Biomedical subjects

M R Murphy

Publications and source records attributed to M R Murphy.

At least 19 recordsLinked to original sources

PubMed2006

Development and evaluation of models to predict the feed intake of dairy cows in early lactation.

Inaccurate prediction of dry matter intake (DMI) limits the ability of current models to anticipate the technical and economic consequences of adopting different strategies for production management on individual dairy farms. The objective of the present study was to develop an accurate, robust, and broadly applicable prediction model and to compare it with the current NRC model for dairy cows in early lactation. Among various functions, an exponential model was selected for its best fit to DMI data of dairy cows in early lactation. Daily DMI data (n = 8,547) for 3 groups of Holstein cows (at Illinois, New Hampshire, and Pennsylvania) were used in this study. Cows at Illinois and New Hampshire were fed totally mixed diets for the first 70 d of lactation. At Pennsylvania, data were for the first 63 d postpartum. Data from Illinois cows were used as the developmental dataset, and the other 2 datasets were used for model evaluation and validation. Data for BW, milk yield, and milk composition were only available for Illinois and New Hampshire cows; therefore, only these 2 datasets were used for model comparisons. The exponential model, fitted to the individual cow daily DMI data, explained an average of 74% of the total variation in daily DMI for Illinois data, 49% of the variation for New Hampshire data, 67% of the variation for Pennsylvania data, and 64% of the variation overall. Based on all model selection criteria used in this study, the exponential model for prediction of weekly DMI of individual cows was superior to the current NRC equation. The exponential model explained 85% of the variation in weekly mean DMI compared with 42% for the NRC equation. Compared with the relative prediction error of 6% for the exponential model, that associated with prediction using the NRC equation was 14%. The overall mean square prediction error value for individual cows was 5-fold higher for the NRC equation than for the exponential model (10.4 vs. 2.0 kg2/d2). The consistently accurate and robust prediction of DMI by the exponential model for all data-sets suggested that it could safely be used for predicting DMI in many circumstances.

Animal Nutritional Physiological Phenomena↗

PubMed2005

Development of a system to predict feed protein flow to the small intestine of cattle.

A data set constructed from research trials published between 1979 and 1998 was used to derive equations to adjust published tabular values for the rumen-undegradable protein (RUP) content of feeds to better predict the passage of nonammonia nonmicrobial N (NANMN) to the small intestine of lactating dairy cows. Both linear and nonlinear forms of equations were considered for making adjustments. Iterative processes were used to estimate equation parameters. A logistic equation was developed and considered to be the most optimal for adjustment of published tabular RUP contents of feeds. The equation is a function of dietary dry matter intake (DMI) and includes terms for tabular RUP and nonprotein N contents of individual feeds. The equation has a standard error of prediction of 69.29 g of NANMN/ d per cow and a root mean square prediction error of 104.63 g of NANMN/d per cow. Independent evaluation of the equation indicated that the concept of variable RUP content for feeds based on DMI is correct. Further refinements may be needed as other data become available to quantify the effects of additional factors on the RUP value of feeds.

Animal Feed↗

PubMed2005

Within-day feeding behavior of lactating dairy cows measured using a real-time control system.

The suitability of a statistical model for describing within-day feeding behavior, and potential relationships between model parameters and commonly measured experimental variables were examined. Forty multiparous, midlactation Holstein cows were fed using a real-time control system to record the date of each visit to a feeder, entrance time, exit time, and feed consumed over a 6-wk period. Daily feed consumption, number of visits, meal duration, and within-visit rate of food intake were then calculated. Two peaks in within-day rates of feed intake were indicated, suggesting that feeding activity was randomly distributed around each peak, that is, binormal. Parameters describing the distributions (means, standard deviations, and the percentage of total feeding activity associated with each peak) were estimated. An adjusted average of 91% of the variation in within-day feeding activity was explained by the binormal model. Relationships between model parameters and commonly measured experimental variables were also identified; behavioral traits were correlated with total feed intake. Feeding activity patterns in literature data were also amenable to reanalysis by the binormal model. Lactating cows consistently exhibited a distinct diurnal pattern in feeding activity; they were most active near sunrise and again near sunset (crepuscular). Effects of various management operations (e.g., feeding and milking times and frequencies, and lighting) on within-day feeding patterns remain to be established, although a statistical model for evaluating them is now available. The patterns may have important implications for scheduling management activities to maximize feed intake and production.

Animal Feed↗

PubMed2005

Prepartum intake, postpartum induction of ketosis, and periparturient disorders affect the metabolic status of dairy cows.

Nutritional management during the dry period may affect susceptibility of cows to metabolic and infectious diseases during the periparturient period. Thirty-five multiparous Holstein cows were used to determine the effect of prepartum intake, postpartum induction of ketosis, and periparturient disorders on metabolic status. Cows were fed a diet from dry-off to parturition at either ad libitum intake or restricted intake [RI; 80% of calculated net energy for lactation (NEL) requirement]. After parturition, all cows were fed a lactation diet. At 4 d in milk (DIM), cows underwent a physical examination and were classified as healthy or having at least one periparturient disorder (PD). Healthy cows were assigned to the control (n = 6) group or the ketosis induction (KI; n = 9) group. Cows with PD were assigned to the PD control (PDC; n = 17) group. Cows in the control and PDC groups were fed for ad libitum intake. Cows in the KI group were fed at 50% of their intake on 4 DIM from 5 to 14 DIM or until signs of clinical ketosis were observed; then, cows were returned to ad libitum intake. During the dry period, ad libitum cows ate more than RI cows; the difference in intake resulted in ad libitum cows that were in positive energy balance (142% of NEL requirement) and RI cows that were in negative energy balance (85% of NEL requirement). Prepartum intake resulted in changes in serum metabolites consistent with plane of nutrition and energy balance. Prepartum intake had no effect on postpartum intake, serum metabolites, or milk yield, but total lipid content of liver at 1 d postpartum was greater for ad libitum cows than for RI cows. The PD cows had lower intake and milk yield during the first 4 DIM than did healthy cows. During the ketosis induction period, KI cows had lower intake, milk yield, and serum glucose concentration but higher concentrations of nonesterified fatty acids and beta-hydroxybutyrate in serum as well as total lipid and triacylglycerol in liver than did control cows. Cows with PD had only modest alterations in metabolic variables in blood and liver compared with healthy cows. The negative effects of PD and KI on metabolic status and milk yield were negligible by 42 DIM, although cows with PD had lower body condition score and BW. Prepartum intake did not affect postpartum metabolic status or milk yield. Periparturient disorders and induction of ketosis negatively affected metabolic status and milk yield during the first 14 DIM.

3-Hydroxybutyric Acid↗

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

Dietary cation-anion difference effects on performance and acid-base status of lactating dairy cows: a meta-analysis.

A meta-analysis was conducted to examine potential empirical relationships between dietary cation-anion difference (DCAD) (Na + K - Cl) and the response of lactating dairy cows. The database was developed from 12 studies published between 1984 and 1997 that included a total of 17 trials, 69 dietary treatments, and 230 cows. Results indicated that DCAD affected performance of lactating dairy cows. Maximum milk yield and feed intake were reached when DCAD was 34 and 40 meq/100 g of feed dry matter, respectively. Blood pH and HCO3 concentrations increased with DCAD, indicating an improved acid-base balance of lactating dairy cows. Changes in urinary pH and urinary excretion of Na, K, and Cl were consistent with varying DCAD, thus dietary acidity or alkalinity. The effects of DCAD were likely mediated via modification of acid-base status in the cows.

Acid-Base Equilibrium↗

PubMed2004

Effect of liquid flavor supplementation of the diet on dairy cows in the transition period.

A 9-wk trial was conducted to study the performance of 24 Holstein cows during the transition period (3 wk prepartum to 6 wk postpartum). Cows were assigned to either a control or liquid-flavored (0.52 mL/kg of feed) total mixed ration in a randomized complete block design. The diets contained corn silage, alfalfa haylage, cottonseed, and a grain mix based on ground corn and soybean meal. Cows were fed to ensure 10% orts, and the diet provided (on a dry matter basis) 13% crude protein, 32% acid detergent fiber, 44% neutral detergent fiber, and 1.54 Mcal/kg of NEL prepartum and 17.5% crude protein, 30% acid detergent fiber, 40% neutral detergent fiber, and 1.57 Mcal/kg of NEL postpartum. An additional 2.3 kg of alfalfa hay was fed during the first 5 d postpartum. Weekly means of dry matter intake (DMI), milk yield, milk protein, milk fat, SNF, somatic cell counts, and body weight (BW) were analyzed using a repeated measures procedure. There was no effect of treatment on these variables, and least squares means were 16.9 and 15.7 kg/d for DMI, 38 and 35.3 kg/d for milk yield, 3.10 and 3.11% for milk protein, 3.69 and 3.74% for milk fat, 8.37 and 8.16% for SNF, 1.99 x 10(5) and 4.33 x 10(5) for somatic cell count, and 631 and 651 kg for BW for cows fed control and flavored diets, respectively. Individual cow daily DMI data were fitted to an exponential model describing pre- and postpartum feed consumption [DMI = a - b x e(-c x t), where DMI was measured in kg, a = asymptotic DMI, b = potential fractional increase in DMI, c = fractional rate of increase in DMI, and t = days prior to calving or days in milk]. Fractional rates of increase in DMI were similar: 0.139 and 0.123/d for control and flavored diets, respectively. Data for both groups were separately analyzed using multiple regression with 3.5% fat-corrected milk as the dependent variable and BW and DMI as independent variables. More BW was mobilized per unit increase in 3.5% fat-corrected milk in cows fed the control than in cows fed the flavored diet. Cows fed the control diet tended to be in more negative energy balance during early lactation than cows fed the flavored diet. It was concluded that feeding flavor improved energy balance of cows in early lactation and may reduce the risk of health or reproductive problems.

Animal Feed↗

PubMed2003

In vitro fermentation characteristics of selected oligosaccharides by swine fecal microflora.

The objective of this study was to quantify the fermentation characteristics of oligosaccharides present in feed ingredients or isolated for dietary supplementation. Substrates studied included short-chain fructooligosaccharides, medium-chain fructooligosaccharides, long-chain fructooligosaccharides, raffinose, stachyose, soy solubles, granular and liquid forms of transgalactooligosaccharides, glucooligosaccharides, mannanoligosaccharides, and xylooligosaccharides. Three healthy pigs that had never received antibiotics served as sources of fecal inoculum. Each substrate was fermented in vitro; samples were taken at 0, 2, 4, 8, and 12 h, and pH change and short-chain fatty acid (SCFA) and gas production determined. Gas production at 12 h did not differ (P > 0.05) among all fructooligosaccharides, transgalactooligosaccharides, soy solubles, and xylooligosaccharides. Raffinose, stachyose, and raffinose + stachyose fermentation resulted in the greatest (P < 0.05) gas production at 12 h of all substrates tested. The rate of gas production was greatest (P < 0.05) for stachyose and least (P < 0.05) for glucooligosaccharides and mannanoligosaccharides. Substrate did not affect (P > 0.05) time to attain maximal rate of gas production. The pH at 12 h for all fructooligosaccharides and xylooligosaccharides did not differ (P > 0.05). The pH values at 12 h for raffinose, stachyose, and raffinose + stachyose were highest (P < 0.05) compared with all other substrates. Total SCFA production at 12 h was similar for all fructooligosaccharides and transgalactooligosaccharides, glucooligosaccharides, and soy solubles. Total SCFA production was greatest (P < 0.05) for xylooligosaccharides, stachyose, and raffinose + stachyose, and least (P < 0.05) for mannanoligosaccharides and raffinose. Stachyose fermentation resulted in the greatest (P < 0.05) rate and earliest time to attain maximal rate of SCFA production. All oligosaccharides studied were readily fermentable but varied in amount and type of SCFA produced. Fermentation of the pure forms of oligosaccharides contained in soy solubles resulted in greater gas production and higher pH compared with soy solubles. The oligosaccharides in the soy solubles matrix seemed to behave differently than their pure counterparts. The high rates of fermentation of most oligosaccharides tested indicate that they may serve as fermentable carbohydrate sources in the terminal small intestine or large intestine of swine.

Animals↗

PubMed2001

Lack of effect of 94 GHz radio frequency radiation exposure in an animal model of skin carcinogenesis.

Although there is no evidence that electromagnetic energy in the radio frequency radiation (RFR) band is mutagenic, there have been suggestions that RFR energy might serve as either a promoter or co-promoter in some animal models of carcinogenesis. Recent developments in electromagnetic technology have resulted in the manufacture of RFR sources capable of generating frequencies in the millimeter wavelength (MMW) range (30-300 GHz). Because absorption of MMW energy occurs in the skin, it is to be expected that long-term detrimental health effects, if any, would most likely be manifest in the skin. In this study we investigated whether a single (1.0 W/cm(2) for 10 s) or repeated (2 exposures/week for 12 weeks, 333 mW/cm(2) for 10 s) exposure to 94 GHz RFR serves as a promoter or co-promoter in the 7,12-dimethylbenz[a]anthracene (DMBA)-induced SENCAR mouse model of skin carcinogenesis. Neither paradigm of MMW exposure significantly affected papilloma development, as evidenced by a lack of effect on tumor incidence and multiplicity. There was also no evidence that MMW exposure served as a co-promoter in DMBA-induced animals repeatedly treated with 12-O-tetradecanoylphorbol 13-acetate. Therefore, we conclude that exposure to 94 GHz RFR under these conditions does not promote or co-promote papilloma development in this animal model of skin carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2000

Comparative effects of extremely high power microwave pulses and a brief CW irradiation on pacemaker function in isolated frog heart slices.

The existence of specific bioeffects due to high peak power microwaves and their potential health hazards are among the most debated but least explored problems in microwave biology. The present study attempted to reveal such effects by comparing the bioeffects of short trains of extremely high power microwave pulses (EHPP, 1 micros width, 250-350 kW/g, 9.2 GHz) with those of relatively low power pulses (LPP, 0.5-10 s width, 3-30 W/g, 9.2 GHz). EHPP train duration and average power were made equal to those of an LPP; therefore both exposure modalities produced the same temperature rise. Bioeffects were studied in isolated, spontaneously beating slices of the frog heart. In most cases, a single EHPP train or LPP immediately decreased the inter-beat interval (IBI). The effect was proportional to microwave heating, fully reversible, and easily reproducible. The magnitude and time course of EHPP- and LPP-induced changes always were the same. No delayed or irreversible effects of irradiation were observed. The same effect could be repeated in a single preparation numerous times with no signs of adaptation, sensitization, lasting functional alteration, or damage. A qualitatively different effect, namely, a temporary arrest of preparation beats, could be observed when microwave heating exceeded physiologically tolerable limits. This effect also did not depend on whether the critical temperature rise was produced by LPP or EHPP exposure. Within the studied limits, we found no indications of EHPP-specific bioeffects. EHPP- and LPP-induced changes in the pacemaker rhythm of isolated frog heart preparation were identical and could be entirely attributed to microwave heating.

Animals↗

PubMed2000

Neural and behavioral teratological evaluation of rats exposed to ultra-wideband electromagnetic fields.

Several investigators have reported teratologic effects of electromagnetic field exposure. The majority of these studies have been performed at levels of exposure that could produce substantial heating of the animals. New and unique sources of ultra-wideband (UWB) electromagnetic fields are currently being developed and tested that are capable of generating nonthermalizing, high-peak-power, microwave (MW) pulses with nanosecond (ns) pulse widths, picosecond (ps) rise times, and an UWB of frequencies. Our study was performed to determine if teratological changes occur in rat pups as a result of (i) daily UWB exposures during gestation days 3-18, or (ii) as a result of both prenatal and postnatal (10 days) exposures. Dams were exposed either to (i) UWB irradiation from a Kentech system that emitted a 55 kV/m-peak E field, 300 ps rise time, and a 1.8 ns pulse width, average whole-body specific absorption rate 45 mW/kg; (ii) sham irradiation; or (iii) a positive control, lead (Pb) acetate solution (2000 microg/ml) continuously available in the drinking water. Offspring were examined for ontogeny (litter size, sex-ratios, weights, coat appearance, tooth-eruption, eye-opening, air-righting, and ultrasonic stress vocalizations). Male pups were tested on various performance measures (locomotor, water-maze learning, and fertilization capabilities). The pups postnatally exposed were examined for hippocampal morphology and operant behavior. Behavioral, functional, and morphological effects of UWB exposure were unremarkable with these exceptions: (i) The UWB-exposed pups emitted significantly more stress vocalizations than the sham-exposed pups; (ii) the medial-to-lateral length of the hippocampus was significantly longer in the UWB-exposed pups than in the sham-exposed animals; (iii) male offspring exposed in utero to UWB mated significantly less frequently than sham-exposed males, but when they did mate there was no difference in fertilization and offspring numbers from the sham group. There does not appear to be a unifying physiological or behavioral relationship among the significant differences observed, and our findings could be due to the expected spurious results derived when a large number of statistical comparisons are made. Significant effects found between our positive-controls and other groups on numerous measures indicates that the techniques used were sensitive enough to detect teratological effects. Bioelectromagnetics 21:524-537, 2000. Published 2000 Wiley-Liss, Inc.

Animals↗

PubMed2000

Partitioning of amino acids flowing to the abomasum into feed, bacterial, protozoal, and endogenous fractions.

We partitioned the flow of amino acids (AA) to the abomasum among rumen undegradable protein (RUP) and bacterial, protozoal, and endogenous fractions using four Holstein cows in midlactation that were equipped with ruminal and abomasal cannulas. A 2 x 2 factorial design with four diets, combinations of high or low ruminally degradable organic matter, and rumen degradable protein, was employed. Crude protein (CP) and AA contents of ruminal bacteria and protozoa and abomasal digesta were determined. Equations for the source compositions and in vivo flows of CP and 16 AA were then solved simultaneously with a linear program to estimate the contribution of RUP, bacterial, protozoal, and endogenous CP to AA flows. The flows of RUP and bacterial AA were not affected by diet. Low dietary RDP increased the flow of protozoal AA to the abomasum, but the ruminally degradable organic matter content of the diet did not affect protozoal AA flow. Across diets, RUP, bacterial, protozoal, and endogenous fractions provided 55, 33, 11, and <1% of the CP, and 62, 26, 12, and <1% of the AA that reached the abomasum. The linear program was a useful tool for partitioning AA that flows to the abomasum. The technique may also allow dietary effects on ruminal microbes and the AA profile of protein flowing to the duodenum to be better understood and perhaps manipulated.

Abomasum↗

PubMed1999

Targeting a SWI/SNF-related chromatin remodeling complex to the beta-globin promoter in erythroid cells.

Chromatin remodeling complexes such as the SWI/SNF complex make DNA accessible to transcription factors by disrupting nucleosomes. However, it is not known how such complexes are targeted to the promoter. For example, a SWI/SNF1-like chromatin remodeling complex erythroid Krüppel-like factor (EKLF) coactivator-remodeling complex 1 (E-RC1) disrupts the nucleosomes over the human beta-globin promoter in an EKLF-dependent manner. However, it is not known whether E-RC1 is targeted specifically to the beta-globin promoter or whether E-RC1 is randomly targeted, but its activity is evident only at the beta-globin promoter. Because E-RC1 cannot remodel chromatin over the beta-globin promoter without EKLF in vitro, it has been proposed that SWI/SNF1-like complexes such as E-RC1 are targeted specifically to the promoter by selectively interacting with promoter-associated transcription factors such as EKLF. In this report, we test this hypothesis in the cellular context by using the ProteIN POsition Identification with Nuclease Tail (PIN*POINT) assay. We find that the Brahma-related gene (BRG) 1 and BRG1-associated factor (BAF) 170 subunits of E-RC1 are both recruited near the transcription initiation site of the beta-globin promoter. On transiently transfected templates, both the locus control region and the EKLF-binding site are important for their recruitment to the beta-globin promoter in mouse erythroleukemia cells. When the beta-globin promoter was linked to the cytomegalovirus enhancer, the E-RC1 complex was not recruited, suggesting that recruitment of the E-RC1 complex is not a general property of enhancers.

Base Sequence↗

PubMed1999

Lack of effects on heart rate and blood pressure in ketamine-anesthetized rats briefly exposed to ultra-wideband electromagnetic pulses.

Fourteen Sprague-Dawley rats were exposed to pulses produced by a Bournlea ultra-wideband (UWB) pulse generator (rise time, 318-337 ps; maximum E field, 19-21 kV/m). Exposures at a repetition frequency of 1 kHz for 0.5 s or to repetitive pulse trains (2-s exposure periods alternating with 2 s of no exposure, for a total of 2 min) resulted in no significant changes in heart rate or mean arterial blood pressure. These results suggest that acute whole-body exposure to UWB pulses does not have a detrimental effect on the cardiovascular system.

Anesthetics, Dissociative↗

PubMed1999

A technique for assessing the effects of olfaction on feed preference in lactating Holstein cows.

Our objective was to develop a method for assessing the effects of olfaction on feed preference. Two multiparous lactating Holstein cows were offered a totally mixed ration consisting of corn silage, alfalfa haylage, and a ground corn and soybean meal-based concentrate mixture (25:25:50 on a DM basis) for their ad libitum consumption in four consecutive 2.5-h periods daily for 5 d. An apparatus was developed that allowed odorants to be distributed at a set rate over two feeding containers with limited possibility of odor carryover. Four odorants and a control (no odorant) were compared against each other. All possible comparisons were conducted on the left and right feeding sides to avoid potential lateral-preference effects. Rank values of 0 or .5 were assigned to each odorant based on the percentage of total feed consumed in a period. A test of overall equality based on the sums of squares of ranks was used to determine whether odors affected preference. The limited results indicated that inhalation of odorants did not affect preference. Rank values were doubled for several odorants when compared with others, which suggested that the sample size limited experimental sensitivity. To attain reasonable power, we estimated that at least six cows were needed per study. Large effects of odorants on feed preference would have been required to reach statistical significance in this trial; however, the method provides a practical technique for testing the effects of olfaction on feed preference in cattle when the suggested number of cows is used.

Animal Feed↗

PubMed1999

Technical note: a device for obtaining time-integrated samples of ruminal fluid.

A device was adapted to allow for time-integrated sampling of fluid from the rumen via a cannula. The sampler consisted of a cup-shaped ceramic filter positioned in the ventral rumen of a cannulated cow and attached to a tube through which fluid entering the filter was removed continuously using a peristaltic pump. Rate of ruminal fluid removal using the device was monitored over two 36-h periods (at 6-h intervals) and was not affected (P > .05) by time, indicating that the system was not susceptible to clogging during this period. Two cows having ad libitum access to a totally mixed ration were used in a split-block design to evaluate the utility of the system for obtaining time-integrated samples of ruminal fluid. Ruminal fluid VFA concentration and pattern in samples collected in two replicated 8-h periods by the time-integrated sampler (at 1-h intervals) were compared with composite samples collected using a conventional suction-strainer device (at 30-min intervals). Each 8-h collection period started 2 h before or 6 h after feeding. Results indicated that total VFA concentration was not affected (P > .05) by the sampling method. Volatile fatty acid patterns were likewise unaffected (P > .05) except that acetate was 2.5% higher (P < .05) in samples collected 2 h before feeding and valerate was 5% higher (P < .05) in samples collected 6 h after feeding by the suction-strainer device. Although significant, these differences were not considered physiologically important. We concluded that use of the ceramic filter improved the sampling of ruminal fluid by simplifying the technique and allowing time-integrated samples to be obtained.

Animals↗

PubMed1999

Ultrawideband radiation and pentylenetetrazol-induced convulsions in rats.

New non-ionizing pulsed systems using ultrawideband (UWB) require safety assessment before they can be used by either military or civilian communities. The development of directed energy weaponry intended for use against electronically vulnerable targets, as well as ground-probing radar systems, have used fast-rise-time high-peak-power electromagnetic pulses characteristic of UWB emitters. It has been postulated that these ultrashort pulses might produce electromagnetic transients resulting in tissue damage. Several challenges to this notion have been posed, however. One report found that rats exposed to UWB after receiving a convulsant drug tended toward longer latency to the onset of convulsions than the no-exposure group. Although not statistically significant, the presence of this trend prompted the present study. An ED99 dose of the convulsant pentylenetetrazol (PTZ) or saline was given just before UWB or sham exposure and resultant seizure activity was recorded. The data from the current study show no effect of UWB exposure on PTZ-induced seizure activity, thereby not supporting the tissue damage concerns, at least for the exposure parameters used here.

Animals↗

PubMed1998

Influence of organic modifier concentration on plate number in micellar electrokinetic chromatography. 1. 2-propanol.

This paper establishes a physicochemical basis for the efficiency losses in micellar electrokinetic chromatography in buffers containing sodium dodecyl sulfate (SDS) and 2-propanol (2PN). Weakly, intermediately, and strongly retained analytes were separated in phosphate/borate buffers containing 50 mM SDS and from 0 to 10% 2PN by volume. Their plate numbers N generally agreed well with predictions of a theory for N based on longitudinal diffusion and instrumental contributions to dispersion. The N's of weakly and intermediately retained analytes were not affected strongly by 2PN over this concentration range, because their diffusion coefficients varied inversely with buffer viscosity and their retention times largely varied directly with viscosity. These combined effects on dispersion almost canceled. However, the N's of strongly retained analytes decreased with increasing 2PN, because their diffusion coefficients varied inversely with viscosity but their retention times increased more rapidly than did viscosity. These combined effects on dispersion did not cancel. These differences occurred because 2PN penetrated the micelles, caused bound counterions to be released, and increased the micellar charge and electrophoretic mobility. As 2PN concentration increased, the micelles electrophoresced increasingly rapidly against the electroosmotic flow. Consequently, strongly retained compounds required increasingly long times to elute.

2-Propanol↗