Biomedical subjects

C G Schwab

Publications and source records attributed to C G Schwab.

At least 19 recordsLinked to original sources

PubMed2006

Dietary forage and nonfiber carbohydrate contents influence B-vitamin intake, duodenal flow, and apparent ruminal synthesis in lactating dairy cows.

The objective of this experiment was to quantify intakes, duodenal flows, and ruminal apparent synthesis (AS) of B-vitamins in lactating dairy cows fed diets varying in forage and nonfiber carbohydrate (NFC) contents. Eight (4 primiparous and 4 multiparous) ruminally and duodenally cannulated Holstein cows were assigned to 4 dietary treatments in a replicated 21-d period, 4 x 4 Latin square design with a 2 x 2 factorial treatment arrangement. Diets, fed as TMR, contained (DM basis) 2 levels of forage (35 and 60%) and 2 levels of NFC (30 and 40%). The forage portion of the diets contained 50% corn silage, 33% alfalfa hay, and 17% grass hay. Soybean hulls and beet pulp (2:1) and corn meal and ground barley (2:1) were included to achieve desired NFC concentrations. No supplemental B-vitamins were fed. B-vitamin AS was calculated as the amount of a specific B-vitamin flowing to the duodenum minus its daily orts-corrected intake. Dry matter and organic matter intakes were higher for cows fed the 35% forage diets and the 40% NFC diets. Increasing dietary forage content decreased ruminal AS of pyridoxine, folic acid, and B12. Increasing dietary NFC content increased ruminal AS of nicotinic acid, nicotinamide, niacin, pyridoxal, B6, and folic acid but decreased AS of B12. Across diets, amounts of B-vitamins synthesized were highest for niacin, followed by riboflavin, B12, thiamin, B6, and folic acid. Biotin AS values were negative for all diets, suggesting either no ruminal synthesis or that destruction by ruminal microflora was greater than synthesis. B-vitamin intake, duodenal flow, and ruminal synthesis are influenced by dietary forage and NFC contents.

Animals↗

PubMed2006

Evaluation of the passage rate equations in the 2001 Dairy NRC model.

Dairy ration formulation to meet protein and amino acid requirements with the National Research Council Nutrient Requirements of Dairy Cattle (NRC, 2001) model depends on accuracy of predicting feed passage rates out of the rumen. The NRC (2001) passage rate (Kp) equations were evaluated for validity and sensitivity to input variables in predicting supplies of rumen degraded protein, rumen undegraded protein, and metabolizable protein. The database used in the development of the 3 Kp equations (for dry forage, wet forage, and concentrate) was used to independently derive the 3 equations using a meta-analysis technique. To extract quantitative relationships between statistically significant input variables and rate of passage, a random coefficients model that used each study effect as a random variable was used. The database was comprised of studies that only used rare earth markers. Outliers were identified by acceptance criteria defined a priori or the difference in fit statistic (DFFITS) value; 319, 63, and 139 treatment means were used to develop the Kp equations for dry forage, wet forage, and concentrate, respectively. We found that the sign of the regression coefficient for concentrate content in diet dry matter in the equation for Kp dry forage was inverted; it should be positive. A sensitivity analysis was conducted with a spreadsheet version of the NRC (2001) model developed for this study, using the Monte Carlo technique. The sensitivity analysis indicated that all Kp predictions were the most sensitive to variation in DM intake, and thus accurate measurement of DM intake is the most important factor in predicting Kp. Predictions for protein supply (rumen degraded protein, rumen undegraded protein, and metabolizable protein) were sensitive to variability in amount of feed crude protein (CP, %DM), digestion rate (Kd) of the B fraction of feed CP (%/h), and the Kp for concentrate (%/h), due to the high proportion of dietary CP in lactating dairy rations coming from concentrates. The sensitivity analysis indicated that accurate determinations of DMI, the Kd of the B fraction of feed CP, and feed CP are the most important variables needed to predict MP supply in lactating dairy cows with the NRC (2001) model. We conclude that the empirical Kp equations in the model are suitable for predicting passage rate in lactating dairy cows. More accurate predictions of Kp will require the development of a more mechanistic model that accounts for more of the biologically important variables (e.g., physical property of particles, liquid flow, and timely variation of intake) affecting passage rate.

Algorithms↗

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

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↗

PubMed2005

Improving intestinal amino acid supply of pre- and postpartum dairy cows with rumen-protected methionine and lysine.

Eighty-four Holstein cows were assigned to a randomized block experiment to determine effects of supplementing pre- and postpartum diets containing highLys protein supplements with rumen-protected Met and Lys. Before parturition, cows received a basal diet with 1) no rumen-protected amino acids (AA), 2) 10.5 g/d of Met from rumen-protected Met, or 3) 10.2 g/d of Met and 16.0 g/d of Lys from rumen-protected Met plus Lys. After parturition, cows continued to receive AA treatments but switched to diets balanced for 16.0 or 18.5% crude protein (CP). Diets were corn-based; supplemental protein was provided by soybean products and blood meal. Cows received treatments through d 105 of lactation. Compared with basal and Met-supplemented diets, Met + Lys supplementation increased yield of energy-corrected milk, fat, and protein, and tended to increase production of 3.5% fat-corrected milk. Significant CP x AA interactions were observed only for milk protein and fat content. Supplementation of the 16% CP diet with Met and Met + Lys had no effect on milk true protein and fat content. However, Met and Met + Lys supplementation of the 18.5% CP diet increased milk protein content by 0.21 and 0.14 percentage units, respectively, and Met supplementation increased fat content by 0.26 percentage units. Results of this study indicate that early-lactation cows fed corn-based diets are responsive to increased intestinal supplies of Lys and Met and that the responses depend on dietary CP concentration, supply of metabolizable protein, and intestinal digestibility of the rumen-undegradable fraction of supplemental proteins.

Amino Acids↗

PubMed2004

Ionophore taste preferences of dairy heifers.

Two taste preference studies were conducted using six Holstein heifers in each experiment to determine preferences for no ionophore, lasalocid, or monensin in the diet. In Exp. 1, individually penned (approx. 5 mo old; 220 +/- 14 kg BW) heifers were fed a basal total mixed ration containing 46% corn silage, 46% grass haylage, and 8% soybean meal (DM basis). There were five treatments (mg/kg BW(-1)*d(-1)): 0 ionophore (control), 1 lasalocid (1L), 2 lasalocid (2L), 1 monensin (1M), or 2 monensin (2M). Ionophores were provided as part of the mineral mix that had been added to the control diet and through an ionophore-grain by-product mix to make the 2L and 2M treatments. All five diets were offered for 7 d, with the first 2 d for adaptation and the last 5 d for measurement of feed intake. The most preferred diet was then removed and the study continued with the four remaining diets. The most preferred diets were again eliminated sequentially, so that only two diets remained on d 13 and 14. Each feeding segment ranking of treatment preferences was determined based on the weight of feed refused at the end of each feeding segment. In Exp. 2, six 6-wk-old heifers (75 +/- 5 kg of BW) were individually fed either 0, 1L, or 1M in a study similar to Exp. 1, except that the most preferred diet was removed after 4 d, with the first day for adaptation and the last 3 d for measurement of feed intake. In Exp. 1, orthogonal contrasts indicated that heifers preferred the 1L and 2L diets over the 1M and 2M diets. Preferences between diet concentrations of ionophores (1 and 2 mg/kg of BW; Exp. 1) and the control and ionophore treatments did not differ, nor was there an interaction between ionophores and their concentration. Dairy heifers previously fed lasalocid prefer lasalocid over monensin when given a choice; however, heifers without previous exposure to an ionophore did not indicate a preference (Exp. 2).

Animal Feed↗

PubMed2004

Evaluation of a colostrum supplement, with or without trypsin inhibitor, and an egg protein milk replacer for dairy calves.

Forty-eight Holstein bull calves were assigned to a 2 x 2 x 2 factorial arrangement in a completely randomized block design. Main effects were colostrum versus a serum-derived colostrum supplement, 0 versus 1 g of trypsin inhibitor added at the initial 2 feedings, and milk replacer containing 0 or 50% CP from whole egg. Calves were bled at 0, 6, 12, 18, and 24 h after birth for determination of serum immunoglobulin (Ig). G. Serum IgG concentrations were lower in calves consuming the colostrum supplement compared with calves consuming colostrum. Apparent efficiency of absorption of IgG was similar. Trypsin inhibitor did not affect IgG concentrations or absorption of IgG. Calves were fed either milk replacer for 28 to 35 d (preweaning phase) and weaned when they consumed 0.7 kg of starter grain for 2 consecutive days. The postweaning phase was from weaning to d 56. Feeding colostrum supplement resulted in higher fecal scores postweaning (1.90 vs. 1.58) and overall (1.85 vs. 1.65) and fewer days medicated preweaning (5.1 vs. 2.2 d) and postweaning (3.9 vs. 1.9 d) and overall (9.0 vs. 4.2 d). Calves were treated for upper respiratory tract infections and diarrhea. Dry matter intake and weaning age were not affected by treatment. Postweaning (1.69 vs. 1.2 kg) and overall (1.22 vs. 1.0 kg), calves that received colostrum and egg milk replacer consumed more dry matter and starter. Postweaning, calves fed colostrum and egg milk replacer had similar or greater body weight and gains compared with calves fed colostrum and milk protein milk replacer. Preweaning, feed efficiency was greater for calves fed colostrum (0.44 vs. 0.34), trypsin inhibitor (0.42 vs. 0.36), and milk protein milk replacer (0.48 vs. 0.30) compared with calves fed colostrum supplement, no trypsin inhibitor, and egg milk replacer, respectively. Trypsin inhibitor increased feed efficiency postweaning. Calves fed trypsin inhibitor and milk protein milk replacer were more efficient preweaning and overall than calves fed trypsin inhibitor and egg milk replacer. Results indicate that the blood derived colostrum supplement did not provide as much IgG as colostrum (4.55 g/L vs. 14.6 g/L, respectively), that feeding 1.0 g of trypsin inhibitor did not enhance serum IgG concentrations, and that the egg milk replacer-fed calves fed colostrum performed nearly as well as calves fed colostrum and the milk protein milk replacer.

Absorption↗

PubMed2003

Supplemental lactoferrin improves health and growth of Holstein calves during the preweaning phase.

Lactoferrin is a milk protein that exhibits broad-spectrum antimicrobial properties. Previous studies indicated that supplemental lactoferrin may alter the microbial populations in the gut of nonruminants and increase preweaning weight gains in calves. In the present study, 40 Holstein calves were used to examine the effects of supplemental lactoferrin (0, 1, 2, or 3 g/d) on health, growth, and feed intake from 3 d of age to 2 wk postweaning. Lactoferrin was mixed and fed with a nonmedicated milk replacer. Calves were housed in individual pens and offered a textured, nonmedicated starter and water for ad libitum consumption. Body weight and heart girth were measuredweekly. Intakes of milk replacer and starter were determined daily. Fecal consistency was monitored three times per week. Calves were weaned when they met certain criteria based on body weight gain and starter intake. Preweaning fecal score responded quadratically, with the group fed 1 g/d of lactoferrin having the lowest score. Overall and preweaning number of days medicated responded in the same manner as fecal score. Preweaning average daily gain and gain-to-feed ratio increased linearly with lactoferrin supplementation, whereas postweaning gain-to-feed ratio decreased linearly with lactoferrin. Overall average daily heart girth gain increased linearly with lactoferrin. Body weight, weaning age, and dry matter intake were not different among treatments. Based on the observed improved gain-to-feed ratios, increased average daily gains, improved fecal scores, and reduced morbidity in preweaned calves, it appears that lactoferrin may be a beneficial supplement in the diets of neonatal calves prior to weaning.

Animals↗

PubMed2002

Lactoferrin supplementation to dairy calves.

Twenty-one Holstein calves (12 bulls, 9 heifers) were used to evaluate the effects of supplemental lactoferrin (0, 1, and 10 g/d) added to colostrum, milk, and milk replacer in a 56-d study. Calves fed lactoferrin (LF) weighed more during wk 2, 3, 4, 5, and 6 than control calves. Calves fed LF had increased preweaning daily weight gains and heart girth gains compared with calves not fed lactoferrin. Calves fed 1 g/d LF had a greater preweaning average daily gain than calves fed 10 g/d of lactoferrin. Hematocrit and serum Fe were unaffected by treatments. Calves were weaned when they had consumed 0.7 kg of calf starter grain for 2 consecutive d and were at least 28 d of age. All calves were weaned by 35 d of age, regardless of starter intake. Calves fed LF consumed more calf starter grain during the preweaning period and met weaning criteria at a younger age. This study indicates that supplementing calf diets with LF is advantageous to calf performance.

Animal Feed↗

PubMed2001

Accuracy and precision of computer models to predict passage of crude protein and amino acids to the duodenum of lactating cows.

To evaluate the ability of several models to accurately and precisely predict the passage of crude protein (CP) and amino acids to the duodenum of lactating cows, we simulated data from six published studies using the 1989 National Research Council equations, the Mepron Dairy Ration Evaluator (version 1.1), the University of Pennsylvania release of the Net Carbohydrate and Protein System (version 2.12p), the Cornell Net Carbohydrate and Protein System (version 3), and CPM Dairy (version 1.0). Models overestimated the passage of CP from microbes by an average of 323 g/d, and underestimated the passage of CP from feed by an average of 874 g/d. These two errors were partially canceled when CP from microbes and feed were summed to estimate passage of total CP to the duodenum. Many dietary composition variables appeared to bias the predictions; however, the influence of any one variable was small. The efficiency of modeling was high for most predictions but was variable for predicting passage of specific individual amino acids to the small intestine depending on the model selected. These simulations indicated no obvious advantage for any model over the others tested. The models responded to changes in diets by altering the amount of protein from microbes and feed that reached the duodenum, resulting in improved accuracy of predictions of duodenal CP passage compared with simply assuming a constant value for passage of CP to the duodenum.

Amino Acids↗

PubMed2001

Prediction of crude protein and amino acid passage to the duodenum of lactating cows by models compared with in vivo data.

To determine whether statistical inferences obtained from predictions by models were similar to those of measured data from individual cows, data from six research trials published between 1989 and 1997 were simulated using the 1989 National Research Council Model, the Mepron Dairy Ration Evaluator (version 1.1), The University of Pennsylvania release of the Net Carbohydrate and Protein System (version 2.12p), The Cornell Net Carbohydrate and Protein System (version 3), and the CPM Dairy (version 1.0). Both predicted and measured protein fractions were analyzed by ANOVA and compared to determine whether statistical inferences among treatments from predictions by the models were similar to those from the measured data. The interpretations and statistical inferences of measured data did not always agree with those for predicted data. All models responded to changes in diet composition and often predicted that dietary changes would result in statistically different amounts of protein and amino acids passing to the duodenum than were observed in the measured data. The direction of predicted change among treatments for passage of nitrogen fractions to the duodenum also did not agree with the measured data a large percentage of the time. Discrepancies in ANOVA and interpretations between predicted and measured data may be due to the reduction in variation associated with modeling biological systems, associative effects of feeds not accounted for by models, inadequate equations in the models, inadequate description of feeds, or experimental error in measured data. Before model simulations of duodenal flow of crude protein and amino acids can be substituted for experimental measurements, better descriptors of main dietary effects, microbial protein production, ruminal protein degradation, and interactions among dietary factors must be developed.

Amino Acids↗

PubMed1997

Effect of yeast culture in the diets of early lactation dairy cows on ruminal fermentation and passage of nitrogen fractions and amino acids to the small intestine.

Eight early lactation, primiparous Holstein cows were fitted with ruminal and duodenal cannulas. The cows were used in a replicated 4 x 4 Latin square design to test the effects of yeast culture (0 vs. 10 g/ d) and dietary crude protein (CP) (16.1 vs. 18.8% of dry matter) in 44% forage diets. Dietary CP differed primarily in ruminally degradable CP (9.1 vs. 11.4% of dry matter). Dry matter intake tended to increase as amount of yeast culture increased. However, yeast culture had no effect on ruminal pH, concentrations of NH3 and volatile fatty acids in ruminal fluid, or ruminal digestibility. Yeast culture increased the ruminal concentration of isobutyrate in cows fed the low CP diet and decreased the concentration of isobutyrate in cows fed the high CP diet. The higher CP diets increased microbial N passage to the duodenum and had no effect on passage of nonmicrobial nonammonia N. Flows to the duodenum of nonmicrobial nonammonia N tended to be higher for cows fed yeast culture. Flows of essential amino acids to the duodenum and the essential amino acid profiles of duodenal digesta and of mixed ruminal bacteria were not altered by yeast culture. Yields of fat and 4% fat-corrected milk were increased by yeast culture supplementation of the low CP diet. Similar tendencies were noted for yields of milk and milk protein.

Amino Acids↗

PubMed1997

Lactational performance of cows fed low or high ruminally undegradable protein prepartum and supplemental methionine and lysine postpartum.

Multiparous Holstein cows (n = 24) were fed diets containing 34 or 41% ruminally undegradable protein (RUP) for 30 d before parturition; then each group was fed a basal diet supplemented with or without ruminally stable Met (10.6 g/d) and Lys (15.2 g/d) for 75 d in the subsequent lactation. Supplementation of Met and Lys increased the milk yield of cows previously fed the low RUP diet, but milk yields before and after amino acid (AA) supplementation were similar for cows previously fed the high RUP diet. Milk protein content (percentage) increased from 2.83 to 2.96 for cows previously fed the high RUP diet. Milk protein yield increased from 1.13 to 1.21 kg/d when Met and Lys were fed. Data on AA concentration in plasma and AA extraction by the mammary gland suggest that the supplementation of Met and Lys corrected a Met limitation. According to the Cornell Net Carbohydrate and Protein System, the lactation diet was limiting for Met for maximum milk yield and was corrected by AA supplementation. Based on limiting AA, allowable milk yield was 42.5 kg/d, and the observed yield was 40.9 kg/d averaged across treatments. The group with the greatest allowable milk yield (45.2 kg/d) had the greatest actual milk yield (43.0 kg/d). The regression equation of observed milk yield on allowable milk yield was Y = 3.4 + 0.8805X.

Animals↗

PubMed1994

Improved techniques for dissociating particle-associated mixed ruminal microorganisms from ruminal digesta solids.

Combinations of physical and chemical methods were evaluated for their ability to remove particle-associated microorganisms (PAM) from saline-washed ruminal digesta solids (SWRDS). Physical methods included chilling and storage, homogenization, multiple extraction, and agitation with marbles. Chemical methods included use of low pH, Tween 80, formaldehyde, methanol, tertiary butanol, and methylcellulose. Microbial removal from SWRDS was determined directly by using epifluorescence microscopy and indirectly by measuring removal of diaminopimelic acid and total purines. Different combinations of methods resulted in removals of 46 to 82% for particle-associated bacteria (PAB), 52 to 98% for particle-associated protozoa (PAP), and 60 to 83% for PAB plus PAP. Two methods were considered most effective, based on microscopy; both removed similar amounts of PAB (79 to 82%) and PAB plus PAP (80 to 83%). In one method, SWRDS were stored for 24 h at 4 degrees C in a solution of pH 2 saline, .1% Tween 80, 1.0% methanol, and 1.0% tertiary butanol. In the other method, SWRDS were incubated for 30 min in .1% methylcellulose before storage for 24 h at 4 degrees C in pH 2 saline, .1% Tween 80, and 1.0% methanol. Common to both treatments was subsequent homogenization of the suspensions for 15 s followed by washing the digesta solids seven times with the treatment solutions. Both methods resulted in values that exceeded those reported previously for removal of PAM from ruminal digesta solids.

Animal Feed↗

PubMed1993

Effect of intestinal blood flow on absorptive site blood flow and lysine absorption as examined in situ in Holstein calves.

Total blood flow from an intestinal segment (TBF) was altered to determine effects on blood flow at the absorptive site (ASBF) and lysine absorption. Venous blood flow was restricted using a peristaltic pump to 20, 35, 50, 65, and 80% of the initial unrestricted rate. Lysine absorption and ASBF were determined from recovery of 14C and 3H in blood from intestinally perfused [14C]L-lysine and 3H2O, respectively. Fluid flux in the intestinal lumen was estimated from the difference in polyethylene glycol concentrations in luminal infusate and effluent. Restriction of TBF proportionally reduced ASBF, which composed 3 to 6% of TBF. Lysine absorption was reduced linearly during reduction of TBF. Fluid absorption varied among calves but was independent of TBF. Differences between loss of radioactive marker from perfusate and recovery in blood suggested a loss of 3H2O from the intestinal segment that was independent of TBF. Changes in blood flow to the small intestine may affect nutrient absorption in ruminants.

Animals↗

PubMed1992

Amino acid limitation and flow to duodenum at four stages of lactation. 1. Sequence of lysine and methionine limitation.

Four Holstein cows with ruminal and duodenal cannulas were assigned to a 4 x 4 Latin square at each of four stages of lactation (peak, wk 4; early, wk 8 to 12; mid, wk 17 to 21; and late, wk 27 to 31). Treatments were duodenal infusions of 1) Met, 2) Lys, 3) Met plus Lys, and 4) casein; periods were 7 to 10 d. Quantities of DL-Met, L-Lys, and casein infused at the four stages of lactation were 12, 30, and 400; 12, 30, and 400; 10, 25, and 333; and 8, 20, and 266 g/d, respectively. Rations were composed of corn and grass-legume silages, corn meal, wheat middlings, soybean meal, and distillers dried grains with solubles. Intake of CP (percentage of NRC) and percentage of total CP from corn sources were (peak) 87, 56; (early) 90, 71; (mid) 98, 73; and (late) 114, 77. Using content and yield of milk protein as primary response criteria, Lys appeared to be first-limiting and Met second-limiting at peak lactation, their infusion together resulted in the same production of milk (40 kg/d) and milk protein (1135 g/d) as did casein. Lysine was first-limiting in early lactation, but whether Met was second-limiting was questionable. The two AA were colimiting in midlactation. There appeared to be no AA deficiencies in late lactation. Amounts of Lys and Met (percentage of total essential AA) in duodenal digesta during peak (12.4, 3.7), early (12.6, 3.5), and midlactation (14.9, 3.9) were not adequate for optimal AA utilization.

Amino Acids↗

PubMed1992

Amino acid limitation and flow to the duodenum at four stages of lactation. 2. Extent of lysine limitation.

Four multiparous Holstein cows with ruminal and duodenal cannulas were assigned to 4 x 4 Latin squares at peak (wk 4), early (wk 14 to 16), mid (wk 21 to 23), and late (wk 29 to 31) lactation to determine, in the presence of supplemental Met, the extent of Lys limitation and its required contribution to total essential AA in duodenal digesta. Treatments were duodenal infusions of 1) water alone or water with 2) 10 g/d of DL-Met plus 10 g/d of L-Lys, 3) 10 g/d of Met plus 20 g/d of Lys, and 4) 10 g/d of Met plus 30 g/d of Lys; quantities were reduced by 20% in late lactation. Rations were corn based (corn and grass-legume silages, corn meal, wheat middlings, soybean meal, and distillers dried grains with solubles) and most limiting in Lys and Met. Intakes of ruminally degraded and undegraded intake protein (percentage of NRC requirements) were (peak) 115, 97; (early) 112, 83; (mid) 113, 87; and (late) 127, 96. Contribution of Lys to passage of total essential AA to the duodenum without infusions were 13.2, 12.4, 13.8, and 14.8% at the four respective stages of lactation. Extent of Lys limitation determined from responses in content and yield of milk protein approximated 25, 20, and 10 g/d during peak, early, and midlactation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1988

Comparison of D-alanine and diaminopimelic acid as bacterial markers in young calves.

D-alanine (DAL) and diaminopimelic acid (DAP) were compared as markers to estimate proportion of bacterial N in total N reaching the abomasum of young calves. Sixteen Holstein bull calves fed complete pelleted starter or unpelleted starter plus hay and weaned at 4 or 8 wk of age were fitted with ruminal and abomasal cannulas and sampled twice weekly from 2 to 11 wk of age. Isolated ruminal bacterial cells contained more DAL than DAP at all weeks and averaged 7.0 and 5.4 mg N/g N, respectively. Weekly mean marker concentrations were highly correlated (.89) in ruminal bacteria, except at 3 wk of age. Concentration of DAL in abomasal digesta was greater than that of DAP at all weeks and averaged 5.2 and 2.4 mg N/g N, respectively. Weekly mean DAL correlated with DAP .61 in abomasal digesta and correlated .57 and .89 with starter intake, respectively. The proportion of bacterial N in total abomasal N was greater at all weeks when estimated by DAL than by DAP and averaged 77% and 46%, respectively. Estimates by DAL exceeded 100% in several cases and reflected large variation in analytical estimates. Estimates by DAL and DAP correlated .33 and .92 with starter intake. D-alanine was not an acceptable bacterial marker in this study.

Alanine↗