Limestone Solubility Research Articles

Effects of limestone solubility on the efficacy of a novel consensus bacterial 6-phytase variant to improve mineral digestibility, retention, and bone ash in young broilers fed low-calcium diets containing no added inorganic phosphate.

This study evaluated the effect of limestone solubility on the capacity of a novel consensus bacterial 6-phytase variant (PhyG) to improve phosphorus (P) and calcium (Ca) digestibility, retention, and utilization in low-Ca broiler diets containing no added inorganic phosphate (Pi). Male Ross 308 broilers (n = 1,152) were fed one of 16 experimental diets from 11 to 21 d of age in a randomized complete design (12 birds/cage, 6 cages/treatment). Diets comprised three positive controls (PC3, PC2, and PC1) containing 1.8, 1.2, or 0.6 g/kg MCP-P and 7.7, 7.0, or 6.2 g/kg Ca, respectively, and a negative control (NC) containing no added Pi (4.4 g/kg P; 2.8 g/kg phytate-P) and 5.5 g/kg Ca from either low or high solubility limestone (LSL or HSL, respectively, [with 42% and 97% solubility after 5 min at pH 3.0]), supplemented with 0, 250, 500, 1,000, or 2,000 FTU/kg of PhyG. Fecal samples collected on days 18 to 20 and ileal digesta collected on day 21 were analyzed for titanium dioxide, Ca, P, and phytate (IP6, inositol hexakisphosphate). Tibias (day 21) were analyzed for ash content. Data were analyzed by factorial analysis (2 limestone solubilities × 4 MCP-P levels and 2 limestone solubilities × 5 phytase dose levels) and exponential regression. Increasing dose levels of PhyG resulted in an exponential increase (P < 0.01) in the apparent ileal digestibility (AID) of P, ileal digestible P content of the diet, ileal IP6 content, and IP6 disappearance in birds fed either HSL or LSL diets, but AID Ca and ileal digestible Ca were exponentially increased by the phytase only in HSL diets (P < 0.01). Relative to HSL, the LSL increased AID P, ileal digestible P, and IP6 disappearance (P < 0.05) but reduced AID Ca, ileal digestible Ca, and retainable Ca (P < 0.05), resulting in reduced retainable P and tibia ash. Phytase exponentially increased the apparent total tract digestibility of P, retainable P, and tibia ash in HSL and LSL diets, but at or above 500 FTU/kg values were higher in HSL than LSL (interaction P < 0.05). The findings highlight that phytase dose-response effects on mineral digestibility and utilization are different for high- and low-solubility limestones, and it is therefore recommended to use digestible rather than total Ca content during diet formulation to ensure an optimal balance of Ca and P, especially in low-Ca diets. In diets containing HSL, higher phytase dose levels may be needed to compensate for the low digestible P content of the basal diet.

Effect of limestone solubility on mineral digestibility and bone ash in nursery pigs fed diets containing graded level of inorganic phosphorus or increasing dose of a novel consensus bacterial 6-phytase variant.

The effect of a novel consensus bacterial 6-phytase variant (PhyG) on total tract digestibility (ATTD) of minerals and bone ash was evaluated in pigs fed diets containing medium- and high-solubility limestone (MSL and HSL, 69.6 and 91.7% solubility, respectively, at 5 min, pH 3.0) in a randomized complete block design. For each limestone, eight diets were formulated: an inorganic phosphate-free negative control (NC) based on wheat, corn, soybean-meal, canola-meal and rice-barn [0.18% standardized total tract digestible (STTD) P and 0.59% Ca]; the NC supplemented with 250, 500, 1,000, or 2,000 FTU/kg of PhyG, and; the NC with added monocalcium phosphate (MCP) and limestone to produce three positive controls (0.33, 0.27, and 0.21% STTD P, and 0.75, 0.70, and 0.64% Ca, respectively; PC1, PC2, PC3). In total, 128 pigs (12.8 ± 1.33 kg, 8 pigs/treatment, housed individually) were adapted for 16 d followed by 4 d of fecal collection. Femurs were collected from euthanized pigs on day 21. Data were analyzed by one-way ANOVA with means separation by Tukey's test, and by factorial analysis (2 x 4: 2 levels of limestone solubility, 4 STTD P levels, and 2 × 5: 2 levels of limestone solubility, 5 PhyG dose levels). Phytase dose-response was analyzed by curve fitting. A consistent negative effect of HSL on ATTD P and Ca was observed in control diets (P < 0.001). Across phytase-supplemented diets, HSL reduced (P < 0.05) ATTD Ca and P (% and g/kg) compared with MSL. Across limestones, increasing phytase dose level increased (P < 0.05) ATTD P exponentially. Limestone solubility had no effect on bone ash, but PhyG linearly increased (P < 0.05) bone ash; 500 FTU/kg or higher maintained bone ash (g/femur) equivalent to PC1. In conclusion, ATTD P and Ca were reduced by a high compared with a medium soluble limestone, but the novel phytase improved ATTD P and Ca independent of limestone solubility.

Modeling improvements in ileal digestible amino acids by a novel consensus bacterial 6-phytase variant in broilers

Data from 13 datasets from 4 trials on the effect of a novel consensus bacterial 6-phytase variant (PhyG) on the apparent ileal digestibility (AID) of amino acids (AA) in broilers were used to model AID AA responses. The datasets were obtained from 3 trial locations (New Zealand, Australia and United States) and collectively incorporated variations in diet composition (feedstuff composition, phytate-P (PP) level, limestone solubility), feed form (mash or pellet), bird genetics (strain), and age at sampling (11–35 d of age). In total, 384 observations were analyzed. First, the relationships between AID of AA (as coefficients) and increasing phytase dose level from 0 to 4,000 FTU/kg were evaluated across all datasets using exponential curve fitting. Second, the percentage unit change in AID of AA at each phytase dose level from baseline (basal diet [BD] without phytase) was calculated separately for each dataset and the data then modeled together using exponential curve fitting. The model-predicted mean coefficient of AID of total AA in basal diets was 0.76 (range 0.56 [Cys] to 0.83 [Glu]), which was increased by PhyG to 0.80 and 0.81 at 2,000 and 4,000 FTU/kg, respectively. Exponential increases in the percentage unit improvement in AID of 18 individual and of total AA with increasing phytase dose level were evident (P < 0.05). Improvements (vs. BD) at 2,000 FTU/kg and 4,000 FTU/kg, respectively, were greatest for Cys (+9.2 and +11.0% units), Met (after deduction of synthetic Met, +8.4 and +9.0% units), and Thr (after deduction of synthetic Thr, +6.2 and +7.3% units). The data demonstrated consistent improvements in the AID of AA by the phytase. The modeling results generated from data gathered from birds sampled at different ages and from different dietary settings with correction of synthetic AA for Lys, Met, Thr, and Trp, enabled a more accurate prediction of the digestible AA contribution from the diet by this novel phytase. This will allow diet-specific AA matrix recommendations to be made in commercial feed formulations.

63 Effect of a Novel Consensus Bacterial 6-phytase Variant on Mineral Digestibility and Bone Ash in Young Growing Pigs Fed Diets with Low and High Soluble Limestone

Abstract The effect of a novel consensus bacterial 6-phytase variant (PhyG) on total tract digestibility (ATTD) of minerals and bone ash was evaluated in piglets fed diets with low and high soluble limestone (LSLM and HSLM, 69 and 92% solubility at 5 min). For each limestone, 8 diets were formulated: an inorganic phosphate-free negative control (NC) diet based on wheat, corn, soybean-meal, canola-meal and rice-barn [0.18% standardized total tract digestible (STTD) P and 0.58% Ca], NC supplemented with 250, 500, 1,000 or 2,000 FTU/kg of PhyG, or with monocalcium phosphate (MCP) to formulate 3 positive controls with 0.21, 0.27, 0.33% STTD P, and 0.64, 0.70 and 0.75% Ca, respectively. In total 128 pigs (12.8 ± 1.33 kg, n=8) were adapted for 14 d followed by 4 d of fecal collection. Femurs were collected on the last day. Data were analyzed as one-way ANOVA and means separated by Tukey test. In addition, a 2 × 4 factorial analysis was performed to test the effect of limestone solubility at different MCP levels in control diets, a 2 × 5 factorial analysis was performed to determine the effect of limestone solubility at different phytase levels. Phytase dose-response was analyzed by orthogonal polynomial. Across phytase diets, HSLM reduced (P &amp;lt; 0.05) ATTD Ca and P compared with LSLM. A consistent negative effect on ATTD P was also observed with HSLM in control diets. Across limestones, increasing phytase increased (P &amp;lt; 0.05) ATTD Ca and P in a linear or exponential manner. Limestone solubility had no impact (P = 0.69) on bone ash. PhyG linearly increased (P &amp;lt; 0.05) bone ash and 250 FTU/kg of PhyG maintained bone ash compared to PC. In conclusion, limestone solubility showed a negative impact on ATTD P and Ca, the novel consensus phytase improved ATTD P and Ca regardless of limestone.

Egg Shell Quality and Bone Status as Affected by Environmental Temperature, Ca and Non-Phytate P Intake and in vitro Limestone Solubility in Single-Comb White Leghorn Hens

Environmental temperature (ET) often changes the nutrient intake/output for layers. Changing feed formulations based on ET may need to be utilized to obtain optimum performance, shell quality and bone status. This study was conducted to investigate the effects of temperature, Ca intake, non-phytate P (NPP) intake and in vitro limestone solubility (LS) on egg-shell quality and bone status in commercial White Leghorn hens. Egg mass and shell weight per unit surface area (SWUSA) decreased with increasing ET (p lower than 0.05), especially when ET was 29.7 C (cycling mean ET)or a constant ET was 32.2 C. Feeding layers a low soluble larger particle size limestone instead of a highly soluble limestone produced beneficial effects for SWUSA at the thermoneutral ET (21.1 C) but the beneficial effect was less or disappeared when ET was higher than 26.6 C in EXP 1 and 2. Feeding layers 245 and 353 mg NPP/h/d supported satisfactory bone status at 21.1 C, however layers housed at higher than 30 C needed an additional intake of 50 mg NPP/h/d to support bone integrity. Results of EXP 1 and 2 indicates that 48 week old layers housed in thermoneutral or warmer ET require a minimum of 4.2 g Ca/h/d for maintaining optimum shell quality and bone integrity. Feeding low LS (34.1% in vitro solubility) improved egg shell quality only for hens housed in thermoneutral ET (21.1 C) and did not improve egg shell quality at higher ET (constant or cycling). Daily NPP intake of 245 and 353 mg/h/d supported optimum egg production and bone status at 21.1 C, respectively. A higher NPP and Ca intake may be required for bone status compared to egg production, especially in older hens.

Quantitative Evaluation of Karst Developmental Differences Based on Improved Analytic Hierarchy Process and Multidimensional Extension Matter Element Model

In this study, limestone solubility, rock thickness, burial depth, hydrodynamic cycle, and geological tectonic of mine No. 13 in the Pingdingshan coalfield (China) were selected to evaluate the degree of karst development. The weight of each index factor to the karst development was determined by using the improved analytic hierarchy process. The multidimensional extensional matter model was used to determine the degree of karst development of the four mining areas (named 1st to 4th) of the Pingdingshan mine No. 13. The results show that the degree of karst development differs zonally, with 1st and 2nd mining areas presenting the lowest degree of karst development (grade II-IV, for an average quantification value of 3.0) and 4th mining area having the highest degree (grade IV-V, for an average quantification value of 4.7). In the vertical direction, the development degree of the vertical layer L1-L4 karst in the Carboniferous Taiyuan Formation is grade IV-V, with an average quantitative value of 4.5, whereas the layers L5-L7 in the Taiyuan Formation had a III-V grade, with an average quantitative value of 3.75, and the Cambrian limestone grade was II-IV, for an average quantitative value of 2.75, i.e., the development degree of karst gradually decreases from shallow to deep.

Modification of a limestone solubility method and potential to correlate with in vivo limestone calcium digestibility

ABSTRACTWork was done to modify a limestone solubility assay to improve predictions of in vivo apparent ileal digestibility of Ca (AID Ca) in broilers and impacts on AID P. Limestones (LIME) were obtained from 3 commercial sources. LIME-1 (0.633 mm mean diameter, GMD); LIME-2 (ground sub-sample of LIME-1, GMD = 0.063 mm); LIME-3 (GMD = 0.326 mm), and LIME-4 (GMD = 0.831 mm). Solubility was determined at 5, 15, and 30 min of incubation using either a 0.2 N HCl (S1) or a pH 3 HCl (pH = 0.26) solution buffered with 3 M glycine (S2) to mimic gizzard and proventriculus pH. An AID trial was conducted with 320 Ross 708 male broilers. Treatments (Trt) were no added LIME, or added LIME-1, 2, 3, and 4 to achieve 0.67% Ca, to a basal diet (no added inorganic P, 0.07% Ca) with or without 1,000 U phytase/kg (36 h, 23 to 24 D of age, n = 8, 4 birds/n). Distal ileal digesta was collected from all birds and pooled by pen. Irrespective of interaction, LIME solubilized quicker and more completely with S1 vs. S2 at all time points (P < 0.05). LIME-2 solubilized the quickest, while LIME-3 had the lowest solubility through all incubation times (P < 0.05). The AID Ca was 66.30, 47.46, 19.93, and 66.33% for LIME-1, 2, 3, and 4, respectively (0 U/kg, P < 0.05). Phytase inclusion increased AID Ca by 15% on average (P < 0.05). The AID P dig was highest in no LIME added diet (74.91%) and adding LIME reduced (P < 0.05) AID P to 23.14, 12.78, 65.47, and 37.40%, for LIME-1, 2, 3, and 4, respectively in the absence of phytase. Regression showed that GMD, 15- and 30-min solubility were critical for AID Ca (R2 between 0.978 and 0.988). In conclusion, the solubility dynamics including speed and extend of solubilization, rather than a single timepoint, yield better predictions for in vivo Ca digestibility of LIME.

The Effect of Feeding Various Limestone Particle Sizes, Limestone Solubility and Calcium Intake on Bone Status and Shell Quality of a Commercial White Layer Strain from 18-65 Weeks of age

The Effect of Feeding Various Limestone Particle Sizes, Limestone Solubility and Calcium Intake on Bone Status and Shell Quality of a Commercial White Layer Strain from 18-65 Weeks of age

Effect of Dietary Calcium Intake and Limestone Solubility on Egg Shell Quality and Bone Parameters for Aged Laying Hens

Effect of Dietary Calcium Intake and Limestone Solubility on Egg Shell Quality and Bone Parameters for Aged Laying Hens

Evaluating the Factors Influencing Limestone-Dissolution Characteristics in the Karst Regions of Guizhou, China

Abstract Guizhou, China, is known for the abundance of subterranean drainage systems with sinkholes. Sinkholes may develop when acidic water starts to dissolve the surface of bedrock or bedding planes. The dissolution characteristics of limestone play a crucial role in the development of sinkholes. The main objective of this study was to develop a quantitative tool for evaluating the dissolution ability for sinkhole formations in the karst regions of Guizhou. The present study investigates a number of properties of limestone that may influence the dissolution in the karst regions of Guizhou. Over 200 rock samples were collected and tested to determine the CaO/MgO ratio, clast content, clastic/matrix ratio, primary porosity, permeability, and fracture density. A quantitative approach was developed to synthesize the influences of these multiple factors to establish the order of the limestone solubility in different regions of Guizhou via numerical modeling using the analytical hierarchy process (AHP) theory. It was found that the solubility of the karstic limestone from different geological formations was in the following descending order: Carboniferous Huanglong-Maping Formation, Permian Qixia-Maokou Formation, Cambrian Qingxudong Formation, and Triassic Yongningzhen Formation. As the water-bearing capacity of the geological formations in these regions is closely associated with underground cavern and sinkhole formations, the approach explored in the present study may have strong implications for the exploration and utilization of karst groundwater resources.

An efficient method for determining the balanced solubility of lime in a predetermined time period

The leaching of dissolved calcium (Ca) and magnesium (Mg) carbonates is the main cause for decalcination of soils. The efficiency of various limes in replacing the carbonates and stabilising the available Ca content depends on the dynamics of lime solubility. The latter depends on the material and the size of its particles: the finer the material, the sooner it will dissolve and leach. To reduce the leaching of the Ca into the soil and to stabilise the available Ca content, the particle-size distribution on the basis of the solubility of lime particles with different sizes was determined so that lime would dissolve equally in a balanced way during the anticipated time. While the solubility of limestone particles of different sizes was being assessed in distilled water, the pH of water was brought to 4.0 by adding potassium biphthalate C8H5O4K: it was discovered that the solubility dynamics of all the lime applied to the soil can be controlled by means of its particle-size distribution. In the field trial, the soil contained the available Ca after the application of limestone (particle-size distribution: <0.16 mm 7%, <0.5 mm 25%, <2 mm 76% and <4 mm 93%) both at the beginning of the trial and in its third to fourth year at an equal and optimum level for the growth of field crops (1.50 g kg−1, with the base saturation around 80%). Considering the importance of Ca in soil and the leaching of a notable part of it, it is possible, by means of regulating the limestone solubility dynamics by the particle-size distribution, to improve the resistance of limes to leaching and erosion and to stabilise the Ca content in soil.

Effect of Acidity and Elevated PCO2on Acid Neutralization within Pulsed Limestone Bed Reactors Receiving Coal Mine Drainage

Limestone has potential for reducing reagent costs and sludge volume associated with the treatment of acid mine drainage (AMD), but its use has been restricted by slow dissolution rates and sensitivity to scale forming reactions that retard transport of H+ at the solid–liquid interface. We evaluated a pulsed limestone bed (PLB) remediation process designed to circumvent these problems through use of intermittently fluidized beds of granular limestone and elevated carbon dioxide pressure. PLB limestone dissolution (LD, mg/L), and effluent alkalinity (Alk, mg/L) were correlated with reactor pressure (PCO2 , kPa), influent acidity (Acy, mg/L) and reactor bed height (H, cm) using a prototype capable of processing 10 L/min. The PLB process effectively neutralized sulfuric acid acidity over the range of 6–1033 mg/L (as CaCO3) while generating high concentrations of alkalinity (36–1086 mg/L) despite a hydraulic residence time of just 4.2–5.0 min. Alk and LD (mg/L CaCO3) rose with increases in influent acidity and PCO2 (p < 0.001) according to the models: Alk = 58 + 38.4 (PCO2 )0.5 + 0.080 (Acy) – 0.0059(PCO2 )0.5 (Acy); LD = 55 + 38.3 (PCO2 )0.5 + 1.08 (Acy) – 0.0059 (PCO2 )0.5 (Acy). Alkalinity decreased at an increasing rate with reductions in H over the range of 27.3–77.5 cm (p < 0.001). Carbon dioxide requirements (Q(avg)CO2 , L/min) increased with PCO2 (p < 0.001) following the model Q(avg)CO2 = 0.858 (PCO2 )0.620, resulting in a greater degree of pH buffering (depression) within the reactors, a rise in limestone solubility and an increase in limestone dissolution related to carbonic acid attack. Corresponding elevated concentrations of effluent alkalinity allow for sidestream treatment with blending. Numerical modeling demonstrated that carbon dioxide requirements are reduced as influent acidity rises and when carbon dioxide is recovered from system effluent and recycled. Field trials demonstrated that the PLB process is capable of raising the pH of AMD above that required for hydrolysis and precipitation of Fe3+ and Al3+ but not Fe2+ and Mn2+.

English

Passive treatment of acid rock drainage (ARD) is typically limited by the chemistry of the ARD. Anaerobic, ferrous iron-dominated ARD can be treated directly with limestone in an anoxic limestone drain (ALD), but alkalinity generation is limited because the high pH (5 - 6) reduces limestone solubility. Oxygenated, ferrous iron-dominated ARD cannot be treated directly with limestone due to the potential for armoring by iron oxyhydroxide precipitates. Vertical flow wetlands that rely on biological processes are typically employed. Reducing and alkalinity producing systems (RAPS) are one type of VFW that requires biological pretreatment of ARD to remove oxygen. The biological pretreatment typically adds alkalinity to the ARD, limiting the alkalinity generated in the RAPS via limestone dissolution by low er the solubility of limestone. The low pH ( 1300 mg·L -1 ) is neutralized in the LBOS with an average 600 mg·L -1 of additional alkalinity measured in the effluent; total alkalinity generated in the LBOS averages > 1800 mg·L -1 . Limestone dissolution accounts for 80 - 95% of the total alkalinity generated in the system. Limestone dissolution is very rapid and occurs in a thin (2 - 5 cm) dissolution front that advances as the limestone is depleted. Armoring due to iron oxyhydroxide precipitates apparently does not limit limestone dissolution, as limestone consumption above the dissolution front is nearly complete with greater than 85% of the limestone removed; limestone below the front is apparently unaffected. Sizing recommendations are made based on the influent acidity load and the volume of limestone in the LBOS.

The relationship of calcium intake, source, size, solubility in vitro and in vivo, and gizzard limestone retention in laying hens

A 10-d trial was conducted to investigate the relationship of Ca particle size (CPS), dietary Ca level (DCL), limestone source (LS), limestone solubility in vitro (LST) and in vivo (LSV), and limestone retention in the gizzard (LRG). A total of 120 molted Leghorn hens, 88 wk of age, were randomly assigned into a 2 x 3 x 4 factorial arrangement of treatments with LS (A and B), DCL (1.95, 3.72, and 5.32%), and CPS of each limestone source (average U.S. Screen Nos. 5, 8, 14, and 27). The in vitro solubility of the four respective particle sizes were 29.8, 45.8, 49.3, and 63.1% for Source A; and 36.3, 54.8, 57.7, and 67.6% for Source B. The limestone retention in the gizzard of Source A was greater than that of Source B. The limestone retention in the gizzard was increased as in vitro solubility decreased (P < 0.001) or dietary Ca level increased (P < 0.001). The in vivo solubility of the limestone was decreased as dietary Ca level increased (P < 0.001). The in vivo solubility was negatively correlated (P < 0.05) with in vitro solubility for Source A when Ca was fed at 3.72%. The data showed that larger particle size limestone (> 0.8 mm) with lower in vitro solubility (30 to 50%) was retained in the gizzard for a longer time, which increased the in vivo solubility (94% maximum). The results support the concept that larger particle size or lower in vitro solubility may increase Ca retention for layers.

Improved In Vitro Methods for Determining Limestone and Oyster Shell Solubility

Experiments were conducted to determine the effect of changing the acid volume, acid normality, and incubation time on in vitro solubility values of various test calcium samples. A 200 mL volume of 0.2N HC1 solution combined with 2.0 g sample size and 10 min incubation time at 42°C produced a limestone solubility range of 20.96% to 78.15% for the samples used. This procedure produced a model for determining limestone or oyster shell weight loss (WL): WL = 1.809 + 0.601 × ln (pH change) (adjusted R2=.961); solubility percentage was calculated as WL × 100/initial sample weight. This in vitro solubility procedure produced a higher limestone solubility range for the test samples, indicating its ability to better distinguish among different quality limestone and oyster shell sources. An in vitro assay using less than 2g of sample produced a higher standard error of the mean when large-particle limestone and oyster shell samples were tested.

Comparison of Various In Vitro Methods for the Determination of Limestone Solubility

A technique for measuring limestone solubility in vitro was developed. Nine limestone sources each screened to four different sizes (average United States screen number = 6, 15, 35, and 100, respectively) were used for the assays. Solubility was reported as the percentage weight loss of the limestone sample during the 10-min in vitro assay. A similar experiment was conducted to obtain both the values of pH changes and the number of moles of proton consumed during the 10-min reaction. The model for predicting solubility (Y) from the pH change (X) was Y = 22.0450 + 5.92771n(X) – 1.24941n(X)2 – .36921n(X)3; the model for predicting solubility from proton consumption (Z) was Y = .5563 + 302.8400 Z. The model for percentage of hydrogen ion disappearance involved a Degree 4 polynomial equation and was not used to predict solubility. When the particle size within each source decreased, the newly developed percentage of weight loss method showed a more gradual increase in solubility when compared with the method of Rabon and Roland reported in 1985. The two methods for obtaining percentage of weight loss ranked the samples within each source in the same order; however, some discrepancies existed between results of the two methods when ranking was done with samples from different sources. The relationship between solubility and size was not linear but involved a Degree 4 polynomial equation. The pH plateau time method had relatively less predictive power of solubility.

Effect of Calcium Source, Particle Size, Limestone Solubility In Vitro, and Calcium Intake Level on Layer Bone Status and Performance

Experiments were conducted to examine the effect on layer performance of dietary calcium source, particle size (average United States Screen Numbers 6, 8, 12, 18, 35, and 100) and calcium intake level (2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 g/day). Egg production and egg weight were not affected by any of the treatments. Size and calcium intake level significantly affected shell weight, shell weight per unit surface area, specific gravity, and shell thickness. Bone ash expressed as a percentage of fat-free dry weight was not affected by calcium intake level, but bone ash concentration (bone ash per unit volume) and bone-breaking strength were linearly related to calcium intake level. Regressed shell quality traits and various bone parameters related to solubility instead of particle size produced a better fitted line.

In Vivo Limestone Solubilization in Commercial Leghorns: Role of Dietary Calcium Level, Limestone Particle Size, In Vitro Limestone Solubility Rate, and the Calcium Status of the Hen

Three experiments were conducted to determine the possible interaction of particle size, in vitro limestone solubility rate, and the Ca status of the hen, respectively, with dietary Ca level and in vivo Ca solubilization in laying hens. The in vivo Ca solubilization in hens was determined by subtracting Ca recovered as limestone in the excreta (by repeated washing) from Ca fed as limestone. Limestones of two different particle sizes [.5 to .8 mm (small) versus 2 to 5 mm (large)] with the same in vitro solubility rates were used in Experiment 1. Limestones of two different in vitro solubility rates (4 versus 10%/15 min in .079 N HCl) with the same particle size in Experiment 2 were assessed for in vivo Ca solubilization. In both experiments, laying hens were fed diets containing graded levels of Ca: 1.5, 3.0, 4.5, and 6.0%. In Experiment 3, hens fed a Ca-deficient (1%) diet for 1 wk were compared with hens fed a diet containing 3.75% Ca to assess in vivo Ca solubilization as influenced by graded dietary Ca levels: 1.5, 3.0, and 4.5% Ca.In vivo Ca solubilization in hens was influenced (P<.05) by dietary Ca level (inverse relationship), limestone particle size (large particle greater than small particle), and Ca status of hens (Ca-deficient hens greater than normal hens). In vivo Ca solubilization in laying hens, for the particle size tested, was not influenced by in vitro limestone solubility rate. Dietary Ca level had a significant interaction (P<.05) with limestone particle size (Experiment 1) and with Ca status of hens (Experiment 3) in influencing in vivo Ca solubilization in laying hens.

Development and Economic Implications of Paleokarst, Molas Pass Area, Southwestern Colorado: ABSTRACT

With the emergence of the Mississippian Leadville Limestone, a climatically specific subaerial tower-karst surface developed in the Molas Pass area, with 80 ft of local relief. Much of this surface is buried under different thicknesses of the Early Pennsylvanian Molas Formation, in part a regolith of siltstone and residual clays from the limestone solution. Rising like small peaked knobs from a plain are three examples of the tower karst found near Molas Pass, the Molas Lake tower, Waterfall tower, and Sultan Creek tower. These illustrate the relatively low limestone solubility, strong fracturing, both joint and fault, and high water-table variations conducive to both tower and the related Kegelkarst formation. Folding may produce adverse conditions for the karst tending to hasten cavern integration and limestone removal. Tower karst and the predominance of kaolinite in the lower Molas, together with silica and hematite produced from soil ferralitization, suggest a subtropical to tropical climate with heavy rainfalls followed by rapid evaporation. The modern localization of this type of karst to areas below 30° of latitude implies a northward migration of the Molas Pass area since the Early Pennsylvanian. The complex stratigraphic relations between the fine-grained Leadville Limestone and the underlying Ouray dolomitic grainstone have made their field separation difficult and may indicate which areas were above and below sea level during the karst formation. This suggests a relative elevation of 100-200 ft for the Leadville at the time of the maximum tower-karst formation. The geologic controls on tower-karst development as observed in the Molas Pass area correlate well with the climate and geologic controls in a modern tower-karst analogue, central Jamaica. An understanding of the mechanisms of tower-karst formation and burial is directly applicable to petroleum stratigraphic trap location as in the Elk Basin field of northern Wyoming-southern Montana, and the localization of base metal sulfide ore deposits as at Gilman, Colorado. End_of_Article - Last_Page 915------------

Some effects of environment on ore deposition

Many ore deposits that are zoned or limited in vertical range appear to be related to stocks, to have formed near surface, or to occur in carbonate rocks. These relations can be explained by evidence from thermochemistry, thermodynamics, and thermal conductivity. 1) Metallic sulfides appear to be carried by ore fluids as complex ions or in the gas state. Deposition of such sulfides takes place through exothermic reactions when temperatures are reduced. Energy losses caused by thermal conduction and by work losses in fluids rising to lower pressures reduce temperatures and counteract heats of sulfide deposition. 2) When ore fluids are much hotter than surrounding host rock and/or when the enclosing host is rapidly heated by ore fluids, heat losses through thermal conduction are high. Such losses, which are anticipated near intrusive rocks, should cause a steep temperature gradient outward from the heat source and may cause relatively rapid sulfide deposition, reflected by nonpersistence or zoning. 3) Work losses that are highest in rising fluids near to the surface may cause the observed nonpersistence and zoning of near-surface sulfide deposition. 4) Limestone replacement by sulfides appears to be controlled by changes in chemistry in the ore fluids caused by large interchanges of material between host and fluid and by limestone solubility, which increases when temperature decreases. In such replacements energy losses caused by thermal conduction, work, and endothermic wall-rock reactions are probably of minor importance. 5) Deposition is persistent in silica-silicate host rock and in an environment with low work and heat conductivity losses. 6) Wall-rock alteration, except for limestone replacement, is not a cause of sulfide deposition. Large quantities of material are not exchanged and alteration is commonly exothermic or neutral.