| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Center of Evaluation and Research in Nutrition, ADISSEO France SAS, 03600 Commentry, France
Corresponding author: Jean-Claude Robert; e-mail: jean-claude.robert{at}adisseo.com.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Key Words: dairy cow • methionine • methionine hydroxy analog ester • bioavailability
Abbreviation key: AUC = area under the curve, BPMC = basal plasma Met concentration, HMB = 2-hydroxy 4-(methylthio)-butanoic acid, HMBi = isopropyl ester of 2-hydroxy 4-(methylthio)-butanoic acid, MetDi = digestible Met, SmM = Smartamine M.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Among the possible strategies, the optimization of Met intakes by modulation of diet composition is difficult and remains unsuccessful because feed ingredients that are rich in Met (such as corn-based complements) do not lead to the ideal AA profile (NRC, 2001). Indeed, when Met requirements were met, other AA (such as Lys) deficiencies appear such as considered in the AA submodel of the Cornell Net Carbohydrate and Protein System and in the AA submodel developed in France by Rulquin (cited in NRC, 2001). Supplements of crystalline Met in the ration have been excluded because free Met is quickly and almost totally degraded by the microorganisms in the rumen (NRC, 2001). Consequently, technologies have been developed to supply rumen-protected forms of Met available for dairy cow metabolism. A first strategy of protection was based on physical protection of Met using a surface coating made of a fatty acid and pH-sensitive polymer mixture, or fat, saturated fatty acids, and mineral matrices. However, handling restrictions for feed manufacturing in the field prompted the suppliers to investigate alternative solutions such as chemically modified forms of Met. Among them, DL-2-hydroxy-4-(methylthio)-butanoic acid (HMB) was already used successfully for Met supply to monogastric animals. However, in dairy cows, HMB supplementation used to have an effect on rumen fermentations that induced an increase in the fat yield but extremely rarely in the protein yield (Bhargava et al., 1977; Lundquist et al., 1985; Hansen et al., 1991) Thus, HMB did not seem to effectively replace absorbed Met for milk protein synthesis.
In the present paper, the kinetic evolution of plasma Met concentrations following supplementation with the isopropyl ester of HMB (HMBi), a new form of rumen-protected Met, was described and compared with that of Smartamine M (SmM; Adisseo France SAS, Antony, France), a physically rumen-protected product for which Met bioavailability in lactating dairy cows is considered a reference in the field (Schwab, 1995). The Met bioavailability in SmM was first estimated to be 80% from the determination of its rumen resistance and intestinal availability by nylon bag studies, as reported by Schwab (1995). Later, Met availability in SmM was estimated using different experimental approaches and was determined to be 75.0 to 97.1% (SED = 11) according to proportions of grass and corn silage in the diets estimated by digestibility tests (Robert and Williams, 1997) or 75 ± 11% in a blood test in which the calibration curve was linear and established by steady-state levels of plasma Met concentrations after duodenal infusions of 0 to 30 g of Met in lactating cows (Rulquin and Kowalczyk, 2003). The aims of the present study were to determine the Met bioavailability of HMBi by using a relationship between the area under the curve (AUC) of plasma Met concentrations observed in response to increasing rumen spot-doses of Met (0 to 40 g) supplied to dry, nongestating, mature cows as SmM used as a reference (80% of bioavailability).
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Due to their mature, dry, nongestating conditions, the cows were limit-fed and received individually twice a day a ration composed of permanent grassland hay and concentrate, the proportions and chemical composition of which are presented in Table 1
. The concentrate was distributed at 0800 and 1545 h, and the hay at 0800 and 1600 h in 2 equivalent meals. The average amounts of feed distributed were 2.05 ± 0.03 and 6.42 ± 0.10 kg/d on a DM basis for concentrate and hay, respectively. Cows had free access to water. A salt lick was freely available to supply minerals (4000 mg/kg of Mg, 10,000 mg/kg of Zn, 8250 mg/kg of Mn, 1500 mg/kg of Cu, 120 mg/kg of Mo, 100 mg/kg of I, 100 mg/kg of Co, 15 mg/kg of Se; Sodioligo, Compagnie des Salins du Midi et des Salines de l’Est, Montpellier, France).
|
Plasma Kinetics of Metabolites Following HMBi or SmM Supplementation
The HMBi (MetaSmart; Adisseo France SAS) is a chemical derivative of HMB. Plasma concentrations of isopropyl alcohol, acetone, HMB, and Met were determined repeatedly on 15 dry, mature, nongestating Holstein cows following HMBi supplementation (50 g Met equivalent). Moreover, a direct comparison between HMBi and SmM was made on 7 of these cows according to a crossover design to compare their plasma Met evolution after supplementation with the 2 different products (50 g Met equivalent) and to validate the results of Met bioavailability calculated using the calibration curve.
Item Supply
The supplements (HMBi and SmM) were deposited directly through the cannula into the rumen at the level of the liquid phase just under the fibrous material. The HMBi was distributed at the time of the morning meal on the day of the experiment (d 1) and SmM was given at the time of the evening meal on the day before the experiment (d 0). Preliminary studies conducted in our laboratory (unpublished data) indicated that plasma Met response to SmM supplementation was preceded by a 10-h lag resulting from the retention of SmM in the rumen followed by progressive destruction of its coating matrix in the strongly acidic environment of the abomasum.
Blood Sampling and Chemical Analysis
For all 19 cows, blood samplings began on the day before the Met supplementation (d 0) at 0900, 1100, and 1500 h. Then, on the day of supplementation (d 1), blood was collected regularly once every 1 or 2 h for the first 14 h postsupplementation. Finally, blood samples were obtained on the days after supplementation (d 2 and 3) at 0600, 0800, 1100, and 1500 h. When SmM was used for Met supplementation, sampling was sustained until 72 h postsupplementation (d 4).
The blood samples were collected using an S-Monovette (Sarstedt Aktiengesellschaft & Co., Nümbrecht, Germany) containing lithium chloride and heparin through the intermediary of a catheter (Cavafix Certo Splittocan 375 – B; Braun Medical Inc., Bethlehem, PA) positioned in the jugular vein. After centrifugation for 10 min at 1450 x g, plasma was harvested then stored at –20°C until subsequent metabolite analysis (HMB, Met, or solvents).
Plasma HMB Assay
The concentration of HMB was assayed in 2-mL plasma samples from the cows treated with HMBi. The macromolecular nitrogen was eliminated by treatment with an equal volume of acetonitrile followed by centrifugation for 10 min at 8100 x g (room temperature). The supernatant was harvested and the pellet was rinsed with solution A (deionized water adjusted to pH 2.0 with orthophosphoric acid 85% and acetonitrile in a 92:8 ratio, vol/vol) and filtered using a 0.45-µm filter (Millipore, Bedford, MA). The solution was pooled with the supernatant, the volume completed to 20 mL with solution A, and the preparation was filtered using a cellulose disk AW03 (Millipore). The HMB was quantified in the samples by UV detection at 214 nm after separation on a Hibar prepacked RT-250-4 LichroSorb RP18 (5 µm) column (Merck KgaA, Darmstadt, Germany) under isocratic conditions with an HPLC apparatus HP 1100 (Agilent Technologies, Palo Alto, CA). The mobile phase was solution A distributed at a flow rate of 0.8 mL/min. The injection volume of the samples was 20 µL. The linearity of HMB quantification was good between 2.0 and 134.2 µM of plasma. The recovery yield was 99.5 to 101.2% for concentrations between 13.4 and 134.2 µM. The intra- and interassay variations were 0.1 and <6%, respectively. The concentration of HMB in the plasma samples was expressed in micromoles per liter after correction for standard variations and dilution values.
A previous experiment conducted in our laboratory had demonstrated that HMBi was undetectable (detection limit = 0.52 µM) in the jugular plasma of the cows even though supplemented with 50 g of Met equivalent as HMBi (data not shown). Consequently, the HMBi assay in plasma was not performed in the present study.
Plasma Met Assay
Methionine analysis in plasma was performed after depletion of macromolecular nitrogen by treatment with 10% (vol/wt) 5-sulfosalicylic acid (3.15 M). After centrifugation for 10 min at 11,670 x g (room temperature), the supernatant was collected. The pellet was washed several times with a lithium salt buffer (pH 2.2) containing 33.3 mM trilithium citrate (Merck KGaA), 35.2 mM citric acid, 0.5% thiodiethylene glycol (Sigma Chemical Co., St. Louis, MO), 0.28% HCl, and octanoic acid (2 drops for 2 L of buffer), and the supernatants were pooled. The final volume was adjusted to 5.0 mL with the lithium salt buffer and the preparation was filtered through a 0.2-µm filter (Millipore) before storage at 4°C until assay. The Met concentration was determined in 50 µL of sample by ion-exchange chromatography using a Beckman 6300 AA analyzer (Beckman Instruments, Palo Alto, CA) at 570 nm after postcolumn ninhydrin derivatization. Calibration was achieved with a 50 µM mixture (in 0.1 N HCl) of acid, neutral, and basic AA for calibrating AA analyzers (Sigma Chemical Co.). Finally, 1.25 mM of 2-amino-2-deoxy-D-gluconic acid (Sigma Chemical Co.) and S-(2-aminoethyl)-L-cysteine hydrochloride (Fluka, Buchs, Switzerland) were used as internal standards in calibration solutions and samples. The lower limit of quantification of the Met concentration was established at 1.94 µM and the mean coefficient of variation was 0.92%. Met concentration in the plasma samples was expressed in micromoles per liter after correction for calibration adjustment, internal standard variations, and dilution values.
Plasma Isopropyl Alcohol and Acetone Assays
Plasma concentrations of isopropyl alcohol and acetone were determined after HMBi supplementation in 4 cows with a GLC (type 8500; Perkin-Elmer, Norwalk, CT) equipped with a headspace injection system for specific determination of the volatile components of the samples. A 50 m x 0.32 mm capillary column lined with a 1-µm dimethylpolysiloxane film (HP-1; Agilent Technologies) was used at a maximum temperature of 280°C to separate the volatile products, which were detected by flame ionization. Peak areas were calculated using the software of the chromatograph. Acetone and isopropyl alcohol concentrations in the samples were calculated from the difference in peak areas between isopropyl alcohol or acetone from the sample with or without adding an internal standard solution. Values were expressed in micromoles per liter of plasma.
Data Analysis and Modeling
Plasma kinetics of HMB and Met concentrations after HMBi supplementation were modeled using the nonlinear regression of the software Sigma Plot 6.00 (2000; SPSS Inc., Chicago, IL) and peak time after supplementation and height were determined.
The basal plasma Met concentration (BPMC) was determined for each cow as the mean of the Met values quantified at 0900, 1100, and 1500 h on d 0, and at 0800 h on d 1. The BPMC value was subtracted to concentrations determined for the respective cow after supplementation. The resulting values corresponded to the increases in plasma Met concentrations observed after supplementation and were used to draw the curves of Met increases related to the time after supplementation. The elemental trapezoidal AUC were calculated by multiplying the mean of the Met increases between 2 consecutive times of sampling and the duration of the interval between the samplings (Welling, 1986). The total AUC was the sum of the elemental AUC calculated all along the sampling kinetics.
The modeling of the relationship between MetDi doses and AUC quantification after supplementation with increasing doses of MetDi as SmM was performed using a nonlinear regression with the SigmaPlot 6.00 software (SPSS Inc.). The resulting relationship was used 1) to determine MetDi content from HMBi supplementation of the 15 cows, and 2) to compare MetDi values from HMBi and SmM on 7 cows of the 15.
Finally, Met bioavailability in HMBi was calculated as the ratio between the digestible Met estimated from the calibration curve and the dose level of supplementation, and the result was expressed in percentage of the amount of Met or Met equivalent supplied by the product.
Statistical Analyses
Relationship between digestible Met and plasma Met concentrations.
Data from Met kinetics were tested for normality, variance homogeneity, and compared by ANOVA using the StatView 5.0 software (SAS Institute, 1998) according to the following model:
 |
where Yij
was the BPMC or the AUC calculated from Met concentrations, 
i was the cow effect (n = 4), ßj was the period effect (n = 4), 
k was the dose level of MetDi supplemented as SmM (n = 4), and 
ijwas the residue.
Comparison of plasma Met kinetics and bioavailability from HMBi and SmM supplementations.
Data from Met kinetics were tested for normality and variance homogeneity, and compared by ANOVA with the StatView 5.0 software (SAS Institute, 1998) according to the following model:
 |
where Yij was the BPMC, the Met peak time value or height after supplementation, the AUC calculated from Met concentrations, the MetDi in the spot dose or the bioavailability of the product, i was the treatment effect (HMBi or SmM), ßj was the cow effect (n = 7), and ij was the residue.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Plasma Met concentrations were determined repeatedly for 72 h after spot-dose administration of increasing doses of SmM to 4 cows in a Latin square design. Kinetic evolutions were drawn and concentrations were used to calculate AUC values for each cow and each dose tested, after subtraction of the BPMC values. The cow effect was significant (P = 0.0245), but not the period or the treatment effects for the BPMC values. It suggested that each cow would have specific plasma Met status, at least before supplementation with additional Met. After supplementation with SmM, AUC values tended to depend on the cow (P = 0.0774) but as expected, the main effect was the treatment (P = 0.0009; Figure 1).
|
.
Evolution of Plasma Concentrations of Isopropyl Alcohol, Acetone, HMB, and Met Following HMBi Supplementation
Isopropyl alcohol and acetone concentrations in plasma were determined in 4 of 15 cows during the 24 h following HMBi supplementation in the rumen with particular attention to the first 8 h. As previously reported in the literature (Thin and Robertson, 1953), isopropyl alcohol was undetectable in peripheral plasma of control cows (Figure 2). Its plasma concentration quickly increased in the 2 h following HMBi supplementation to reach an average maximal value of 44.1 ± 27.5 µM. This level was largely lower than the 1.4 mM reported for ketotic cows (Bruce and Lopez, 2000). Its plasma clearance by the liver was a natural physiological process. It was slow (t
= 19.8 h) but regular during the subsequent hours, at least until the end of the first 24 h postsupplementation.
|
). However, the increase lasted almost 6 h and the concentration reached a peak value of 385.7 ± 35.3 µM. These concentrations were around 10-fold lower than values reported for ketotic dairy cows (Bruce and Lopez, 2000). Then, the concentration decreased linearly with a half-life of 22.6 h. Based on the half-life and peak height values, the basal values of isopropyl alcohol and acetone have been estimated to be restored 40 and 46 h after supplementation, respectively. Isopropyl alcohol and acetone metabolisms are tightly dependent, especially in ruminants. Indeed, isopropanol that could be easily absorbed through the stomach or the intestine wall would reach the liver to be oxidized by the hepatic enzymes of the alcohol dehydrogenase family (E.C. 1.2.1.3). The resulting acetone would be either oxidized into carbon dioxide after entering into the tricarboxylic acid cycle, or secreted back into the blood stream. In lactating dairy cows, acetone could also be used for hepatic neoglucogenesis or direct secretion into milk. Furthermore, plasma acetone could also return to the rumen (via direct transfer from blood capillaries of the rumen wall or via secretion into saliva) to be reduced back into isopropyl alcohol by the rumen microorganisms. In this way, it would constitute a metabolic cycle favoring the transfer of 2 reducing hydrogens from the rumen to the liver (Bruce and Lopez, 2000). In the present study, circulating isopropyl alcohol was likely resulting from HMBi hydrolysis and the rather high isopropanol and acetone half-lives might be due to subsequent acetone–isopropyl alcohol recycling by rumen microorganisms. Moreover, the acetone concentration was nearly 10-fold higher than the isopropyl alcohol concentration, suggesting that the liver process for oxidation of the alcohol into ketone is highly efficient and rapid, in agreement with its putative role in detoxification (Bruce and Lopez, 2000).
Plasma HMB concentrations after HMBi supplementation were determined on 15 cows for 27 h and used to model the response (Figure 3). The mean basal HMB concentration in plasma was very low (3.26 ± 1.00 µM, n = 15; Table 2) and close to the limit of quantification (2.3 µM) of the assay. However, HMB would not probably be a physiological plasma metabolite because Met catabolism by rumen microorganisms would produce preferentially the desulfurized (2-aminobutyric acid) and the oxidized forms (Met sulfoxide) rather than the deaminated form (HMB) of Met (Or-Rashid et al., 2001).
|
|
) fit best with a standard rational model described by the relation y = ax/(1 + bx2) where a = 592.6478 and b = 1.8722 (R2 = 0.7019, SEE (standard error of estimate) = 51.6632, P < 0.001). The model seemed to indicate that the kinetics of HMB concentration in plasma comprised 2 phases. In the first 5 h, plasma HMB concentrations varied very rapidly and the kinetics presented a peak shape. It could be seen that the HMB appearance following HMBi supplementation in the rumen was easily observable in the peripheral blood as soon as 10 min after supplementation in the rumen. Moreover, according to the model, the maximal HMB concentration (216.57 µM) was reached in the first hour following supplementation. On the other hand, HMBi is always undetectable in the plasma from peripheral blood both before and after supplementation in the rumen (unpublished data). Consequently, the increase in plasma HMB concentration after HMBi supplementation would result from HMBi absorption and then hydrolysis into HMB. Moreover, it is clear that the mechanism of HMBi transfer from the rumen juice to the peripheral blood, during which its hydrolysis into HMB occurs, is very rapid and efficient. However, the present knowledge does not allow determination of whether the hydrolysis process takes place in the lumen of the digestive tract (i.e., before absorption as HMB), or in the digestive wall or in the liver of the cow (after HMBi absorption). Nevertheless, the lack of a lag time between HMBi supplementation and HMB peak development in the peripheral blood clearly suggests that HMBi absorption does not occur in the intestine—the mean retention time of the liquid phase in the rumen was estimated to be 8.7 h in dairy cows (Mambrini and Peyraud, 1997) and 10 h in grazing bovines (Lechner-Doll et al., 1991). Rather, it would indicate that HMBi was absorbed directly through the rumen wall, at least during the first 5 h following HMBi supplementation. Evidence for AA (or some of their chemical derivatives) absorption through the rumen wall has been already observed in vivo in multicatheterized sheep (Rémond et al., 2000), in empty-and-washed rumen (Veresegyhazy et al., 2001), or ex vivo by using parabiotic chambers (McCollum et al., 2000). Moreover, HMBi is a Met analog esterified with an isopropyl function that could change its lipophilic properties allowing its passage through biological membranes. Indeed, preliminary studies in multicatheterized ruminants or using the empty-and-washed rumen approach would confirm the efficient ruminal absorption of HMBi (Graulet et al., 2004; Noziere et al., 2004). Finally, a recent comparison of the rumen degradability of 3 Met sources (HMBi, HMB, and DL-Met) performed in lactating cows showed that only 2.3% of the HMBi dose of supplementation could bypass the rumen toward the omasum (Noftsger et al., 2005). Consequently, the significant increase in the milk protein concentration observed with the HMBi treatment in the latter study probably resulted from rumen absorption of HMBi more than a low passage rate to the intestine, in agreement with our present hypothesis. The end of the first phase took place around the fifth hour postsupplementation and was followed by a second phase, in which plasma HMB concentrations returned slowly to the basal values (24 h after supplementation). It is more difficult to explain the significance of this second phase in the 2-phase model because it might reflect the superposition of different processes of HMBi: absorption and hydrolysis at the rumen level, rumen bypass, and then intestinal absorption.
Plasma Met concentrations after HMBi supplementation were also determined on 15 cows for 48 h and used to model the response (Figure 4). The mean BPMC in plasma was 20.29 ± 0.74 µM before supplementation, which corresponded to values observed in lactating cows (Pisulewski et al., 1996; Koenig et al., 2002). As for HMB concentrations, the kinetics of plasma Met concentrations (Figure 4) best fit with a standard rational model described by the relation y = (a + bx)/(1 + cx2) where a = 22.6024, b = 70.6179, and c = 0.00766 (R2 = 0.744, standard error of estimate = 23.4872, P < 0.0001). Plasma Met concentration levels increased quickly during the first 3 h following HMBi supplementation (7-fold the basal values) until values exceeded 140 µM (Table 2). Then, Met concentrations decreased slowly to restore the basal values, as could be observed 48 h after supplementation. The comparison between HMB and Met kinetics seems to indicate that the HMB provided by HMBi supplementation was converted into Met by the cow tissues. Studies on monogastric species have shown that HMB would be first oxidized into 2-keto-4-(methylthio)-butanoic acid before a transamination reaction process to produce Met (Dibner and Knight, 1984; Dibner and Ivey, 1992). The 2 enzymes acting in HMB conversion into 2-keto-4-(methylthio)-butanoic acid were identified as L--hydroxy acid oxidase (EC 1.1.3.15) and D-hydroxy acid dehydrogenase (EC 1.1.99.6) for the L- and D-HMB stereoisomers, respectively. Their activities have been shown to be the highest in the liver and kidneys but were also present in numerous other tissues in the chick (Dibner and Knight, 1984). Moreover, they were also described in the ruminal and omasal epithelium in the ovine (McCollum et al., 2000). Furthermore, Met synthesis from HMB was demonstrated in vivo to be especially active in the kidneys, liver, rumen, and the small intestinal parts of growing lambs (Wester et al., 2000). Consequently, it can be supposed that when supplemented intraruminally, HMBi was first absorbed by the rumen wall, then hydrolyzed into HMB and isopropyl alcohol, which were subsequently converted into Met by the cow tissues and acetone in the liver.
|
). The corresponding MetDi (i.e., metabolizable Met) was determined using the previous relationship. Thus, the mean digestible Met equivalent in the spot dose of HMBi was 24.20 ± 1.02 g, which corresponded to a mean Met bioavailability of 48.34 ± 2.05% in HMBi (Table 2). To our knowledge, it is the first time a chemical derivative of hydroxy analog of Met was demonstrated to provide significant amounts of plasma Met to cows. Indeed, in previous studies, the resistance to fermentation by rumen microorganisms of several molecules, including methyl or ethyl esters of HMB, had been compared in vitro (Patterson and Kung, 1988). Those authors observed that methyl and ethyl esters of HMB were rapidly converted to HMB, which was then degraded as observed in vitro (Windschitl and Stern, 1988) or in vivo (Langar et al., 1978; Jones et al., 1988). Then, they concluded that these molecules were not able to supply Met to cows (Patterson and Kung, 1988). More recently, another group reported HMB bypass values close to 40 to 50% observed from ruminal and duodenal digestibilities in dairy cows in early lactation (Koenig et al., 2002). The discrepancy with the previous results could be explained by the difference in the dose level or the mode of supplementation, by species differences, or by the physiological status of the animals. Moreover, HMB had a very moderate effect on plasma Met concentrations (Koenig et al., 2002) and did not increase milk protein content and yield (St-Pierre and Sylvester, 2005) indicating that HMB could not effectively meet the Met requirements of the dairy cow. In the present study, around 50% of the HMBi would be protected from ruminal degradation by absorption through the rumen wall. The remaining 50% would be hydrolyzed by the rumen microorganisms and the resulting HMB mostly degraded.
Comparison of Met Plasma Kinetics and Bioavailability Between HMBi and SmM
The comparison between HMBi and SmM was conducted in a crossover experimental design including 7 dry Holstein cows that received a direct spot supplementation into the rumen by cannula. Plasma Met kinetics were compared for 48 h after HMBi supplementation. Mean characteristics of the kinetics are presented in Table 3. The mean BPMC were not different between the 2 treatments and were similar to the previous measurements. The kinetics of plasma Met concentrations was very different between HMBi and SmM supplementations as illustrated by the peak description (Table 3). Indeed, as shown above, there was no lag-time after HMBi supplementation and the Met concentrations increased quickly to reach the peak value only 4 h after supplementation. The high values lasted only 4 h, and then the plasma concentrations decreased slowly to restore the basal values 30 h after supplementation (data not shown). By contrast, the plasma Met concentrations were still at the basal values 10 h after SmM supplementation, then increased rapidly 5- to 6-fold in the following 2 h to reach a 16-h lasting plateau (data not shown). The calculated mean peak time for SmM was 22.4 h and was significantly different from the HMBi value (P = 0.001). However, the peak heights were not different between the 2 products. Consequently, the AUC value for SmM was 1.87-fold higher than the HMBi value (P = 0.0026, Table 3). The corresponding MetDi values were calculated with the calibration curve obtained above. Values for MetDi were significantly higher for SmM than for HMBi treatment (x1.44, P = 0.0044). The mean Met bioavailability of SmM and HMBi estimated by this blood test method were 74.44 ± 2.15 and 52.84 ± 3.40%, respectively. The value obtained for SmM was in agreement with the practical value (80% reported by Schwab, 1995) and the previous estimations (close to 75%) obtained by digestibility (Robert and Williams, 1997) and blood tests (Rulquin and Kowalczyk, 2003). This would indicate that the present calibration curve would be a useful tool to efficiently estimate Met bioavailability of different Met-based products. Finally, our results indicated that Met bioavailability from HMBi was as high as 71% of that of Met from SmM.
|
In the present experiment, Met bioavailability in HMBi was established to be 48% by a blood test method performed on 15 dry cows and using a calibration curve established with SmM. Moreover, the Met availability of HMBi corresponded to 71% of the value for SmM by direct comparison of the 2 products on 7 cows. The main evidence of these results is that HMBi provides substantial amounts of Met (as observed in plasma) to the cow, as this has been previously reported for SmM (Blum et al., 1999). Consequently, Met from HMBi would support milk protein synthesis in the mammary gland as observed with Met from SmM in lactating dairy cows. It can thus be concluded that HMBi is a very effective form of dietary Met supplementation for the lactating dairy cows.
|
ACKNOWLEDGEMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Received for publication November 24, 2004. Accepted for publication June 14, 2005.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  H. Rulquin, B. Graulet, L. Delaby, and J. C. Robert Effect of different forms of methionine on lactational performance of dairy cows. J Dairy Sci, November 1, 2006; 89(11): 4387 - 4394. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
) and acetone (
) concentrations in the plasma of 4 cows during the 24 h following intraruminal supplementation with a spot dose (50-g Met equivalent) of HMBi [2-hydroxy 4-(methylthio)-butanoic acid isopropyl ester].
