Biomedical subjects

D A Christensen

Publications and source records attributed to D A Christensen.

At least 19 recordsLinked to original sources

PubMed2003

Effects of flaxseed supplementation on milk production, milk fatty acid composition and nutrient utilization by lactating dairy cows.

Twelve multiparous Holstein cows at 72 +/- 20 days in milk were used in a switch-back design with 14-d periods to determine the effect of replacing barley grain into a dairy total mixed ration with micronized or raw flaxseed on nutrient digestibility, milk yield, milk composition. Total mixed diets were (DM basis) 50% barley silage, 50% concentrate mix mainly rolled barley grain and canola meal. Diets were supplemented with 1 kg raw (RF) or micronized (MF) flaxseed to substitute 1 kg of rolled barley grain (C). Neutral detergent fibre, ADF and CP digestibility of the diets were not significantly affected by supplementation; however, calcium digestibility was reduced by 62% and 46% when raw and micronized flax were fed, respectively. Milk yield (38.3, 39.6, and 38.4 kg/d for diets C, RF and MF, respectively) was similar for all diets. Milk fat (3.50, 3.48, and 3.52%) and protein (3.31, 3.34, and 3.31%) for diets C, RF and MF, respectively, were not affected by treatment diets. Concentrations of c9, t11 conjugated linoleic acid (CLA; 0.51, 0.72 and 0.76 g/100 g fatty acids) in milk fat increased (P<0.05) similarly among the two flaxseed supplemented diets. The RF and MF diets significantly increased the C18:1, C18:1 trans-11, C18:2 cis-9, cis-12 and C18:3 in milk fat however, C12:0, C14:0 and C16:0 were significantly reduced compared with control. Replacing barley grain with flaxseed in the diet of lactating cows increased the beneficial fatty acids in milk without depressing nutrient digestibility. Micronization of flaxseed did not reveal any advantage over raw flaxseed.

Animal Feed↗

PubMed2003

Comparison of the National Research Council-2001 model with the Dutch system (DVE/OEB) in the prediction of nutrient supply to dairy cows from forages.

The objective of this study was to compare the DVE/OEB system (DVE = truly absorbed protein in the small intestine; OEB = degraded protein balance) and the NRC-2001 model in the prediction of supply of protein to dairy cows from selected forages: alfalfa (Medicago sativa L. cv. Pioneer and Beaver) and timothy (Phleum pratense L. cv. Climax and Joliette). Comparisons were made in terms of 1) ruminally synthesized microbial CP, 2) truly absorbed protein in the small intestine, and 3) degraded protein balance. In addition, the effects of variety and cutting stage of the selected forages on the potential nutrient supply to dairy cows were also studied. The results showed that the predicted values from the DVE/OEB system and the NRC-2001 model had significant correlations with high R (>0.96) values. However, using the DVE/OEB system, the overall average microbial protein supply based on available energy was 12% higher, and the truly absorbed protein in the small intestine was 15% lower than that predicted by the NRC-2001 model. The difference was also found in the prediction of the degraded protein balances, which was 11% higher based on data from the NRC-2001 model. These differences are due to considerably different factors used in calculations in the two models, although both are based on similar principles. This indicates that a further refinement is needed for a modern protein evaluation and prediction system. In addition, this study showed that the two alfalfa varieties studied (Pioneer vs. Beaver) had no effect, but cutting stage had a profound influence on ruminally synthesized microbial CP (93, 96, 86 g/kg DM at stage of early bud, late bud, and early bloom, respectively) and truly absorbed intestinal protein predicted by the DVE/OEB system (80, 79, 67 g/kg DM at stage of early bud, late bud, and early bloom, respectively). With timothy, both variety (Climax vs. Joliette) and cutting stage had significant impacts on the potential protein supply predicted by both models. The potential protein supply (DVE or MP) to the dairy cow from Climax timothy was higher than that from Joliette timothy (DVE: 46 vs. 32 g/kg DM; MP: 61 vs. 38 g/kg DM). With increasing stage of cutting, the potential protein supply (DVE or MP) was reduced (DVE: 53, 39, 25 g/kg DM; MP: 62, 51, 36 g/kg DM at stage of joint, prebloom head, and full head, respectively).

Animal Feed↗

PubMed2002

Effect of concentrate level and feeding management on chewing activities, saliva production, and ruminal pH of lactating dairy cows.

Eight ruminally cannulated lactating Holstein cows were used in a double 4 x 4 Latin square to determine the effects of 1) proportion of barley silage [40, 50, and 60% of dry matter (DM)] in the diet, and 2) feeding a total mixed ration (TMR) compared with separate ingredients (SI) on chewing activities, saliva production, and ruminal pH. Although cows fed SI were offered a diet containing 50% silage, they actually consumed a diet containing 43% silage (DM basis). Dry matter intake and milk yield were similar for all diets (18.2 kg of DM/d and 27.2 kg/d, respectively). Cows fed the 40% silage TMR spent more time eating than cows fed SI (243 vs. 198 min/d), but rumination time was similar (546 min/d). Eating time was similar among the TMR diets, but rumination time increased from 498 to 516 and 584 min/d as silage in the TMR increased from 40 to 50, and then to 60%, respectively. The secretion of saliva per gram of feed was 4.43, 3.18, and 1.19 ml/g of DM with consumption of silage, TMR, and concentrate, respectively. Resting salivation rate was similar for all diets (101 ml/min). Regardless of the diet, cows secreted 239 +/- 17 L/d of saliva, and ruminal pH was below 5.8 for 10 h/d. Results indicated increased chewing time did not increase total daily saliva secretion because increased eating and ruminating saliva was associated with decreased resting saliva. Feeding SI increased the risk of acidosis, because cows ate a higher proportion of concentrate than intended.

Animal Feed↗

PubMed2002

Chewing activity, saliva production, and ruminal pH of primiparous and multiparous lactating dairy cows.

Four multiparous (MP) and four primiparous (PP) ruminally cannulated lactating Holstein cows were used in a double 4 x 4 Latin square design to study the chewing behavior, saliva production, and ruminal pH of cows in the first or subsequent lactation. Cows were fed one of four diets; three total mixed rations containing 40, 50, or 60% silage (DM basis), and a separate ingredient diet containing 50% concentrate. Dry matter intake was higher for MP cows than for PP cows (19.2 vs. 17.1 kg/d) but not as a percentage of body weight (2.97 +/- 0.06%). Multiparous cows spent more time eating than PP cows (260 vs. 213 min/d, respectively), even after adjustment for dry matter intake (13.8 vs. 12.4 min/kg DM). Multiparous cows also spent more time ruminating per day than PP cows (560 vs. 508 min/d, respectively). Eating salivation rate was not affected by parity, but resting salivation rate was higher for MP cows than for PP. Although MP cows spent more time chewing than PP cows, total daily saliva production was only numerically higher for MP cows because the increase in saliva produced during chewing was accompanied by a decrease in saliva produced during resting. Furthermore, pH profiles tended to be lower for MP cows than for PP cows. Multiparous cows may have a greater risk of incurring acidosis than PP cows because increased salivary secretion associated with increased chewing may not sufficiently compensate the increment of fermentation acids produced in the rumen due to high feed intake.

Animals↗

PubMed2001

Calculation of electric fields induced in the human knee by a coil applicator.

Calculations are presented of the induced electric fields and current densities in the cartilage of the knee produced by a coil applicator developed for applying pulsed magnetic fields to osteoarthritic knees. This applicator produces a sawtooth-like magnetic field waveform composed of a series of 260-micros pulses with a peak to peak magnitude of approximately 0.12 mT in the cartilage region. The simulations were performed using a recently developed 3 dimensional finite difference frequency domain technique for solving Maxwell's equations with an equivalent circuit model. The tissue model was obtained from the anatomically segmented human body model of Gandhi. The temporal peak electric field magnitude was found to be -153 mV/m, averaged within the medial cartilage of the knee for the typical dB/dt excitation levels of this coil. The technique can be extended to analyze other excitation waveforms and applicator designs.

Bone and Bones↗

PubMed2001

Manipulation of cattle growth to target carcass quality.

Two trials were conducted to determine the effects of breed type, backgrounding program, and backfat end point (USBFEP) as determined by ultrasound on the performance and carcass characteristics of feedlot steers. Trial 1 utilized 144 large-framed Charolais- (304.6 +/- 16.3 kg) and 144 medium-framed Hereford-cross steers (294.8 +/- 20.9 kg). Trial 2 utilized 88 medium-framed Angus (289.5 +/- 15.0 kg), 88 large-framed Charolais- (299.8 +/- 17.7 kg), and 88 medium-framed Hereford-cross (291.1 +/- 20.9 kg) steers. Within breed type, short- (70 d) or long-term (126 d) backgrounding programs (Trial 1) and 6- or 12-mm USBFEP (Trials 1 and 2) were assigned. In both trials, carcass size was greater (P < 0.05) for the large-framed Charolais-cross steers, longer backgrounding, and fatter USBFEP treatments. Lean meat yield was greater (P < 0.05) for Charolais- than Hereford-cross steers (Trial 1) and for the leaner USBFEP (Trials 1 and 2). Marbling was greater (P < 0.05) for Angus- (Trial 2) and Charolais- (Trials 1 and 2) than Hereford-cross steers (Trials 1 and 2) and for the fatter end point (Trials 1 and 2). It was concluded that breed type, backgrounding program, and USBFEP were effective in altering growth and could be used to target carcass traits of interest for value-based marketing programs.

Animal Husbandry↗

PubMed2001

Evaluation of the 1996 NRC beef model under western Canadian environmental conditions.

Two feedlot trials were conducted to evaluate the 1996 NRC beef model under western Canadian conditions. In the first trial, 144 Charolais- (304.6 +/- 16.3 kg) and 144 Hereford- (295.1 +/- 20.8 kg) cross steers were used, whereas the second trial used 88 Angus- (289.7 +/- 15.0 kg), 88 Charolais- (299.8 +/- 17.9 kg), and 88 Hereford- (291.1 +/- 20.9 kg) cross steers. Diets were based on barley silage, rolled barley grain, canola meal, and cereal straw and were analyzed according to the 1996 NRC methodologies. Animal performance and environmental data were collected for 24 pens of steers per trial for the backgrounding and finishing periods. Levels 1 and 2 of the 1996 NRC model were used to generate predictions of DMI and ADG for each pen. Results showed that actual finishing DMI was accurately predicted for Trial 1 and for the combined trials but not for Trial 2. Predicted ADG was lower (P < 0.05) than actual ADG for all feeding periods except Level 1 of the Trial 1 finishing period. All ADG residuals were significant (P < 0.05), indicating inaccurate prediction of ADG in all feeding periods. The 1996 NRC model consistently predicted that protein was not limiting gain. Further investigations and model refinement regarding animal energy requirements under cold weather conditions and effects of limit feeding are required to increase the accuracy of the 1996 NRC model in predicting animal performance.

Animal Feed↗

PubMed2000

Factors affecting acoustically triggered release of drugs from polymeric micelles.

A custom ultrasonic exposure chamber with real-time fluorescence detection was used to measure acoustically-triggered drug release from Pluronic P-105 micelles under continuous wave (CW) or pulsed ultrasound in the frequency range of 20 to 90 kHz. The measurements were based on the decrease in fluorescence intensity when drug was transferred from the micelle core to the aqueous environment. Two fluorescent drugs were used: doxorubicin (DOX) and its paramagnetic analogue, ruboxyl (Rb). Pluronic P-105 at various concentrations in aqueous solutions was used as a micelle-forming polymer. Drug release was most efficient at 20-kHz ultrasound and dropped with increasing ultrasonic frequency despite much higher power densities. These data suggest an important role of transient cavitation in drug release. The release of DOX was higher than that of Rb due to stronger interaction and deeper insertion of Rb into the core of the micelles. Drug release was higher at lower Pluronic concentrations, which presumably resulted from higher local drug concentrations in the core of Pluronic micelles when the number of micelles was low. At constant frequency, drug release increased with increasing power density. At constant power density and for pulse duration longer than 0.1 s, peak release under pulsed ultrasound was the same as stationary release under CW ultrasound. Released drug was quickly re-encapsulated between the pulses of ultrasound, which suggests that upon leaving the sonicated volume, the non-extravasated and non-internalized drug would circulate in the encapsulated form, thus preventing unwanted drug interactions with normal tissues.

Antibiotics, Antineoplastic↗

PubMed2000

Influence of particle size on the effectiveness of the fiber in barley silage.

We used eight multiparous Holstein cows in a 4 x 4 Latin square design to evaluate the effects and possible interactions between silage particle size and concentrate level on chewing activities and productivity of cows fed barley-based total mixed rations (TMR). Diets were designed with two forage-to-concentrate ratios (low forage, 45:55, high forage 55:45), combined with two theoretical chop lengths of barley silage (short = 4.68 mm and long = 18.75 mm). Diets were formulated to provide similar and above-minimum neutral detergent fiber recommended for cows in early lactation. Increasing silage particle size of the forage did not affect dry matter intake. The 3.5% fat-correct milk and fat yields trended higher for increased particle size. Percent milk protein was higher for short particle size. Increasing the concentrate levels in the diets increased proportions of milk protein and lactose, but not milk fat. Cows fed short silage spent 90 min less per day chewing and ruminating than did those on long silage. Total chewing activity per kilogram of forage intake was higher for cows on long silage compared with those on short silage diets. Although a reduction in silage particle size did not depress milk fat, rumination and chewing activity were significantly reduced. These results suggest that particle size of the silage may have dominant control over chewing activity despite adequate neutral detergent fiber intakes.

Animal Feed↗

PubMed2000

Effects of pea, barley, and alfalfa silage on ruminal nutrient degradability and performance of dairy cows.

Six Holstein cows in early lactation were used in a double 3 x 3 Latin square design to determine the effects of feeding diets with pea silage, relative to barley silage, or alfalfa silage. Cows were fed rations formulated to contain 50:50 forage:concentrate ratio. Two ruminally fistulated cows were used in a randomized complete block design to determine ruminal nutrient degradability for pea silage relative to barley and alfalfa silages. Pea silage contained lower neutral detergent fiber (NDF), acid detergent fiber, and starch concentrations but higher crude protein than barley silage. Compared with alfalfa silage, pea silage had higher starch and NDF but lower crude protein content. Pea and alfalfa silage had similar effective ruminal degradability of dry matter, which was higher than that of barley silage. The rate of degradation and effective ruminal degradability of NDF was highest for alfalfa silage, intermediate for pea silage and lowest for barley silage. Results of the lactation trial showed that dry matter intake and milk yield were not affected by forage source. Milk composition was similar for cows fed pea or barley silage; however, cows fed pea silage produced milk with a higher fat and a lower protein percentage than those fed the alfalfa silage. Pea silage can replace barley or alfalfa silage as a forage source for dairy cows in early lactation.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Multiple-analyte fluoroimmunoassay using an integrated optical waveguide sensor.

A silicon oxynitride integrated optical waveguide was used to evanescently excite fluorescence from a multianalyte sensor surface in a rapid, sandwich immunoassay format. Multiple analyte immunoassay (MAIA) results for two sets of three different analytes, one employing polyclonal and the other monoclonal capture antibodies, were compared with results for identical analytes performed in a single-analyte immunoassay (SAIA) format. The MAIA protocol was applied in both phosphate-buffered saline and simulated serum solutions. Point-to-point correlation values between the MAIA and SAIA results varied widely for the polyclonal antibodies (R2 = 0.42-0.98) and were acceptable for the monoclonal antibodies (R2 = 0.93-0.99). Differences in calculated receptor affinities were also evident with polyclonal antibodies, but not so with monoclonal antibodies. Polyclonal antibody capture layers tended to demonstrate departure from ideal receptor-ligand binding while monoclonal antibodies generally displayed monovalent binding. A third set of three antibodies, specific for three cardiac proteins routinely used to categorize myocardial infarction, were also evaluated with the two assay protocols. MAIA responses, over clinically significant ranges for creatin kinase MB, cardiac troponin I, and myoglobin agreed well with responses generated with SAIA protocols (R2 = 0.97-0.99).

Animals↗

PubMed1999

Pupil-size effects in fiber optic stellar interferometry.

The effects of finite telescope pupil sizes on the measurement of fringe visibility in fiber optic stellar interferometry are described. It is shown theoretically that the measured fringe visibility is equal to the cross correlation of the magnitude of the source's mutual coherence function with the cross correlation of the telescopes' effective pupil functions. If the telescopes' effective pupil diameters are not small compared with the width of the source's mutual coherence function, then the measured fringe visibility will be correspondingly distorted. The theoretical results are verified experimentally in a fiber optic Mach-Zehnder interferometer.

Extraterrestrial Environment↗

PubMed1999

Evaluation of wheat-based thin stillage as a water source for growing and finishing beef cattle.

Two trials were conducted to evaluate the nutritional value of wheat-based thin stillage as a water source for cattle. In Trial 1, 20 large-framed steers were fed a basal diet based primarily on barley grain and barley silage, with ad libitum access to water or thin stillage at one of three DM concentrations (2, 4, and 6.7%) in a completely randomized design. The trial consisted of a 70-d growing period and a finishing phase. In Trial 2, total-tract nutrient digestibility coefficients of the basal diet and water treatments fed in the growing period were determined in a randomized complete block design using 12 medium-framed steers. The results showed that when only DMI from the basal diet was considered, there was a linear reduction (P<.01) in DMI and a linear improvement (P<.01) in the gain:feed ratio with no effect on daily gain as thin stillage DM concentration increased. No differences were detected in DMI or efficiency of gain when total DMI (basal diet and thin stillage) was considered. Carcass traits indicated a trend toward increased (P<.06) carcass fat with increasing thin stillage DM concentration. Results of Trial 2 indicated a linear improvement (P<.05) in apparent digestibility of DM, CP, NDF, and energy of the total diet (basal diet and thin stillage) as thin stillage DM concentration increased. We concluded that supplementing growing and finishing cattle with thin stillage reduced the amount of the basal diet required for gain and improved nutrient utilization.

Animals↗

PubMed1999

Feeding value of wheat-based thin stillage: in vitro protein degradability and effects on ruminal fermentation.

Two experiments were conducted to evaluate the nutritive value of wheat-based thin stillage as a fluid source for ruminants. In vitro CP degradability of thin stillage was estimated relative to canola meal and heated canola meal in a completely randomized design. Four ruminally cannulated steers were used in a double cross-over design to determine the effects of consuming thin stillage or water as drinking sources on ruminal fermentation traits. The in vitro CP degradability of thin stillage (55.4%) was lower (P<.05) than that of canola meal (59.4%) and higher than that of heated canola meal (31.6%). Ruminal pH for steers consuming thin stillage was higher (P<.05) at 1000 and 1100 and lower (P<.05) at 1900 and 2000 than that for steers consuming water. Total VFA followed a pattern that was the reverse of that reported for pH. Ruminal NH3 N levels were higher (P<.05) for steers fed thin stillage than for water-fed steers through most of the collection period. Ruminal fluid and particulate matter passage rates were not affected by treatment and averaged .165 and .06 /h, respectively. The amount of thin stillage and water that did not equilibrate with the ruminal fluid and, thus, was considered to bypass the rumen was estimated to be 51.9 and 59.2% of total fluid consumed, respectively. Feeding wheat-based thin stillage had no adverse effects on ruminal metabolism.

Animals↗

PubMed1997

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields.

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.

Bone Wires↗

PubMed1997

Effect of chelating agents on the excretion of copper, zinc and iron in the bile and urine of sheep.

The effect of tetrathiomolybdate (TM), disodium calcium ethylenediamine tetraacetate (EDTA), D-penicillamine (PEN), 2-3 dimercapto-1-propanol (BAL) and dimethyl dithiocarbamate (DDC) administration on biliary and urinary excretion of copper (Cu), zinc (Zn) and iron (Fe) was investigated in sheep on a low Cu diet (Group A) and a high Cu diet (Group B). Only biliary Cu excretion increased significantly (P<0.01) with TM treatment. Urinary Cu excretion increased (P<0.01) following PEN treatment. TM, EDTA, PEN, BAL and DDC adminstration increased Cu excretion via bile and urine by 254, 11, 266, 46 and 16%, respectively in Group A sheep, and by 354, 13, 196, 20 and (-) 31% in Group B sheep. Urinary Zn excretion increased (P<0.01) following EDTA and PEN treatments. Only urinary Fe excretion increased (P<0.01) with EDTA treatment. The results show that TM and PEN are the most efficient decoppering agents, but PEN unlike TM also removes Zn. The major routes of excretion of Cu chelates by TM and PEN are different. TM increases Cu excretion significantly (P<0.05 in Group A and P<0.01 in Group B) in bile with only a slight increase in urinary Cu whereas PEN increases Cu excretion significantly (P<0.01) in urine. Therefore from a therapeutic view, a combination therapy of TM and PEN would be useful to maximize Cu removal from the body.

Animals↗

PubMed1997

Use of real-time ultrasound to evaluate live animal carcass traits in young performance-tested beef bulls.

Young bulls were ultrasonically scanned to 1) study breed differences for 12th rib fat depth (USFAT) and longissimus muscle area (USREA), 2) evaluate the nature and predictability of USFAT and USREA development, and 3) determine the effect of age (YFAT and YREA, respectively) or weight (WREA) adjustments on USFAT and USREA. Angus (AA), Charolais (CH), Hereford (HH), Shorthorn (SS), and Simmental (SM) bulls (n = 886) were studied in 2 yr at two stations. Breed differences were observed for end of test USFAT (AA = SS > HH > CH = SM, P < .05) and USREA (CH = SM > SS = AA > HH, P < .05). Within-breed coefficients of variation were 29.8 to 48.4% for end of test USFAT and from 9.0 to 10.8% for end of test USREA. In most bulls, USFAT development was neither linear nor quadratic (P > .05), but USREA development was linear (P < .05). Prediction equations were characterized by low r2 and high residual standard deviation (RSD) values, although those for d-84 USREA had r2 values from .63 to .70 and RSD values from 4.09 to 5.80 cm2. High associations were obtained between end of test USFAT with YFAT (r = .83 to .91, P < .05) and USREA with YREA (r = .74 to .84, P < .05) but not for end of test USREA with WREA (r = .31 to .56, P < .05). These results indicate that end of test ultrasound measurements may be a useful addition to performance testing programs.

Adipose Tissue↗

PubMed1996

Femtomolar sensitivity using a channel-etched thin film waveguide fluoroimmunosensor.

A dual channel, evanescent fluoroimmunoassay format is used to detect femtomolar analyte concentrations (i.e. less than 1 part per trillion [w/w]) on an etched channel siliconoxynitride thin film integrated optical waveguide. Two assays are used to demonstrate the dose-response behaviour of the sensor: (1) a direct assay of a fluorescently-labeled protein ligand binding to an immobilized protein receptor, and (2) an indirect sandwich assay of a non-fluorescent protein ligand binding to an immobilized protein receptor, as detected by the binding of a fluorescently-labeled secondary receptor protein. A red-emitting cyanine dye (Cy-5), which minimized background fluorescence and scatter losses of the waveguide, was used in both assays. To our knowledge, this is the first report of femtomolar sensitivity in an immunosensing instrument.

Biosensing Techniques↗