11 to 26 kg of BW; and to compare the bioefficacy of DL-Met and HMTBA for nursery pigs below the optimium TID SAA requirement by using a corn-soybean meal-based diet supplemented with high concentrations of synthetic AA.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Experiment 1
Two concurrent experiments were conducted to determine the TID Lys and SAA requirement of 12- to 25-kg modern lean-genotype nursery pigs. To determine the TID Lys requirement, 662 nursery pigs (Triumph 4 x PIC C22; initial BW 12.2 ± 0.18 kg) were allotted to 1 of 5 dietary treatments in a randomized complete block design with 6 replicate pens (3 barrows and 3 gilts) per treatment.
Dietary treatments provided 1.10, 1.20, 1.30, 1.40, or 1.50% of TID Lys, respectively. In the dietary formulations, soybean meal was held constant and dietary Lys content was increased by adding L-Lys·HCl with additional synthetic AA (L-Thr and L-Trp) supplied as necessary to meet the minimum ideal AA ratios. The minimal TID SAA, Thr, Trp, Ile, and Val to Lys ratios were 60, 65, 17, 60, and 68%, respectively (Table 1).
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; Fu et al., 2004). With soybean meal held constant, dietary SAA content was increased by adding HMTBA as 88% aqueous solution of ALIMET feed supplement (Novus International Inc., St. Louis, MO). The minimal TID Thr, Trp, Ile, and Val to Lys ratios were 65, 17, 60, and 68%, respectively (Table 1
). For the TID Lys and SAA requirement studies, pigs were randomly allotted within 2 nursery rooms (30 pens in each room) concurrently, regardless of treatments, to reduce any potential room effect. Pigs were housed (20 to 22 pigs per pen) in an environmentally controlled research facility located on a commercial farm. Pens (3.05 m x 1.82 m) had slatted plastic flooring and were equipped with a 1-cup water unit and a 6-hole nursery feeder. Body weights and feed intakes were recorded at trial initiation (d 0) and termination (d 21).
Experiment 2
To confirm the TID SAA requirement determined in Exp. 1, 638 nursery pigs (Triumph 4 x PIC C22; 13.0 ± 0.16 kg) were allotted by BW to 1 of 5 dietary treatments in a randomized complete block design with 6 replicate pens (3 barrows and 3 gilts) per treatment. Dietary treatments were 0.63, 0.70, 0.77, 0.83, and 0.90% TID SAA (Table 1). All pigs were housed (20 to 22 pigs per pen) in the same research facility as in Exp. 1 for a 20-d experimental period. Body weights and feed intakes were recorded at trial initiation (d 0) and termination (d 20).
Experiment 3
A total of 1,232 pigs (Triumph 4 x PIC C22; initial BW 11 ± 0.30 kg) were allotted to 1 of 7 dietary treatments within 2 nursery rooms (28 pens in each room) in a randomized complete block design to reduce potential room effect. There were 8 replicate pens (4 barrows and gilts) per treatment (20 to 22 pigs per pen). Pigs were housed in the same research facility as in Exp. 1 and 2 for a 21-d experiment. Body weights and feed intakes were recorded at trial initiation (d 0) and termination (d 21).
The basal diet was a corn-soybean meal-based diet supplemented with high concentrations of synthetic essential AA (0.7% L-Lys·HCl along with L-Thr, L-Trp, L-Ile, and L-Val) and nonessential AA (L-Glu and L-Gly) to have a dietary TID Lys concentration of 1.30% and maintain minimal ideal AA ratios to Lys and minimal N content (TID Lys:CP ratio, <7%).
Ratliff et al. (2004) reported that nursery pigs fed this diet had similar growth performance to pigs fed a typical corn-soybean meal-based diet supplemented with L-Lys·HCl, HMTBA, and L-Thr. With no supplemented HMTBA or DL-Met, the current basal diet contained a TID SAA concentration of 0.50%, approximately 35% below the TID SAA requirement as determined in Exp. 1 and 2, and below the concentrations in commercially available diets that are based on least cost optimization with available ingredients. Hence, pigs on these diets should be responsive to Met supplementation (Table 1). It was previously reported and confirmed in Exp. 1 that the TID Lys requirement for 11- to 29-kg pigs of the same genotype in this facility was 1.32% (Fu et al., 2004). Therefore, the dietary TID Lys in Exp. 3 was formulated near the requirement (1.30% TID Lys) to maximize the response to HMTBA, DL-Met supplementation, or both. Other essential AA to Lys ratios were formulated at a minimal TID Thr, Trp, Ile, and Val of 65, 18, 60, and 68%, respectively. Diets 2 to 7 consisted of the basal diet supplemented with 3 equimolar levels of HMTBA or DL-Met (0.06, 0.12, and 0.18% Met activity) to correspond to TID SAA concentrations of 0.56, 0.62, and 0.68%, respectively (Table 1).
Diet Analysis
Amino acid composition of the diets was determined after acid hydrolysis, whereas total SAA content was determined after performic acid oxidation, and Trp content was determined after alkaline hydrolysis (AOAC, 1995). Dietary HMTBA was determined using the HPLC method adapted from Ontiveros et al. (1987). Results of Met source analysis confirmed that supplemental DL-Met and HMTBA were added correctly with a correlation of analyzed to theoretical supplementation levels of greater than 97% across experiments (detailed analyzed supplemental DL-Met and HMTBA content and dietary nutrient compositions are described in Tables 1 and 2).
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Because there was no 2-way interaction of TID SAA concentration and experiment, data for the estimation of TID SAA requirement from Exp. 1 and Exp. 2 were also pooled for statistical analysis. In Exp. 1 and 2, 3 different methods were used to estimate the optimum TID Lys and SAA concentration for each experiment. The first estimate was obtained using the 1-slope broken-line methodology (Robbins et al., 1979) or 2-slope broken-line regression model (Robbins, 1986) if 1-slope broken-line did not apply. The second estimate was determined by establishing the first point where the quadratic curve intersected the 1-slope broken-line (on the plateau) according to the methodology of Parr et al. (2003) or intersected the 2-slope broken-line (above the breakpoint) according to the methodology of Gaines et al. (2005). The third estimate was based on the 95% upper asymptote (95% quadratic maximum) calculated from the quadratic model according to the methodology of Lamberson and Firman (2002).
In Exp. 3, the linear regression slope ratio method was applied to determine the relative bioefficacy of HMTBA vs. DL-Met by using ADG or G:F regressed on dietary TID SAA concentrations according to the methodology of Spencer et al. (2000), in which the basal diet was included as the common basal point. Furthermore, for the entire experimental period, the ADG over basal (as dependent variable) was regressed on TID Met intake over basal or dietary Met addition level (as independent variable) and fit to linear, quadratic, and exponential regression models for HMTBA and DL-Met, respectively. The goodness of fit of the combined models (2-way combination of linear, quadratic, and exponential regression) was tested using the Schwarz Bayesian Information Criteria (BIC) index (Sy and Gupta, 2004) and the NLMixed procedure of SAS. This methodology ensured an unbiased model selection process for each Met source independently based on the actual results of the experiment rather than assuming a prior dose response relationship between the Met sources (Gonzalez-Esquerra et al., 2004a). The model with the best goodness of fit (as indicated by the lowest BIC value) was then used for further calculation of the relative bioefficay of HMTBA vs. DL-Met on an equimolar basis.
An alpha level of P < 0.05 was used as the criterion for statistical significance.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). There was no difference in ADFI with increasing TID Lys concentration (quadratic; P = 0.12). Final BW of pigs fed TID Lys concentrations from 1.10 to 1.50% tended to be linearly increased (linear; P < 0.07). Based on the estimates using the 1-slope broken-line model, the first x-intercept value of the broken-line and quadratic model, and 95% of upper asymptote, the optimal TID Lys concentration estimates for ADG were 1.28, 1.32, and 1.32%, respectively (Figure 1; Table 3). No broken-line analysis or quadratic regression can be applied for the G:F data because of the linear response of G:F to increasing TID Lys concentrations. Practically, G:F data seem to plateau at 1.4% TID Lys.
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). Based on the estimates using the broken-line model, the first x-intercept value of the broken-line and quadratic model, and 95% of the upper asymptote, the optimal TID SAA concentration estimates for ADG were 0.72, 0.76, and 0.74%, respectively, and for G:F were 0.80, 0.84, and 0.84%, respectively (Table 3).
Experiment 2
During the 20-d period, increasing dietary TID SAA from 0.63 to 0.90% increased ADG (quadratic; P < 0.04) and improved G:F (quadratic; P < 0.05; Table 4), which was in agreement with Exp. 1. There was no difference in ADFI with increasing TID SAA concentration (linear; P = 0.18), which was not consistent with Exp. 1. Based on the estimates using the 1-slope broken-line model, the first x-intercept value of the broken-line and quadratic model, and 95% of upper asymptote, the optimal TID SAA concentration estimates for ADG were 0.76, 0.77, and 0.76%, respectively (Table 4), whereas for G:F, the optimal concentrations were 0.80, 0.83, and 0.81%, respectively (Table 4). Thus, the estimates were consistent with the results of Exp. 1.
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) indicated there was increased ADG (quadratic; P < 0.01) and improved G:F (linear; P < 0.001) with dietary TID SAA concentration increasing from 0.63 to 0.90%, indicating a SAA deficiency in the basal diet (Table 4). The pooled ADFI linearly decreased with increasing TID SAA concentration from 0.63 to 0.90% (linear; P < 0.01). Based on the estimates using the 2-slope broken-line model, the first x-intercept value of the broken-line and quadratic model, and 95% of the upper asymptote, the optimal TID SAA concentration estimates for ADG were 0.73, 0.77, and 0.75%, respectively (Figure 2; Table 4). For G:F, the optimal TID SAA concentrations were 0.80, 0.83, and 0.83%, respectively (Figure 3; Table 4).
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). Therefore, the data for the 2 sources were pooled for statistical analysis to test the linear and quadratic effects of increasing the TID SAA concentrations. When dietary TID SAA increased from 0.50 to 0.68%, a linear increase resulted for ADG (P < 0.001), ADFI (P < 0.05), G:F (P < 0.001), and final BW (P < 0.001; Table 6). Pigs fed the 0.68% TID SAA diet had the greatest ADG (linear; P < 0.001) and best G:F (quadratic; P < 0.001) among all TID SAA diets (Table 6); this was a 22% greater ADG response and a 13% greater G:F response over the basal diet containing 0.50% TID SAA.
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). When G:F was used as the response criteria and regressed on dietary TID SAA concentration, the relative bioefficacy of HMTBA vs. DL-Met was 110% with 95% CI of 82 to 137% (Figure 5). Because CI of the linear regression slope ratios for ADG and G:F included 100%, the relative bioefficacy determinations for HMTBA vs. DL-Met were not different.
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and Figure 6, the linear-linear model (with the lowest BIC index) of ADG over basal regression on Met intake over basal represented the best goodness of fit of the current data for HMTBA and DL-Met, in which the relative bioefficacy of HMTBA vs. DL-Met by this method was 111% with 95% CI of 83 to 138%. Using the lower confidence limit of 83%, this method would have detected HMTBA to have been significantly different from DL-Met if its true efficacy was >17% lower than DL-Met.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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) is 1.19% for 5- to 10-kg and 1.01% for 10- to 20-kg pigs. However, for pigs with high lean tissue deposition and high protein accretion rate, the TID Lys requirement was estimated to be 1.42% for maximal ADG and 1.52% for optimal G:F of 7- to 14-kg pigs of lean-genotype pigs (Triumph 4 x PIC C22; Gaines et al., 2003). Lenehan et al. (2003) also found that the TID Lys requirement was 1.40% for maximal growth performance of 10- to 20-kg PIC (L337 x C22) pigs regardless of sex. Le Bellego et al. (2002) reviewed a large body of literature and estimated the TID Lys requirement of 5- to 25-kg pigs to be 1.21 and 1.40% for pigs with ADG of 500 and 600 g, respectively. In the current study (Exp. 1), the ADG of 12- to 25-kg nursery pigs was close to 600 g, and the TID Lys requirement plateaued at 1.30% for ADG and 1.4% for G:F, in agreement with the review of Le Bellego et al. (2002). The 1-slope broken-line analysis indicated a TID Lys requirement of 1.28%, and both the x-intercept value of the broken-line and quadratic curve and 95% quadratic maximum indicated a TID Lys requirement of 1.32% for maximal ADG. These results were consistent with previous publications of the same genotypes, which estimated the TID Lys to be 1.32% for 11- to 29-kg pigs (Fu et al., 2004) and 1.33% for 11- to 25-kg pigs (Kendall et al., 2002). The increased TID Lys requirement has also been demonstrated in other genotypes such as Genetiporc crossbred pigs (Schneider et al., 2004) when ADG of 10- to 20-kg pigs was linearly improved with increasing TID Lys from 0.90 to 1.30%. In the most recent collaborative work of NCCC-42 Committee on Swine Nutrition (Hill et al., 2005), the Lys requirement was reported to be at least 0.2% greater than NRC (1998) recommendation for 7-to 23-kg pigs regardless of genotype, sex, and experimental locations.
According to the ideal ratio of essential AA to Lys (Wang and Fuller, 1989; Wang and Fuller, 1990; Chung and Baker, 1992a) for the maintenance and protein accretion requirement, dietary TID SAA requirement should be increased as the Lys requirement of modern lean-genotype pigs is increased. The NRC (1998) estimated requirement for total SAA was 0.65%, and TID SAA was 0.58% for 10- to 20-kg pigs. In Exp. 1 and 2, the TID SAA requirement plateaued at 0.77% for maximal ADG and 0.83% for optimal G:F. The TID SAA requirement estimates for PIC genotype (Triumph 4 x PIC C22) pigs in the current study was slightly greater than the report of Schneider et al. (2004), which indicated that the TID SAA requirement was 0.68 to 0.71% for ADG and 0.70 to 0.75% for G:F of 10- to 20-kg Genetiporc crossbred pigs. Interestingly, we observed linearly decreased ADFI in Exp. 1, but not in Exp. 2, with increasing dietary HMTBA supplementation up to 0.27% (corresponding TID SAA 0.90%). In a similar study with 10- to 20-kg nursery pigs, Schneider et al. (2004) reported that increased dietary HMTBA addition up to 0.25% (with a dietary TID SAA 0.81%) had no impact on ADFI for 10-to 20-kg pigs. In a toxicity study, Vazquez-Anon et al. (2003a) found that 1% dietary supplemental DL-Met resulted in significantly decreased ADFI, but 1% dietary HMTBA addition did not reduce ADFI of 21- to 43-kg pigs. It was not clear why ADFI in Exp. 1 was reduced with increasing dietary HMTBA addition (up to 0.27%), which was also not observed in several recent studies with dietary HMTBA addition up to 0.21% (Gaines et al., 2005).
In a review to determine Met or SAA requirements in pigs, Peak (2005) reported that the TID SAA requirement was 10.2 or 10.9 mg/g of ADG for individually or group fed pigs, respectively. Moehn et al. (2005), using indicator AA oxidation methodology, determined that the individually fed 7- to 10-kg pig had a TID Met requirement of 0.34% with a variation between 0.30 and 0.38%, slightly greater than the NRC (1998) recommendation of 0.32%. Shoveller et al. (2003) reported that the Met requirement of parenterally fed pigs was only 69% of the enterally fed pigs, indicating the extraction of SAA by first-pass splanchnic metabolism may be responsible for the difference in the requirement. There are inconsistent reports regarding the Cys replacement value of SAA requirement for pigs. Chung and Baker (1992b) reported that in the dietary formulation of 10- to 15-kg weaning pigs, no more than 50% of the total SAA requirement could be furnished by Cys. However, Curtin et al. (1952) estimated that 53% of SAA could be satisfied by Cys in 10- to 20-kg weaned pig diets, and Baker et al. (1969) indicated that under ad libitum feeding conditions, the Cys replacement value was 56% for optimal weight gain of pigs less than 30 kg. In the basal diets of our current studies, the TID Met:Cys ratios were 48:52 in Exp. 1, 2, and 3. Because we are estimating the TID SAA (Met+Cys) requirement, the dietary Met:Cys ratio may not have much effect on the estimation; nevertheless, this warrants further research. The discrepancy of the TID SAA requirement estimate in the current study vs. previous literature reports can be attributed to a variety of factors: (1) dietary Lys concentrations; (2) analytical determinations of SAA; (3) lack of information regarding Met and Cys bioavailability; (4) pig weight range and genotype differences; (5) difference in feed ingredients; (6) individual vs. group feeding; (7) enteral or parenteral feeding; (8) varying degree of stress and environment pathogen loads; (9) dietary Met:Cys ratios; (10) different response variables used for predicting the requirement; and (11) different statistical methodology applied to determine the estimated requirement (Chung and Baker, 1992c; Shoveller et al., 2003; Gaines et al., 2005).
Various methods of analyzing the growth response surface indicated that the optimal TID Lys requirement was 1.28 to 1.32% for ADG and 1.4% for G:F (Exp. 1). Correspondingly, the TID SAA requirement from the pooled results of Exp. 1 and 2 was 0.73 to 0.77% for ADG, and 0.80 to 0.83% for G:F. Therefore, the calculated "true" ideal TID SAA:Lys ratio based on the current requirement study was 57.0 to 58.3% for ADG and 57.1 to 59.3% for G:F, which was in agreement with our recent findings of 59.0% for ADG and 60.8% for G:F for 8- to 26-kg pigs (Gaines et al., 2005). In a review by Peak (2005), the TID SAA:Lys ratio was suggested to be 60 to 62% for modern lean-genotype nursery and growing pigs. Usry (2000) determined the TID SAA:Lys ratio was 58% for the optimal growth of modern 11- to 27-kg PIC (L327 x C22) pigs. Our results indicated that the TID SAA requirement has increased in conjunction with improved genetic selection for lean-genotype pigs, whereas the TID SAA:Lys ratio seems to remain relatively constant compared with previous publications with the commensurate increase in Lys requirement. The similar TID SAA:Lys ratio for different genotypes estimated by both the ratio study and the requirement study validates the ideal protein concept (Wang and Fuller, 1989; Wang and Fuller, 1990; Baker, 1997). The TID Lys and SAA requirements determined in the current study indicate that greater Lys and SAA are needed to optimize G:F than to maximize ADG. This may be because weight gain is a function of lean and fat deposition, and water deposition associated with protein deposition is energetically efficient (Brown et al., 1973; Kerr, 1993); therefore, it takes greater Lys and other essential AA (e.g., SAA) to optimize the protein composition of the weight gain and the resulting feed efficiency than to maximize gain per se.
There has been debate over the biological efficacy of HMTBA relative to DL-Met. In previous dose-response comparisons, it was concluded that HMTBA and DL-Met supply equimolar amounts of L-Met for nursery pigs (Knight et al., 1998; Jansman and de Jong, 1999; Gaines et al., 2005). Comparable growth responses (Urbanczyk et al., 1981) when feeding HMTBA and DL-Met on an equimolar basis were also reported in growing pigs. Collectively, these data are in contrast to other research reports (Roth and Kirschgessner, 1986; Locatelli and Hall, 2005) indicating less than equimolar activity of HMTBA compared with DL-Met in pigs. Based on N balance studies, Romer and Abel (1999) reported that HMTBA and DL-Met demonstrated no difference in bioefficacy for N retention for pigs and chickens when both Met sources were supplemented on an equimolar basis. However, HMTBA has also been reported to have lower bioefficacy than DL-Met based on N balance studies (Schmidt et al., 1998; Schindler et al., 2000; Kim et al., 2005). It is difficult to resolve these conflicting results that may be due to differing basal diets, experimental design, and statistical analysis methodology, which cannot be determined from abstract reported results.
The current bioefficacy experiment used a corn-soy basal diet that was 35% below the SAA requirement and shown to be highly responsive to Met supplementation based on ADG (22%) and G:F (13%) responses over basal. Previous work with this diet demonstrated that addition of 1% nonessential AA as a 50:50 blend of Gln and Gly was required to produce performance equal to a 21% CP corn-soybean meal starter diet (Ratliff et al., 2004). Validation of the test basal diet to this extent has seldom been reported previously for Met source comparisons in swine. Because there was only a linear response to Met supplementation regardless of source (Exp. 3), it can be concluded that all diets supplemented with HMTBA or DL-Met were tested in a sensitive part of the response curve that was below the estimated requirement in Exp. 1 and 2 and therefore did not represent the maximum response that might be obtainable with either Met source. However, the lack of Met source or Met source x TID SAA concentration interaction for growth performance clearly demonstrated that there was no bioefficacy difference between the 2 Met sources within the range of dietary TID SAA tested.
Selection of regression models to estimate bioefficacy will affect results. When the nonlinear common pleatau asymptotic regression model (Finney, 1978; Littell et al., 1997) is used to generate a slope ratio, the model assumes that the compounds being compared will have the same form of dose responses and approach a common asymptote. However, it has been shown in broilers (Vazquez-Anon et al., 2003a,b) and turkeys (Gonzalez-Esquerra et al., 2004a,b) that different dose responses and plateau responses can occur for HMTBA and DL-Met. Perhaps this is due to fundamental differences in the molecules in terms of how they are absorbed, transported, and converted to L-Met (Dibner and Knight, 1984). If indeed the 2 compounds follow different dose response curves, there is no single factor to describe the difference; rather the relative bioefficacy depends on which part of the response curve is used. Schindler et al. (2000) and Locatelli and Hall (2005) used the nonlinear common pleatau asymptotic regression method to estimate the relative bioefficacy of these Met sources, which might explain their lower bioefficacy estimates for HMTBA than DL-Met. In the current study, we determined that the linear regression of ADG over basal on Met intake over basal was the best fit to use to estimate the relative bioefficacy of 2 Met sources, which also indicated there was no Met source difference.
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Footnotes |
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2 Data in this paper were presented in part at 2004 ASAS Midwest Meeting (Abstract No. 154), 2004 ASAS National Meeting (Abstract No. 574), and 2005 ASAS Midwest Meeting (Abstract No. 161).
3 Corresponding author: alleeg{at}missouri.edu
Received for publication August 24, 2005. Accepted for publication January 17, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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