JDS
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Girard, C. L.
Right arrow Articles by Lobley, G. E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Girard, C. L.
Right arrow Articles by Lobley, G. E.
J. Dairy Sci. 88:660-670
© American Dairy Science Association, 2005.

Effects of Dietary Supplements of Folic Acid and Rumen-Protected Methionine on Lactational Performance and Folate Metabolism of Dairy Cows*

C. L. Girard1, H. Lapierre1, J. J. Matte1 and G. E. Lobley2

1 Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Lennoxville, QC, Canada J1M 1Z3
2 Rowett Research Institute, Bucksburn, Aberdeen, UK

Corresponding author: Christiane L. Girard; e-mail: girardch{at}agr.gc.ca.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
The present experiment was undertaken to determine the interactions between dietary supplements of folic acid and rumen-protected methionine on lactational performance and on indicators of folate metabolism during one lactation. Fifty-four multiparous Holstein cows were assigned to 9 blocks of 6 cows each according to their previous milk production. Within each block, 3 cows were fed a diet calculated to supply methionine as 1.75% metabolizable protein, equivalent to 70% of methionine requirement, whereas the 3 other cows were fed the same diet supplemented with 18 g of a rumen-protected methionine supplement. Within each diet, the cows received 0, 3, or 6 mg/d of folic acid per kg of body weight. Rumen-protected methionine increased milk total solid concentration but not yield. Supplementary folic acid increased crude protein and casein concentrations in milk of cows fed no supplementary methionine and the effect increased as lactation progressed; it also decreased milk lactose concentration. Folic acid supplements had the opposite effects on milk crude protein, casein, and lactose concentrations in cows fed rumen-protected methionine. Milk and milk component yields and dry matter intake were unchanged. Folic acid supplementation increased serum folates and this response was greater at 8 wk of lactation. It decreased serum cysteine in cows fed rumen-protected methionine, whereas it had no effect in cows fed no supplementary methionine. The highest serum concentrations of cysteine but the lowest of vitamin B12 were observed at 8 wk of lactation. Serum clearance of folic acid following an i.v. injection of folic acid was slower at 8 wk of lactation. During this period, the high concentrations of serum folates and cysteine, the low serum concentrations of vitamin B12 and methionine, and the slow serum clearance of folates strongly suggest that the vitamin B12 supply was inadequate and interfered with folate use. It could explain the limited lactational response to supplementary folic acid observed in the present experiment.

Key Words: dairy cow • lactation • folic acid • rumen-protected methionine

Abbreviation key: ECM = energy-corrected milk, ILR = irreversible loss rate, MP = metabolizable protein, 5-methyl-THF = 5-methyl-tetrahydrofolate, RPM = rumen-protected methionine, THF = tetrahydrofolate.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Folic acid is a B-complex vitamin and has the single and important biochemical function in mammals to accept and release one-carbon units (Choi and Mason, 2000). This role is essential for the synthesis of purine and pyrimidine, the initiation of protein synthesis, and the formation of the primary methylating agent, S-adenosylmethionine (Bailey and Gregory, 1999). In most species, ingested folic acid is rapidly reduced and methylated across the gastrointestinal wall and the liver to 5-methyl-tetrahydrofolate (5-methyl-THF) (Le Grusse and Watier, 1993). This reaction is irreversible and the methyl group of 5-methyl-THF can only be released through transfer to homocysteine to form methionine and tetrahydrofolate (THF) (Bässler, 1997). Tetrahydrofolate is the active form of folates and acts as the acceptor of one-carbon units from different reactions (Bässler, 1997).

Lactation increases the demand for methylated compounds (synthesis of milk choline, creatine, creatinine, and carnitine) and for methionine to support milk protein synthesis (Xue and Snoswell, 1985). In ruminants, as net absorption of these methylated compounds is inadequate to meet requirements, they need to be synthesized de novo (Snoswell and Xue, 1987) from gluconeogenic precursors, such as glycine and serine, the primary sources for the required methyl groups (Armentano, 1994). During early lactation, however, these increased demands occur at the same time as the increased pressure to synthesize glucose (to support the elevated lactose output) and this may create a shortage in precursors for de novo synthesis of methylated compounds. Under such circumstances, other sources of methyl groups need to be used. These include methionine, which can be converted to homocysteine and then metabolized to cysteine if insufficient sources of methyl groups are available to enable remethylation of homocysteine to methionine. Less methionine may be available to support milk protein output due to the activity of this other role of methionine as a methyl group precursor. This concept is supported by the observations where estimated supply of methionine did not meet requirements of the lactating dairy cow (NRC, 2001), and supplementary folic acid increased milk and milk protein yields and milk protein concentrations (Girard et al., 1995, Girard and Matte, 1998). These data suggested that synthesis of folic acid by the rumen microflora did not fulfill the needs of the animal and that when there is a shortage in precursors for de novo synthesis of methylated compounds, supplementary folic acid improved efficiency of transfer of one-carbon units and spared methionine for anabolic outputs. Thus, optimal milk production involves adequate supply of both methyl group precursors and the appropriate cofactors (folates, B12) to support the various metabolic transfers.

Therefore, it was hypothesized that supplementary folic acid affects lactational performance through increased regeneration of methionine from homocysteine. The present experiment was undertaken to determine the interactions between dietary supplements of folic acid in the presence or absence of additional dietary methionine [supplied as a rumen-protected methionine (RPM) supplement] given daily from 1 mo prepartum throughout a 305-d lactation period on milk production and composition as well as on uptake of folates by cow tissues.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Cows and Treatments
Fifty-four multiparous Holstein cows from the dairy herd at the Agriculture and Agri-Food Canada Research Center (Lennoxville, PQ, Canada) were assigned to 9 blocks of 6 cows each according to their milk production during the previous lactation. Cows were kept in a tie-stall barn equipped with mattress under 16 h/d of light (0530 to 2130 h) and were milked twice daily at 12-h intervals. Care of cows followed the recommended code of practice of Agriculture Canada (1990) and the guidelines of the Canadian Council of Animal Care (1993). The experiment began approximately 1 mo before the expected time of calving and continued for a 305-d lactation period. The basal TMR is described in Table 1Go. Silage DM was determined weekly to maintain a constant ratio of ingredients.


View this table:
[in this window]
[in a new window]
  		Table 1. Composition of the total mixed diet (DM basis).
 
Within each block, 3 cows were fed a diet calculated (NRC, 2001) to supply methionine as 1.75% of metabolizable protein (MP), equivalent to 70% of methionine requirement (NRC, 2001), and the other 3 cows were fed the same diet supplemented with 9 g of Smartamine M (Rhône-Poulenc Animal Nutrition, Mississauga, ON, Canada) before calving and 18 g of Smartamine M after calving. With a methionine content of 88%, 91% rumen by-pass, and 97.8% digestibility, the batch of Smartamine M used in the present experiment supplied 14.1 g of methionine per day to bring the estimated methionine supply to 2.2% of MP. Within each diet, the cows received 0, 3, or 6 mg of folic acid (Rovimix 10% pteroyl-monoglutamic acid, Hoffmann-LaRoche, Cambridge, ON, Canada) daily per kilogram of BW. Those amounts were adjusted for individual BW at the beginning of the experiment, at calving, and at 8, 18, 28, and 38 wk of lactation. Orts were removed every day at 1000 h, and the dietary supplements of folic acid and RPM were incorporated into 500 g of the grass silage used in the total mixed diet and fed immediately to the cows to insure complete ingestion of the supplements. Cows were fed ad libitum. The TMR was distributed in 8 equal meals per day, every 3 h.

Sampling Procedure
Milk production was recorded at each milking throughout lactation. Milk was sampled at 2 consecutive milkings (on evening of one day and morning of the following day) every 4 wk. The amount of feed offered was recorded daily, and orts were recorded on 5 d per wk. Cows were weighed at the beginning of the experiment, at calving, and at 8, 18, 28, and 38 wk after calving.

Whole blood and blood serum were collected by jugular venipuncture, using a Vacutainer system, at the beginning of the experiment (4 wk before the expected time of calving). At 8, 18, 28, and 38 wk after calving, a 3-d blood sampling procedure was performed. On d 0, each cow was implanted with a jugular catheter. On d 1, one basal blood sample was withdrawn (S0), at 1000 h, approximately 24 h after the last supplemented meal. Packed cell volume, hemoglobin, serum concentrations of folates, vitamin B12, homocysteine, methionine, and cysteine were determined 4 wk before the expected time of calving, and at 8, 18, 28, and 38 wk of lactation on the basal blood sample (S0) of d 1.

At 8, 18, 28, and 38 wk of lactation, on d 1, just after the basal blood sample was collected, sterile saline (0.9% NaCl) was injected intravenously through the jugular catheter. On d 2 (at the same time as the previous day), an i.v. bolus of 50 µg of folic acid per kg of BW, prepared as a solution of 10 mg/mL of pteroylmonoglutamic acid (ICN Biochemicals, Cleveland, OH) was injected through the jugular catheter and the catheter was carefully flushed with 2 mL of a solution of sterile bovine heparin (20 IU/L). On d 1 and 2, blood was collected at 5, 15, 30, 60, 120, 240, and 480 min postinjection and only serum concentrations of folates were determined in these blood samples. During those 2 d, the cows received no folic acid or RPM supplements.

Analyses
Folates and vitamin B12.
The procedures for folate determination in serum and milk and vitamin B12 determination in serum using a radioassay (Quantaphase Folate II and Quantaphase B12, Bio-Rad Laboratories (Canada) Ltd, Mississauga, ON, Canada) were as described by Girard and Matte (1988, 1998).

Blood hemoglobin and packed cell volume.
Packed cell volume was determined by microcentrifuge, and blood hemoglobin was measured by the method of Drabkin (Manet, 1969).

Milk components.
Milk fat was determined using the Röse-Gottlieb method (AOAC, 1990; method 905.02), ash was determined by thermogravimetry (LECO Corp., St. Joseph, MI), total N was determined using a combustion procedure (LECO Corp.), noncasein N was determined using a modification of method 16.041 (AOAC, 1990; LECO Corp.), casein N was calculated as the difference between total and noncasein N. Lactose was determined by calculation (total DM in milk minus the other milk components chemically determined). Milk urea was determined according to the method of Broderick (1985).

Determination of total homocysteine, cysteine, and methionine in blood serum.
Total homocysteine, methionine, and cysteine were determined in blood serum by a modification of the method described by Malinow et al. (1989).

Blood serum was centrifuged at 1854 x g for 10 min and frozen at –20°C less than 1 h after blood collection. Before analysis, 200 µL of serum, 100 µL of ultrapure water, 300 µL of 9.0 M urea (pH 9.0), 50 µL of n-amylalcohol, and 50 µL of NaBH4 (10% wt/vol) in 0.1 N NaOH (NaBH4 solution prepared fresh daily) were incubated in a borosilicate tube at 50°C for 30 min. The tubes were cooled on ice and 500 µL of 12% perchloric acid (vol/vol) were added. After 5 min, the content of the tubes was transferred to Eppendorf tubes and centrifuged at 13,000 x g for 7 min. The supernatant was passed through a 0.45-µm polyvinylidene fluoride filter.

Standard curves for homocysteine, methionine, and cysteine were determined at the beginning and end of each daily run. The concentration of each amino acid was calculated from peak areas. Standards of homocysteine were prepared by dissolving 100 mg of L-homocysteine thiolactone (H-6503; Sigma Chemical Co., St. Louis, MO) in 5 mL of 5.0 M NaOH. After 5 min of incubation at room temperature, 5 mL of 5.0 M HCl was added to achieve pH 4.5. The preparation was partitioned in tubes (1.2 mL) and frozen at –70°C until used. Standard curves of homocysteine and methionine were prepared by adding known amounts of homocysteine and methionine to 200 µL of pooled serum, and standard curves of cysteine were prepared by adding known amounts of a solution of cysteine to 100 µL of ultrapure water. Standards were subsequently prepared as previously described for serum samples.

High-pressure liquid chromatography was performed (HPLC system Gold Beckman, Module solvent 126, autosamples 507E, Mississauga, ON, Canada) using an electrochemical detector (Coulochem II (ESA), Concord, ON, Canada) set as follows: guard cell (model 5020; E = +1400 mV), analytical cell (model 5010, E1 = +400 mV; E2 = +1200 mV). Sensitivity was set to 10 µA for detection of homocysteine and methionine and 20 µA for cysteine. The analytic column was a 4.6 x 250 microsorb-in (R0086200C5 – Rainin, Varian, Mississauga, ON, Canada) protected with a guard column (4.6 x 4.5 ultrasphere ODS, 243533, Beckman, Mississauga, ON, Canada).

The mobile phase consisted of 10 mM sodium phosphate monobasic, 0.03 mM 1-octanesulfonic acid, and 2.5% acetonitrile. This was prepared by dissolving 2.392 g of NaH2PO4 and 0.01296 g of 1-octanesulfonic acid in ultrapure water, adjusting the pH to 2.7 with phosphoric acid, and adding ultrapure water to 2 L. Then 50 mL of acetonitrile was added, mixed, and the solution was filtered through a 0.22-µm nylon membrane filter. During the analysis, helium was bubbled continuously through the buffer. The solvent was pumped through the column at 1.3 mL/min at 3000 psi. An injection volume of 20 µL was used. The system was equipped with an automatic sample injector. Each sample was injected twice, first for detection of homocysteine and methionine and, second for detection of cysteine, with the electrochemical detector set to a lower sensitivity (cysteine is present in high concentrations in cow serum).

Calculations of Serum Folate Kinetics
The serum concentrations following the injection of folic acid were corrected for the background concentrations observed the previous day at the same times after saline injection. A double exponential model (Shipley and Clark, 1972) was fitted to these corrected concentrations:


where C(t) denotes the corrected concentration t minutes after injection. This model describes a scenario where some of the injected folates that leave the serum pool are returned within 4 h postinjection. The estimates of A1, A2, g1, and g2 were obtained from nonlinear regression and then used to calculate the following quantities of interest. The volume of the primary pool (V, l) was calculated as Dose / (A1 + A2), where Dose is the injected folates (µg). The rate constant of the primary pool, k (min–1), is given by k = A1 g1 + A2 g2 / (A1 + A2). The reasonable fits obtained by such an approach indicate that first-order kinetics apply i.e., outflows from the pools can be assumed equal to pool size x a fixed rate constant.

Clearance rate was calculated as Dose / (A1/g1 + A2/ g2), irreversible loss rate (ILR, µg/min) was calculated as clearance rate x Cinitial, where Cinitial is the concentration (µg/L) before injection of saline on d 0. The flux through the primary pool (µg/min) was obtained from k x Cinitial x V. Flux represents total flows into and out of a pool (i.e., multiple entries and exits of a molecule are quantified), whereas ILR measures unidirectional transfers through the same pool (i.e., the difference between entry and exit).

Statistical Analyses
Four cows, assigned to different treatments, were removed from the experiment at calving or in early lactation due to health problems unrelated to the experimental treatments.

Energy-corrected milk (ECM) was calculated according to Tyrrell and Reid (1965). Total milk production, ECM, and feed intake for a 305-d lactation period were analyzed using the MIXED procedure of SAS (1999) according to a randomized complete block design.

Average milk production, ECM, milk composition (concentration and yield of each component) and feed intake, serum concentrations of folates and vitamin B12, packed cell volume, blood hemoglobin, and serum homocysteine, methionine, and cysteine and serum folate kinetics at 8, 18, 28 and 38 wk of lactation as well as BW (5 measurements per cow) were analyzed using the MIXED procedure of SAS (1999) according to a randomized complete block design with repeated measures in time.

The treatment structure was a complete factorial design with 2 levels of methionine and 3 levels of folic acid. Polynomial contrasts were used to further investigate differences among levels of folic acid supplementation. When the interaction folic acid x methionine reached a level of significance of 95%, contrasts were used within each level of methionine. Results are reported as LSmeans and SE except when a natural logarithm transformation was used to restore normal distribution when the results are reported as anti-natural logarithm LSmeans with the interval of confidence at 95%.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Lactational Performance
At the beginning of the experiment, 4 wk before the expected time of calving, BW was similar between treatments (694 ± 11 kg; P > 0.3). There was no effect of dietary treatments on BW during lactation (P > 0.4), with BW averaging 637 ± 11, 624 ± 9, 653 ± 8, 679 ± 9, and 685 ± 10 kg at calving, 8, 18, 28, and 38 wk of lactation, respectively (time effect, P < 0.001).

Total milk production (10,584 ± 137 kg), ECM (9943 ± 110 kg), and feed intake (7137 ± 3.1 kg of DM) for the 305-d lactation were unaffected by folic acid supplementation or RPM (P > 0.2; Table 2Go).


View this table:
[in this window]
[in a new window]
  		Table 2. Dry matter intake and lactational performance (LSmeans) of dairy cows according to the dietary supplementations in folic acid and rumen-protected methionine (RPM).
 
There was no effect of folic acid supplements or RPM on milk component yields (P > 0.14) and milk fat and ash concentrations (P > 0.07; Table 2Go). Dietary supplements of RPM increased milk total solids concentrations from 120.7 to 124.2 g/kg (SE 1.6; P = 0.01). The dietary supply of methionine modified the effects of supplementary folic acid on milk concentrations of lactose (quadratic effect of folic acid x methionine, P = 0.04; Table 2Go) and urea (linear effect of folic acid x methionine, P = 0.02; Table 2Go). On average, milk crude protein and casein concentrations were higher in cows fed RPM, (methionine effect, P ≤ 0.005). However, the responses of milk crude protein and casein concentrations to supplementations with folic acid and RPM changed during lactation (folic acid x methionine x time, P = 0.04; Table 3Go). With the diet not supplemented with RPM, as lactation progressed, folic acid supplementation increased crude protein and casein concentrations (quadratic effect of folic acid x time, P = 0.07), whereas the opposite trend was observed in cows fed RPM (quadratic effect of folic acid x time, P = 0.06).


View this table:
[in this window]
[in a new window]
  		Table 3. Crude protein and casein concentrations (LSmeans) in milk during lactation according to the dietary supplementations in folic acid and rumen-protected methionine (RPM).1
 
Concentrations and amounts of folates secreted in milk during lactation were increased by folic acid supplements (quadratic effect of folic acid, P < 0.009; Table 2Go). Milk folates decreased as lactation progressed and the decrease is greater in cows fed folic acid supplements (quadratic effect of folic acid x time, P ≤ 0.02; not shown).

Blood Variables
Serum concentrations of vitamin B12, blood hemoglobin, and packed cell volume.
At the beginning of the experiment, serum vitamin B12 (263.2 ± 12.6 pg/mL), blood hemoglobin (11.44 ± 0.17 g/dL), and packed cell volume (32.4 ± 0.5%) were similar between treatments (P > 0.2).

There was no effect of supplementary folic acid or RPM on serum concentrations of vitamin B12 (P > 0.3), blood hemoglobin (P > 0.5), or packed cell volume (P > 0.3), although those variables changed with stage of lactation (P < 0.001; Table 4Go).


View this table:
[in this window]
[in a new window]
  		Table 4. Blood and serum variables and serum folate kinetics following an intravenous bolus of folic acid according to the stage of lactation (LSmeans, 95% confidence interval or SE).
 
Serum concentrations of folates.
At the beginning of the experiment, serum folates (8.52 ± 0.47 ng/mL) were similar between treatments (P > 0.2). They increased linearly with the amounts of folic acid ingested but the increase due to folic acid supplementation was larger 8 wk after calving than later in lactation (folic acid x time, P = 0.02; Table 4Go).

Serum concentrations of sulfur amino acids.
At the beginning of the experiment, total serum methionine (19.7 ± 1.1 µmol/L), homocysteine (7.1 ± 1.0 µmol/ L), and cysteine (231.1 ± 4.7 µmol/L) were similar between treatments (P > 0.2).

Total serum methionine and homocysteine were lower in unsupplemented cows, 15.5 (14.2 to 16.9) and 4.0 (3.6 to 4.4) µmol/L than in cows fed RPM, 25.3 (23.3 to 27.7) and 5.0 (4.8 to 5.8) µmol/L (P < 0.001). Folic acid supplements did not modify serum methionine (P > 0.4) but tended to decrease serum homocysteine (linear effect of folic acid, P = 0. 06); 5.1 (4.5 to 5.7), 4.4 (3.9 to 5.0) and 4.4 (3.9 to 5.0) µmol/L for cows fed 0, 3, and 6 mg of folic acid per kg of BW, respectively. The lowest concentrations of methionine (time effect, P = 0.004) and homocysteine (time effect, P = 0.001) were observed at 8 wk of lactation (Table 4Go).

On average, serum concentrations of total cysteine were higher in cows fed RPM (P = 0.002) but they were altered by the dietary supplements of folic acid (methionine x quadratic effect of folic acid, P = 0.008). They also changed throughout lactation according to methionine supplementation (time effect x methionine, P = 0.03). In cows fed RPM, serum cysteine was lowered by folic acid supplementation; averaging 227.9 (213.8 to 242.0), 190.1 (175.4 to 204.9), and 208.1 (193.2 to 223.1) µmol/ L for cows fed 0, 3, or 6 mg of folic acid per kg of BW daily, respectively (quadratic effect of folic acid, P = 0.005). The highest concentration of cysteine was observed at 8 wk of lactation (time effect, P ≤ 0.04; Table 4Go). In cows without supplementary methionine, folic acid supplementation had no effect on serum concentrations of cysteine. Values were 196.7 (182.6 to 210.8), 194.1 (179.4 to 208.9), and 188.3 (173.5 to 203.0) µmol/L, for cows fed 0, 3, or 6 mg of folic acid per kg BW daily, respectively (P = 0.54), and they did not vary through lactation (time effect, P = 0.46; Table 4Go).

Serum Folate Kinetics Following an Intravenous Bolus of Folic Acid
From the 2-pool model fit, the estimated size of the initial pool was approximately 2.3-fold the plasma pool and was not affected by treatment (P > 0.1). The rate constant (k) of this pool was 0.09/min, again independent of treatment (P > 0.1). The clearance rate of folates did vary with stage of lactation (P = 0.04; Table 4Go), however, and was lower during early (2.37 L/min) compared with late (2.66 L/min) lactation. Furthermore, both ILR and flux were increased by dietary folic acid supplementation (P ≤ 0.005; Table 5Go). Flux also showed an effect of stage of lactation (P = 0.005), with the highest value at 18 wk of lactation (Table 4Go).


View this table:
[in this window]
[in a new window]
  		Table 5. Serum folate kinetics (LSmeans) following an intravenous bolus of folic acid according to the dietary supplementations in folic acid and rumen-protected methionine (RPM).
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Lactational Performance
The absence of response in milk production and DMI to supplementation with RPM is similar to those frequently reported in the literature. In a nonexhaustive review of the literature between 1993 and 2003, only 1 (Vanhatalo et al., 1999) of 22 papers looking at the effect of RPM fed to dairy cows reported an increase in milk production, and none described an effect on DMI (Aldrich et al., 1993; Guinard and Rulquin, 1995; Jurjanz et al., 1996; Overton et al., 1996; Armentano et al., 1997; Chilliard and Doreau, 1997; Pacheco-Rios et al., 1997, 1999; Rulquin and Delaby, 1997a, b; Robinson et al., 1998; Blum et al., 1999; Pisulewski and Kowalski, 1999; Vanhatalo et al., 1999; Krober et al., 2000; Berthiaume et al., 2001; Younge et al., 2001; Pisulewski et al., 2002; Kowalski et al., 2003; Leonardi et al., 2003; Misciattelli et al., 2003; Noftsger and St-Pierre, 2003). The major effect of RPM supplements is an increase in milk protein concentration and yield (Guinard and Rulquin, 1995; Jurjanz et al., 1996; Armentano et al., 1997; Chilliard and Doreau, 1997; Pacheco-Rios et al., 1997, 1999;Rulquin and Delaby, 1997a, b; Krober et al., 2000; Kowalski et al., 2003; Leonardi et al., 2003; Misciattelli et al., 2003; Noftsger and St-Pierre, 2003). Overall, in the present experiment, RPM did increase milk crude protein (total nitrogen) and casein concentration but without any changes in milk protein yield. This latter finding maybe due to the numerically lower milk production, 33.0 vs. 34.6 (SE 1.0) kg/d for cows fed or not fed RPM, respectively.

As in previous experiments (Girard et al., 1995; Girard and Matte, 1998), no effect of supplementary folic acid on DMI or BW of cows was observed. Nevertheless, in those experiments, supplementary folic acid increased milk production and milk protein concentrations and yields in multiparous cows but had no such effects on primiparous cows. In the present experiment, however, multiparous cows showed no effect of supplementary folic acid on any of those parameters although as lactation progressed, supplementary folic acid did increase milk protein concentration in cows fed no supplementary methionine.

Changes in milk concentrations of urea and lactose in response to folic acid supplementation differed according to the level of methionine provided by the diet. An increase in milk concentration of urea reflects an increment in blood concentration. High urea concentrations usually result from an excess of rumen-degradable protein absorbed as ammonia or from an increment in amino acid oxidation, having both as end-product hepatic ureagenesis (Hof et al., 1997). In this study, because all cows were fed the same basal diet, it is unlikely that ammonia absorption differed between treatments. In cows fed no supplementary folic acid, milk concentrations of urea and lactose were higher with the basal diet than with RPM supplementation. Therefore, it can be speculated that in cows receiving no methionine and folic acid supplementations, amino acids were used as gluconeogenic substrates with, consequently, increased nitrogen losses by deamination. When supplementary folic acid was provided, milk urea and lactose concentrations decreased when the basal diet was fed but increased in cows fed RPM. This may indicate a different shift in the use of amino acids as gluconeogenic substrates. How this might happen is unclear but glycine and serine do form an important component of the folate cycle and may be used as sources of one-carbon units in the presence of adequate folates. However, the observed changes in milk urea, although significant, were small, and changes in milk lactose are to be interpreted with caution because these were determined by difference.

As in the present experiment, Girard and Matte (1998) observed a progressive decrease in folate concentrations in milk throughout lactation and a quadratic response of milk folates to folic acid supplementation. However, in the 1998 study, milk folates were increased similarly by the 2 levels of supplementation used (2 and 4 mg/kg of BW per d), whereas in the present experiment, as lactation progressed, the response of milk folates to folic acid supplementation was smaller for cows fed 6 mg (per kg of BW) of folic acid daily than for those fed 3 mg. In women, milk folates are stable, and responses to folic acid supplementation are only seen in malnourished mothers (Tamura et al., 1980; Kirksey, 1986; Keizer et al., 1995; Mackey and Picciano, 1999). Those results confirm that milk secretion of folates in cows, as in humans, is not due to passive transfer but rather is regulated at the level of the mammary gland.

Metabolic Variables
Supplementary folic acid had no effect on packed cell volume or blood hemoglobin, as reported previously in multiparous cows (Girard et al., 1995; Girard and Matte, 1999).

Serum concentrations of vitamin B12 increased through lactation, a similar pattern to that observed by Girard and Matte (1999), although the concentrations were lower than previously reported for multiparous cows and, instead, were similar to those of primiparous cows (Girard and Matte, 1999). Stangl et al. (2000b) observed plasma concentrations of approximately 108 pg/mL in growing cattle fed a cobalt-deficient diet and 271 pg/mL in those fed a cobalt-adequate diet. In the present experiment, serum vitamin B12 increased from 189 pg/mL at 8 wk of lactation to 275 pg/mL at 38 wk of lactation indicating a possible lack of vitamin B12 in early lactation despite an adequate supply of cobalt.

As previously reported (Girard and Matte, 1999), serum concentrations of folates increased linearly with folic acid supplementation, and reached their highest value in supplemented cows in early lactation. They decreased thereafter to a plateau at 16 to 18 wk of lactation. In the present experiment, blood samples for serum folate determination were taken 24 h after ingestion of the dietary supplements and all serum folates, even in cows fed supplementary folic acid, were in the form of 5-methyl-THF (C. L. Girard, unpublished data). In many species, serum folates are present as the monoglutamate of 5-methyl-THF (Lucock, 2000), but retention and concentration of folates by tissues require conversion of pteroylmonoglutamates to pteroylpolyglutamates (Shane, 1989). 5-Methyl-tetrahydrofolate is a poor substrate for the enzyme responsible for the elongation of the glutamate chain (Shane, 1989) and the methyl group can be removed only through one vitamin B12-dependent reaction, methionine synthase, in the regeneration of methionine from homocysteine (Shane et al., 1977). This demethylation of 5-methyl-THF is rate limiting for the cellular accumulation of folates (Lucock, 2000). Consequently, in the present experiment, the higher serum concentrations of folates in early lactation cows fed supplementary folic acid at a time when serum B12 was low could reflect a decreased ability of the cells to retain and use folates.

This hypothesis is supported by the observation that serum clearance of folic acid during the 8 h following an i.v. bolus of folic acid was slower at 8 wk of lactation. Herbert and Zaluski (1962), as cited by Gregory and Quinlivan (2002), observed that, during vitamin B12 deficiency, serum clearance of total folates (measured by Lactobacillus casei) was less rapid than serum clearance of nonmethylated folates (measured by Streptococcus faecalis). The authors interpreted this as an accumulation of folates in a nonmetabolically available form, i.e., 5-methyl-THF. In the present experiment, it is possible that a low supply of vitamin B12 interfered with tissue uptake of folates by inhibiting the demethylation of 5-methyl-THF. This explanation is in accordance with the observations that later in lactation, when serum vitamin B12 increased, serum clearance of folic acid was accelerated while in cows fed supplementary folic acid, serum concentrations of folates were decreased as compared with concentrations earlier in lactation. Overall, the folate kinetics, following a bolus dose, fitted reasonably to a 2-compartment model. Of course, a more complex system may exist biologically but this could only be defined by more detailed experimental approaches using labeled tracer folates and sampling of secondary and tertiary folate pools. The data do indicate, however, that folates both enter and leave the primary pool (plasma), as shown by the difference between flux (total flow) and ILR (net unidirectional flow). At all levels of folic acid supplementation, flux was approximately twice that of ILR (Table 5Go). At zero supplementation, this means that total flow from the pool was 80 µg/min with a return of 40 µg/min, leaving an irreversible loss (net unidirectional movement) of 40 µg/min. The model cannot resolve, however, whether the 40 µg/min return was from the same pool into which the 80 µg/min flowed or another pool(s).

Ingestion of RPM increased serum concentrations of methionine in a range similar to those reported in the literature (Aldrich et al., 1993; Overton et al., 1996; Pacheco-Rios et al., 1997; Rulquin and Delaby, 1997a, b; Robinson et al., 1998, 1999; Pisulewski and Kowalski, 1999; Vanhatalo et al., 1999; Krober et al., 2000; Pisulewski et al., 2002). Serum concentrations of homocysteine were also higher in cows fed RPM. Overall, however, homocysteine concentrations were lower than observed for growing cattle (7.4 and 7.8 µmol/L; Stangl et al., 2000a, b).

At 8 wk of lactation, MP supply was lower than MP requirements and the decrease in serum concentrations of methionine and homocysteine could reflect the demand for protein synthesis. This should have been concomitant with a decrease in serum concentrations of cysteine but it was not the case in the present experiment in which serum concentrations of cysteine peaked in early lactation in cows fed RPM. Later in lactation, increased dietary intake and lower milk protein output should have resulted in increased catabolism of dietary methionine to cysteine. Nonetheless, as discussed below, other factors must also operate, as plasma cysteine concentrations were lower in late lactation than during early lactation, and were similar in the presence and absence of RPM.

The methionine cycle is of major importance for cellular metabolism. Among its numerous roles, it regulates the balance between methionine and cysteine for protein synthesis and provides the pathway by which methyl groups are transferred from 5-methyl-THF to a broad variety of substrates (Finkelstein, 1990). According to the model proposed by Reed et al. (2004), based on data obtained in humans and rats, a lack of vitamin B12 (and the subsequent interference with folate use) would decrease methionine concentration in liver due to a reduction of the activity of the methionine synthase and then, homocysteine remethylation. In the present experiment, the lowest serum concentrations of methionine were observed at 8 wk of lactation at a time where serum concentrations of vitamin B12 reached their lowest values. Those observations could give a supplementary indication, although an indirect one, that the vitamin B12 status of the cows was low enough at this physiological stage to interfere with the methionine cycle.

Homocysteine has 2 metabolic fates. First, it is transformed to cystathionine (by the enzyme cystathionine synthase) and then cysteine, which is then used for protein, glutathione, and taurine synthesis, or degraded to sulfate. Second, homocysteine can accept a methyl group from 5-methyl-THF or betaine and be reconverted to methionine (Martinov et al., 2000). In humans and rats, high dietary supply of methionine increases the concentration of S-adenosylmethionine, which activates cystathionine synthase and, thus, cysteine formation (Selhub, 1999). Conversely, decreased methionine supply reduces S-adenosylmethionine concentration, with consequent lower activity of cystathionine synthase and less cysteine formation (Reed et al., 2004). These concepts could account for the higher plasma cysteine concentration for the cows fed RPM.

In cows fed supplementary methionine, supplementary folic acid reduced serum concentrations of both homocysteine and cysteine and this may be explained by increased conversion of homocysteine to methionine, as similar responses have been observed with humans given additional folates (Bunout et al., 2000; Mayer et al., 2002). The regeneration of methionine may have been inhibited during early lactation, however, because of low availability of vitamin B12. This would increase the size of the homocysteine pools and stimulate production of cysteine, particularly in cows fed RPM.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
ACKNOWLEDGEMENTS
 REFERENCES
 
Dietary supplements of folic acid and RPM modified milk crude protein and casein concentrations but not yield in mid- and late-lactation. In early lactation, 8 wk after calving, serum concentrations of folates and cysteine were increased whereas vitamin B12 and methionine were decreased. These data, coupled with the slower serum clearance of folates following an i.v. bolus of folic acid suggest that low supply in vitamin B12 during early lactation could interfere with folate use. Other studies are necessary to determine if supplementary vitamin B12 given in early lactation, impacts on lactational performance of dairy cows fed supplementary folic acid and RPM.


   ACKNOWLEDGEMENTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
REFERENCES
 
The authors are grateful to Michel Perreault, Gabriel Larivière, and Guylaine Fortin for animal care, to Chrystiane Plante and Sylvie Provencher for technical assistance, to Steve Méthot for statistical advice, and John Kelly for useful discussions and preparation of the experimental diet. Rumen-protected methionine was kindly provided by Rhône-Poulenc Animal Nutrition (Mississauga, ON, Canada) and pteroylmonoglutamic acid by Hoffmann-LaRoche (Cambridge, ON, Canada). A special thank you to Grietje Holtrop; analysis of serum kinetics would have been more rudimentary without her.


   FOOTNOTES
 
* Contribution no. 843. Back

Received for publication June 22, 2004. Accepted for publication October 14, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 


Agriculture Canada. 1990. Recommended Code of Practice for Care and Handling of Dairy Cattle, Publ. No. 1853/E, Agriculture Canada, Ottawa, ON.

Aldrich, J. M., L. D. Muller, and G. A. Varga. 1993. Effect of somatotropin administration and duodenal infusion of methionine and lysine on lactational performance and nutrient flow to the small intestine. Br. J. Nutr. 69:49–58.[Medline]

Association of Official Analytical Chemists. 1990. Official Methods of Analysis. 15th ed. AOAC, Arlington, VA.

Armentano, L. E. 1994. Impact of metabolism by extragastrointestinal tissues on secretory rate of milk proteins. J. Dairy Sci. 77:2809–2820.[Abstract]

Armentano, L. E., S. J. Bertics, and G. A. Ducharme. 1997. Response of lactating cows to methionine or methionine plus lysine added to high protein diets based on alfalfa and heated soybeans. J. Dairy Sci. 80:1194–1199.[Abstract]

Bailey, L. B., and J. F. Gregory, III. 1999. Folate metabolism and requirements. J. Nutr. 129:779–782.[Abstract/Free Full Text]

Bässler, K. H. 1997. Enzymatic effects of folic acid and vitamin B12. Int. J. Vit. Nutr. Res. 67:385–388.

Berthiaume, R., P. Dubreuil, M. Stevenson, B. W. McBride, and H. Lapierre. 2001. Intestinal disappearance and mesenteric and portal appearance of amino acids in dairy cows fed ruminally protected methionine. J. Dairy Sci. 84:194–203.[Abstract]

Blum, J. W., R. M. Bruckmaier, and F. Jans. 1999. Rumen-protected methionine fed to dairy cows: Bioavailability and effects on plasma amino acid pattern and plasma metabolite and insulin concentrations. J. Dairy Sci. 82:1991–1998.[Abstract]

Broderick, G. A. 1985. Alfalfa silage or hay versus corn silage as the sole forage for lactating dairy cows. J. Dairy Sci. 68:3262–3271.[Abstract/Free Full Text]

Bunout, D., A. Garrido, M. Suazo, R. Kauffman, P. Venegas, P. de la Maza, M. Petermann, and S. Hirsch. 2000. Effects of supplementation with folic acid and antioxidant vitamins on homocysteine levels and LDL oxidation in coronary patients. Nutrition 16:107–110.[Medline]

Canadian Council on Animal Care. 1993. Guide to the Care and Use of Experimental Animals, 2nd ed. Vol. 1. E. D. Rolfert, B. M. Cross, and A. A. McWilliam, ed. Canadian Council on Animal Care, Ottawa, ON.

Chilliard, Y., and M. Doreau. 1997. Influence of supplementary fish oil and rumen-protected methionine on milk yield and composition in dairy cows. J. Dairy Res. 64:173–179.[Medline]

Choi, S.-W., and J. B. Mason. 2000. Folate and carcinogenesis: An integrated scheme. J. Nutr. 130:129–132.[Abstract/Free Full Text]

Finkelstein, J. D. 1990. Methionine metabolism in mammals. J. Nutr. Biochem. 1:228–237.[Medline]

Girard, C. L., and J. J. Matte. 1988. Blood serum concentrations of folates and vitamin B12 during growth period of white veal calves. Can. J. Anim. Sci. 68:455–460.

Girard, C. L., and J. J. Matte. 1998. Dietary supplements of folic acid during lactation: Effects on the performance of dairy cows. J. Dairy Sci. 81:1412–1419.[Abstract]

Girard, C. L., and J. J. Matte. 1999. Changes in serum concentrations of folates, pyridoxal, pyridoxal-5-phosphate and vitamin B12 during lactation of dairy cows fed dietary supplements of folic acid. Can. J. Anim. Sci. 79:107–113.

Girard, C. L., J. J. Matte, and G. F. Tremblay. 1995. Gestation and lactation of dairy cows: A role for folic acid? J. Dairy Sci. 78:404–411.[Abstract]

Gregory, J. F., III, and E. P. Quinlivan. 2002. In vivo kinetics of folate metabolism. Annu. Rev. Nutr. 22:199–220.[Medline]

Guinard, J., and H. Rulquin. 1995. Effects of graded amounts of duodenal infusions of methionine on the mammary uptake of major milk precursors in dairy cows. J. Dairy Sci. 78:2196–2207.[Abstract]

Hof, G., M. D. Vervoorn, P. J. Lenaers, and S. Tamminga. 1997. Milk urea as a tool to monitor the protein nutrition of dairy cows. J. Dairy Sci. 80:3333–3340.[Abstract]

Jurjanz, S., O. Colin-Schoellen, and F. Laurent. 1996. Effect of starch nature of the energy concentrate and of a methionine supply on the rearing performance of dairy cows. Ann. Zoot. 45:467–476.

Keizer, S. E., R. S. Gibson, and D. L. O’Connor. 1995. Postpartum folic acid supplementation of adolescents: Impact on maternal folate and zinc status and milk composition. Am. J. Clin. Nutr. 62:377–384.[Abstract/Free Full Text]

Kirksey, A. 1986. Effects of vitamin supplementation on vitamin levels in human milk: Vitamin B-6, vitamin C and folacin. Pages 339–348 in Human Nutrition 2. Maternal and environmental factors. M. Hamosh and A. S. Goldman, ed. Plenum Press. New York, NY.

Kowalski, Z. M., P. M. Pisulewski, and M. Gorgolu. 2003. Effects of protected methionine and variable energy supply on lactational responses in dairy cows fed grass silage-based diets. J. Anim. Feed Sci. 12:451–464.

Krober, T. F., M. Kreuzer, M. Senn, W. Langhans, and F. Sutter. 2000. Lactational and metabolic effects in cows of lysine and methionine added to a ration deficient according to the INRA method. Arch. Tierernahr. 53:375–394.[Medline]

Le Grusse, J., and B. Watier. 1993. Les vitamines. Données biochimiques, nutritionnelles et cliniques. Centre d’étude et d’information sur les vitamines, Produits Roche. Neuillysur-Seine, France.

Leonardi, C., M. Stevenson, and L. E. Armentano. 2003. Effect of two levels of crude protein and methionine supplementation on performance of dairy cows. J. Dairy Sci. 86:4033–4042.[Abstract/Free Full Text]

Lucock, M. 2000. Folic acid: Nutritional biochemistry, molecular biology, and role in disease processes. Mol. Genet. Metab. 71:121–138.[Medline]

Mackey, A. D., and M. F. Picciano. 1999. Maternal folate status during extended lactation and the effect of supplemental folic acid. Am. J. Clin. Nutr. 69:285–292.[Abstract/Free Full Text]

Malinow, M. R., S. S. Kang, L. M. Taylor, P. W. K. Wong, B. Coull, T. Inahara, D. Mukerjee, G. Sexton, and B. Upson. 1989. Prevalence of hyperhomocyst(e)inemia in patients with peripheral arterial occlusive disease. Circulation 79:1180–1188.[Abstract/Free Full Text]

Manet, L. 1969. Techniques usuelles de biologie clinique. Page 39 in Hématologie. Éditions médicales Flammarion. Paris, France.

Martinov, M. V., V. M. Vitvitsky, E. V., Mosharov, R. Banerjee, and F. I. Ataullakhnov. 2000. A substrate switch: A new mode of regulation in the methionine metabolic pathway. J. Theor. Biol. 204:521–532.[Medline]

Mayer, O., J. Filipovsky, M. Hromadka, V. Svobodova, J. Racek, P. Stehlik, L. Trefil, and M. Zarybnicka. 2002. Treatment of hyperhomocysteinemia with folic acid: Effects on homocysteine levels, coagulation status, and oxidative stress markers. J. Cardiovasc. Pharmacol. 39:851–857.[Medline]

Misciattelli, L., V. F. Kristensen, M. Vestergaard, M. R. Weisbjerg, K. Seirsen, and T. Hvelplund. 2003. Milk production, nutrient utilization and endocrine responses to increased postruminal lysine and methionine supply in dairy cows. J. Dairy Sci. 86:275–286.[Abstract/Free Full Text]

National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th rev. ed. National Academy Press, Washington, DC.

Noftsger, S., and N. R. St-Pierre. 2003. Supplementation of methionine and selection of highly digestible rumen undegradable protein to improve nitrogen efficiency for milk production. J. Dairy Sci. 86:958–969.[Abstract/Free Full Text]

Overton, T. R., D. W. LaCount, T. M. Cicela, and J. H. Clark. 1996. Evaluation of a ruminally protected methionine product for lactating dairy cows. J. Dairy Sci. 79:631–638.[Abstract]

Pacheco-Rios, D., W. C. McNabb, J. P. Hill, T. N. Barry, and D. D. S. Mackenzie. 1997. The effects of methionine supplementation upon milk composition and production of dairy cows in late lactation. Proc. Nutr. Soc. New Zealand. 22:184–191.

Pacheco-Rios, D., W. C. McNabb, J. P. Hill, T. N. Barry, and D. D. S. Mackenzie. 1999. The effects of methionine supplementation upon milk composition and production of forage-fed dairy cows. Can. J. Anim. Sci. 79:235–241.

Pisulewski, P. M., and Z. M. Kowalski. 1999. The effect of protected lysine and methionine on milk yield and its composition in lactating dairy cows fed grass silage-based rations. J. Anim. Feed Sci. 8:341–353.

Pisulewski, P. M., Z. M. Kowalski, and M. Gorgulu. 2002. Lactational responses to ruminally-protected methionine in cows fed a low-protein grass silage based-diet. J. Anim. Feed Sci. 11:189–203.

Reed, M. C., H. F. Nijhout, R. Sparks, and C. M. Ulrich. 2004. A mathematical model of the methionine cycle. J. Theor. Biol. 226:33–43.[Medline]

Robinson, P. H., W. Chalupa, C. J. Sniffen, W. E. Julien, H. Sato, K. Watanebe, T. Fujida, and H. Suzuki. 1998. Ruminally protected lysine and methionine for lactating dairy cows fed a ration designed to meet requirements for microbial and postruminal protein. J. Dairy Sci. 81:1364–1373.[Abstract]

Rulquin, H., and L. Delaby. 1997a. Effects of the energy balance of dairy cows on lactational responses to rumen-protected methionine. J. Dairy Sci. 80:2513–2522.[Abstract]

Rulquin, H., and L. Delaby. 1997b. Lactational responses of grazing dairy cows to rumen-protected methionine. Ann. Zoot. 46:409–415.

SAS Institute. 1999. SAS User’s Guide: Statistics, Version 6 ed. SAS Institute, Inc., Cary, NC.

Selhub, J. 1999. Homocysteine metabolism. Annu. Rev. Nutr. 19:217–246.[Medline]

Shane, B. 1989. Folylpolyglutamate synthesis and role in the regulation of one-carbon metabolism. Vit. Horm. 45:263–335.[Medline]

Shane, B., J. E. Watson, and E. L. R. Stockstad. 1977. Uptake and metabolism of [3H]folate by normal and by vitamin B-12 and methionine-deficient rats. Biochim. Biophys. Acta 497:241–252.[Medline]

Shipley, R. A., and R. E. Clark. 1972. Tracer methods for in vivo kinetics, theory and applications, Academic Press, London, UK.

Snoswell, A. M., and G.-P. Xue. 1987. Methyl group metabolism in sheep. Comp. Biochem. Physiol. 88B:383–394.

Stangl, G. I., F. J. Schwarz, B. Jahn, and M. Kirchgessner. 2000a. Cobalt-deficiency-induced hyperhomocysteinaemia and oxidative status of cattle. Br. J. Nutr. 83:3–6.[Medline]

Stangl, G. I., F. J. Schwarz, H. Müller, and M. Kirchgessner. 2000b. Evaluation of the cobalt requirement of beef cattle based on vitamin B12, folate, homocysteine and methylmalonic acid. Br. J. Nutr. 84:645–653.[Medline]

Tamura, T., Y. Yoshimura, and T. Arakawa. 1980. Human milk folate and folate status in lactating mothers and their infants. Am. J. Clin. Nutr. 33:193–197.[Abstract/Free Full Text]

Tyrrell, H. F., and J. T. Reid. 1965. Prediction of the energy value of cow’s milk. J. Dairy Sci. 48:1215–1223.

Vanhatalo, A., P. Huhtanen, V. Toivonen, and T. Varvikko. 1999. Response of dairy cows fed grass silage diets to abomasal infusions of histidine alone or in combinations with methionine and lysine. J. Dairy Sci. 82:2674–2685.[Abstract]

Xue, G.-P., and A. M. Snoswell. 1985. Regulation of methyl group metabolism in lactating ewes. Biochem. Int. 11:381–385.[Medline]

Younge, B. A., J. J. Murphy, M. Rath, and B. K. Sloan. 2001. Effect of dietary absorbable methionine and lysine concentrations on milk production and composition of dairy cows offered grass-silage based diets. Irish. J. Agric. Food. Res. 40:1–11.


This article has been cited by other articles:


Home page
 J ANIM SCIHome page
F. Simard, F. Guay, C. L. Girard, A. Giguere, J.-P. Laforest, and J. J. Matte
Effects of concentrations of cyanocobalamin in the gestation diet on some criteria of vitamin B12 metabolism in first-parity sows
J Anim Sci, December 1, 2007; 85(12): 3294 - 3302.
[Abstract] [Full Text] [PDF]

Home page
 J DAIRY SCIHome page
B. Graulet, J. J. Matte, A. Desrochers, L. Doepel, M.-F. Palin, and C. L. Girard
Effects of Dietary Supplements of Folic Acid and Vitamin B12 on Metabolism of Dairy Cows in Early Lactation
J Dairy Sci, July 1, 2007; 90(7): 3442 - 3455.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
T. J. Vickers, G. Orsomando, R. D. de la Garza, D. A. Scott, S. O. Kang, A. D. Hanson, and S. M. Beverley
Biochemical and Genetic Analysis of Methylenetetrahydrofolate Reductase in Leishmania Metabolism and Virulence
J. Biol. Chem., December 15, 2006; 281(50): 38150 - 38158.
[Abstract] [Full Text] [PDF]

Home page
 J DAIRY SCIHome page
E. C. Schwab, C. G. Schwab, R. D. Shaver, C. L. Girard, D. E. Putnam, and N. L. Whitehouse
Dietary Forage and Nonfiber Carbohydrate Contents Influence B-Vitamin Intake, Duodenal Flow, and Apparent Ruminal Synthesis in Lactating Dairy Cows
J Dairy Sci, January 1, 2006; 89(1): 174 - 187.
[Abstract] [Full Text] [PDF]

Home page
 J DAIRY SCIHome page
C. L. Girard and J. J. Matte
Effects of Intramuscular Injections of Vitamin B12 on Lactation Performance of Dairy Cows Fed Dietary Supplements of Folic Acid and Rumen-Protected Methionine
J Dairy Sci, February 1, 2005; 88(2): 671 - 676.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Girard, C. L.
Right arrow Articles by Lobley, G. E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Girard, C. L.
Right arrow Articles by Lobley, G. E.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH