Biomedical subjects

A N Pell

Publications and source records attributed to A N Pell.

30 records · Page 2Linked to original sources

PubMed1996

Fixing the leaky pipeline: women scientists in academia.

Although the number of women receiving doctorates and in academic positions has increased over the past 20 yr, females still are under-represented on university faculties. The extent of and reasons for this inequity are discussed. There are four critical periods that influence the retention of women in science: early childhood, adolescence, college, and the graduate school/job entry period. For each of the later three periods, the paper addresses the relationship between self-esteem and job performance, the quality and impacts of classroom interactions, and the role of the advisor/mentor. In addition, some of the difficulties in combining career and family responsibilities are considered. Effective networking and mentoring play an important role at the faculty level. If our goal is to have a scientific community open equally to all members of the general population, it is necessary to keep adolescent girls involved in math and science and to maintain their self-esteem. New faculty need to be more completely included in departmental and professional activities through both formal programs and good neighborliness on the behalf of existing faculty.

Animal Husbandry↗

PubMed1996

Prediction of ruminal volatile fatty acids and pH within the net carbohydrate and protein system.

A steady-state model of the production, absorption, passage, and concentration of ruminal VFA and pH is developed from published literature data and is structured to use the feed descriptions and inputs from the net carbohydrate and protein system. Included are the effects of pH on growth rate and yield of structural and non-structural carbohydrate-fermenting bacteria; production of acetate, propionate, butyrate, lactate, and methane; conversion of lactate to VFA; ruminal absorption of acids; and prediction of ruminal pH from dietary measures and from ruminal buffering and acidity. The root mean square error of predicted total VFA concentration was 12 mM. Individual VFA fractions were inadequately predicted. In a review of literature data, effective NDF (eNDF) provided a better correlation with ruminal pH than forage or NDF. Digestion rate of NDF remained at normal levels above pH 6.2, which corresponds to a minimum eNDF of 20% of dietary DM. Further research is needed to determine the individual VFA produced from carbohydrate fractions at various pH, the appropriateness of partitioning the starch and pectin carbohydrate pool into slowly and rapidly degraded fractions, and the effect on microbial yield, total tract digestibility, and predicted energy values of feeds.

Acetates↗

PubMed1996

Effect of maturity on digestion kinetics of water-soluble and water-insoluble fractions of alfalfa and brome hay.

Alfalfa and bromegrass, each harvested at five different stages of maturity, were separated into water-insoluble and -soluble fractions. The NDF concentrations ranged from 19 to 43% for alfalfa and from 42 to 58% for brome. The rates of digestion, by mixed ruminal microflora, of the unfractionated forage and of the water-insoluble and -soluble fractions were measured in vitro using pressure sensors to monitor gas production. Both forages showed the expected decline in fiber digestibility with increasing maturity. A dual-pool logistic model gave pool sizes, specific rates, and a single lag time for both the faster- and slower-digesting fractions. The main difference between alfalfa and brome was in the soluble pool. This pool produced approximately 40% of the total gas in alfalfa, 25% in brome. The specific digestion rates of the brome soluble pool were approximately 50% higher than those for alfalfa. Net VFA production showed a somewhat higher acetate: propionate ratio for brome (3.2) compared with alfalfa (2.2), but there was little change with increasing maturity within a given forage. Gas production curves for the unfractionated forage showed a 0 to 10% positive deviation from curves created by adding data from separate digestion of the insoluble and soluble forage fractions. Gas measurements offer a promising approach to the study of the water-soluble extracts of forages and the interaction of the soluble- and insoluble-fractions during fermentation.

Acetates↗

PubMed1996

Predicting ad libitum dry matter intake and yields of Jersey cows.

Two data files were used that contained weekly mean values for ad libitum DMI of lactating Jersey cows along with appropriate cow, ration, and environmental traits for predicting DMI. One data file (n = 666) was used to develop prediction equations for DMI because that file represented a number of separate experiments and contained more diversity in potential predictors, especially those related to ration, such as forage type. The other data file (n = 1613) was used primarily to verify these equations. Milk protein yield displaced 4% FCM output as a prediction variable and improved the R2 by several units but was not used in the final equations, however, for the sake of simplicity. All equations contained adjustments for the effects of heat stress, parity (1 vs. > 1), DIM > 15, BW, use of recombinant bST, and other significant independent variables. Equations were developed to predict DMI of cows fed individually or in groups and to predict daily yields of 4% FCM and milk protein; equations accounted for 0.69, 0.74, 0.81, and 0.76 of the variation in the dependent variables with standard deviations of 1.7, 1.6, 2.7, and 0.084 kg/ d, respectively. These equations should be applied to the development of software for computerized dairy ration balancing.

Animal Feed↗

PubMed1995

Isolation and characterization of an anaerobic ruminal bacterium capable of degrading hydrolyzable tannins.

An anaerobic diplococcoid bacterium able to degrade hydrolyzable tannins was isolated from the ruminal fluid of a goat fed desmodium (Desmodium ovalifolium), a tropical legume which contains levels as high as 17% condensed tannins. This strain grew under anaerobic conditions in the presence of up to 30 g of tannic acid per liter and tolerated a range of phenolic monomers, including gallic, ferulic, and p-coumaric acids. The predominant fermentation product from tannic acid breakdown was pyrogallol, as detected by high-performance liquid chromatography and mass spectrometry. Tannic acid degradation was dependent on the presence of a sugar such as glucose, fructose, arabinose, sucrose, galactose, cellobiose, or soluble starch as an added carbon and energy source. The strain also demonstrated resistance to condensed tannins up to a level of 4 g/liter.

Animals↗

PubMed1995

Measurement and kinetic analysis of the neutral detergent-soluble carbohydrate fraction of legumes and grasses.

The fermentation of the neutral detergent-soluble (NDS) fraction of two legumes (clover, alfalfa) and two grasses (timothy, guinea grass) was measured using a curve subtraction technique with in vitro gas production data from the whole forage and the isolated neutral detergent-extracted fiber. The NDF disappearance and VFA production also were measured. There were no significant differences between the VFA patterns from whole forage and NDF. There was a good linear correlation between the volume of gas produced and the mass of fiber digested in the NDF samples. Analysis of the gas curves with a dual-pool logistic model gave a lag value, digestion rates and pool sizes for the whole forage, the fiber component, and the NDS fraction. Rates for the NDS fraction ranged from .152 h-1 for clover to .191 h-1 for timothy. These rates are appreciably lower than values assumed in some models. Application of a triple-pool logistic model revealed the presence of faster-digesting material in the legumes. We discuss several different ways to measure the NDS pool size. The simplest method requires only a single gas measurement at the end of in vitro digestion of the whole forage coupled with an NDF disappearance measurement. The curve subtraction technique can provide information on the size and digestion kinetics of the NDS pool. This information is useful both for model studies and for agronomic research and may help us to understand the nutritional significance of this fast-digesting carbohydrate fraction.

Carbohydrate Metabolism↗

PubMed1995

Validity of using accumulated gas pressure readings to measure forage digestion in vitro: a comparison involving three forages.

Gas output from in vitro digestion of forage can be used to measure both forage digestibility and the kinetics of microbial digestion. Two different approaches are used to measure gas volumes: 1) either the gas is collected at atmospheric pressure and its volume determined directly, or 2) the gas accumulates in a fixed volume container, and the volume is calculated from pressure changes. We have used the latter technique to study the in vitro digestion of alfalfa, timothy, and corn silage by ruminal microorganisms in bottles of different sizes. We measured pH changes, NDF disappearance, and VFA concentrations and characterized the digestion profiles using a single- or dual-pool logistic model. Bottle size had a slight effect on pH but was not associated with changes in any of the other characteristics measured including the kinetic parameters. Gas measurements based on pressure increases in a fixed volume container appear to offer a valid alternative to methods based on gas collection at atmospheric pressure. We present an equation to adjust pressure sensor calibration values for use in different sized containers.

Animal Feed↗

PubMed1994

Kinetics of fiber digestion from in vitro gas production.

In vitro gas production, measured by computer-interfaced pressure sensors, was used to follow the digestion of a crystalline processed cellulose, a bacterial cellulose, and mixtures of these substrates by mixed ruminal bacteria. A first-order, substrate limited model (simple exponential with lag) and two bacterial growth models (logistic, Gompertz) were tested to fit these data. No single pool model gave an optimal fit to all substrates, but dual pool versions of both the logistic and Gompertz models fitted the data extremely well. Derivations of these models in the context of gas production are presented. The dual pool version of the exponential model commonly used to analyze fiber digestion was not able to reproduce the slope variations seen with mixed substrates. A modified dual pool logistic equation, with a single lag value, was selected to model the in vitro digestion of these substrates. The model was able to predict adequately both the input composition and the kinetic parameters for a defined mixture and gave a good fit (r2 > .995) to data from all the single and mixed substrates tested. This model may be useful for interpreting gas accumulation from natural feedstuffs.

Animal Feed↗

PubMed1993

Technical note: forage in vitro dry matter digestibility as influenced by fiber source in the donor cow diet.

Objectives of this study were to determine the influence of five donor cow diets that differed in source of fiber on true in vitro DM digestibility of eight forages. Test forages included two alfalfa (31.2 and 38.3% NDF), corn silage (50.2% NDF), oat forage (48.2% NDF), perennial rye (62.1% NDF), two reed canarygrasses (55.9 and 68.1% NDF), and timothy (68.2% NDF). Sources of fiber in donor cow diets were alfalfa haylage or alfalfa haylage plus either corn cobs, cottonseed hulls, oat hulls, or soy hulls. In addition, the effect of filtering through sintered glass crucibles or filter paper (two replicates each) was evaluated. There were differences (P < .01) among feeds in in vitro DM digestibility, but there were no interactions (P > .05) between test forages and either source of fiber in donor diets or filtration method. There was an interaction between source of fiber in the donor diet and method of filtration (P < .01). Samples inoculated with ruminal fluid from cows fed diets with oat hulls or soy hulls had lower (P < .01) in vitro DM digestibility when filtered on crucibles than on filter paper. Filtration method did not affect (P > .05) in vitro DM digestibility of samples inoculated with ruminal fluid from other diets. The in vitro DM digestibility of samples inoculated with ruminal fluid from cows fed alfalfa haylage was less than the in vitro DM digestibility when other inocula were used. The source of fiber in the donor cow diet and filtration method can affect in vitro DM digestibility, but relative ranking of forages was unaffected by these variables.

Animal Feed↗

PubMed1993

Computerized monitoring of gas production to measure forage digestion in vitro.

The techniques reported in this paper were developed to facilitate the study of the kinetics of forage digestion in vitro by measuring gas production. Fiber disappearance as a measure of the reaction rate has been replaced by the use of computerized pressure sensors to monitor the gaseous products (CO2, CH4) of microbial metabolism. The recording system described requires a computer, pressure sensors, an interface card, and appropriate software to monitor gas production continuously. Several variables, including sample size, inoculum size, vessel size, and type of pressure sensor, have been investigated to determine ranges within which gas production can be measured accurately, and the reproducibility of the results has been established. Because this technique uses small (100-mg) samples, a modified NDF method has been introduced that allows determination of extent of digestion at the end of an incubation in which gas production has been monitored. A strong linear relationship existed between NDF disappearance and gas production.

Acetates↗

PubMed1992

Effects of a prolonged-release formulation of sometribove (n-methionyl bovine somatotropin) on Jersey cows.

Milk production, feed efficiency, health, and reproduction were evaluated in 46 Jersey cows that received either 500 mg of sometribove (n-methionyl bST) in a prolonged-release formulation or an equivalent volume of excipient bi-weekly beginning at 60 +/- 3 DIM. Cows were fed a TMR for ad libitum intake and were milked twice daily. Treatment with sometribove increased 3.5% FCM production 5.3 kg/d (31.4%) over controls. Milk composition was not changed, except that milk P content averaged 51 ppm higher in bST-treated cows. Net energy intake was 4.8 Mcal/d (22.9%) higher in the bST-treated cows than in the controls. General health of all cows was good throughout the study, but the cows treated with bST had more cases of mastitis than did the control cows. The bST treatment produced localized reactions at the site of injection in some cows, but these reactions did not affect milk production. Sometribove treatment had no effect on reproductive performance; 85% of the treated and 100% of the control cows calved successfully. Treatment with bST for a full lactation did not affect performance during the initial 60 d of the subsequent lactation.

Animals↗

PubMed1991

Effect of long-term bovine somatotropin (sometribove) treatment on nitrogen (protein) distribution in Jersey milk.

Twenty-six Jersey cows were assigned randomly to one of two treatments. Twelve cows received biweekly subcutaneous injection of 500 mg of sometribove, USAN (recombinant methionyl bovine somatotropin), beginning 60 +/- 3 d postpartum and continuing throughout one lactation. Fourteen control animals received injections of placebo carrier. Milk samples were taken biweekly on weeks alternate to injection when differences in milk components were expected to be greatest compared with controls. The milk samples were analyzed for total nitrogen, noncasein nitrogen, and non-protein nitrogen. The average SCC for control and treatment groups was 44,000 +/- 47,000 and 56,000 +/- 65,000. Milk from sometribove-treated cows was significantly lower in total protein (3.92, 4.12%), true protein (3.74, 3.95%), and casein (3.11, 3.34%) than that from control cows on d 8 of the 14 d injection cycle. Casein as a percentage of true protein was lower (83.38, 84.52%), and non-protein nitrogen as a percentage of total nitrogen was higher (4.61, 4.26%) in milk from treated cows. The theoretical yield of Cheddar cheese was ca. .07% less for milk from treated cows than from control cows due to ca. 1% less casein as a percentage of true protein in the former. The differences in nitrogen distribution represent the response during the middle of the injection cycle when milk output was the highest and milk protein the lowest rather than the average response for the injection cycle. The results of the study indicate minimal impact on the cheese manufacturer because in practice milk is commingled from many dairies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗