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Biomedical subjects

M B Hall

Publications and source records attributed to M B Hall.

At least 19 recordsLinked to original sources
PubMed2003

Challenges with nonfiber carbohydrate methods.

Nonfiber carbohydrates (NFC) encompass a compositionally and nutritionally diverse group exclusive of those carbohydrates found in NDF. Their content in feeds has often been described as a single value estimated by difference as 100% of dry matter minus the percentages of CP, NDF (adjusted for CP in NDF), ether extract, and ash. A calculated value was used because of difficulties with assays for individual NFC, but it does not differentiate among nutritionally distinct NFC. Errors in NFC estimation can arise from not accounting for CP in NDF and when multipliers other than 6.25 are appropriate to estimate CP. Analyses that begin to distinguish among NFC are those for starch, soluble fiber (non-NDF, nonstarch polysaccharides), and low molecular weight carbohydrates (mono- and oligosaccharides). Many starch analyses quantify alpha-glucans through specific hydrolysis of alpha-(1 --> 4) and alpha-(1 --> 6) linkages in the glucan, and measurement of released glucose. Incomplete gelatinization and hydrolysis will lead to underestimation of starch content. Starch values are inflated by enzyme preparations that hydrolyze carbohydrates other than alpha-glucan, measurement of all released monosaccharides without specificity for glucose, and failure to exclude free glucose present in the unhydrolyzed sample. Soluble fiber analyses err in a fashion similar to NFC if estimation of CP requires multipliers other than 6.25, or if contaminants such as CP and starch have not been properly accounted. Depolymerization and incomplete precipitation can also decrease soluble fiber estimates. The low molecular weight carbohydrates have been defined as carbohydrates soluble in 78 to 80% ethanol, which separates them from polysaccharides. They can be measured in extracts using broad-spectrum colorimetric assays (phenol-sulfuric acid assay or reducing sugar analysis of acid hydrolyzed samples) or chromatographic methods. Limitations of the colorimetric assays include lack of differentiation among mono- and oligosaccharides and differences in efficacy of measuring total carbohydrate. More sensitive and precise chromatographic methods require expensive equipment and specialized expertise. Current methods for NFC can separate nutritionally relevant fractions, but questions remain as to which fractions merit analysis and what analyses to use. These issues must be resolved in order to soundly evaluate and explore the roles of carbohydrates in diets.

Animal Feed↗
PubMed2003

Efficiency of converting nutrient dry matter to milk in Holstein herds.

Production of milk from feed dry matter intakes (DMI), called dairy or feed efficiency, is not commonly measured in dairy herds as is feed conversion to weight gain in swine, beef, and poultry; however, it has relevance to conversion of purchased input to salable product and proportion of dietary nutrients excreted. The purpose of this study was to identify some readily measured factors that affect dairy efficiency. Data were collected from 13 dairy herds visited 34 times over a 14-mo period. Variables measured included cool or warm season (high ambient temperature <21 degrees C or >21 degrees C, respectively), days in milk, DMI, milk yield, milk fat percent, herd size, dietary concentrations (DM basis) and kilograms of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and forage. Season, days in milk, CP % and forage % of diet DM, and kilograms of dietary CP affected dairy efficiency. When evaluated using a model containing the significant variables, dairy efficiency was lower in the warm season (1.31) than in the cool season (1.40). In terms of simple correlations, dairy efficiency was negatively correlated with days in milk (r = -0.529), DMI (r = -0.316), forage % (r = -0.430), NDF % (r = -0.308), and kilograms of forage (r = -0.516), NDF (r = -0.434), and ADF (r = -0.313), in the diet, respectively. Dairy efficiency was positively correlated with milk yield (r = 0.707). The same relative patterns of significance and correlation were noted for dairy efficiency calculated with 3.5% fat-corrected milk yield. Diets fed by the herds fell within such a small range of variation (mean +/- standard deviation) for CP % (16.3 +/- 0.696), NDF % (33.2 +/- 2.68), and forage % (46.9 +/- 5.56) that these would not be expected to be useful to evaluate the effect of excessive underfeeding or overfeeding of these dietary components. The negative relationships of dairy efficiency with increasing dietary fiber and forage may reflect the effect of decreased diet digestibility. The results of this study suggest that managing herd breeding programs to reduce average days in milk and providing a cooler environment for the cows may help to maximize dairy efficiency. The mechanisms for the effects of the dietary variables on dairy efficiency need to be understood and evaluated over a broader range of diets and conditions before more firm conclusions regarding their impact can be drawn.

Animal Feed↗
PubMed2002

Metabolic responses of transition Holstein cows fed anionic salts and supplemented at calving with calcium and energy.

The objective of this study was to determine the concentrations of plasma Ca, P, Mg, nonesterified fatty acids (NEFA), 3-hydroxybutyrate (BHBA), and glucose in transition cows fed anionic salts prepartum and provided with calcium and energy supplements at calving. The study was conducted on a Florida Holstein dairy farm from November to December 1997. Treatments consisted of no treatment (n = 30); 60 g of Ca as calcium chloride, orally (n = 30); 110 g of Ca as calcium propionate 510 g plus 400 g of propylene glycol, orally (n = 30); two doses of 60 g of Ca as calcium chloride, one at calving and the second 24 h later, orally (n = 30); and 10 g of Ca as borogluconate, intravenously (n = 30). Treatments were administered within 12 h after parturition. Blood samples were collected at d 1 (parturition), 2, 3, 6, 9, and 12 after calving. Plasma total Ca, P, Mg, NEFA, BHBA, and glucose were measured. There were no differences in the concentrations of the blood metabolites among treatments.

3-Hydroxybutyric Acid↗
PubMed2001

Modeling the active sites in metalloenzymes 5. The heterolytic bond cleavage of H(2) in the [NiFe] hydrogenase of desulfovibrio gigas by a nucleophilic addition mechanism.

The H(2) activation catalyzed by an Fe(II)-Ni(III) model of the [NiFe] hydrogenase of Desulfovibrio gigas has been investigated by density functional theory (DFT/B3LYP) calculations on the neutral and anionic active site complexes, [(CO)(CN)(2)Fe(mu-SH)(2)Ni(SH)(SH(2))](0) and [(CO)(CN)(2)Fe(mu-SH)(2)Ni(SH)(2)](-). The results suggest that the reaction proceeds by a nucleophilic addition mechanism that cleaves the H-H bond heterolytically. The terminal cysteine residue Cys530 in the [NiFe] hydrogenase active site of the D. gigas enzyme plays a crucial role in the catalytic process by accepting the proton. The active site is constructed to provide access by this cysteine residue, and this role explains the change in activity observed when this cysteine is replaced by a selenocysteine. Furthermore, the optimized geometry of the transition state in the model bears a striking resemblance to the geometry of the active site as determined by X-ray crystallography.

Binding Sites↗
PubMed2001

Minimum energy structure of hydridotris(pyrazolyl)borato iridium(V) tetrahydride is not a C(3upsilon) capped octahedron.

Recent synthesis and NMR spectroscopy of neutral Ir(V) complexes hydridotris(3,5-dimethylpyrazol-1-yl)borato tetrahydride (Tp*IrH(4)) and hydridotris(pyrazol-1-yl)borato tetrahydride (TpIrH(4)) have been interpreted as supporting face-capped octahedral structures (C(3upsilon)) with each of three Ir-H bonds trans to an Ir-N bond and the fourth hydride capping the IrH(3) face. Here, density functional geometry optimizations and coupled cluster calculations on hydridotris(pyrazol-1-yl)borato iridium tetrahydrogen find that a C(s) edge-bridged octahedral tetrahydride structure and a C(1) eta(2)-dihydrogen, dihydride structure are local minima and find that the C(3upsilon) structure is a local maximum (second-order saddle point). Several low energy transition states connecting the local minima have been located, and these minima can be used to simulate the experimental NMR spectra. A comparison of the experimental infrared spectrum of Tp*IrH(4) and the harmonic frequency calculations on the C(s), C(1), and C(3upsilon) structures also supports the assignment of the C(s)and C(1) structures as the observed ones.

Borates↗
PubMed2001

A theoretical study of the primary oxo transfer reaction of a dioxo molybdenum(VI) compound with imine thiolate chelating ligands: a molybdenum oxotransferase analogue.

The reaction mechanism of an analogue system of the molybdenum oxotransferases was investigated at the density functional (B3P86) level of theory. Kinetic measurements by Schultz and Holm suggest that the reaction MoO(2)(t-BuL-NS)(2) + X --> MoO(t-BuL-NS)(2) + OX (t-BuL-NS = bis(4-tert-butylphenyl)-2-pyridylmethanethiolate(1-)) occurs through an associative transition state. Our results on the model reaction, MoO(2)(SCH(2)CHNH)(2) + P(CH(3))(3) --> MoO(SCH(2)CHNH)(2) + OP(CH(3))(3), support this hypothesis, and indicate that this reaction proceeds through a two-step mechanism via an associative intermediate. The DeltaH(++) for the first, and rate-determining, step was predicted to be 9.4 kcal/mol, and DeltaH(++) for the second step (release of the OP(CH(3))(3) product) was predicted to be 3.3 kcal/mol. These results are in good agreement with the experimental system, for which the rate determining DeltaH(++) = 9.6(6) kcal/mol. Shultz and Holm's experimental model undergoes a significant ligand rearrangement in the oxo transfer reaction: the reactant, MoO(2)(t-BuL-NS)(2), has a trans-S arrangement of the ligands, while the product, MoO(t-BuL-NS)(2), has a trans-N arrangement. To investigate the driving force behind the ligand rearrangement, four model compounds, that systematically removed the unsaturation at the N and the chelate character of the ligands, were modeled at the B3P86 level of theory. For all models of the dioxo species, the trans-N isomer was higher in energy than the trans-S isomer. The analysis of these results indicated that a trans influence accounts for approximately 16% of the energy difference, the unsaturation at the nitrogens accounts for approximately 26%, and the ring strain from the chelator accounts for approximately 58% of the energy difference between the two isomers (trans-N and trans-S). For all models of the monooxo species, only the trans-N species was a stable geometry. Therefore, for the reverse oxo transfer reaction, ligand rearrangement must occur after or during the attack of the OX substrate.

Journal Article↗
PubMed2001

Modeling the active sites in metalloenzymes. 3. Density functional calculations on models for [Fe]-hydrogenase: structures and vibrational frequencies of the observed redox forms and the reaction mechanism at the Diiron Active Center.

Optimized structures for the redox species of the diiron active site in [Fe]-hydrogenase as observed by FTIR and for species in the catalytic cycle for the reversible H(2) oxidation have been determined by density-functional calculations on the active site model, [(L)(CO)(CN)Fe(mu-PDT)(mu-CO)Fe(CO)(CN)(L')](q)(L = H(2)O, CO, H(2), H(-); PDT = SCH(2)CH(2)CH(2)S, L' = CH(3)S(-), CH(3)SH; q = 0, 1-, 2-, 3-). Analytical DFT frequencies on model complexes (mu-PDT)Fe(2)(CO)(6) and [(mu-PDT)Fe(2)(CO)(4)(CN)(2)](2)(-) are used to calibrate the calculated CN(-) and CO frequencies against the measured FTIR bands in these model compounds. By comparing the predicted CN(-) and CO frequencies from DFT frequency calculations on the active site model with the observed bands of D. vulgaris [Fe]-hydrogenase under various conditions, the oxidation states and structures for the diiron active site are proposed. The fully oxidized, EPR-silent form is an Fe(II)-Fe(II) species. Coordination of H(2)O to the empty site in the enzyme's diiron active center results in an oxidized inactive form (H(2)O)Fe(II)-Fe(II). The calculations show that reduction of this inactive form releases the H(2)O to provide an open coordination site for H(2). The partially oxidized active state, which has an S = (1)/(2) EPR signal, is an Fe(I)-Fe(II) species. Fe(I)-Fe(I) species with and without bridging CO account for the fully reduced, EPR-silent state. For this fully reduced state, the species without the bridging CO is slightly more stable than the structure with the bridging CO. The correlation coefficient between the predicted CN(-) and CO frequencies for the proposed model species and the measured CN(-) and CO frequencies in the enzyme is 0.964. The proposed species are also consistent with the EPR, ENDOR, and Mössbauer spectroscopies for the enzyme states. Our results preclude the presence of Fe(III)-Fe(II) or Fe(III)-Fe(III) states among those observed by FTIR. A proposed reaction mechanism (catalytic cycle) based on the DFT calculations shows that heterolytic cleavage of H(2) can occur from (eta(2)-H(2))Fe(II)-Fe(II) via a proton transfer to "spectator" ligands. Proton transfer to a CN(-) ligand is thermodynamically favored but kinetically unfavorable over proton transfer to the bridging S of the PDT. Proton migration from a metal hydride to a base (S, CN, or basic protein site) results in a two-electron reduction at the metals and explains in part the active site's dimetal requirement and ligand framework which supports low-oxidation-state metals. The calculations also suggest that species with a protonated Fe-Fe bond could be involved if the protein could accommodate such species.

Binding Sites↗
PubMed2001

Modeling the active sites of metalloenzymes. 4. Predictions of the unready states of [NiFe] Desulfovibrio gigas hydrogenase from density functional theory.

Density functional theory has been used to predict the structures of a variety of active site models for the unready states, Ni-A and Ni-SU, of the [NiFe] hydrogenase from Desulfovibrio gigas. By comparing available experimental results on Ni-A, Ni-SU, and Ni-SI with the computational results on these model complexes, we have been able to identify the most likely formulas and structures for the active sites of Ni-A and Ni-SU. Ni-A is predicted to be a Ni(III)-Fe(II) species with the bridging hydroxo ligand, rather than the expected oxo ligand, while Ni-SU is predicted to be a Ni(II)-Fe(II) species with a water molecule coordinated to the Fe center. Both have one of the terminal S atoms (cysteines) protonated.

Binding Sites↗
PubMed2001

Recent theoretical predictions of the active site for the observed forms in the catalytic cycle of Ni-Fe hydrogenase.

Various states or forms of the active site in Ni-Fe hydrogenase, both catalytically active and inactive forms, have been identified and investigated experimentally. Until recently, the geometric structure of each form remained an open question. Several recent theoretical studies with density functional theory have attempted to redress this deficiency. In this commentary, the similarities and differences among the structures proposed by these studies will be addressed.

Catalytic Domain↗
PubMed2001

An assessment of the effectiveness of the Mottep model for increasing donation rates and preventing the need for transplantation--adult findings: program years 1998 and 1999.

The National Minority Organ Tissue Transplant Education Program (MOTTEP) evaluated the effects of a community-implemented health education program for adult members of minority population groups to affect attitude, knowledge, and intent to change behavior. In addition, this study represents 1 of the first major initiatives to formally address prevention as a strategy to contribute to reducing the need for organ/tissue transplantation among minorities in the United States. The study targeted students (youth) and adults representing different ethnic groups (African-Americans, Alaskan Natives, Filipinos, Latinos, and Native Americans) who attended health education presentations addressing organ tissue donation, transplantation, and illness prevention in 15 different cities in churches, schools, and other sites. A cross-sectional study that used questionnaires was designed for collecting data from all participants. This article presents data on the adult sample only. Preintervention and postintervention data were collected from 914 adult participants to determine any immediate effects of the intervention. By using data from matched sets of the preintervention and postintervention questionnaires for all adult participants, there were significant increases in (P < or =.000) trust in doctors, future plans to become organ donors, and in participants' spiritual/religious beliefs about organ/tissue donation. There was also a significant increase (P <.05) in participants' awareness of the perceived need for organ/tissue donation. African-American participants were significantly more likely (P < or =.000) to report trust in doctors, future plans to donate organs/tissue, and perceive the need for donation as a result of MOTTEP presentation. Caucasian participants showed a significant increase (P < or =.007) in trust in doctors, perceived need for organ donation (P < or =.05), and in shifting spiritual/religious beliefs about organ/tissue donation (P < or =.02). Attitudes, knowledge, beliefs, and behavioral intentions about organ/tissue donation and illness prevention can be affected by culturally appropriate health education programs designed for targeted population groups. Sustained changes in behavioral intentions toward organ donation and illness prevention may require multiple educational interventions in different community settings to increase donation rates and improve behavioral health practices to prevent illness.

Adult↗
PubMed2001

Effects of carbohydrates from citrus pulp and hominy feed on microbial fermentation in continuous culture.

Eight dual-flow continuous-culture fermenters were used to evaluate the effect of neutral detergent-soluble carbohydrates (NDSC) on fermentation by ruminal microorganisms. Citrus pulp and hominy feed were added to a basal diet as sources of NDSC, with citrus pulp providing neutral detergent-soluble fiber (NDSF) in the form of pectic substances and with hominy feed in the form of starch. The basal diet contained 26.7% corn silage, 6.0% alfalfa hay and 3.8% cottonseed hulls on a DM basis. The dried citrus pulp diet contained on a DM basis 17.2% CP, 34.7% NDF, 33.7% NDSC, and 14.4% NDSF, whereas the hominy feed diet contained 17.9% CP, 33.2% NDF, 35.9% NDSC, and 8.8% NDSF. Organic matter, DM, and NDF and ADF digestion were not affected by source of carbohydrate. Ammonia N concentration was greater (P < 0.05) for the hominy feed diet (14.2 mg/100 mL) than for the dried citrus pulp diet (9.3 mg/100 mL). Total N, nonammonia N, microbial N, and dietary N flows were not affected by treatments; however, the efficiency of microbial protein synthesis was greater (P = 0.055) for the dried citrus pulp diet than for the hominy feed diet (30.6 vs 27.8 g of bacterial N/kg of OM truly digested). Results from this experiment indicate that NDSF from citrus pulp can provide similar sources of energy compared with starch from hominy feed to support ruminal microbial growth.

Animal Feed↗
PubMed2001

Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses.

To evaluate the response of three tropical forage species to varying rates of nitrogen (N) fertilization [0, 39, 78, 118, 157 kg of N/(ha x cutting)] and five summer harvests, forage DM mass and nutritive value were evaluated in a randomized complete block design with a split-split plot arrangement of treatments. Plots (n = 60) were established in 1996, and five harvests were conducted every 28 d from June through September in 1997 and 1998, with fertilizer applications occuring after each harvest. Fertilization with 78 kg of N/(ha x cutting) increased forage mass in these grasses by 129% (P < 0.01) compared with no N fertilization. Additional N did not result in further increases of forage mass. Bermudagrass (Cynodon dactylon) produced more forage DM [P < 0.01; 1,536 +/- 43 kg/(ha x cutting)] than stargrass [Cynodon nlemfuensis; 1,403 +/- 43 kg/(ha x cutting)] or bahiagrass [Paspalum notatum; 1,297 +/- 43 kg/(ha x cutting)]. Peak forage mass for all species occurred in late June and July. In vitro organic matter digestibility (IVOMD) of stargrass increased (P < 0.01) linearly with fertilization. A quadratic response to N fertilization (P < 0.01) was noted in IVOMD of bermudagrass, whereas bahiagrass was not affected. Bermudagrass was more (P < 0.01) digestible (57.5 +/- 0.4) than stargrass (54.6 +/- 0.4) and bahiagrass (51.9 +/- 0.4%). As fertilization level increased, NDF decreased linearly (P < 0.01) in all three forages. Total N concentration increased (P < 0.01) linearly as N fertilization increased in all forages. Total N concentration was highest (P < 0.01) in stargrass (2.4%, DM basis) compared with bermudagrass (2.2%) and bahiagrass (2.0%). Total N concentration was depressed in all forages for late June and July harvests (P < 0.01). Fertilization increased (P < 0.05) the concentration (% of DM) of all protein fractions. In July and August, nonprotein N was reduced 11.8% (P < 0.01), whereas ADIN increased in July (P < 0.01). Bahiagrass had less N in cell contents than did bermudagrass and stargrass but had a greater concentration of N associated with the cell wall. Managerial factors, including rates of N fertilization and harvest dates, can have profound effects on the nutritional value of forage. An increased understanding of these effects is imperative to improve supplementation programs for ruminants.

Animal Feed↗
PubMed2001

Effects of prepartum dry matter intake and forage percentage on postpartum performance of lactating dairy cows.

The objective of this research was to determine whether different dry matter intakes (DMI) or forage percentages prepartum would have an impact on postpartum performance. Multiparous Holstein cows (n = 41) received either high (H) or low (L) forage rations that were fed free choice (F) or restricted (R), i.e., HF, HR, LF, and LR. The L rations were higher in net energy of lactation and lower in neutral detergent fiber concentrations. After calving, all cows were fed the same ration ad libitum. Prepartum DMI were 8.0 for R versus 12.4 kg/d for F with LF greater than HF (14.1 vs. 10.7 kg/d). Prepartum treatments did not affect postpartum means for DMI, milk yield, milk protein percentage, body weight, body condition score, or plasma glucose concentrations (overall means 1 to 40 DIM were, respectively, 21.1 kg/d, 34.0 kg/d, 3.03%, 624 kg, 3.2, and 66 mg/dl). However, curves from 1 to 40 DIM showed that DMI and milk yield were slightly higher in early lactation in cows whose DMI had been restricted prepartum but mean milk fat percentage was lower (3.10 vs. 3.42%). Plasma NEFA were higher and insulin lower in H versus L before and after calving. High DMI prepartum, at best, showed no advantage over restricted feeding.

Animal Feed↗
PubMed2001

Differences in yields of microbial crude protein from in vitro fermentation of carbohydrates.

The yield of microbial crude protein (CP) from carbohydrate fermentations was examined using trichloroacetic acid (TCA) precipitation of batch cultures. The medium contained ammonium bicarbonate, casein acid hydrolysate, and cysteine hydrochloride as nitrogen sources. Isolated bermudagrass neutral detergent fiber (iNDF) and 60:40 blends of iNDF and sucrose (Suc), citrus pectin (Pec), or corn starch (Sta) (approximately 375 mg of substrate organic matter/vial) were fermented in vitro in two separate fermentation runs with mixed ruminal microbes. Three fermentation tubes for each substrate were destructively sampled at 0, 4, 8, 12, 16, 20, and 24 h. Fermented samples were precipitated at a concentration of 19.4% TCA, and filtered to collect unfermented iNDF and precipitate. Collected residues were analyzed for CP as Kjeldahl N x 6.25. Microbial CP (TCACP) was estimated as TCA-precipitated CP corrected for the TCA-precipitated CP content of substrates at 0 h, and the mean of fermentation blanks from each hour. Medium pH did not decline below 6.49 in any fermentation tube. Comparisons of maximal yields based on the hour in which the measured mean yield was greatest for each substrate in each fermentation indicated that Sta > Suc = Pec > iNDF (P < 0.05). All substrates showed increases in TCACP to their maxima, followed by declines in TCACP. This likely reflects the relative dominance of production or degradation of microbes about the point of substrate limitation. Unlike other substrates, Suc had no detectable lag, and presented a more persistent TCACP yield curve than the other non-NDF carbohydrates (NFC). Regression analysis of TCACP yield over time for iNDF versus other substrates, Pec + Sta versus Suc, and Pec versus Sta indicated that the compared curves were not parallel (P < 0.05). The patterns of TCACP yield over time were cubic for iNDF and Suc, and quartic for Pec and Sta. The maximal yields of TCACP predicted from the regressions were Sta: 34.0 mg at 15.6 h, Pec: 29.9 mg at 13.5 h, Suc: 25.5 mg at 12.6 h, and iNDF: 13.6 mg at 19.3 h. The NDF and NFC carbohydrates examined differed in both maximal yields and temporal patterns of yield of TCACP.

Animal Feed↗