The effect of concentrate supplement type on milk production, nutrient intake, and total-tract nutrient digestion in mid-lactation, spring-calving dairy cows grazing perennial ryegrass (Lolium perenne L.) pasture.

The objective of this study was to evaluate the effect of concentrate supplement type on milk production, nutrient intake, and total-tract nutrient digestion in lactating dairy cows grazing mid-season perennial ryegrass (Lolium perenne L.; PRG) pasture. Twelve primiparous (mean ± standard deviation; 95 ± 30 d in milk and 470 ± 43 kg of body weight) and 68 multiparous (99 ± 24 d in milk and 527 ± 64 kg of body weight) lactating dairy cows were blocked based on pre-study milk yield and parity and randomly assigned to 1 of 4 dietary treatments. The 4 dietary treatments were a non-supplemented PRG control (PRG); PRG supplemented with 4.4 kg of dry matter (DM) per cow per day of citrus pulp and 0.067 kg of DM/cow per day of urea (PRG+C); PRG supplemented with 0.8 kg of DM/cow per day of heat-treated soybean meal (PRG+PP); and PRG supplemented with 3.1 kg of DM/cow per day of a combination of heat-treated soybean meal and citrus pulp (PRG+C+PP). The study consisted of a 2-wk adaptation period and a 10-wk period of data collection. Weekly measurements of milk yield, body weight, body condition score, and feeding and rumination time were made. Nutrient intake and total-tract digestibility were measured during wk 6 of the study. A large soil moisture deficit was experienced during the study that probably reduced herbage growth rate and likely altered the chemical composition of the PRG offered when compared with typical mid-season PRG. Total dry matter intake was increased in cows fed PRG+C compared with cows fed PRG and PRG+PP and was similar to cows fed PRG+C+PP (18.0, 15.9, 16.4, and 17.2 ± 0.41 kg of DM/d, respectively). The apparent total-tract neutral detergent fiber digestibility of cows fed the PRG+C diet was lower compared with the PRG and PRG+PP diets and was similar to the PRG+C+PP diet (0.67, 0.70, 0.70, and 0.69 ± 0.01 g/g, respectively). The energy-corrected milk (ECM) yield of cows fed PRG+C+PP was highest (23.7 kg/d), PRG+C was intermediate (22.2 kg/d), and PRG was lowest (20.8 kg/d). Cows fed PRG+PP produced more ECM (22.9 kg/d) compared with cows fed PRG and produced similar ECM compared with cows fed PRG+C and PRG+C+PP diets. The PRG+PP diet increased milk protein yield compared with the PRG diet, tended to increase milk protein yield compared with the PRG+C diet, and was similar to the PRG+C+PP diet. Milk fat concentration and the composition of milk fat were not influenced by treatment. The results demonstrated that, for cows consuming pasture-based diets, increasing metabolizable protein supply allowed higher milk yield as metabolizable protein was more limiting than metabolizable energy. However, due to the large soil moisture deficit experienced during this experiment, caution is recommended when extrapolating these results to cows consuming typical mid-season PRG herbage.

Microbial composition and omasal flows of bacterial, protozoal, and nonmicrobial amino acids in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.) not supplemented or supplemented with rolled barley.

The objective of this study was to evaluate the effect of rolled barley supplementation on microbial composition and omasal flows of bacterial, protozoal, and nonmicrobial AA in cows fed fresh perennial ryegrass (Lolium perenne L.; PRG). Ten ruminally cannulated multiparous Holstein cows averaging (mean ± standard deviation) 49 ± 23 d in milk and 513 ± 36 kg of body weight were assigned to 1 of 2 treatments in a switchback design. The treatment diets were PRG only or PRG plus 3.5 kg of dry matter rolled barley (G+RB). The study consisted of three 29-d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. A double-marker system was used to quantify nutrient flow entering the omasal canal along with 15N-ammonium sulfate to label and measure the microbial and nonmicrobial omasal flow of AA. Overall, rolled barley supplementation had no effect on the AA composition of the omasal liquid-associated and particle-associated bacteria. Rolled barley supplementation affected the AA concentrations of omasal protozoa; however, the differences were nutritionally minor. Particle-associated bacteria AA flow was increased for all AA, except for Trp and Pro, in cows fed the G+RB diet. Rolled barley supplementation had no effect on protozoal AA flow. On average, protozoa accounted for 23% of the microbial essential AA flow, which ranged from 17 to 28% for Trp and Lys, respectively. The flow of all AA in omasal true digesta increased in cows fed the G+RB diet compared with the PRG-only diet, resulting in a 228 g/d increase in total AA flow in cows fed the G+RB diet. This increase in total AA flow in cows fed the G+RB diet was due to an increase in microbial AA flow. Rolled barley supplementation had no effect on nonmicrobial AA flow. The nonmicrobial AA flow modestly contributed to total AA flow, accounting for 15.6% on average. These results indicated that extensive ruminal degradation of PRG AA occurred (83.5%), and we demonstrated that cows consuming PRG-based diets exhibit a large dependence on microbial AA to support metabolizable AA supply. Rolled barley supplementation can increase the omasal flow of microbial AA in cows consuming PRG-based diets. However, further research is required to elucidate if this increased AA supply can support higher milk yield under such dietary conditions.

Rumen metabolism, omasal flow of nutrients, and microbial dynamics in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.) not supplemented or supplemented with rolled barley grain.

The objective of this study was to evaluate the effect of rolled barley grain (RB) supplementation on rumen metabolism, omasal flow of nutrients, and microbial dynamics in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.; PRG)-based diets. Ten ruminally cannulated Holstein cows averaging (mean ± standard deviation) 49 ± 23 d in milk and 513 ± 36 kg of body weight were assigned to 1 of 2 treatments in a switchback design. The treatment diets were PRG only (G) or PRG plus 3.5 kg of dry matter RB (G+RB). The study consisted of three 29-d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. A double marker system was used to quantify nutrient flow entering the omasal canal along with labeled 15N-ammonium sulfate to measure bacterial, protozoal, and nonmicrobial N flow. Rumen evacuation techniques were used to determine nutrient and microbial pool size, allowing the calculation of fractional rates of digestion and microbial growth. There was no difference in daily milk yield or energy-corrected milk yield between treatments. Milk fat concentration and milk urea N decreased, whereas milk protein concentration increased in cows fed the G+RB diet. During the omasal sampling phase, dry matter intake was higher in cows fed the G+RB diet. Ruminal and total-tract neutral detergent fiber digestibility was lower in G+RB cows; however, no difference was observed in reticulorumen pH. The rumen pool size of fermentable carbohydrate was increased in cows fed the G+RB diet; however, the fractional rate of digestion was decreased. Flow of nonammonia N and bacterial N at the omasal canal increased in cows fed the G+RB diet compared with the G diet. Protozoa N flow was not different between diets; however, protozoa appeared to supply a much larger amount of microbial N and exhibited shorter generation time than previously considered. Feed N ruminal digestibility, corrected for microbial contribution, was similar for both treatments (88.4 and 89.0% for G and G+RB, respectively). In conclusion, RB supplementation did not benefit overall animal performance; however, it reduced ruminal neutral detergent fiber digestibility and increased bacterial N flow. The results demonstrate the large dependence of cows consuming PRG-based diets on microbial N as the main source of nonammonia N supply. Additional quantitative research is required to further describe the supply of nutrients and microbial dynamics in cows consuming PRG-based diets in an effort to determine most limiting nutrients.

Modelling phosphorus dynamics in multi-branch river systems: a study of the Black River, Lake Simcoe, Ontario, Canada.

High rates of nutrient loading from agricultural and urban development have resulted in surface water eutrophication and groundwater contamination in regions of Ontario. In Lake Simcoe (Ontario, Canada), anthropogenic nutrient contributions have contributed to increased algal growth, low hypolimnetic oxygen concentrations, and impaired fish reproduction. An ambitious programme has been initiated to reduce phosphorus loads to the lake, aiming to achieve at least a 40% reduction in phosphorus loads by 2045. Achievement of this target necessitates effective remediation strategies, which will rely upon an improved understanding of controls on nutrient export from tributaries of Lake Simcoe as well as improved understanding of the importance of phosphorus cycling within the lake. In this paper, we describe a new model structure for the integrated dynamic and process-based model INCA-P, which allows fully-distributed applications, suited to branched river networks. We demonstrate application of this model to the Black River, a tributary of Lake Simcoe, and use INCA-P to simulate the fluxes of P entering the lake system, apportion phosphorus among different sources in the catchment, and explore future scenarios of land-use change and nutrient management to identify high priority sites for implementation of watershed best management practises.

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems.

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.

Supplementary concentrate type affects nitrogen excretion of grazing dairy cows.

These experiments were designed to investigate nutritional means of reducing urine N excretion by grazing cows. In experiment 1, 36 Holstein-Friesian cows averaging 92 d in milk were fed either 1 or 6 kg of a high protein concentrate or 6 kg of a low protein concentrate. Pasture dry matter (DM) intake was higher for cows fed 1 kg of high protein concentrate (15.4 +/- 0.62 kg/d) than for cows fed 6 kg of low protein concentrate (13.4 +/- 0.55) but not for cows fed 6 kg of high protein concentrate (13.9 +/- 0.96). The reduction in pasture intake per kg of concentrate DM ingested amounted to 0.35 and 0.47 kg of pasture DM for cows fed 6 kg of high protein and 6 kg of low protein concentrate, respectively. Milk yield and milk protein yield were higher for cows fed 6 kg of high protein concentrate than for cows fed 1 kg of high protein concentrate. Cows fed 6 kg of high protein concentrate had the highest levels of N intake, total N excretion, and urine N excretion. The proportion of N excreted in the urine was lowest for cows fed 6 kg of low protein concentrate. Milk N excretion as a proportion of ingested N was higher for cows fed 6 kg of low protein concentrate than for cows fed 6 kg of high protein concentrate but not for cows fed 1 kg of high protein concentrate. In experiment 2, 24 Holstein-Friesian cows averaging 211 d in milk were supplemented with 4 kg of rolled barley or 4.32 kg of NaOH-treated barley. Milk yield and milk protein yield tended to be higher for cows fed rolled barley than for cows fed NaOH-treated barley. There was no difference in N intake, fecal N excretion, urinary N excretion, or milk N output between diets. Milk urea N concentration was lower for cows fed rolled barley. Significant positive linear relationships were found between N intake and fecal N excretion, urine N excretion, and milk N excretion in experiment 1. In experiment 2, the relationships between N intake and fecal N excretion and urine N excretion were curvilinear, with urine N excretion increasing at a decreasing rate, and fecal N excretion increasing at an increasing rate, as N intake increased. The N excreted by dairy cows may be partitioned to fecal N if supplements based on high concentrations of fermentable organic matter and low concentrations of N are fed. Refinement of this nutritional strategy may allow reduced N excretion without reducing animal performance.

Effect of offering rumen-protected fat supplements on fertility and performance in spring-calving Holstein-Friesian cows.

The objective of this study was to evaluate the effect of two different rumen-protected fat supplements, on reproductive performance and milk production, in grass-based spring calving cows. Two hundred and one Holstein-Friesian cows with an average lactation number of 3.6 (20% first lactation, 16% second lactation and 64% third lactation or greater) were grouped into blocks of three on the basis of calving date, lactation number and previous lactation milk yield for cows of second lactation or greater and on the basis of calving date for first lactation animals. From within-blocks individual animals were assigned at random, within 10 days post-calving, to one of the following three treatments: (1) Megalac Plus 3% (MP; 0.4kg/day, containing Ca salt of palm fatty acids and Ca salt of methionine hydroxy analogue), (2) Megapro Gold (MPG; 1.5kg/day, containing Ca salt of palm fatty acids, extracted rapeseed meal and whey permeate), and (3) Control (C; unsupplemented). Cows were supplemented for on average 103 days (range 54-134 days). The average milk yield over the first 12 weeks of lactation was higher (P<0.05) for both fat supplements compared to C and was higher for MP compared to C over the full lactation. Both supplements reduced (P<0.05) milk protein concentration over the first 6 weeks of lactation. MPG increased (P<0.05) conception rate to first service compared to C. Conception rate to first service was similar (P=0.14) on MP compared to C. For pregnancy to second service, C had a higher (P<0.05) conception rate than MP. There were no significant differences between treatments in overall pregnancy rate, services per conception, number of cows served in the first 3 weeks of the breeding season or the 6-weeks in-calf rate. Comparing the combined fat treatments to C resulted in a higher (P<0.05) conception rate to first service for the fat treatments but no significant difference in overall pregnancy rate. In conclusion, fat supplements increased conception rate to first service but did not significantly affect the proportion of cows pregnant at the end of the breeding season.

Effect of genetic merit and concentrate supplementation on grass intake and milk production with Holstein Friesian dairy cows.

A total of 48 high genetic merit (HM) and 48 medium merit (MM) cows, each given a low (LC), medium (MC), or high (HC) level of concentrate supplementation, were used in a split-plot design experiment, which was run in three consecutive years, to evaluate animal production responses. Individual cow intakes were estimated twice each year while at pasture; measurement period 1 (MP1) was in May/June, and measurement period 2 (MP2) was in early September, corresponding on average to d 110 and 200 of lactation, respectively. In MP1, cows were offered 0 (LC), 3 (MC), and 6 kg (HC), whereas in MP2 the levels were 0 (LC), 0 (MC), and 4 kg (HC) of concentrate daily. Genotype had a significant effect on all milk production parameters in MP1 and MP2. The HM cows had the highest yield of milk, fat, protein, and lactose, whereas the MM cows had the highest milk fat, protein, and lactose concentrations. The HM cows had significantly higher grass dry matter intake (GDMI) estimates. In MP1, the average responses, per kg concentrate dry matter, was +1.10 kg of milk, +0.038 kg of protein, +0.032 kg of fat. The corresponding values in MP2 were +0.94 kg of milk, +0.037 kg of protein, and +0.025 kg of fat. The response to concentrate was linear and independent of preexperimental milk yield. In MP1, the partial regression coefficients relating daily GDMI to an increase in 1 kg of preexperimental milk yield (PMY), preexperimental BW (PBW), and concentrate intake (CI) were 0.123, 0.006, and -0.54, respectively, whereas the corresponding values in MP2 were 0.190,0.007, and-0.444, respectively. This study indicates that with high yielding dairy cows, on gras only GDMI of 17 kg of supporting milk yield of 30-kg/d is achievable. In this scenario, concentrate supplementation will result in lower substitution rates, and higher milk yield response than previously published with lower yielding cows.

A comparison of different allergometric tests, skin prick test, Pharmacia UniCAP and ADVIA Centaur, for diagnosis of allergic diseases in children.

BACKGROUND: The diagnosis of allergic disease is performed by skin prick tests (SPT) or through the demonstration of specific IgE in a blood sample via an in vitro test. The measurement of IgE concentration against allergens provides critical information in clinical allergy. Standardized and reproducible methods contribute to the quality of diagnosis and treatment of allergic disease. METHODS: In this study we evaluated the performance of a new specific IgE method, developed by ALK-Abellò for Bayer Diagnostics to run on their ADVIA Centaur immunoassay system. One hundred and fifty-one children with allergic diseases (both food and inhalant allergies) were tested for specific IgE (sIgE) via SPT and in vitro tests (UniCAP system, Pharmacia, and ADVIA Centaur immunoassay system, Bayer Diagnostics) and the test results were correlated with the clinical data. RESULTS: Statistical analysis revealed no significant difference between the two in vitro tests compared with clinical history. The sensitivities and specificities are similar, but the UniCAP system method has higher sensitivity. In the children with cow's milk allergy, the UniCAP system has sensitivity of 91% and specificity of 70%; the ADVIA Centaur immunoassay has sensitivity of 82% and specificity of 74%. In hen's egg allergy, UniCAP system has 94% sensitivity and 64% specificity, and the ADVIA Centaur system has 88% sensitivity and 52% specificity. In inhalant allergies, the two methods show statistically similar performances for both grass pollen allergies (UniCAP sensitivity 100%, specificity 73%; ADVIA Centaur sensitivity 95%, specificity 79%) and in the dust mites allergies (UniCAP sensitivity 91%, specificity 62%; ADVIA Centaur sensitivity 86%, specificity 64%). In cat allergies, the systems showed equivalent results (UniCAP sensitivity 100%, specificity 71%; ADVIA Centaur sensitivity 100%, specificity 70%). Using the UniCAP system, the geometric mean of sIgE values in children with clinical allergy is significantly higher than in sensitized ones. The ADVIA Centaur system shows a similar trend with the exclusion of cow's milk and Dermatophagoides farinae allergens. With this last method the mean value of sIgE is higher in sensitized than in symptomatic children. CONCLUSION: The new ADVIA Centaur method compares favorably with the results obtained on the UniCAP system. If other studies continue to confirm this data, then the advantages are numerous: the use of only a small quantity of serum (25 micro l per allergen), rapid turnaround time, minimal hands-on time, and no interference from IgG.

Rumen fermentation and nutrient flows for cows fed grass and grass supplemented with molassed beet pulp pellets.

An experiment was carried out to determine the effect of a grass diet and a concentrate supplement on rumen fermentation and nutrient flows to the duodenum. Perennial ryegrass was cut and fed indoors to eight rumen- and duodenum-cannulated Friesian cows with or without 3 kg/d of molassed beet pulp in a randomized design experiment. The dry matter intake of grass was significantly lower for cows fed the concentrate supplement (13.6 vs. 11.5 kg of dry matter/d), but total dry matter and organic matter (OM) intakes were similar for cows fed both diets. Cows fed the supplement had higher mean concentrations of total volatile fatty acids (108 vs. 89 mmol/L) and a higher percentage of butyrate in total volatile fatty acids (13.5 vs. 11.6 mol/100 mol). There were no differences between the diets in the flow of OM to the duodenum or in the extent of OM digestion in the rumen. Flows of nonammonia N, microbial N, and amino acids to the duodenum tended to be higher for cows fed the supplemented diet than for those fed ryegrass only. The efficiency of microbial protein synthesis also tended to be higher for cows fed the supplemented diet (42 vs. 37.7 g/kg of OM apparently digested in the rumen and 28.2 vs. 26 g/kg of OM truly digested in the rumen). Overall, there were indications that the supplement caused better capture of N in the rumen and increased the efficiency of microbial protein synthesis.

Regenerative healing of incisional wounds in murine fetal lungs maintained in organ culture.

Although fetal dermal repair is known to be fundamentally different from adult healing, the response to wounding in other organs is less well characterized. Scarless repair in mid-gestation dermis with a transition to adult-type healing at term has been shown in fetal organ culture. A lung explant culture system was used to investigate whether wound repair in the fetal lung shows characteristics similar to those found in fetal dermis. Lungs from 14-day and 18-day Cd-1 murine fetuses and 2-day-old newborns, (term = 20 days, n = 24) were wounded by linear incision and incubated at 37 degrees C, in a 21% O2, 5% CO2 environment, in BGJb supplemented with vitamin C and antibiotics. Medium was changed daily. Samples were fixed at 7 days and embedded in paraffin. Sections were stained with hematoxalyn-eosin and Masson Trichrome. Additional 14-day and 18-day samples were frozen in freon and immunohistochemical staining for TGF-beta performed. Other frozen tissues from each time point were homogenized and used to assay for endogenous TGF-beta levels by Western blot analysis. Histology showed reconstitution of tissue architecture across the wound in 14-day and 18-day specimens. In representative histological sections, intact bronchial architecture developed across the previous wound site. No cellular inflammatory response was observed, and collagen deposition was undetectable at the site of the wound by Trichrome staining. By 22 days the lung explants showed a much less ordered repair, including disorganized collagen deposition.(ABSTRACT TRUNCATED AT 250 WORDS)

31P NMR study of insulin effects on the isolated perfused rabbit urinary bladder.

Insulin stimulates hexose transport, intermediary metabolism, and cell growth and development. These effects are well-documented in skeletal but not smooth muscle. 31P NMR spectroscopy was performed on rabbit urinary bladders (n = 4) to characterize insulin's actions on smooth muscle. The bladder and its vasculature were surgically isolated from the animal and perfused with a PSS/red blood cell perfusate. After a control steady state was achieved (approx 1-2 h), insulin (0.100 mU/ml) was added to the perfusate. Relative levels of intracellular phosphorylated compounds, pH, and free Mg2+ were measured and compared to control values. Also, extracellular pH and fractional volume were assessed using phenylphosphonate, a 31P NMR extracellular pH and volume indicator. Insulin induced significant increases in PCr (16 +/- 9%) at the expense of Pi, intracellular pH (delta pH 0.24 +/- 0.07), and fractional extracellular volume (49 +/- 1%). Intracellular free Mg2+ and extracellular pH did not change. These results indicate that in situ smooth muscle is sensitive to physiological levels of insulin. In fact, insulin improves the energy state of smooth muscle cells and the overall tissue perfusion.

Phenylphosphonate: a 31P-NMR indicator of extracellular pH and volume in the isolated perfused rabbit bladder.

31P-NMR has been used extensively to estimate intracellular pH. It also can be used to measure extracellular pH and volume when an NMR-detectable extracellular phosphorous probe is used. Phosphonic acids have been suggested as useful 31P-NMR extracellular markers. The present study was designed to assess the utility of phenylphosphonic acid (PPA) as a 31P-NMR extracellular marker in perfused smooth muscle. Rabbit bladder strips were exposed to PPA concentrations of 1-20 mM. Tension development in response to maximal carbachol challenges (10 microM) was independent of PPA concentration. Addition of PPA (6 mM) to the perfusate supplying the isolated resting rabbit bladder had no effect on 31P-NMR-detectable phosphatic compounds. PPA's resonance frequency was distinctly downfield from endogenous phosphates and demonstrated a pH-dependent chemical shift of +/- 1.12 ppm/pH unit over the range of 6.4 to 7.6 with a pK' of 7.09 at 23 degrees C. The time courses for washing PPA in and out of the resting bladder were best described by monotonic exponential growth (r = 0.972; n = 3) and decay (r = 0.972; n = 3) equations, respectively. Rate and time constants for PPA wash-in (0.039 +/- 0.004 min-1 and 25.7 +/- 2.3 minutes) and washout (0.038 +/- 0.000 min-1 and 26.3 +/- 0.0 minutes) were not significantly different. Using steady state PPA and ATP peak intensities and concentrations, an extracellular-to-intracellular ratio was calculated to be 0.31 +/- 0.03 (n = 3). These data indicate that PPA remains distributed exclusively in the extracellular spaces.(ABSTRACT TRUNCATED AT 250 WORDS)

31P NMR spectroscopy, chemical analysis, and free Mg2+ of rabbit bladder and uterine smooth muscle.

31P NMR spectra of isolated rabbit bladder and uterus were obtained under steady-state arterial perfusion in vitro at rest and while stimulated. The spectra contained seven major peaks: phosphoethanolamine, sn-glycero(3)phosphocholine, inorganic phosphate (Pi), phosphocreatine, and the gamma, alpha, and beta peaks of ATP. Chemical analyses, high-pressure liquid chromatography, and NMR spectroscopy of aqueous extracts of bladders identified a number of other components that also made contributions to, but were not resolved in, the spectra of the intact tissues: UTP, GTP, UDP-Glc, NAD+, phosphocholine, and sn-glycero(3)phosphoethanolamine. Intracellular pH of unstimulated bladders and uteri, measured from the chemical shift of the Pi peak, was 7.10 +/- 0.09 S.D. and 7.01 +/- 0.12 S.D., respectively. The chemical shift of the beta-ATP peak in the smooth muscles was significantly upfield (-0.3 ppm) compared to the chemical shift observed in striated muscles (cat biceps and rat myocardium). An ADP peak was identified in stimulated and ischemic bladders. The chemical shifts of the nucleotides observed in perfused bladders were calibrated as a function of free Mg2+ concentration in solutions containing phosphocreatine, Pi, ADP, and ATP at an ionic strength of 180 mM. We derived the following estimates for the intracellular free Mg2+ concentration: uterus, 0.40 mM; unstimulated bladder, 0.46 mM; stimulated and ischemic bladder, 0.50 mM (from the ATP chemical shift) and 0.45 (from the ADP chemical shift); cat biceps, 1.5 mM; and rat myocardium, 1.4 mM.