Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation

The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mumol/min) into the mesenteric vein were determined. Neither blood flow nor O2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mumol/min per mumol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.     

Protein requirements of growing steers limit-fed corn-based diets

In Exp. 1, six steers (254 kg) were used in a 6 x 4 incomplete Latin square to determine the effects of solvent-extracted soybean meal alone or in combination with rumen-protected methionine and lysine on N balance in steers limit-fed a high-corn diet to gain 1.1 kg/d. The basal diet contained (DM basis) 80% rolled corn, 15% alfalfa, and .9% urea (13.9% CP), and 2 or 4% soybean meal replaced corn to give CP concentrations of 14.8 and 15.6%, respectively. Each diet was fed with and without 5 g/d of Smartamine-ML (.75 and 2.0 g of rumen-protected methionine and lysine, respectively). Nitrogen retention increased linearly (P = .09) with level of soybean meal. Rumen-protected methionine and lysine had no effect on N balance. In Exp. 2, seven steers (233 kg) were used in a 7 x 4 incomplete Latin square experiment to investigate optimal levels and sources of CP for steers limit-fed to gain 1 kg/d. Treatments included a negative-control diet (urea; 11.7% CP) and six diets containing either 13.5, 15.4, or 17.2% CP with either solvent-extracted or expeller-processed soybean meal. Diets provided 75, 87.5, 100, or 112.5% of estimated CP requirement for a gain of 1 kg/d. The basal diet contained 83% rolled corn, 15% alfalfa, and .2% urea. Nitrogen retention increased linearly (P = .006) with soybean meal addition, and no differences were observed between CP sources. The CP system underpredicted the protein requirements of limit-fed steers under our conditions.     

A primate model for enteral nutrition by tube

To establish an animal model for the controlled study of enteral nutrition by tube, five adult chair-adapted primates (Macaca fasicularis) had gastrostomy and jejunostomy tubes placed for the delivery of a modified protein isolate diet. Following 7 days of postoperative depletion with a hypocaloric infusion of dextrose (20 kcal, 0 g N/kg/day), the animals were repleted for 10 days with tube feedings (124 kcal, 0.73 g N/kg/day). There was no operative mortality or morbidity and each animal demonstrated conversion to anabolism by significant weight gain, positive nitrogen balance, and net protein synthesis as determined by [15N]glycine protein turnover rates. Significant correlation was found between caloric intake and nitrogen balance at the level of nitrogen provided in this diet (r = 0.88, p less than 0.05). This model was found to be well suited for the surgical and nutritional techniques required for the long-term study of enteral nutrition by tube.     

Infusion of soy and casein protein meals affects interorgan amino acid metabolism and urea kinetics differently in pigs

For routine evaluation of the quality of dietary protein, amino acid scoring patterns were used. Evaluation of this pattern for soy and casein revealed that these proteins are of almost equal quality. However, in vivo studies showed a large difference. To study the biological effects of meals with casein and soy protein, the contributions of individual amino acids to net protein retention and amino acid kinetics in gut, liver and muscle in healthy pigs were investigated. Isonitrogenous enteral nutrition, infused at a rate of 10 mL. kg body wt-1. h-1 and consisting of maltodextrin (137 g/L) with added casein (53 g/L) or soy protein (68 g/L), was given to conscious, healthy female multicathetized pigs (20-22 kg, n = 12). A primed-constant infusion protocol with L-[ring-2,6-3H]phenylalanine, L-[3,4-3H]valine and [15N-15N]urea was used to measure amino acid and urea kinetics in gut, liver and muscle. Measurements were done postabsorptively and 2-6 h after initiation of the enteral nutrition. During the meal, appearance of amino acids into the portal vein and the uptake by the liver was lower with casein infusion. Muscle uptake did not differ. Gut protein synthesis tended to be lower with soy infusion (P = 0.1). Liver protein synthesis and degradation were higher with casein infusion (P < 0.05), while in muscle, soy infusion stimulated protein turnover (P < 0.05). In comparison to the postabsorptive condition, liver urea production was unchanged after casein infusion, while it was significantly increased after soy infusion. These results suggest that the quality of soy protein is inferior to that of casein protein.     

Effects of a dietary mixture of meat and bone meal, feather meal, blood meal, and fish meal on nitrogen utilization in finishing Holstein steers

Our objective was to determine to what extent rate and efficiency of protein gain in finishing cattle can be enhanced by feeding an amino acid-balanced mixture of undegraded intake proteins. The Cornell Net Carbohydrate and Protein System (CNCPS) model was used to formulate a corn-based diet that would meet the rumen requirements for 410-kg large-framed steers with an estrogen implant and fed an ionophore. The CNCPS model was also used to formulate a highly undegradable intake protein (UIP) mixture from meat and bone meal, blood meal, fish meal, and hydrolyzed feather meal to provide the amino acids needed to supplement those derived from microbial protein to better meet amino acid requirements for growth. Four Holstein steers weighing 407 kg were offered a 90:10 concentrate-forage diet at hourly intervals at 95% of ad libitum intake. The steers were injected with 500 microg of estradiol-17beta at 12-h intervals to mimic the effects of an estrogenic implant. Treatments planned consisted of inclusion of the UIP mixture at 0, 2.5, 5, and 7.5% of the diet DM. Dry matter intake was fixed at 6.4 kg/d, and DM digestibility was not significantly affected by varying the amount of UIP addition. Apparent digestibility of N increased (P = .011) from 63.8 to 65.8, 70.7, and 71.5%, the amount of N absorbed increased (P = .001) from 73 to 84, 100, and 106 g/d, and N balance increased (P = .003) from 20 to 30, 33, and 39 g/d when UIP was fed at 0, 2.6, 5.2, and 7.8% of diet DM, respectively. The efficiency of N use increased 39.7%, and biological value increased 31.6% when the UIP mixture was added to the diet. Circulating concentrations of plasma urea N (PUN) were increased (P = .017) from 4.5 for the control diet to 5.7, 6.2, and 6.1 mg/dL when the UIP mixture was added at 2.6, 5.2, and 7.8%, respectively. Corresponding IGF-I concentrations were also increased from 491 to 558 and 624 ng/mL with 2.6 and 5.2% levels of UIP addition. Plasma glucose, NEFA, and insulin concentrations were not affected by feeding the UIP mix. The rate and efficiency of N use for growth improved with addition of an amino acid-balanced UIP mixture to the diet.     

The professional identity of the nurse: concept analysis and development

Urea kinetics were measured in normal women after 5 d consuming a low protein diet [LP, 67 mg N/(kg.d), 0.42 g protein/(kg.d)]. To determine whether the availability of methionine limits the utilization of nonessential nitrogen from low protein diets, the study was repeated on four further occasions with the addition of dietary supplements of L-methionine, 9 mg N/(kg.d) (LP-M); urea, 52 mg N/(kg.d) (LP-U); urea and methionine (LP-UM); or urea, 26 mg N/(kg.d), and glycine, 26 mg N/(kg.d), (LP-UG). Urea kinetics were derived after prime and intermittent oral doses of [15N15N]urea from the measurements of enrichment by isotope ratio mass spectrometry in urea isolated from urine. Nitrogen balance was significantly improved when the women consumed LP-U and LP-UG, but not LP-M or LP-UM. The urinary excretion of 5-L-oxoproline was measured as a marker of glycine availability and was significantly lower when women consumed LP-U and LP-UG compared with either LP or LP-M and LP-UM. There was a significant correlation between urinary 5-L-oxoproline and urinary sulfate excretion (r = 0.68, P = 0.00003). The availability of methionine was not limiting for nitrogen metabolism when women consumed these diets, whereas the response to supplementation with urea alone or urea with glycine showed that the availability of nonessential nitrogen was limiting. Glycine is consumed in the detoxification of excess methionine, and supplementation with methionine appeared to place a competitive demand on the availability of glycine for other metabolic processes.     

Cottonseed meal or feather meal supplementation of ammoniated tropical grass hay for yearling cattle

Despite high N intake by cattle consuming ammoniated forages, improvements in ADG might be expected be feeding proteins that supply ruminally available and(or) undegraded intake protein. Growth studies with 220-kg steers were conducted to evaluate ammoniated hay plus a liquid cane molasses-based supplement containing urea or a combination of urea and .07, .14, or .21 kg of CP daily from cottonseed meal (CSM) or feather meal (FM). Steers grazed dormant pasture and were fed hay plus 1.36 kg of DM daily per steer of the supplement. In each of 3 yr, total DM intake was similar (P > .60) among treatments, averaging 3.0% of BW. Daily gain by steers supplemented with urea and maximum ADG were similar across years, ranging from .21 to .23 kg and .50 to .60 kg, respectively. In all years for CSM supplementation, and in two of the three years for FM supplementation, increasing level of CP supplementation resulted in linear (P < .01) increases in ADG and gain:feed ratio (GF), with no differences (P > .10) between the protein sources. In one year, ADG and GF by steers supplemented with FM were maximized at the .07 kg of CP level, suggesting greater efficiency of protein utilization in FM. Improved performance by cattle fed ammoniated tropical grass hay may be obtained by feeding a protein supplement that provides preformed protein that is either moderately or highly resistant to ruminal degradation. Ruminal degradation characteristics of protein sources may influence efficiency of protein utilization in cattle fed ammoniated tropical grass hay plus molasses-based supplements.     

Effect of dietary corn starch intake on ruminal, small intestinal and large intestinal starch digestion in cattle

In Exp. 1, 24 yearling Holstein steers averaging 340 kg were fed either an alfalfa hay diet at a maintenance level of metabolizable energy (ME) intake or corn silage-corn diets at one, two or three times maintenance ME intake. After a 42-day adjustment period, steers were fed individually, and digestibilities of total alpha-glucosides, starch oligosaccharides and glucose were determined at 2-week intervals, with chromic oxide used as an indicator. Steers fed the alfalfa hay diet had higher (P less than .05) total tract digestibilities of total alpha-glucosides and starch than steers fed the corn diets. Fecal starch (percentage of dry matter) in steers fed the corn diets increased (P less than .05) from approximately 11 to 31% as level of ME intake increased from one to three times maintenance. Starch digestibilities for the corn diets fed at one, two and three times maintenance were 81.4, 76.4 and 76.0%, respectively. However, these trends toward reduced starch digestibilities were not significant. There appeared to be no apparent adaption of alpha-glucoside digestibility in the total digestive tract among steers fed different levels of corn over the intervals observed. In Exp. 2, four Holstein steers (350 KH) were each fitted with duodenal and ileal reentrant cannulas and fed either a low or a high level of corn. Alpha-glucoside intakes for animals given the low and high levels of cord averaged 1.7 and 3.2 kg, respectively. Steers fed the high level of corn digested more (p less than .05) alpha-glucoside in the total tract (2.9 vs 1.6 kg), reticulo-rumen (2.3 vs 1.2 kg) and large intestine level of corn. Steers fed the high level of corn also digested more corn in the small intestine (.415 vs .221 kg) than steers fed the lower level; however, differences were not significant. Although there were trends toward lower partial digestion coefficients (expressed as a percentage of alpha-glucoside presented to that segment) in the total tract, reticulo-rumen and small intestine for steers fed the high corn diet, the magnitude of the differences was not significant.     

The effects of acute and chronic protein depletion and accretion on plasma concentrations of insulin-like growth factor-1, fibronectin and total protein for ruminants nourished by intragastric infusion of nutrients

The relationships of N input or protein status and the concentrations of serum insulin-like growth factor-1 (IGF-1), plasma fibronectin (FN) and total protein (TP) were examined in three experiments with steers and sheep nourished by intragastric infusion of nutrients. In Expt 1, three steers (340 kg live weight) were infused with three levels of volatile fatty acids (0, 300 and 600 kJ/kg metabolic weight (W0.75) per d) and six levels of casein (0, 200, 400, 650, 1500 and 2500 mg N/kg W0.75 per d). Each N treatment was imposed for 5 d. In Expts 2 and 3, five groups of sheep (about 35 kg live weight) were infused with casein at 500 mg N/kg W0.75 per d for 2 weeks followed by 1500, 500 or 50 mg N/kg W0.75 per d in Expt 2, and in Expt 3, with 100 mg N/kg W0.75 per d for 6 weeks or 10 mg N/kg W0.75 per d for 4 weeks. Non-protein energy was maintained constant at 500 kJ/kg W0.75 per d throughout. Daily N balance and total body N content at the end were measured, and protein status was defined as a percentage of cumulative N accretion or depletion in relation to the total body N content at maintenance. It was found that IGF-1 and FN responded rapidly and substantially to altered N input, and that when daily N input was maintained constantly at sub-maintenance, their continuous declines were related closely to progressive protein depletion in the sheep. Plasma TP concentration was independent of N input when N input was altered acutely in the steers, but declined significantly and gradually with severe, chronic body protein depletion in the sheep. Plasma content of TP in the sheep however reduced acutely with a reduction in N input. Plasma volume fell substantially over the first 2 weeks of protein depletion, compensating for the declines in TP content and maintaining TP concentration plateau. The possible implications of the changes in TP concentration and content (concentration x volume) to body protein loss in sheep are discussed.     

Abomasal infusion of cis or trans fatty acid isomers and energy metabolism of lactating dairy cows

Diets for dairy cows that provide or induce formation of trans isomers of polyunsaturated fatty acids result in reduced percentages of milk fat. The effect of abomasal infusion of trans-C18:1 fatty acid isomers on energy utilization by mature cows was determined. Six multiparous Holstein cows in midlactation had ad libitum access to a basal diet containing 50% forage and 50% concentrate. Treatments were 1) no infusion, 2) infusion of 630 g/d of a fat mixture high in cis-C18:1 isomers (64% cis-C18:1; 68% high oleic sunflower oil and 32% cocoa butter), and 3) infusion of 623 g/d of a fat mixture high in trans-C18:1 isomers (42% trans-C18:1; 90% partially hydrogenated soybean oil and 10% high linoleic safflower oil). The experiment was a replicated 3 x 3 Latin square design with 4-wk periods. Measurements of energy balance were made in open circuit respiration chambers during wk 4 of each period. Fat infusion increased milk production by 2.5 kg/d; apparent digestibility of DM, OM, energy, ADF, and ash by 1 to 4 percentage units; metabolizable energy by 11%; and NEL of the diet by 15%. Milk fat percentage and yield were higher when cows were infused with cis-C18:1 than when they were infused with trans-C18:1 (4.12% and 1.41 kg/d vs. 3.15% and 1.06 kg/d, respectively). Infusion of fat increased milk production, but trans-C18:1 reduced milk fat and energy output.     

An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves

Ruminally degradable intake protein (DIP) and metabolizable indispensable amino acid (MIAA) requirements of feedlot steers were evaluated. Dietary treatments consisted of isocaloric 80% concentrate steam-flaked corn-based diets containing either .8% urea, 1.5% fish meal (FM), 3.0% FM, 4.5% FM, or 4.5% soybean meal (SBM). Treatment effects on characteristics of ruminal and total tract digestion were evaluated using four Holstein steers (249 kg) with cannulas in the rumen and proximal duodenum. Ruminal digestibility of OM (RDOM; P < .05) and feed N (P < .01) and microbial N flow (MNF; P < .01) to the small intestine were greater with urea as the supplemental N source. The level of DIP was closely associated (R2 = .89) with MNF. Postruminal digestibility of OM was greater (P < .05) for FM than for urea-supplemented diets, compensating for lower RDOM. There were no treatment effects (P > .10) on DOM. As the level of FM was increased, MIAA increased linearly (P < .01). Intestinal MIAA were similar (P > .10) for urea- and SBM-supplemented diets. Treatment effects on 56-d growth performance were evaluated using 100 medium-framed crossbred steers (231 kg). Daily weight gain (linear effect; P < .01), DM intake (linear effect; P < .10), feed efficiency (linear effect; P < .05), and diet NE (linear effect; P < .05) increased with level of FM supplementation. Daily weight gain (P < .10) and DM intake (P < .05) were greater for urea- than for SBM-supplemented diets. Using bovine tissue as the reference protein, the biological value (based on chemical score) of the intestinal chyme protein averaged 73%; methionine was first-limiting. There was a close association (R2 = .99) between methionine supply to the small intestine and observed/expected dietary NE. The metabolizable methionine requirement (MMETR, g/d) of medium-framed feedlot steers can be reliably predicted from measures of BW and ADG (MMETR = 1.565 + .0234ADG[268 - (29.4 x .0557BW(.75)ADG(1.097))/ADG] + .0896BW(.75)). There was a very close association (R2 = .89) between DIP and MNF (MNF = 13.7DIP - .66DIP(2) + 25.9). At maximal observed synthesis, DIP accounted for 76% of the MNF. A minimum of 100 g DIP/kg of total tract digestible OM was required to maximize RDOM and MNF.     

Free amino acid supplementation to steers: effects on ruminal fermentation and performance

Three studies were conducted to evaluate amino acid utilization by cattle. In Exp. 1, five steers (580 kg) were fed 86% rolled corn diets with mixtures of amino acids containing up to 6 g/d DL-Met, 24 g/d L-Lys, 6 g/d L-Thr, and 3 g/d L-Trp. Treatments had little effect on ruminal fermentation, diet digestibility, N flow to the duodenum, or microbial efficiency. Ruminal concentrations of Met and Lys increased linearly (P < .05) with amino acid supplementation, whereas Thr responded quadratically, and Trp was not altered. In Exp. 2, four steers (414 kg) were used to measure effects of dietary monensin or laidlomycin propionate in high-grain diets supplemented with amino acids. Ionophores had no significant effect on ruminal fermentation or outflows of amino acids from the rumen. In Exp. 3, 100 steers (287 kg initial BW) were fed diets containing 1% of a nonprotein N source. Treatments were 1) no supplemental N (UREA), 2) UREA plus soybean meal (SBM), 3) UREA plus 2 g/d DL-Met, 8 g/d L-Lys, 2 g/d L-Thr, and 1 g/d L-Trp, or 4) UREA plus 4 g/d DL-Met, 16 g/d L-Lys, 4 g/d L-Thr, and 2 g/d L-Trp. During the growing period (diets based on whole-plant milo silage), gains were higher for SBM-supplemented steers than for UREA steers and intermediate for steers supplemented with amino acids. Few significant differences in performance were observed among treatments during the finishing phase (diets based on dry-rolled corn) or for the entire experiment, but cattle fed SBM or amino acids tended to be fatter and have better marbling scores and quality grades. Amino acids did not greatly alter ruminal fermentation or cattle performance.     

Effects of varying levels of duodenal or midjejunal glucose and 2-deoxyglucose infusion on small intestinal disappearance and net portal glucose flux in steers

Six crossbred steers (261 +/- 18 kg BW) fitted with hepatic portal, mesenteric venous and arterial catheters, and duodenal, midjejunal, and ileal cannulas were used in a replicated 3 x 3 Latin square design to determine the effect of varying levels and site of glucose plus 2-deoxyglucose (2DG) infusion on net portal-drained visceral flux. Steers were fed chopped alfalfa in six equal portions daily at 1.5% of BW. Glucose (0, 9, or 18 g/h) and 2DG (0, 1, or 2 g/h) were infused continuously through the duodenal or midjejunal cannula (two infusion sites) at total glucose plus 2DG infusion rates of 0, 10, or 20 g/h. Arterial and portal blood samples were taken simultaneously at 20-min intervals from 5 to 9 h of infusion. Portal blood flow was determined by continuous infusion of p-aminohippurate and net flux was calculated as venous-arterial concentration (PA) difference times blood flow. Arterial concentration of glucose was not affected (P > .10) by glucose plus 2DG infusion, whereas arterial concentration of 2DG was greater (P < .05) when glucose plus 2DG was infused into the duodenum and increased (linear, P < .10) as amount of glucose plus 2DG infused into both the duodenum and midjejunum increased. Net portal flux and PA difference of glucose and 2DG were greater (P < .05) when glucose plus 2DG was infused into the duodenum. Although 2DG was infused at 10% of the total glucose plus 2DG infusion, it accounted for only 1.7 and .7% of the glucose plus 2DG appearing in portal blood when glucose plus 2DG was infused at 10 and 20 g/h, respectively. We conclude that glucose is more readily absorbed across the proximal-half than the distal-half of the small intestine, and that passive diffusion is a minor route of glucose absorption.     

Current concepts of amino acid and protein metabolism in the mammary gland of the lactating ruminant

Milk protein responses to protein nutrition are typically poor and, in part, may be due to the low efficiency (approximately 25 to 30%) of converting dietary N into milk. Posthepatic availability of amino acids (AA) is not limited, yet only approximately 30% is converted into milk. The poor capture of AA by the mammary gland may relate to the imbalanced and uncoordinated timing of nutrient delivery to the gland. The infusion of essential AA improves the efficiency of utilization (0.31); however, further catabolism of AA within the mammary gland suggests that AA transport is not a major limitation. These losses may serve ancillary or functional roles, but mammary oxidation of some AA occurs only when AA extraction exceeds the stoichiometric requirements for milk protein synthesis. Intracellular substrate supply may be more limiting than is the appartus for protein synthesis. Studies utilizing isotope labeling and conducted in vitro and in vivo now suggest that circulating peptides and proteins can serve as sources of perhaps all AA for casein synthesis, but the source of these remains elusive. Constitutive protein and casein turnover contribute significantly (42 to 72%) to mammary protein synthesis. All AA are extensively channeled through an intermediary protein pool or pools that have rapid turnover rates. The AA are then incorporated into casein, which appears to be fixed in association with protein turnover. The mammary gland is a major controller of its metabolism, and the mechanisms of AA extraction and conversion into milk protein are linked to secretion events. Blood flow may be a key point of regulation whereby mechanisms sense and respond to nutrient supply and balance to the gland via alterations in hemodynamics.     

Dynamic lung function changes following long-term work in polluted environments

15N-labelled glycine, ammonium chloride, and L-aspartic acid were infused intravenously into a series of non-diabetic adults at a constant rate for 4 to 8 hours. Midway during the infusion, a pulse of 8-10 units of regular insulin was injected as a pulse or infused at a constant rate for the remainder of the 15N infusion period. Frequent urine specimens were collected during the infusion period. The 15N enrichment of the urinary urea, ammonia, and amino acids increased smoothly with time until the insulin was given. The pulse of insuline caused a downturn on the N enrichment. We concluded from this that a) the effect of a pulse of insulin on human urea and ammonia metabolism lasted for about one hour; and b) insulin affected glutamine distribution in the plasma.     

A noninvasive method for measuring urea kinetics with a single dose of [15N15N]urea in free-living humans

A noninvasive method is described in which the endogenous rate of urea production can be determined in normal, free-living adults. A single dose of [15N15N]urea was given orally, and the amount of label excreted as [15N15N]urea and [15N14N]urea in urine over the subsequent 48 h was measured. From the rates of excretion of labeled and unlabeled urea the rate of urea production was derived. Using this single-dose protocol the rate of urea production was 207 +/- 56 (mean +/- SD) mg N/(kg.d) in six normal adult men consuming 74 g protein/d. These results were not different when compared with rates of urea production obtained with a prime/intermittent protocol in an earlier study in the same individuals [199 +/- 20 mg N/(kg.d)]. We conclude that urea kinetics can be measured noninvasively with a single dose of [15N15N]urea and that this method may be suitable for use in free-living individuals to determine urea production rates for habitual dietary intakes.     

Lasalocid effects on ruminal degradation of protein and postruminal supply of amino acids in Holstein steers

Five ruminally and duodenally cannulated Holstein steers (305 kg) were used in a switchback experiment with three periods to evaluate two experimental treatments: a basal diet with or without 45 ppm of lasalocid. The basal diet contained approximately 43% rolled corn, 45% alfalfa hay, and 10% soybean meal (DM basis). Lasalocid did not affect feed intake or ruminal digestion of OM and NDF. Ruminal digestion of ADF tended to increase with supplemental lasalocid. Total tract digestion of OM, NDF, ADF, and N and intestinal flow of amino acids were not affected by lasalocid. Also, the ratio of microbial to nonmicrobial N fractions at the duodenum remained unchanged. Ruminal pH and concentrations of NH3, VFA, peptides, and amino acids were not affected by lasalocid. Ruminal protease activity decreased with supplemental lasalocid, but this decrease was not reflected in other variables, such as ruminal concentrations of peptides and amino acids. Ruminal deaminase activity remained unchanged. Thus, we concluded that dietary lasalocid did not alter ruminal protein degradation or postruminal flow of amino acids.     

Effect of NIDDM on the kinetics of whole-body protein metabolism

We postulated that dietary protein utilization and body protein metabolism are altered in hyperglycemic individuals with non-insulin-dependent diabetes mellitus (NIDDM). This was tested by estimating the kinetics of protein metabolism in obese NIDDM patients in the hyperglycemic state of isoenergetic feeding and in the normoglycemic state induced by the prolonged use of a very-low-energy diet (VLED) and comparing them with results in obese nondiabetic subjects studied previously. Seven obese subjects with NIDDM (one male, six females, body mass index = 35.8 +/- 2.0 kg/m2) were given a 1.7 MJ (410 kcal) all protein (93 g/day) diet derived from hydrolyzed collagen and supplemented with tryptophan and methionine, which provides 16% of its amino acids as essential, a multivitamin and mineral supplement, and 16 mmol KCl for 42 days. During the seven-day isoenergetic diet and at weeks 4 and 6 of the VLED, amino nitrogen (N) flux rate was calculated from the urine [15N]urea enrichment by using the 60-h oral [15N]glycine method to obtain the integrated feeding-fasting metabolism. Rates of synthesis (S) and breakdown (B) were calculated from N flux. At day 7 of the isoenergetic diet, whole-body N flux, S, B, and resting metabolic rate (RMR) were 12-24% greater (P < 0.05) in the NIDDM subjects than observed in nondiabetic obese subjects. Mean plasma glucose decreased (P < 0.05) from the isoenergetic period (14.9 +/- 2.4 mM) to 7.2 +/- 1.2 mM at week 4 and 6.5 +/- 1.1 mM at week 6 of the VLED. RMR declined progressively by 25% at week 5 of the VLED. Corresponding significant (P < 0.05) decreases from isoenergetic feeding to weeks 4 and 6 of the VLED occurred in whole-body N flux (from 51 +/- 2 to 42 +/- 1 g N/day), in S (from 38 +/- 3 to 24 +/- 1 g N/day), and in B (from 39 +/- 3 to 26 +/- 1 g N/day) resulting in net losses (S-B). S-B was significantly more negative (P < 0.05) in NIDDM than in the nondiabetic obese subjects at week 4 (-1.5 +/- 0.5 vs. 0.9 +/- 0.3 g N/day) but not at week 6 (-1.3 +/- 0.4 vs. -0.9 +/- 4 g N/day). During the VLED, N balance became less negative with time but never reached equilibrium in NIDDM. Thus, abnormal protein metabolism is present in NIDDM in the isoenergetic fed state with moderate hyperglycemia and persists during a VLED that restores glycemia to near normal.     

Alfalfa and escape protein supplements for grazed corn residues

Two calf corn-residue grazing trials were conducted to evaluate the effect of supplementing with two alfalfa hays (Medicago sativa), varying in their amount of CP and ADF, with and without escape protein (EP). In Trial 1, heifers (204 kg) grazed (1.36 heifers/ha) non-irrigated fields for 92 d. No difference (P > .05) in ADG was found when medium-protein (16.3% CP) and high-protein (18.0% CP) alfalfa hays were provided at 2.7 kg of DM.heifer-1.d-1. In Trial 2, 60 steers (257 kg) were supplemented individually with medium-protein (17.6% CP) alfalfa hay, 1.86 (MPL) and 2.27 kg DM (MPH), and one level of high-protein (18.7% CP) alfalfa hay, 1.86 kg DM (HPL). In a 2 x 3 factorial arrangement of treatments, steers were fed with or without EP (113 g.steer-1.d-1 from blood meal and corn gluten meal). Steers grazed a non-irrigated corn residue field (2.58 steers/ha) for 57 d and were watered and individually supplemented overnight. Diet quality and composition was estimated by collecting extrusa samples twice each week using four esophageally fistulated steers. No effects of alfalfa protein content or level (P > .05) were reflected in gain: 357, 309, and 326 g.steer-1.d-1 for steers receiving MPL, MPH, or HPL alfalfa treatments, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiple phosphorylation of chicken protein tyrosine phosphatase 1 and human protein tyrosine phosphatase 1B by casein kinase II and p60c-src in vitro

The objectives of this study were to evaluate milk choline as an indicator of choline absorption and to use milk choline to evaluate the efficacy of a rumen-protected choline supplement. In a preliminary 4-wk experiment, two Holstein cows in early lactation were abomasally infused with either 0 or 60 g/d of choline chloride in 2 L of water, which was used as a carrier. Choline infusion increased milk choline secretion from 1.95 to 3.95 g/d during the 2-wk choline infusion period. In Experiment 2, four Holstein cows in early lactation were abomasally infused with 0, 25, 50, and 75 g/d of choline chloride in 2 L of water using a 4 x 4 Latin square design with 1-wk experimental periods. Milk choline secretion was 2.56, 3.62, 3.72, and 3.82 g/d for the respective choline treatments. In Experiment 3, 10 Holstein cows in midlactation were fed either 0 or 50 g/d of choline using an experimental rumen-protected choline supplement during a 2-wk experiment. Milk choline secretion was increased from 2.12 to 2.99 g/d with the supplemental choline. Results of these experiments demonstrated that milk choline is responsive to postruminal choline supply and can be used as a qualitative indicator of choline absorption.