A fecal test for assessing phosphorus overfeeding on dairy farms: evaluation using extensive farm data.

Managing P on dairy farms requires the assessment and monitoring of P status of the animals so that potential overfeeding may be minimized. Numerous published studies have demonstrated that for lactating dairy cows, increasing P concentrations in diets led to greater P excretion in feces. More recent work reported that inorganic P (P(i)) in 0.1% HCl extracts of feces (fecal extract P(i), g/kg) closely reflects dietary P changes. This has led to the proposal that 0.1% HCl fecal extract P(i) may serve as an indicator of the animal's P status (adequate or excessive) when compared with a benchmark value. Here, we present the results of an extensive evaluation of the proposed fecal P indicator test. With samples (n=575) from >90 farms, fecal total P (TP, g/kg) and fecal extract P were positively correlated with dietary P (X, g/kg): TP=1.92X - 0.17 (R2=0.36); fecal extract P=1.82X - 2.54 (R2=0.46). Fecal extract P was responsive to dietary P changes, whereas the remaining P, calculated as TP minus fecal extract P, was not. A provisional benchmark value of fecal extract P representing near-adequate P status was set at 4.75g/kg. Assessment of the farm data using the benchmark indicated that 316 out of 575 data points were associated with possible P overfeeding. Advantages of the fecal-based test over feed-based analysis to assess P status are discussed. The fecal extract P method is a simple and practical test that can be used as an assessment tool for helping dairy producers improve P management and reduce their environmental footprint.

Manure sampling for nutrient analysis: variability and sampling efficacy.

Reliable estimation of nutrient concentrations is required to manage animal manure for protecting waters while sustaining crop production. This study was conducted to investigate sample variability and reliable nutrient analysis for several manure types and handling systems. Serial samples were collected from dairy, swine, and broiler poultry operations while manure was being loaded onto hauler tanks or spreaders for field application. Samples were analyzed for total solids (TS), total nitrogen (N), ammoniacal nitrogen (NH4-N), total phosphorus (P), and potassium (K). The least number of samples needed for reliable testing of total N and P, defined as +/- 10% of the experimental means with 99% probability, was obtained for each farm using a computer-intensive random resampling technique. Sample variability within farms, expressed as the coefficient of variation (CV), was mostly 6 to 8% for farms that used agitation of manure storages but several times higher (20-30%) on farms where no agitation was applied during the sampling period. Results from the random resampling procedure indicated that for farms that used agitation, three to five samples were adequate for a representative composite for reliable testing of total N and P; whereas for farms without agitation, at least 40 samples would be required. Data also suggest that using book values for manure nutrient estimations could be problematic because the discrepancies between book standards and measured farm data varied widely from a small amount to several fold.

A survey of dairy farming in Pennsylvania: nutrient management practices and implications.

A survey was conducted to collect information on nutrient management practices on dairy farms in south-central Pennsylvania. Of the 994 responding farms, the average farm consisted of 64 lactating cows, 10 dry cows, 41 heifers, and 17 calves with 69.7 ha of tillable land. Manure from lactating cows was mainly collected on a daily basis (84% of the farms) and stored as slurry or liquid (73%), while dry cow and heifer manure was collected weekly or less frequently (69 and 85% of the farms) and stored as solid stack or bedded pack (67 and 82%). Manure utilization featured consistent use of on-farm spreading, with limited incorporation, to corn or small grain fields before planting. Spreading on perennial forages or pasture was also common. Irrigation or injection of manure occurred on less than 5% of the farms. Only 20% of the farms reported manure nutrient testing, contrasting to over 90% for soil testing. Farm advisors and their services can be of vital importance in helping producers make conscientious management decisions for enhanced nutrient utilization. For example, ration balancing involved the services of feed and mineral sales representatives (85% of the farms), independent consultants (12%), and veterinarians (5%). Manure nutrient crediting to determine manure application rates was made by fertilizer dealers (40%), crop advisors and independent consultants (31%), and others. Nutrient management strategies and efforts must address the specific needs of farms with different animal densities and nutrient balances in order to be effective and applicable on the majority of farms.

An assessment of ammonia emissions from dairy facilities in Pennsylvania.

A survey of 715 Holstein dairy farms in Pennsylvania was used to construct demographics for the average Holstein dairy farm. The average Holstein dairy farm was composed of 69 lactating cows; 11 nonlactating, pregnant cows; 44 heifers; and 18 calves. Milk production averaged 27.3 kg (60.0 lb). Crop area averaged 73.6 ha. Milk production, crop area and type, average county yields, and herd animal groups were used to construct a typical feeding program for these farms. Typical rations were constructed for six feeding groups (three milk production groups, one nonlactating group, two heifer groups) to meet milk production, pregnancy, and growth requirements. Rations were constructed based on three forage qualities (excellent, average, and poor) typically observed on Pennsylvania dairy farms. Data for animal description (milk production, body weight, growth, and pregnancy status) and ration components and amounts consumed for each animal group were input into the excretion model of the Dairy Nutrient Planner computer program (DNP). Excretion of fecal N and dry matter (DM), urinary N, and total P and K were produced for each animal group and used to assess potential volatile losses of N. Work at the Marshak Dairy, New Bolton Center, indicates the majority of urinary N is rapidly lost as ammonia from dairy facilities. Based on this observation, the losses of N as ammonia were estimated to be 4.63, 4.62, and 4.28 tonne/year for the farm with excellent, average, and poor quality forages, respectively. Volatile losses of N may be reduced most by controlling levels of urea in urine. Urinary N may be reduced through dietary manipulation of protein and carbohydrate sources. Conversion of urea to ammonia may be reduced by altering the pH of barn floors and gutters. Entrapment of ammonia may be accomplished by acidification of manure slurry. Atmospheric ammonia contributes to acid rain, eutrophication of estuaries and lakes, and particulate air pollution. Reduction of ammonia emissions from dairy barns can significantly reduce atmospheric pollution and improve air and water quality.

A compartmental model depicting short-term kinetic changes in selenium metabolism in ewes fed hay containing normal or inadequate levels of selenium.

Changes in Se metabolism were studied in ewes fed hay containing normal or inadequate levels of Se. After intravenous injection of 75Se-sodium selenite, blood, feces and urine were collected at different times, and the concentrations of labeled and unlabeled Se were determined. Ewes were killed 1, 5, 9 or 14 d after tracer injection, and tissues were obtained for determination of radioactivity and Se concentration. The data were fitted to a compartmental model using the SAAM/CONSAM computer program, and kinetic parameters and steady-state transport rates were estimated. Daily Se intake (Vi) and fecal excretion (VF) were significantly (P < 0.001) higher in the ewes fed normal hay (6.06 +/- 1.09 and 3.36 +/- 0.88 mumol/d, respectively) than in those fed Se-deficient hay (0.64 +/- 0.18 and 0.26 +/- 0.15 mumol/d). The net absorption (Va) of Se was significantly higher in ewes fed normal hay [3.19 +/- 0.82 mumol/d by the balance method, Va = Vi-(VF -Vf) (Vf = endogenous fecal Se) and 1.05 +/- 0.38 mumol/d by using the model (plasma entry rate, U(1))] than in those fed hay deficient in Se [0.57 +/- 0.33 mumol/d (balance) and 0.28 +/- 0.08 mumol/d (model)]. The efficiency of absorption [alpha = U(1) divided by Vi] was significantly higher (0.46 +/- 0.19) in ewes fed Se-deficient hay than in those fed normal hay (0.18 +/- 0.09). Simultaneous fitting of the tracer data of both the groups showed that changes in hepatic extraction and urinary and fecal excretion were sufficient and necessary to account for the kinetic differences observed between treatments.

Kinetic analysis of D-xylose absorption after its intragastric administration to mares deprived of food.

Multicompartmental analysis was applied to study the kinetics of D-xylose distribution after its intragastric administration to healthy mares deprived of food for 12, 36, 72, and 96 hours. Disposition of D-xylose was described by a 5-compartment model. Maximal plasma D-xylose concentration was similar for 12 and 36 hours of food deprivation and was greater (P = 0.0001) than the values for 72 and 96 hours. Peak concentration of D-xylose appeared progressively later as food deprivation proceeded (P = 0.0001). Fractional rate of transfer (k1,6) was less after 96 hours of food deprivation, compared with 12 hours (P = 0.0001), and percentage of D-xylose absorbed was reduced (P = 0.0441) after food deprivation. Fractional rate of transfer (k6,5), representing gastric emptying, tended to progressively decrease with food deprivation. Results indicated that formal kinetic analysis can be applied to D-xylose absorption kinetics in horses. Reduction in the extent of D-xylose absorption after food deprivation may be partly caused by decreased rate of D-xylose absorption across the small intestinal mucosa, but other factors, such as gastric emptying and nonabsorptive losses, may also be involved.

Clearance from plasma of triacylglycerol and cholesteryl ester after intravenous injection of chylomicron-like lipid emulsions in rats and man.

Chylomicrons transport fat and cholesterol via lymphatic vessels from the intestine into the bloodstream. The understanding of the metabolism of chylomicrons in man has been slowed by the difficulty of obtaining lymph chylomicrons for experimental studies. Acceptable methods for the study of chylomicron clearance in man are required, because the metabolism of chylomicrons may be abnormal in diseases such as diabetes mellitus. Metabolism of chylomicrons may also play a role in the development of atherosclerosis. In the present work, lipid emulsions were used as a physical model of chylomicrons. Triacylglycerol-rich lipid emulsions labelled with tracer amounts of radioactive triolein and cholesteryl oleate were prepared by sonication and purified by density gradient ultracentrifugation, then injected into unanaesthetized rats and normal human subjects. Plasma radioactivities were measured for 30 min in rats and 90 min in human subjects. Rat lymph chylomicrons were also injected into rats for comparison with the clearance of the lipid emulsions. The plasma clearance data for triacylglycerols and cholesteryl esters were fitted with a kinetic model using the SAAM/CONSAM programs. Multiple studies analysis of the individual studies in each group was used to obtain estimates of the parameter average values and variabilities. The plasma residence times of the lipid labels were obtained from the fitted clearance data. Our results suggest that information about chylomicron metabolism in man can be obtained by analysis of the plasma clearance data following the injection of suitably labelled chylomicron-like lipid emulsions. Our data provide a baseline for comparisons with individuals having abnormalities of lipid metabolism or risk factors for arteriosclerosis.

Kinetic analysis of D-xylose distribution after intravenous administration to mares.

Multicompartmental analysis was applied to study the kinetics of D-xylose distribution after IV administration to healthy mares deprived of food for 12 and 96 hours. Urinary excretion of D-xylose was measured over a 15-hour period after administration. The plasma D-xylose concentrations in this study were in the range found after oral tolerance testing. The disposition of D-xylose was described by a two-compartment model with linear kinetic characteristics. Total volume of distribution decreased significantly (P < 0.025) from 0.270 L/kg of body weight after the 12-hour period of food deprivation to 0.235 L/kg after the 96-hour period. Fractional rate of transfer between the central and peripheral compartments did not change after 96 hours without food. Approximately a third of the D-xylose administered was recovered in the urine. Difference in urinary elimination between the 12- and 96-hour periods was not significant. Nonrenal elimination rate was determined to be twice the renal elimination rate. The results indicated that formal kinetic analysis can provide useful information about D-xylose distribution in horses. The decreased D-xylose space found after a 96-hour period of food deprivation would tend to increase the plasma D-xylose concentration, and this may help in the interpretation of the D-xylose absorption test applied to anorectic horses.

Vancomycin kinetics in plasma and synovial fluid following intravenous administration in horses.

Vancomycin hydrochloride was infused intravenously (i.v.) over a 30-min period in five horses at doses of 6.6, 11.0 and 15.4 mg/kg. Vancomycin concentration in plasma and synovial fluid samples was measured using a polarization immunoassay. A pharmacokinetic model was developed to accommodate the special features of the present study. The data were described by a two compartment open model with synovial fluid as an additional compartment in exchange with plasma. Minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) were measured for Staphylococcus aureus and Enterococcus sp. using isolates from hospital patients. Based on the pharmacokinetic model and MIC/MBC data, a practical therapeutic protocol for vancomycin administration was established at doses of 4.3-7.5 mg/kg given as a 1-h infusion every 8 h.

Application of models to determination of nutrient requirements: experimental techniques employing tracers.

This paper concerns some issues involved in the design of tracer experiments for the development of whole-body compartmental models of nutrient metabolism. It focuses on tracer administration protocol, use of multiple tracers, sampling strategy, measurement types and experiment duration in a pragmatic approach to obtaining data suitable for analysis and interpretation with use of models.

Comparison of receptor binding, biological activity, and in vivo tracer kinetics for 1,25-dihydroxyvitamin D3, 1,25-dihydroxyvitamin D2, and its 24 epimer.

Scatchard analyses of 1,25-dihydroxyvitamin D receptors (VDR) from chick and rat intestine, bovine thymus, pig kidney cells (LLC-PK1), and human breast cancer cells (T-47D) demonstrated that 1,25-dihydroxyvitamin D3 (1,25-D3) and 1,25-dihydroxyvitamin D2 (1,25-D2) had equal affinities for VDR. 24-Epi-1,25-dihydroxyvitamin D2 (24-epi-1,25-D2) exhibited affinities for VDR equal to that of 1,25-D2 and 1,25-D3 in most of these tissues. Scatchard analysis with 24-epi-[3H]1,25-D2 underestimated total VDR by 50-70% in rat intestine, LLC-PK1, and T-47D cells. The biological activity of 24-epi-1,25-D2 was found to be only 30-70% of 1,25-D3 and 1,25-D2 as determined by in vivo induction of intestinal calcium transport and bone calcium resorption in the rat and in vitro induction of 23- and 24-hydroxylase activities in T-47D cells. In vivo tracer kinetic studies demonstrated that in the rat 1,25-D3 and 1,25-D2 kinetics were similar, whereas 24-epi-1,25-D2 had a 25% shorter plasma half-life and was cleared from the body 2.8 times faster than the natural hormones. This more rapid clearance of 24-epi-1,25-D2 along with reduced VDR binding appears to explain the reduced biological activity of 24-epi-1,25-D2. Our data clearly demonstrate that although there are differences in side chain structure between 1,25-D2 and 1,25-D3, the VDR binding, biological activity, and whole body tracer kinetics of these two metabolites are virtually identical. However, movement of the 28 methyl of 1,25-D2 from its natural S configuration to the R configuration significantly alters the activity of this hormone.

Kinetic modeling of selenium metabolism in nonpregnant ewes.

The kinetics of selenium metabolism in three nonpregnant ewes were studied by the intravenous injection of 75Se-sodium selenite and measurement of radioactivity responses in blood, tissues and excreta. Stable selenium measurements were also made to determine selenium intake, excretion in feces and urine, and mass of selenium in tissues. Immediately following tracer injection, there was a rapid disappearance of radioactivity from plasma reflecting the uptake of the element by the liver and blood cells. The decrease in plasma radioactivity ceased abruptly by 30-45 min, and was followed by an increase to a peak by 3-4 h and a more gradual biphasic decline thereafter. A kinetic model of selenium metabolism in the whole animal was constructed employing the SAAM/CONSAM computer program. The multiphasic response of plasma radioactivity during a physiological steady state was explained on the basis of rapid hepatic uptake of selenium and its subsequent reappearance in the circulation in protein-bound form followed by further metabolism and excretion of the element. The model provides reference parameter values for 75Se-sodium selenite kinetics in selenium-replete, mature nonpregnant ewes for comparison with the kinetics in animals whose selenium status may be altered.

Evidence that discrimination against ergocalciferol by the chick is the result of enhanced metabolic clearance rates for its mono- and dihydroxylated metabolites.

Studies on the discrimination between ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) by chickens have led to conflicting conclusions. To investigate this problem in more detail, radiolabeled vitamin D and vitamin D metabolites were administered intravenously, which allowed determination of their relative plasma clearance rates. The study involved three groups of adult male chickens (five per group). Birds in group 1 were co-dosed with [3H]vitamin D2 and [3H]vitamin D3. Birds in group 2 were co-dosed with [3H]25-dihydroxyvitamin D2 and [3H]25-dihydroxyvitamin D3 and birds in group 3 were co-dosed with [3H]1,25-dihydroxyvitamin D3 and [3H]1,25-dihydroxyvitamin D2. The results indicated that the plasma turnover rate of [3H]vitamin D2 is 1.5 times faster than that of [3H]vitamin D3. Plasma turnover of the 25-hydroxylated metabolites differed, with [3H]25-dihydroxyvitamin D2 clearing faster (11 times) than [3H]25-dihydroxyvitamin D3. The largest difference appeared in the 1,25-dihydroxyvitamin D2 turnover rates with 1,25-dihydroxyvitamin D2 clearing approximately 33 times faster then [3H]1,25-dihydroxyvitamin D3. These data, therefore, indicate that discrimination against vitamin D2 sterols in the chick occurs primarily between steps in the metabolism of vitamin D and not at the point of metabolism or excretion of the parent vitamin.

The effects of natural exposure to high levels of zinc and cadmium in the immature pony as a function of age.

To study the effects of environmental exposure to zinc and cadmium in immature foals, five pregnant ponies were raised within 2.9 km of the New Jersey Zinc Smelter in Palmerton, Pennsylvania. The mares and their foals were kept outdoors on timothy hay and orchard grass. The foals were examined daily for signs of illness and blood samples were taken monthly for estimation of serum zinc, copper, and ceruloplasmin levels. The foals were sacrificed at 2.5, 4.5, 8.5, 13.5, and 18.5 months of age. Necropsy revealed generalized osteochondrosis in joints of the limbs and cervical vertebrae, lymphoid hyperplasia, and eosinophilia. Two of the foals had developed mild lameness. The concentrations of zinc, cadmium, copper, lead, magnesium, and calcium were determined in liver, kidney cortex, and pancreas. The concentration of cadmium and zinc were the only elements that were greatly elevated in all three tissues as compared to control animals. The concentration of cadmium was directly correlated with age in the three tissues (e.g., 23.9 to 212.7 micrograms/g wet wt in kidney cortex), whereas zinc was significantly increased (range 132 to 954 micrograms/g wet wt in liver) but there was no correlation with age. It was concluded that the development of osteochondrosis is associated with increased exposure to zinc and possibly cadmium. The classical signs of cadmium toxicosis, such as renal damage and osteomalacia, were not observed.

24-Hydroxylation of 1,25-dihydroxyergocalciferol. An unambiguous deactivation process.

1,24,25-Trihydroxyergocalciferol was isolated from bovine kidney homogenates incubated with 1,25-dihydroxyergocalciferol and from chick kidney homogenates incubated with 24,25-dihydroxyergocalciferol. The identity was established by ultraviolet absorbance, sensitivity to periodate, nuclear magnetic resonance, and mass spectrometry. The new metabolite had an affinity equal to 1,24,25-trihydroxycholecalciferol for the bovine-thymus and chick-intestinal 1,25-dihydroxyvitamin D receptor and had an affinity twice that of 1,24,25-trihydroxycholecalciferol for the rat-intestinal receptor. It was 3- and 6-fold less competitive than either 1,25-dihydroxycholecalciferol or 1,24,25-trihydroxycholecalciferol, respectively, for the rat plasma vitamin D transport protein. 1,24,25-Trihydroxyergocalciferol was at least 10-fold less active than 1,25-dihydroxycholecalciferol, 1,25-dihydroxyergocalciferol, and 1,24,25-trihydroxycholecalciferol at stimulating intestinal-calcium transport and was also relatively ineffective at stimulating bone-calcium resorption in rats. Moreover, in rats, [3H]1,24,25-trihydroxyergocalciferol was cleared from plasma approximately 40% faster than [3H]1,24,25-trihydroxycholecalciferol. These data suggest that C-24 hydroxylation of 1,25-dihydroxyergocalciferol represents a significant in vivo deactivation step, whereas equivalent deactivation of 1,25-dihydroxycholecalciferol seems to involve metabolic steps subsequent to C-24 hydroxylation (C-24 ketonization). C-24 ketonization of 1,25-trihydroxyergocalciferol would not be anticipated due to the presence of the 24(S)-methyl group. These results reveal further dissimilarities between ergocalciferol and cholecalciferol metabolism in mammals and suggest a mechanism for the lesser tendency of ergocalciferol to cause hypercalcemia relative to cholecalciferol.

Calcium homeostasis in cows, with special reference to parturient hypocalcemia.

Calcium homeostasis is described in terms of controlled, disturbing, and controlling signals. Plasma calcium concentration [( Ca]p) and bone calcium mass (Mb) are the two main controlled signals. Disturbing signals include calcium intake (Vi) and clearance of plasma calcium to feces ( Clf ), bone (Clo+), placenta (Clp), and milk ( Clm ). Clo+ is a disturbing signal for [Ca]p and a controlling signal for Mb. Homeostasis is maintained by input control. Fractional renal calcium reabsorption (alpha r) decreases when calcium entry into plasma is excessive, but usually calcium entry rate (VT) responds effectively to small changes in [Ca]p associated with changes in disturbing signals. With increases in Vi, both fractional calcium absorption (alpha d) and fraction of bone calcium removed (lambda b) decrease to maintain VT at an appropriate level. As Clo+ declines with advancing age, [Ca]p rises slightly but VT decreases: a 1% change in [Ca]p would lead to a 13% change in VT. In heavily lactating cows, this response of VT may be enhanced. Parturient hypocalcemia may be the result of delayed negative feedback responses of lambda b (1 wk) and alpha d (1 day). Positive feedback between [Ca]p and gut motility may lead to transient suppression of VT during hypocalcemia, despite high plasma parathyroid hormone and 1,25-dihydroxyvitamin D3 concentrations. Parturient paresis is an example of a disordered accelerative response in a complex control system amenable to a variety of physiologically rational management procedures.

Kinetics of glucose metabolism in sheep.

The kinetics of glucose cycling in 24 ewes bearing twins were studied 1 month before term by bolus injections of [6-3H]- and [U-14C]glucose. The function representing glucose carbon recycling was determined by deconvolution of the [3H]glucose from the [14C]glucose decay curves in plasma by using the SAAM and CONSAM programs, and a model for kinetics of glucose cycling was developed. The [3H]glucose data were fitted by four compartments, and an additional three compartments were required to explain recycling. The results show that labelled carbon was still recycling to plasma 2 days after the injection of tracer. By contrast, a similar analysis on a non-pregnant sheep, with data taken from the literature, showed that no more material was recycled after 1 day. It appears that a larger fraction (20 v. 5%) of the carbon 6 of glucose recycles in pregnant than in non-pregnant sheep. This presumably reflects the metabolism by the feto-placental unit and the increased rate of glucose metabolism during pregnancy.

Environmental zinc and cadmium pollution associated with generalized osteochondrosis, osteoporosis, and nephrocalcinosis in horses.

Several suspect causes of chronic zinc/cadmium toxicosis in horses near a zinc smelter were investigated following observations of lameness, swollen joints, and unthriftiness, particularly in foals. Two foals born and raised near the smelter were lame and had joint swellings that were attributable to severe generalized osteochondrosis. Zinc and cadmium concentrations were markedly increased in the pancreas, liver, and kidney. The serum of 1 foal, zinc and potassium concentrations were high, whereas calcium and magnesium concentrations were low. Marked nephrocalcinosis and osteoporosis were observed in this foal. Nephrocalcinosis also was observed in his dam, who died of a punctured lung following rib fractures, though there was no history of trauma. The joint cartilage lesions were similar to those induced experimentally in animals fed high-zinc diets and may have been the result of zin-induced abnormality of copper metabolism. The osteoporosis and nephrocalcinosis were consistent with chronic cadmium toxicosis.

Parathyrin and calcium homeostasis in the fetus.

The response of plasma parathyrin (PT) in cattle fetuses to changes in plasma calcium was investigated in utero. Resting plasma calcium levels for 4 fetuses averaged 3.1 mg/dl higher than for their mothers. Fetal PT levels (0.67 ng/ml) were half those of the mother (1.40 ng/ml). Hypocalcemia induced by EDTA infusion evoked a rise in plasma PT in 2 or 3 fetuses. The relationship between plasma PT and calcium levels in these fetuses was curvilinear, PT rising from about 0.7 ng/ml at 13 mg calcium/dl to a plateau of about 1.6 ng/ml below 10 mg calcium/dl. This contrasted with one of the mothers in which PT rose above 3 ng/ml when plasma calcium fell from 9 to 7 mg/dl. During infusion of EDTA to mother or fetus there were no changes in plasma calcium or PT levels in the respective fetus or mother.