Biomedical subjects

D R Mertens

Publications and source records attributed to D R Mertens.

At least 19 recordsLinked to original sources

PubMed1999

Mechanical maceration of alfalfa.

Maceration is an intensive forage-conditioning process that can increase field drying rates by as much as 300%. Because maceration shreds the forage and reduces its rigidity, improvements in bulk density, silage compaction, and ensiling characteristics have been observed. Macerating forage also increases the surface area available for microbial attachment in the rumen, thereby increasing forage digestibility and animal performance. Feeding trials with sheep have shown increases in DMI of 5 to 31% and increases in DM digestibility of from 14 to 16 percentage units. Lactation studies have demonstrated increases in milk production and BW gain for lactating Holstein cows; however, there is a consistent decrease in milk fat percentage when dairy cattle are fed macerated forage. In vitro studies have shown that maceration decreases lag time associated with NDF digestion and increases rate of NDF digestion. In situ digestibility studies have shown that maceration increases the size of the instantly soluble DM pool and decreases lag time associated with NDF digestion, but it may not consistently alter the rate or extent of DM and NDF digestion.

Agriculture↗

PubMed1999

Effect of diet on populations of three species of ruminal cellulolytic bacteria in lactating dairy cows.

The effects of four contrasting diets were determined on populations of three species of ruminal cellulolytic bacteria (Ruminococcus albus, Ruminococcus flavefaciens, and Fibrobacter succinogenes) using oligonucleotide probes to rRNA. Diets based on alfalfa silage or corn silage as the primary fiber source were formulated to contain either 24 or 32% neutral detergent fiber measured after alpha-amylase treatment. The diets were fed twice daily to four ruminally fistulated, lactating Holstein cows in a trial using a Latin square design. The cows fed the alfalfa silage diets had higher dry matter intakes and milk production and smaller pH fluctuations than did cows fed the corn silage diets (0.3 vs. 0.8 units). The total populations of the three cellulolytic species at 3 h after feeding ranged from 0.3 to 3.9% of the bacterial domain; R. albus was generally the most abundant of the three species. The data are in general agreement with population assessments obtained by some traditional methods of culture enumeration. Although diet and individual cows had major effects on ruminal pH and volatile fatty acid concentrations and on milk production and composition, differences in cellulolytic populations that were attributable to individual cows were larger than those attributable to diet, suggesting that each cow maintained a unique assemblage of cellulolytic species.

Animals↗

PubMed1999

A dairy herd model for use in whole farm simulations.

A dairy herd submodel was created for integration with other farm submodels to form DAFOSYM, a dairy farm simulation model. The herd submodel determines the best mix of available feeds to meet the fiber, energy, and protein requirements for each of six animal groups. The groups are early-, mid-, late-, and nonlactating cows, heifers over 1 yr old, and younger heifers. Feed intake, milk production, and manure dry matter and nutrient (N, P, and K) excretions are functions of the nutrient content of the diets. Required feed characteristics include crude protein, rumen degradable protein, acid detergent insoluble protein, net energy of lactation, neutral detergent fiber, total digestible nutrients, P, and K concentrations. Feed intake is predicted with fill and roughage units. These units are functions of feed neutral detergent fiber adjusted for particle size distribution and the relative rate of ruminal digestibility or physical effectiveness of the fiber. The herd submodel predicted feed intakes, nutrient requirements, diets, and manure excretions similar to those recommended or measured for dairy animals. When integrated with other farm components in DAFOSYM, the comprehensive model provides a useful tool for evaluating the long-term performance and economics of alternative dairy farm systems.

Animal Feed↗

PubMed1999

Feeding strategy, nitrogen cycling, and profitability of dairy farms.

On a typical dairy farm today, large amounts of N are imported as feed supplements and fertilizer. If this N is not recycled through crop growth, it can lead to large losses to the atmosphere and ground water. More efficient use of protein feed supplements can potentially reduce the import of N in feeds, excretion of N in manure, and losses to the environment. A simulation study with a dairy farm model (DAFOSYM) illustrated that more efficient feeding and use of protein supplements increased farm profit and reduced N loss from the farm. Compared to soybean meal as the sole protein supplement, use of soybean meal along with a less rumen degradable protein feed reduced volatile N loss by 13 to 34 kg/ha of cropland with a small reduction in N leaching loss (about 1 kg/ha). Using the more expensive but less degradable protein supplement along with soybean meal improved net return by $46 to $69/cow per year, dependent on other management strategies of the farm. Environmental and economic benefits from more efficient supplementation of protein were generally greater with more animals per unit of land, higher milk production, more sandy soils, or a daily manure hauling strategy. Relatively less benefit was obtained when either alfalfa or corn silage was the sole forage on the farm or when relatively high amounts of forage were used in animal rations.

Animal Feed↗

PubMed1997

Creating a system for meeting the fiber requirements of dairy cows.

Current NRC recommendations for dairy cattle provide limited guidance to nutritionists for meeting the fiber and carbohydrate needs of lactating cows. The NRC provide only minimum recommendations for fiber and no accommodation for factors such as physical effectiveness of fiber, interactions with nonfibrous carbohydrates, or animal attributes, which can affect the optimality of dairy rations. To be an improvement, any new system for meeting the fiber requirements of dairy cows must be based on 1) feed characteristics that can be defined and preferably be determined quantitatively using routine laboratory methods and 2) animal requirements that correspond to critical feed characteristics and vary with feeding situation, ration composition, and attributes of the animal. Published data were used to develop coefficients for defining the physical effectiveness or roughage value of feeds and the fiber requirements of dairy cows. Information in this paper is intended to provide practical guidelines for improving current fiber recommendations and to serve as an idealized framework for future research on meeting the fiber requirements of dairy cows. The system is based on NDF as the measure of total chemical fiber in feeds. Adjustments for the effectiveness of NDF in maintaining milk fat production and optimizing ruminal fermentation are based on the particle size and inherent characteristics of NDF that affect chewing activity, ruminal pH, and milk fat production.

Animal Nutritional Physiological Phenomena↗

PubMed1997

Correlation of acid detergent lignin and Klason lignin with digestibility of forage dry matter and neutral detergent fiber.

The acid detergent lignin and Klason lignin methods were compared for their correlation with forage digestibility. Thirty-six forages, including C3 legumes and C3 and C4 grasses, were analyzed for sulfuric acid detergent lignin, Klason lignin, and in vitro digestibilities of dry matter (DM) and neutral detergent fiber (NDF). Twenty of these forages were also fed to lambs at restricted intake for measurement of DM and NDF digestibilities. Lignin concentrations determined by the two lignin methods were positively correlated, and the Klason lignin value was always greater than the acid detergent lignin concentration. The largest differences were observed for grass forages. Digestibilities of forage DM and NDF were negatively correlated with both lignin methods for the in vitro system and the lamb digestibility trials. The degree of correlation for the two lignin methods with digestibility was generally similar across all forages and within forage classes. Slopes of linear regressions of digestibility on lignin concentration did not differ between legumes and grasses. Although the sulfuric acid detergent lignin and Klason lignin procedures gave very different estimates of forage lignin concentration, they were similarly correlated with digestibility and should yield predictions of forage digestibility that have similar accuracy.

Animal Feed↗

PubMed1997

Prediction of excretion of manure and nitrogen by Holstein dairy cattle.

A compilation of N balance data (n = 1801) was partitioned into four groups to define the mean excretion of manure and N and to develop empirical equations to estimate these excretions from Holstein herds. Mean excretion of manure for cows that averaged 29 kg/d of milk production was 3 kg/d per 1000 kg of body weight (BW) more than the value for dairy cows reported by the American Society of Agricultural Engineers; N excretion was 0.09 kg/d per 1000 kg of BW higher than the value reported by the American Society of Agricultural Engineers. Mean excretion of manure and N for cows that averaged 14 kg/d of milk production and that for nonlactating cows were substantially lower than the values reported by the American Society of Agricultural Engineers. Growing and replacement cattle excreted 10 kg/d per 1000 kg of BW more manure and 0.11 kg/d per 1000 kg of BW more N than was reported by the American Society for Agricultural Engineers for beef cattle. Estimation of manure and N excretion was more accurate than mean values when using regression equations that included variables for milk production, concentration of crude protein and neutral detergent fiber in the diet, BW, days in milk, and days of pregnancy. Equations that contained intake variables did not significantly affect predictions of manure and N excretion, and the use of such equations is discouraged unless dry matter intake is measured and not estimated. Accurate estimates of excreta output could improve the planning of storage and handling systems for manure and the calculation of nutrient balances on dairy farms.

Animal Nutritional Physiological Phenomena↗

PubMed1995

The prediction of methane production of Holstein cows by several equations.

Ruminants are one of many sources contributing to atmospheric methane. The accuracy of seven published equations for methane prediction was evaluated using a data file consisting of 16 experiments (602 observations). Methane energy emissions ranged from .89 to 7.21 Mcal/d for Holstein cows. The DMI ranged from 9.7 to 28.7 kg/d for lactating cows and 4.0 to 12.9 kg/d for nonlactating cows. Mean dietary concentrations of ADF, CP, and ether extract were similar for lactating and nonlactating cows (20.9, 16.5, and 3.0% for lactating cows versus 21.2, 15.7, and 2.9% for nonlactating cows, respectively). Milk production ranged from 2.7 to 55.9 kg/d. Prediction equations were ranked by correlation coefficients and error of prediction. Prediction of methane energy loss from lactating and nonlactating Holstein cows with equations based on the daily total intake or intake of digested cellulose, hemicellulose, and nonfiber carbohydrates (OM - NDF - CP - ether extract) provided the highest correlation coefficients for reproducibility and the lowest errors of prediction. Predictions were poor for lactating cows when a quadratic function of DMI was used. In general, equations estimated methane production more accurately and precisely for nonlactating than for lactating cows.

Animals↗

PubMed1994

Nutrient requirements and feed costs associated with genetic improvement in production of milk components.

Dietary requirements for NEL and absorbed true protein were summarized for marginal production of milk components because of genetic improvement through selection. Shelled corn and soybean meal were used to meet marginal nutrient requirements and were assigned variable concentrations of absorbed true protein, depending on rumen-available energy and protein. Mean ratios among national averages for shelled corn to milk prices and soybean meal to milk prices (DM: standardized milk, dollars per kilogram) over a recent 25-yr period were .52 and 1.20, respectively. Stability of these relationships over time permits estimation of feed costs from milk price as prices inflate. Feed costs per kilogram of component, expressed as kilograms of standardized milk with equivalent value, were 1.00 for lactose, 1.89 for fat, and 3.49 for protein. Costs of milk protein were higher if production of absorbed true protein was limited by rumen-available energy, suggesting that selection for fat or lactose, in addition to protein, may be beneficial. High feed costs for milk protein indicate a need for adequate compensation to producers for milk protein and consideration of feed costs during selection. A net value index is proposed that considers feed costs associated with marginal production of individual milk components.

Animal Feed↗

PubMed1993

Metabolizable energy and absorbed protein requirements for milk component production.

Metabolic pathways of milk component synthesis were used to estimate metabolizable energy and absorbed protein requirements for lactation. Amounts of ATP and AA used for synthesis of each component from absorbed substrates were determined. Coefficients were adjusted to account for additional inefficiencies and to define requirements in terms of dietary supply based on NRC energy requirements and N balance data. Assuming that 10% of glucose required was derived from AA, metabolizable energy and absorbed protein requirements were 6.02 Mcal and .136 kg/kg of lactose, 13.43 Mcal and .127 kg/kg of fat, and 7.57 Mcal and 1.069 kg/kg of protein, respectively; an additional .144 Mcal/kg of milk was required for milk volume. For production of milk containing 4.8% lactose, 3.5% fat, and 3.3% protein, absorbed protein required for lactose and fat may account for 14.1 and 9.6%, respectively, of total absorbed protein required for milk production. Efficiency of protein utilization for milk protein synthesis may be as high as 90% when 10% of glucose requirements must be supplied by AA. Expressing nutrient requirements for lactation on a component basis enables calculation of requirements for milk production of any composition and does not rely on correlations between major milk components.

Absorption↗

PubMed1993

System of equations for fulfilling net energy and absorbed protein requirements for milk component production.

Objectives were to develop a system of equations for formulating rations to meet absorbed protein requirements, to define NEL requirements for individual milk components, and to evaluate the effects of changes in milk composition on requirements for absorbed protein and NEL recommended by NRC or by a proposed system based on milk components. By combining parameters in the NRC degradable protein system, a set of two equations was derived that can be solved to meet absorbed protein requirements when either ruminally available protein or energy limits microbial protein synthesis. Heats of combustion were used to estimate NEL requirements for milk components. Maintenance requirements for absorbed protein and NEL were obtained from NRC. To eliminate the dependence of DMI prediction on milk fat concentration, as assumed by NRC, DMI was estimated using the NDF concentration of the feed and the NEL requirement of the cow. The proposed system of requirements, based on milk components and the matrix of equations for meeting absorbed protein requirements, not only accounts for differences in the degradability and microbial yield of feeds but also more logically matches differences in nutrient requirements for milk components associated with changes in milk composition.

Absorption↗

PubMed1992

Kinetics of hydration and effect of liquid uptake on specific gravity of small hay and silage particles.

Kinetics of hydration of ground hay and silage particles (2-mm screen), determined by a pycnometric technique, was best described by a two- and one-pool exponential model, respectively. Fractional rates of hydration of the large pool, detected in hay particles only, and of the small pool present in both hay and silage particles averaged .135 and .021 min-1, respectively. When hydration was complete, liquid associated with particles averaged 1.16, 1.90, and .83 g/g of insoluble DM for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Functional specific gravity, which accounts for the effect of associated gas volume, averaged 1.54, 1.46, and 1.54, but unit specific gravity, calculated to include the effect of gases and liquid of hydration, averaged 1.22, 1.14, and 1.26 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Preservation of forage as silage not only lowered gas volume, but also reduced water-holding capacity, both of which contribute to greater unit specific gravity and faster rate of escape from the rumen. In addition, estimates of unit specific gravity of approximately 1.2 indicate that even in the absence of associated gas, hydrated forage particles would tend to escape the rumen at a slower rate than that achieved by more dense particles.

Animal Feed↗

PubMed1992

Effect of microbial fermentation on functional specific gravity of small forage particles.

Two experiments were designed to determine the effect of gas production during in vitro digestion on functional specific gravity (FSG) of forage particles. In Exp. 1, FSG of ground alfalfa hay decreased from 1.123 to 1.049 between 3 and 9 h of incubation and increased thereafter to reach a plateau at 1.309 after 30 h of incubation. Gas production peaked at 6 h, but gas associated with particles increased until 9 h of incubation. Gas associated with solid residue was correlated to gas production (r = -.67) but also was influenced by gas holding capacity and rate of escape from the particles. In Exp. 2, measurements were performed on ground alfalfa hay, alfalfa silage, and bromegrass hay containing 42.6, 35, and 66.4% NDF, respectively. Gas production seemed to be related to the amount of readily available substrate. Although at 9 h of incubation more gas was produced by alfalfa silage (.235 mL.min-1.g of DM-1) than by bromegrass hay and alfalfa hay (.087 and .187 mL.min-1.g of DM-1, respectively), gas associated with particles was greater for alfalfa hay (.416 mL/g of DM) than for bromegrass hay and alfalfa silage (.256 and .281 mL/g of DM, respectively). The increase in FSG was more rapid for alfalfa silage than for the hays. After 27 h of digestion, gas associated with particles (milliliters per gram of DM) and FSG were .164, 1.226; .147, 1.235; and .001, 1.467 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Gas produced during fermentation delayed the increase in specific gravity of forage particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1992

Impact of in vitro fermentation techniques upon kinetics of fiber digestion.

Three in vitro fermentation experiments were conducted to examine the impact on kinetics of fiber digestion of microminerals and tryptone addition, media reduction, fermentation vessel, CO2 gassing regimen, and buffer type. Alfalfa and bromegrass hays were incubated for 0, 4, 8, 12, 18, 24, 30, 36, 48, 72, and 96 h and analyzed for NDF. Kinetic measures of fiber digestion were estimated using nonlinear regression with iteratively reweighted least squares. In Experiment 1, continuous CO2 gassing increased rate and decreased lag time prior to NDF digestion compared with purging a non-CO2-saturated buffer at inoculation. Vessel type (50-ml polypropylene tube, 125-ml pyrex Erlenmeyer flask), use of additives (microminerals, tryptone), and media reduction had no effect on kinetics of NDF digestion. In Experiment 2, elimination of both media reduction and nutritive additives increased the lag time prior to NDF digestion. In Experiment 3, continuous CO2 gassing of buffer in 125-ml Erlenmeyer flasks resulted in faster rates of NDF digestion than CO2-saturated buffer in 50-ml screw-cap polypropylene tubes. The method that yielded the fastest rates and shortest lag times of NDF digestion consisted of continuous CO2 gassing, reduction, and use of additives to ensure that no nutrient limited fiber digestion.

Animals↗

PubMed1992

Development of buffer systems for pH control and evaluation of pH effects on fiber digestion in vitro.

An in vitro buffering system capable of pH control between pH 5.8 and 6.8 was developed to examine the effect of media pH on disappearance of NDF at various times of fermentation and to assess initially the effect of media pH on kinetics of NDF digestion. The pH conditions selected for evaluation of these buffer systems were 5.8, 6.2, and 6.8. Use of McIlvaine's solution with sodium bicarbonate was not successful because of rapid drifting of pH downward during fermentation. To evaluate the effectiveness of citric or phosphoric acids as components of phosphate-bicarbonate buffer systems, alfalfa silage and a mixture of alfalfa silage and corn grain (1:1 mixture, dry basis) were fermented for 0, 12, 24, 48, and 72 h. The pH of each flask was measured at 0, 4, 12, 24, 48, and 72 h postinoculation, and pH was readjusted with bicarbonate solution when necessary. Drifting of media pH downward was more noticeable when phosphoric acid was used to adjust the buffer pH than with citric acid. Citric acid had no adverse effects on NDF digestion compared with phosphoric acid when used to adjust a phosphate-bicarbonate buffer system. Alfalfa hay, bromegrass hay, and corn silage were incubated for 0, 12, 24, 48, 72, or 96 h at pH 5.8 or 6.8 using the phosphate-bicarbonate buffer system adjusted with citric acid. Estimation of kinetics of NDF digestion indicated that a decrease in media pH from 6.8 to 5.8 resulted in a marked reduction in NDF digestion; the largest apparent difference was extended digestion lag time.

Animal Feed↗

PubMed1992

Influence of buffer pH and raw corn starch addition on in vitro fiber digestion kinetics.

The impact was studied of buffer pH (5.8, 6.2, and 6.8) on in vitro digestion kinetics of NDF from alfalfa hay, bromegrass hay, corn silage, and alfalfa and bromegrass hays with raw corn starch added to approximate a ration containing 30% NDF. Ash-free NDF was determined at 0, 6, 12, 18, 24, 30, 36, 48, 72, and 96 h of fermentation. Kinetic parameters were estimated by nonlinear regression using an iteratively reweighted least squares technique. Addition of raw corn starch decreased fiber digestion rate for alfalfa hay and lag for bromegrass hay. Both rate and lag of NDF digestion of all substrates were affected negatively below pH 6.2. Predicted ruminal NDF digestibilities (as percentage of that at pH 6.8 treatment) declined below pH 6.2 for all forages; addition of starch decreased predicted ruminal NDF digestibility by 23% for both alfalfa and bromegrass hays, even at pH 6.8. Results suggest that low pH decreases fiber digestion rate and increases lag and that starch accentuates this effect for some substrates.

Animal Feed↗

PubMed1991

Fluid and particulate retention times in sheep as influenced by intake level and forage morphological composition.

Objectives of this study were 1) to measure small-particle and liquid mean retention time (MRT) of 12 grass hays similar in NDF (61.3 +/- 1.9% NDF) but differing in morphological composition and to relate passage rates to proportions of blade, sheath and stem and 2) to evaluate the influence of MRT of small and large blade and stem fractions and large sheath fractions, in addition to morphological composition, on intake and digestibility of the 12 hays. In each of two periods, 24 sheep (wethers) were offered one of 12 hays at three consecutive levels of feeding: (L1) ad libitum, allowing 15% refusal; (L2) restricted to 100% of hay consumed ad libitum by an individual wether during L1; and (L3) 1.8% of BW on a DM basis. Hays offered included two sorghum-sudan, four barley, four oat and two pearl millet. Marked particles were pulse-dosed in L2 and L3. Large and small particles of stem and leaf were extracted with neutral detergent and marked with Cr or rare earth metals. Marked large and small stem particle MRT generally were longer (P less than .05) than those of corresponding large and small blade particles. Large sheath particles generally had an intermediate (P less than .05) MRT between those of large stem and blade particles. Mean retention times of marked fractions were lower (P less than .05) in L2 than in L3. Small particle MRT in L2 was longer than MRT for liquid, though correlations were high (r = .74 to .86, P less than .01). Large particles were retained longer than small particles. Particle size, morphology, and percentage of stem in the forage influenced the mean retention time. Use of representative samples of all fractions fed to measure retention times may lead to a better understanding of ruminal function and to improvements in explanations of intake regulation, because marked fractions do not behave identically for all forages.

Animal Feed↗

PubMed1991

Effect of source and amount of fiber on kinetics of digestion and specific gravity of forage particles in the rumen.

This experiment investigated the relationship between kinetics of digestion and change in specific gravity during in situ incubation. Nine cows were fed three sources of fiber (corn silage, alfalfa silage, or alfalfa hay) in diets formulated to contain 25, 30, or 35% NDF in three simultaneous 3 x 3 Latin squares. Method of alfalfa preservation did not influence rate of digestion or rate of increase in specific gravity of forage particles measured by a flotation technique. Prior to incubation, specific gravity of forage particles was in increasing order: alfalfa hay, alfalfa silage, and then corn silage. Essentially, all particles with a specific gravity less than 1.0 shifted to a higher specific gravity fraction by hydration within the first 4 h of incubation. From 4 to 56 h of incubation, percentage of residual DM that settled in solution having specific gravity of 1.3 increased linearly from 21 to 27% for corn silage but exponentially from 3 to 20% for alfalfa forages. Fractional rates of DM and NDF digestion and increase in percentage of residual DM having a specific gravity greater than 1.3 increased with the amount of fiber in the alfalfa diets and were correlated positively, suggesting that rate of increase in specific gravity, which affects rate of passage from the rumen, is influenced by rate of digestion of forage particles.

Animal Feed↗