Biomedical subjects

H Lapierre

Publications and source records attributed to H Lapierre.

At least 19 recordsLinked to original sources

PubMed2007

Effect of protein supply on hepatic synthesis of plasma and constitutive proteins in lactating dairy cows.

The effects of metabolizable protein (MP) supply on the synthesis of plasma total proteins and albumin, as well as total hepatic protein synthesis, were determined in 6 multicatheterized lactating Holstein cows. Three TMR formulated to supply the same amount of energy but different amounts of MP, 1,922 (low), 2,264 (medium), and 2,517 g of MP/d (high), were fed every 2 h according to a double 3 x 3 Latin square design. For the low and high MP treatments, the cows were continuously infused with [(2)H(5)]Phe (d5-Phe) into a jugular vein for 8 h (1.3 mmol/h) on d 21 of each period. Concentration and isotopic enrichment of d5-Phe were measured for free plasma Phe, plasma total proteins, and albumin on hourly samples collected between 3 and 8 h. Low MP decreased the plasma albumin concentration (32.3 vs. 33.7 +/- 0.11 g/L) but the plasma total protein concentration was unchanged (74.1 vs. 75.6 +/- 1.13 g/L). Incorporation of d5-Phe over time into both plasma total proteins and albumin was linear (R(2) > 0.98). Neither fractional nor absolute synthesis rates of plasma total proteins (6.8 vs. 6.5 +/- 0.65%/d; 168 vs. 154 +/- 19.9 g/d) or albumin (3.4 vs. 3.4 +/- 0.10%/d; 36.3 vs. 36.5 +/- 1.11 g/d) were affected by the MP supply. Net hepatic removal of Phe was lower with the low-MP diet (-12.3 vs. -20.2 +/- 1.98 mmol/h). As a result, net hepatic Phe removal used for total export protein synthesis (17.9 vs. 11.1 +/- 1.83%) and albumin synthesis (4.6 vs. 2.9 +/- 0.54%) tended to be greater at low MP. These results suggest that hepatic synthesis of plasma proteins, including albumin, is maintained in lactating dairy cows even when the protein supply is reduced.

Animal Nutritional Physiological Phenomena↗

PubMed2006

Milk from forage as affected by carbohydrate source and degradability with alfalfa silage-based diets.

Milk from forage (MF) is an estimation of the milk produced solely from forage intake. It is calculated by subtracting milk production theoretically allowed by concentrates from total milk production, assuming that maintenance requirements are covered by the forage portion of the diet. Eight multiparous Holstein cows in early lactation were used in a replicated 4 x 4 Latin square design to evaluate the impact on MF of different sources of carbohydrate with forage that was high in RDP. Diets were alfalfa-based total mixed rations that were formulated to provide similar concentrations of NEL and CP while differing in rumen degradability of concentrate carbohydrates. Treatments were 1) cracked corn (control), 2) ground corn (GC), 3) GC plus wheat starch (GC+S), and 4) GC plus dried whey permeate (GC+W). The GC and the GC+S treatments increased MF as calculated on a protein basis (14.8 vs. 10.5 kg) and increased average MF production (8.6 vs. 5.5 kg) compared with the control. Protein of forage was used more efficiently with GC and with GC+S, as shown by the lower differences between allowable MF, which estimates the potential for milk production from forage, and MF on a protein basis for these 2 treatments when compared with the control. Compared with the control, DMI increased with GC and GC+S; GC+W yielded the highest DMI. Milk production with GC+W (35.8 kg/d) was lower than with GC and GC+S (37.5 kg/d) but was higher than the control (34.0 kg/d). Milk fat concentration was higher with GC+W and lower with GC+S; GC and the control had intermediate values. Milk urea was higher with the control diet compared with the other 3 treatments. Results emphasize the advantage of using concentrates of higher degradability in the rumen to improve MF and milk production when feeding silage with high rumen-degradable protein.

Ammonia↗

PubMed2006

Effect of ruminally protected methionine on splanchnic metabolism of amino acids in lactating dairy cows.

The effect of ruminally protected Met (RPM) on splanchnic metabolism was measured in 3 primiparous and 3 multiparous Holstein cows. Doses of RPM (0, 36, and 72 g/d) were tested in a replicated 3 x 3 Latin square design, over 3 consecutive 14-d experimental periods. A mixed ration was fed in 12 equal meals per d (average dry matter intake: 17.5 +/- 0.08 kg/d). Indwelling catheters were surgically implanted in the mesenteric artery and the portal and hepatic veins for blood collection, as well as in 2 distal branches of the mesenteric vein for infusion of p-aminohippurate to determine blood flow. On d 14 of each period, a temporary catheter was inserted into a mammary vein and 6 hourly blood samples were collected to determine plasma concentrations of metabolites, hormones, and their respective fluxes across the splanchnic bed and mammary glands. Yields of milk (32.8, 32.0, and 32.9 +/- 0.92 kg/d) and protein (1,028, 1,053, and 1,075 +/- 28.7 g/d) were unaffected by level of RPM. However, the true protein content in milk from primiparous cows increased linearly (2.92, 3.09, and 3.34 +/- 0.077%). The addition of RPM linearly increased the net flux of Met across the portal-drained viscera, which resulted in increased arterial Met concentrations (25, 29, and 40 +/- 1.1 microM). Although it had no significant effect on net portal and hepatic fluxes of other essential amino acids, RPM resulted in a linear increase in the total splanchnic output of Ile, Leu, Phe, and Thr. These results suggest that feeding RPM triggered a homeostatic response resulting in less utilization of certain essential amino acids through the gastrointestinal tract and liver. Net mammary uptake of Met did not change with the addition of RPM. However, mammary extraction of Met decreased in a linear fashion in response to increased arterial inflow.

Amino Acids↗

PubMed2006

What is the true supply of amino acids for a dairy cow?

Improving the prediction of milk protein yield relies on knowledge of both protein supply and requirement. Definition of protein/amino acid supply in ruminants is a challenging task, due to feedstuff variety and variability and to the remodeling of nutrient intake by the rumen microflora. The questions arise, therefore, how and where should we measure the real supply of AA in the dairy cow? This review will follow the downstream flow of AA from duodenum to peripheral tissue delivery, with a glance at the efficiency of transfer into milk protein. Duodenal AA flow comprises rumen undegradable feed, microbial protein, and endogenous secretions. Most attention has been directed toward definition of the first two contributions but the latter fraction can represent as much as 20% of duodenal flow. More information is needed on what factors affect its magnitude and overall impact. Once digested, AA are absorbed into the portal vein. The ratio of portal absorption to small intestinal apparent digestion varies among essential AA, from 0.43 (threonine) to 0.76 (phenylalanine), due to the contributions of preduodenal endogenous secretions to the digestive flow, non-reabsorption of endogenous secretions and gut oxidation of AA. Few data are available on these phenomena in dairy cows but the evidence indicates that they alter the profile of AA available for anabolic purposes. Recent comparisons of estimated duodenal flux and measured portal flux have prompted a revisit of the NRC (2001) approach to estimate AA flows at the duodenum. Changes to the model are proposed that yield predictions that better fit the current knowledge of AA metabolism across the gut. After absorption, AA flow first to the liver where substantial and differential net removal occurs, varying from zero for the branched-chain AA to 50% of portal absorption for phenylalanine. This process alters the pattern of net supply to the mammary gland. Overall, intermediary metabolism of AA between the duodenum and the mammary gland biologically explains the decreased efficiency of the transfer of absorbed AA into milk protein as maximal yield is approached. Therefore, variable, rather than fixed, factors for transfer efficiencies must be incorporated into future predictive models.

Absorption↗

PubMed2006

Effect of casein and propionate supply on mammary protein metabolism in lactating dairy cows.

The effects of casein (CN) and propionate (C3) on mammary AA metabolism were determined in 3 multiparous Holstein cows fitted with both duodenal and ruminal cannulas and used in a replicated Youden square with six 14-d periods. Casein (743 g/d in the duodenum) and C3 (1,041 g/d in the rumen) infusions were tested in a factorial arrangement. For each period, L-[1-(13)C]Leu (d 11) and NaH[13C]O3 (d 13) were infused into a jugular vein, and blood samples were taken from the carotid artery and the mammary vein to determine Leu kinetics and net uptake of AA. Both CN and C3 treatments separately increased milk protein concentration and yield. With CN there was a general response in mammary protein metabolism, involving increases in Leu net uptake (30%), the uptake:output ratio (8%), protein synthesis (11%), secretion in milk protein (21%), and oxidation (259%). In contrast, C3 treatments tended to increase only Leu in milk protein (7%) and, when in combination with CN, to reduce Leu used for protein synthesis (5%). Across all treatments, most Leu uptake by the mammary gland was accounted for as Leu in milk or oxidized, and the Leu balance was therefore achieved without involvement of either net peptide use or production. Mammary uptake of group 1 AA increased to match milk output with all infusions. In contrast, mammary uptake of group 2 AA exceeded output to a greater extent with CN than with C3 infusions, whereas the increment in uptake of group 3 AA increased with C3 treatments. Overall, these data suggest that different mechanisms operate to improve milk protein production when either protein or energy is supplied.

Amino Acids↗

PubMed2006

Comparison of net portal absorption with predicted flow of digestible amino acids: scope for improving current models?

This study was undertaken to determine the relationship between measured net portal absorptions (NPA) and flows of digestible essential amino acids (EAA) predicted with the National Research Council model (NRC, 2001) or the Cornell Net Carbohydrate and Protein System model (CNCPS, version 5.0.34). Net portal absorption data were obtained from 33 measurements of portal-arterial plasma EAA concentration differences among 8 treatments in lactating dairy cows, with plasma flow estimated from downstream dilution of para amino-hippurate. The predicted digestible flows from NRC (2001) related better than CNCPS to NPA observed in our studies, as shown by the lower standard errors on the slopes for all EAA and lower root mean prediction errors for all EAA except Met and Phe. However, the partitioning of the prediction error indicated a systematic underprediction (mean bias) for the NRC model (2001), with the exception of Ile. It is important to note that a relationship of unity was not expected, as discussed in the paper, because of losses of EAA through portal-drained viscera metabolism. A revised set of predictive equations for digestible EAA was obtained using a subset of data from NRC (2001) limited to trials conducted with dairy cows. This increased the predicted flows of digestible EAA by only 2%. Flows of digestible EAA were also estimated using a factorial approach, assuming an AA composition for each fraction of the duodenal flow estimated by NRC (undegradable, microbial, and endogenous proteins). This resulted in a slight improvement in the slope of the regression between predicted flows and measured NPA, but still yielded predicted digestive flows that were too low to support observed NPA. Finally, on the basis of literature values, increment of the digestibility of the undegradable fraction of forages and of microbial protein is suggested to improve the relationship between predicted digestible flows and NPA. Overall, this study indirectly confirms, across EAA, smaller losses through gut metabolism for His, Met, and Lys, intermediate losses for the branched-chain AA with the higher losses for Thr.

Amino Acids, Essential↗

PubMed2006

Effect of postruminal glutamine supplementation on immune response and milk production in dairy cows.

Seventeen multiparous Holstein cows were used to examine the effect of an increased duodenal supply of Gln on immune function and production. Cows received continuous abomasal infusions of water (control: n = 8) or 300 g/d of Gln (n = 9) for 21 d starting within 48 h of calving. There were nonsignificant increases in milk and milk protein yields in response to Gln supplementation. Glutamine treatment had no effect on plasma glucose, nonesterified fatty acids (NEFA), or beta-hydroxybutyrate (BHBA) concentrations but did tend to increase plasma urea N concentration. The Gln treatment resulted in an increase of 108 microM in the plasma Gln concentration. Total essential AA concentrations decreased with the Gln treatment, whereas total nonessential AA concentrations were unaffected. T Lymphocyte proliferation did not differ between the control and Gln-treated cows. Treatment had no effect on the relative abundance of CD8 T cells but did increase the abundance of CD4 T cells. Cytokine production, as measured by IFN-gamma concentration determined in vitro in concanavalin-A-stimulated peripheral blood mononuclear cells, was similar between the treatments. Over the first 3 wk following calving, Gln supplementation had limited effects on milk production, metabolic parameters, and immune function.

3-Hydroxybutyric Acid↗

PubMed2005

Effects of dietary supplements of folic acid and rumen-protected methionine on lactational performance and folate metabolism of dairy cows.

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 B(12) 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 B(12) and methionine, and the slow serum clearance of folates strongly suggest that the vitamin B(12) supply was inadequate and interfered with folate use. It could explain the limited lactational response to supplementary folic acid observed in the present experiment.

Animals↗

PubMed2004

Milk protein synthesis as a function of amino acid supply.

Most prediction schemes of milk protein secretion overestimate milk protein yield from dairy cows at high protein intakes, thereby overestimating milk protein yield response to protein supplementation. This study was conducted to determine factors contributing to such an overestimation. Using published studies, a database was constructed that was limited to amino acid (AA) infusion studies, as then only the digestible amino acid of dietary origin needed to be estimated, whereas the amount infused was known exactly, thereby reducing the dependence on estimated values. Although milk protein yield was positively related with total energy supply, and both digestible duodenal supply and infused AA, in this database there was no relationship between milk protein yield response above control treatments and the nutrient status of the cows (energy or protein). Total milk protein yield was defined as a function of individual AA supply, using a segmented-linear and a logistic model to obtain estimates of the efficiency of conversion of AA into milk protein. Except for Lys and Met supply, the segmented-linear model yielded lower root mean square error and better correlation, but both models were similar in their reliability. For both models, the estimated efficiency of conversion of AA to milk differed among AA. Estimations of the ideal profile of AA for lactating dairy cows were similar between models, with requirements for Lys and Met in line with 2001 National Research Council recommendations. The major difference is that the segmented-linear model yields a constant efficiency of conversion of an AA until requirements are met, with zero efficiency beyond this point. The logistic model allows for an estimation of the decreasing marginal efficiency of conversion of AA as the supply approaches the requirements. The use of variable efficiency factors should improve our ability to predict protein yield in response to supplemental protein.

Amino Acids↗

PubMed2004

Effect of level of metabolizable protein on splanchnic flux of amino acids in lactating dairy cows.

The response of splanchnic tissue metabolism to different levels of metabolizable protein (MP) was measured in 6 catheterized multiparous lactating Holstein cows. Three diets, balanced to provide similar energy intakes and increasing amounts of MP (g/d)-1922 (low), 2264 (medium), and 2517 (high)-were fed during 21-d experimental periods according to a replicated Latin square. On d 18, 19, or 20, six hourly blood samples were collected simultaneously from the portal and hepatic veins plus an artery to determine net fluxes of nutrients across the portal-drained viscera and the liver. Yields of milk and protein increased, as did urinary N excretion with increasing MP. Portal absorption of essential amino acids (EAA) increased linearly with increasing MP supply, as did liver removal of His, Met, and Phe. In contrast, liver removal of the branched-chain AA (BCAA) and lysine was unaffected by diets. With increasing MP, the ratio of milk output to postliver supply of BCAA, Thr, and Lys decreased linearly, indicating oxidation of these AA in the peripheral tissues. Concomitant to a decreased catabolism of EAA in the liver (His, Met, Phe, and Thr) and/or in peripheral tissues (BCAA, Lys, and Thr), the efficiency of transfer of absorbed EAA into milk protein decreases markedly as protein supply increases. The efficiency of transfer of absorbed AA into milk also varies greatly between AA. These 2 important factors should be taken into account when building predictive schemes for milk protein output.

Amino Acids↗

PubMed2003

Effects of corn silage processing and amino acid supplementation on the performance of lactating dairy cows.

This experiment was conducted to determine the effect of crop processing and amino acid supplementation on dairy cow performance. Corn silage processed (PCS) or unprocessed (UCS) was used as the main forage (45% of dry matter, DM) in a total mixed ration (TMR). Each TMR was either supplemented (AA) or not (AAO) with ruminally protected amino acids (lysine, 3 g/d and methionine, 14 g/d). Thirty-two (551 kg) Holstein cows were randomly assigned to four treatments: PCS-AA, PCS-AA0, UCS-AA, and UCS-AA0 in a 2 x 2 factorial structure. Between wk 7 and 17 of lactation, cows were fed ad libitum TMR comprising 45% of corn silage plus 1 kg of grass hay once a day. The UCS presented better fermentation characteristics than PCS. Dry matter intake (DMI) of the TMR was not affected by treatment and averaged 22.7 kg/d. Energy-corrected milk (ECM) production was 9% higher with UCS than with PCS (33.1 vs. 30.1 kg/d). Milk efficiency was therefore 6% higher with UCS than with PCS (1.43 vs. 1.35 kg ECM/kg of DMI). The concentration of major milk constituents (fat, protein, lactose, urea) was not affected by treatments. Apparent digestibility of DM, organic matter, N, starch, acid detergent fiber, and neutral detergent fiber were similar among treatments. The effective ruminal degradability of DM, starch, and protein, however, was greater with PCS than with UCS. Amino acid supplementation had no effect on milk production nor on milk constituents, whether it was used with processed corn silage or with unprocessed corn silage. These data indicate that feeding UCS resulted in a greater milk production compared with PCS. The numerically higher DMI, a potentially greater intestinal digestion of starch or the better conservation of UCS could have contributed to the greater milk production.

Amino Acids↗

PubMed2002

Variations in mammary metabolism during the natural filling of the udder with milk over a 12-h period between two milkings.

Two groups of four Holstein cows, one in their second and the other in their third or fourth lactation, were used to study temporal variations of mammary metabolism over a 12-h period between two milkings. Blood samples were collected every 30 min from an artery and a mammary vein during a 12-h interval between two milkings. Isoleucine, leucine, lysine, methionine, and phenylalanine mammary net fluxes varied or tended to change over time after milking with a similar pattern between whole blood and plasma. For these amino acids, whole blood and plasma net fluxes reached their maximum over the first 8 h after milking. Simultaneously, respiratory quotients decreased linearly and varied from 2.31 to 2.01 during the first 8 h of the period, suggesting active mammary lipogenesis. From 8 to 12 h after milking, mammary amino acid net fluxes decreased, while mammary oxygen uptake tended to increase with a concomitant decrease in the respiratory quotient reaching 1.84 to 1.40. These findings suggest that, beginning 8 h after milking, mammary uptake of amino acids starts to decrease and catabolic processes appear promoted; this phenomenon could help to explain the increase in milk production reported in the literature with increased milking frequency.

Amino Acids, Essential↗

PubMed2002

Peripartum performance and metabolism of dairy cows in response to prepartum energy and protein intake.

Twenty-six multiparous Holstein cows were used to examine the effects of prepartum energy and protein intake on periparturient metabolism and lactation performance. Two levels of energy, 1.65 Mcal/kg of net energy for lactation (NEL) and 1.30 Mcal/kg of NEL, and two levels of protein, 17.0% CP and 12.5% CP, were tested according to a factorial arrangement in a randomized block design. Dietary treatments were fed ad libitum from 21 d before expected calving date to the day of calving. After calving, all cows were fed the same diet. Increased nutrient density did not affect prepartum feed intake, but postpartum intake was higher for cows fed the high-energy diets. Treatment had no effect on cow body weight and body condition score, however, cows fed the high-energy diets were in greater energy balance throughout the study. Milk and milk component yields were unaffected by treatment. Cows fed the high-energy diets had lower plasma nonesterified fatty acid concentrations than cows fed the low energy diets (354.3 vs. 439.9 mumol/L). Hepatic triglyceride concentrations were lower for cows on the high-energy diets than for those on the low-energy diets. Liver glycogen was unaffected by treatment. Acetyl-CoA carboxylase and fatty acid synthase abundance was significantly lower at calving than pretreatment, and higher for cows on the high-energy diets relative to those on the low-energy diets. The activity of acetyl-CoA carboxylase and lipoprotein lipase was greatly decreased with the onset of lactation. Increased protein intake prepartum resulted in elevated plasma beta-hydroxybutyrate concentrations postpartum. Prepartum plasma urea nitrogen was increased and 3-methylhistidine decreased by the high protein treatments. Overall, increased energy density of prepartum diets had beneficial effects on feed intake and lipid metabolism but did not improve lactation performance. Increasing the protein content of the prepartum diet did not appear to confer any advantages to cow productivity.

3-Hydroxybutyric Acid↗

PubMed2002

Effect of supply of metabolizable protein on splanchnic fluxes of nutrients and hormones in lactating dairy cows.

The effect of the supply of metabolizable protein on splanchnic fluxes of nutrients and hormones was measured in six catheterized late-lactation Holstein cows in a crossover design. Two isonitrogenous diets (16.3% CP), but differing in rumen protein degradability and estimated metabolizable protein (MP) supply (1654 g/ d, Lo-MP; 1930 g/d, Hi-MP) were fed, each over a 35-d experimental period. On d 34 or 35, net fluxes of nutrients and hormones across the portal-drained viscera, the liver, and total splanchnic tissues were determined. Portal absorption of total, essential, nonessential, and branched-chain amino acids (AA) increased with the Hi-MP diet. Approximately 76% of the additional metabolizable protein supply was recovered as extra AA-N absorption in the portal vein. Liver removal of AA was not different between diets, and this resulted in a greater net release across the splanchnic tissues for the Hi-MP diet. This extra AA supply provided substrates for the observed increased milk protein yield for the Hi-MP diet. Fractional efficiencies of conversion of absorbed individual essential AA into milk protein ranged from 0.42 to 0.68. The corresponding efficiencies for utilization of postsplanchnic AA supply were 0.42 to 1.80. Provision of methionine, phenylalanine, and histidine beyond the liver were similar to outputs in milk protein but the other essential AA were supplied to peripheral tissues in excess of milk output, indicative of oxidative mechanisms in nonhepatic tissues. Net fluxes of glucose, NH3-N, and urea were not affected by the diets. Neither arterial concentrations of insulin, somatotropin, or IGF-1, nor net transfers across the portal-drained viscera or liver of insulin, were affected by the diets. Although portal release of glucagon was not different between the diets, a smaller proportion was removed by the liver on the Hi-MP diet. Metabolism of AA across the splanchnic tissue bed is a major determinant of the quantity and the profile of AA delivered to peripheral tissues.

Amino Acids↗

PubMed2002

Effect of supply of metabolizable protein on whole body and splanchnic leucine metabolism in lactating dairy cows.

The effect of the supply of metabolizable protein (MP) on protein metabolism across the splanchnic tissues was determined in six catheterized lactating Holstein cows. In a crossover design, two isonitrogenous (16.3% CP) diets balanced to provide a low (Lo-MP) or high (Hi-MP) supply of MP were fed over 35-d periods. After 24 d of feeding, N balance was determined over a 6-d period. On d 33, [13C] sodium bicarbonate was infused into one jugular vein for 6 h, and hourly breath samples were collected. On d 34 or 35, L[1-(13)C] leucine was infused into one jugular vein, and between 2 to 6 h of infusion, breath and blood samples were taken hourly from the portal and hepatic veins and an artery. Isotopic enrichments of plasma leucine, 4-methyl-2-oxopentanoate, and expired CO2 were determined for calculation of leucine kinetics. Net leucine absorption was greater, either on a direct basis (leucine transfer only) or corrected for portal-drained viscera metabolism to 4-methyl-2-oxopentanoate and CO2 for the Hi-MP diet. There were no effects of diet on hepatic net flux of leucine across the liver, and, thus, more leucine was available to peripheral tissues with the Hi-MP diet. Combined with an increment in portal absorption of most of essential AA, this led to increased milk protein output, although it only represented 16% of the additional available leucine. Whole body leucine oxidation was also greater for the Hi-MP diet, as was leucine used for protein synthesis. Despite these changes, MP supply did not affect irreversible loss rate of leucine by portal-drained viscera and the liver; these averaged 35 and 20% of whole body irreversible loss rate, respectively. These ratios confirm the high metabolic activity of splanchnic tissues in lactating dairy cows, which are even greater than previously reported in growing ruminants.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Effect of dietary fiber on endogenous nitrogen flows in lactating dairy cows.

The effect of dietary fiber on endogenous N secretion was studied using a 15N isotope dilution technique in four fistulated Holstein cows. Two isonitrogenous diets differing only in fiber (NDF and ADF) content were used in a crossover design. One diet (HF) contained 37.4% NDF, while the other (LF) contained 23.3%. A new model was developed to estimate endogenous N secretions and losses for the preintestinal, intestinal, and the total sections of the gastrointestinal tract. Three precursor pools: TCA-soluble fraction of plasma, intestinal mucosa, and milk were compared. Although endogenous losses estimated with the model were numerically different for each precursor pool selected (TCA-soluble fraction > mucosa > milk), treatment effects were similar. As intestinal mucosa is probably closest to the precursor pool, these data are discussed. Non-urea N endogenous secretions contributed 13% of the duodenal N flow but were not affected by the fiber content of the diet. The nonurea N endogenous flow at the duodenum was comprised of approximately equal inputs from endogenous N direct, and that incorporated into the microbial biomass. Total endogenous N flows at the duodenum exceeded, by nearly twofold, estimated inputs of urea-N to microbial biomass. Metabolic fecal output averaged 17% of fecal N and was not affected by level of dietary fiber, but net losses from secretions occurring in the small intestine were higher with the low fiber diet. Overall, endogenous N secretions represented 30% of total digestive tract protein synthesis.

Animals↗

PubMed2001

Net flux of folates and vitamin B12 through the gastrointestinal tract and the liver of lactating dairy cows.

In study 1, four cows had a ruminal canula, a catheter in the right ruminal vein and an ultrasonic flow probe around the right ruminal artery; a catheter was placed in the auricular artery on experimental days. Blood samples were taken every 10 min from -20 to 60 min after ruminal infusion of 5.79 mmol pteroylmonoglutamic acid and cyanocobalamin. There was a net release of these vitamins across the rumen wall following the infusion (P=0.06). In studies 2 and 3, four cows had catheters in the portal, one hepatic and two mesenteric veins and one mesenteric artery. Plasma flow was determined using p-aminohippurate. In study 2, blood samples were taken before and every 30 min for 6 h after feeding 0 or 4 mg of pteroylmonoglutamic acid. Flow of folates through the portal-drained viscera (PDV) and the total splanchnic tissues (TSP) tended to increase with the ingestion of pteroylmonoglutamic acid (P=0.19). In study 3, blood samples were collected every 30 min for the first 3 h to calculate plasma flow and basal net fluxes of folates and vitamin B12. The cows were fed 2.6 g pteroylmonoglutamic acid and 500 mg cyanocobalamin; blood samples were taken every 2 h for 24 h. Vitamin supplements increased the net release of folates and vitamin B12 from PDV (P=0.04) and TSP (P=0.13). The present results demonstrate that, in dairy cows, at doses reported to improve animal performance, passage of pteroylmonoglutamic acid to the portal blood appears during the 6 h following its ingestion, whereas for cyanocobalamin, it is a slow process, not yet completed 24 h after its ingestion.

Animal Nutritional Physiological Phenomena↗

PubMed2001

Intestinal disappearance and mesenteric and portal appearance of amino acids in dairy cows fed ruminally protected methionine.

An experiment was conducted to compare the rates of disappearance of amino acids (AA) from the small intestine and their net appearance in the blood draining only the small intestine (mesenteric-drained viscera) and the whole gastrointestinal tract (portal-drained viscera) of cows fed a silage-based diet supplemented or not with ruminally protected Met. Five lactating dairy cows (118+/-4 DIM) equipped with duodenal and ileal cannulae (n = 2) or a duodenal cannula only (n = 3), two of which were multicatheterized, were fed a TMR top dressed with 0 or 72 g of ruminally protected Met per day. The addition of ruminally protected Met to the diet increased the duodenal flux of Met leading to a higher apparent digestibility of Met in the small intestine. Sixty-six percent of Met from ruminally protected Met bypassed the rumen and 82% of that Met disappeared from the small intestine. Arterial plasma Met concentrations numerically increased with ruminally protected Met (45 vs. 18 microM), while total AA concentration decreased. Feeding ruminally protected Met resulted in higher concentrations of urea-N and glucose in arterial plasma. Milk production and milk composition were unaffected. The disappearance of essential AA across the small intestine was equivalent (101%) to their flux through the mesenteric-drained viscera while the portal:mesenteric-drained viscera flux ratio for each essential AA varied from 38% for Thr to 76% for Phe. The portal:mesenteric-drained viscera flux ratio for Met was 66%. These results confirm observations made with pigs and sheep.

Amino Acids↗