Effects of feeding a quebracho-chestnut tannin extract on lactating cow performance and nitrogen utilization efficiency.

The effects of feeding a quebracho-chestnut tannin extract mixture on performance and nitrogen (N) utilization were assessed with 36 multiparous lactating Holstein cows (mean ± standard deviation; 706 ± 59 kg of body weight; 126 ± 20 d in milk) randomly assigned to 3 dietary treatments in a randomized complete block design. Following a 2-wk covariate adjustment period, cows were fed their assigned treatment diets for 13 wk. Rice hulls were removed from a total mixed ration with a 54:46 forage:concentrate ratio (% of dry matter; DM), and a tannin extract mixture from quebracho and chestnut trees (2:1 ratio) was included at 0, 0.45, and 1.80% of dietary DM. There was no interaction between dietary treatments and experimental week for the reported measurements except milk lactose percentage. Overall, treatments did not affect milk yield (48.6 ± 7.8 kg/d), fat- and protein-corrected milk (46.1 ± 7.6 kg/d), milk fat content (3.88 ± 0.65%) and yield (1.85 ± 0.38 kg/d), and true protein yield (1.45 ± 0.21 kg/d). However, incremental levels of tannin extracts in the diet produced a linear increase in DM intake (29.2 to 30.9 kg/d) and a linear decrease in kilograms of milk per kilogram of DM intake (1.67 to 1.57 kg/kg) and MUN (12.2 to 10.8 mg/dL). Furthermore, there was a quadratic effect of tannin extracts on milk true protein content (2.96, 3.13, and 3.00% for 0, 0.45, and 1.80% tannin extract, respectively) and a tendency for linear and quadratic response for body weight gain (0.31, 0.16, and 0.44 kg/d for 0, 0.45, and 1.80% tannin, respectively). Intake of N increased linearly (782, 795, and 820 g/d) and N utilization efficiency (milk N/intake N) decreased linearly (0.300, 0.301, and 0.275 for 0, 0.45, and 1.80% tannin, respectively). Relative to the 0% diet, 1.80% tannin extract reduced estimated urinary N excretion by 11%. In this study, adding 0.45% tannin extract to the diet reduced feed efficiency but had a positive effect on milk protein content. Feeding a tannin extract mixture from quebracho and chestnut may reduce environmental labile urinary N excretion without affecting milk yield but at the expense of a lower feed utilization efficiency.

Short communication: Identifying challenges and opportunities for improved nutrient management through the USDA's Dairy Agroecosystem Working Group.

Nutrient management on US dairy farms must balance an array of priorities, some of which conflict. To illustrate nutrient management challenges and opportunities across the US dairy industry, the USDA Agricultural Research Service Dairy Agroecosystems Working Group (DAWG) modeled 8 confinement and 2 grazing operations in the 7 largest US dairy-producing states using the Integrated Farm System Model (IFSM). Opportunities existed across all of the dairies studied to increase on-farm feed production and lower purchased feed bills, most notably on large dairies (>1,000 cows) with the highest herd densities. Purchased feed accounted for 18 to 44% of large dairies' total operating costs compared with 7 to 14% on small dairies (<300 milk cows) due to lower stocking rates. For dairies with larger land bases, in addition to a reduction in environmental impact, financial incentives exist to promote prudent nutrient management practices by substituting manure nutrients or legume nutrients for purchased fertilizers. Environmental priorities varied regionally and were principally tied to facility management for dry-lot dairies of the semi-arid western United States (ammonia-N emissions), to manure handling and application for humid midwestern and eastern US dairies (nitrate-N leaching and P runoff), and pasture management for dairies with significant grazing components (nitrous oxide emissions). Many of the nutrient management challenges identified by DAWG are beyond slight modifications in management and require coordinated solutions to ensure an environmentally and economically sustainable US dairy industry.

Invited review: Enteric methane in dairy cattle production: quantifying the opportunities and impact of reducing emissions.

Many opportunities exist to reduce enteric methane (CH4) and other greenhouse gas (GHG) emissions per unit of product from ruminant livestock. Research over the past century in genetics, animal health, microbiology, nutrition, and physiology has led to improvements in dairy production where intensively managed farms have GHG emissions as low as 1 kg of CO2 equivalents (CO2e)/kg of energy-corrected milk (ECM), compared with >7 kg of CO2 e/kg of ECM in extensive systems. The objectives of this review are to evaluate options that have been demonstrated to mitigate enteric CH4 emissions per unit of ECM (CH4/ECM) from dairy cattle on a quantitative basis and in a sustained manner and to integrate approaches in genetics, feeding and nutrition, physiology, and health to emphasize why herd productivity, not individual animal productivity, is important to environmental sustainability. A nutrition model based on carbohydrate digestion was used to evaluate the effect of feeding and nutrition strategies on CH4/ECM, and a meta-analysis was conducted to quantify the effects of lipid supplementation on CH4/ECM. A second model combining herd structure dynamics and production level was used to estimate the effect of genetic and management strategies that increase milk yield and reduce culling on CH4/ECM. Some of these approaches discussed require further research, but many could be implemented now. Past efforts in CH4 mitigation have largely focused on identifying and evaluating CH4 mitigation approaches based on nutrition, feeding, and modifications of rumen function. Nutrition and feeding approaches may be able to reduce CH4/ECM by 2.5 to 15%, whereas rumen modifiers have had very little success in terms of sustained CH4 reductions without compromising milk production. More significant reductions of 15 to 30% CH4/ECM can be achieved by combinations of genetic and management approaches, including improvements in heat abatement, disease and fertility management, performance-enhancing technologies, and facility design to increase feed efficiency and life-time productivity of individual animals and herds. Many of the approaches discussed are only partially additive, and all approaches to reducing enteric CH4 emissions should consider the economic impacts on farm profitability and the relationships between enteric CH4 and other GHG.

Estimating phosphorus loss in runoff from manure and fertilizer for a phosphorus loss quantification tool.

Nonpoint-source pollution of fresh waters by P is a concern because it contributes to accelerated eutrophication. Given the state of the science concerning agricultural P transport, a simple tool to quantify annual, field-scale P loss is a realistic goal. We developed new methods to predict annual dissolved P loss in runoff from surface-applied manures and fertilizers and validated the methods with data from 21 published field studies. We incorporated these manure and fertilizer P runoff loss methods into an annual, field-scale P loss quantification tool that estimates dissolved and particulate P loss in runoff from soil, manure, fertilizer, and eroded sediment. We validated the P loss tool using independent data from 28 studies that monitored P loss in runoff from a variety of agricultural land uses for at least 1 yr. Results demonstrated (i) that our new methods to estimate P loss from surface manure and fertilizer are an improvement over methods used in existing Indexes, and (ii) that it was possible to reliably quantify annual dissolved, sediment, and total P loss in runoff using relatively simple methods and readily available inputs. Thus, a P loss quantification tool that does not require greater degrees of complexity or input data than existing P Indexes could accurately predict P loss across a variety of management and fertilization practices, soil types, climates, and geographic locations. However, estimates of runoff and erosion are still needed that are accurate to a level appropriate for the intended use of the quantification tool.

A model for phosphorus transformation and runoff loss for surface-applied manures.

Agricultural P transport in runoff is an environmental concern. An important source of P runoff is surface-applied, unincorporated manures, but computer models used to assess P transport do not adequately simulate P release and transport from surface manures. We developed a model to address this limitation. The model operates on a daily basis and simulates manure application to the soil surface, letting 60% of manure P infiltrate into soil if manure slurry with less than 15% solids is applied. The model divides manure P into four pools, water-extractable inorganic and organic P, and stable inorganic and organic P. The model simulates manure dry matter decomposition, and manure stable P transformation to water-extractable P. Manure dry matter and P are assimilated into soil to simulate bioturbation. Water-extractable P is leached from manure when it rains, and a portion of leached P can be transferred to surface runoff. Eighty percent of manure P leached into soil by rain remains in the top 2 cm, while 20% leaches deeper. This 2-cm soil layer contributes P to runoff via desorption. We used data from field studies in Texas, Pennsylvania, Georgia, and Arkansas to build and validate the model. Validation results show the model accurately predicted cumulative P loads in runoff, reflecting successful simulation of the dynamics of manure dry matter, manure and soil P pools, and storm-event runoff P concentrations. Predicted runoff P concentrations were significantly related to (r2=0.57) but slightly less than measured concentrations. Our model thus represents an important modification for field or watershed scale models that assess P loss from manured soils.

Effect of methodology in estimating and interpreting water-extractable phosphorus in animal manures.

Manure water-extractable phosphorus (WEP) data are used in indices and models to assess P transport in runoff. Methods to measure WEP vary widely, often without understanding the effect on how much P is extracted. We conducted water extractions on five dairy, swine, and poultry manures to assess single and sequential extractions, drying manures, solution to solid (cm3 g(-1)) extraction ratios, and P determination method. We found little difference in WEP of single or sequential extractions. Increasing extraction ratio from 10:1 to 250:1 resulted in more WEP recovered, but in a diminishing fashion so that ratios of 200:1 and 250:1 were not significantly different. Patterns of increased WEP with extraction ratio varied with manure type, presence of bedding material, and drying treatment. Fresh and air-dried manures had similar patterns, but differed substantially from oven-dried (90 degrees C) manures. The differential effect of oven-drying on WEP was greatest for dairy and poultry manure, and less for swine manure. We analyzed water extracts colorimetrically before and after digestion, to examine the potential effect of P determination by inductively coupled plasma (ICP) spectroscopy. Digested extracts always contained more P. For manures with bedding, drying decreased the difference in P measured before and after digestion. The opposite was true for manures without bedding. Results highlight the influence of methodology on manure WEP measurement and caution needed when comparing data across studies using different WEP methods. Overall, our results point to a need for a standard manure water extraction method.

Predicting dissolved phosphorus in runoff from manured field plots.

Dissolved inorganic P transport in runoff from agricultural soils is an environmental concern. Models are used to predict P transport but rarely simulate P in runoff from surface-applied manures. Using field-plot data, we tested a previously proposed model to predict manure P in runoff. We updated the model to include more data relating water to manure ratio to manure P released during water extractions. We verified that this update can predict P release from manure to rain using published data. We tested the updated model using field-plot and soil-box data from three manure runoff studies. The model accurately predicted runoff P for boxes, but underpredicted runoff P for plots. Underpredictions were caused by runoff to rain ratios used to distribute P into runoff or infiltration. We developed P distribution fractions from manure water extraction data to replace runoff to rain ratios. Calculating P distribution fractions requires knowing rainfall rate and times that runoff begins and rain stops. Using P distribution fractions gave accurate predictions of runoff P for soil boxes and field plots. We observed relationships between measured runoff to rain ratios and both P distribution fractions and a degree of error in original predictions, calculated as (measured runoff P/predicted runoff P). Using independent field-plot data, we verified that original underpredictions of manure runoff P can be improved by calculating P distribution fractions from measured runoff to rain ratios or adjusting runoff to rain ratios based on their degree of error. Future work should test the model at field or watershed scales and at longer time scales.

Relating soil phosphorus to dissolved phosphorus in runoff: a single extraction coefficient for water quality modeling.

Phosphorus transport from agricultural soils contributes to eutrophication of fresh waters. Computer modeling can help identify agricultural areas with high potential P transport. Most models use a constant extraction coefficient (i.e., the slope of the linear regression between filterable reactive phosphorus [FRP] in runoff and soil P) to predict dissolved P release from soil to runoff, yet it is unclear how variations in soil properties, management practices, or hydrology affect extraction coefficients. We investigated published data from 17 studies that determined extraction coefficients using Mehlich-3 or Bray-1 soil P (mg kg(-1)), water-extractable soil P (mg kg(-1)), or soil P sorption saturation (%) as determined by ammonium oxalate extraction. Studies represented 31 soils with a variety of management conditions. Extraction coefficients from Mehlich-3 or Bray-1 soil P were not significantly different for 26 of 31 soils, with values ranging from 1.2 to 3.0. Extraction coefficients from water-extractable soil P were not significantly different for 17 of 20 soils, with values ranging from 6.0 to 18.3. The relationship between soil P sorption saturation and runoff FRP (microg L(-1)) was the same for all 10 soils investigated, exhibiting a split-line relationship where runoff FRP rapidly increased at P sorption saturation values greater than 12.5%. Overall, a single extraction coefficient (2.0 for Mehlich-3 P data, 11.2 for water-extractable P data, and a split-line relationship for P sorption saturation data) could be used in water quality models to approximate dissolved P release from soil to runoff for the majority of soil, hydrologic, or management conditions. A test for soil P sorption saturation may provide the most universal approximation, but only for noncalcareous soils.

Effect of poultry diet on phosphorus in runoff from soils amended with poultry manure and compost.

Phosphorus in runoff from fields where poultry litter is surface-applied is an environmental concern. We investigated the effect of adding phytase and reducing supplemental P in poultry diets and composting poultry manures, with and without Fe and Al amendments, on P in manures, composts, and runoff. We used four diets: normal (no phytase) with 0.4% supplemental P, normal + phytase, phytase + 0.3% P, and phytase + 0.2% P. Adding phytase and decreasing supplemental P in diets reduced total P but increased water-extractable P in manure. Compared with manures, composting reduced both total P, due to dilution of manure with woodchips and straw, and water-extractable P, but beyond a dilution effect so that the ratio of water-extractable P to total P was less in compost than manure. Adding Fe and Al during composting did not consistently change total P or water-extractable P. Manures and composts were surface-applied to soil boxes at a rate of 50 kg total P ha(-1) and subjected to simulated rainfall, with runoff collected for 30 min. For manures, phytase and decreased P in diets had no significant effect on total P or molybdate-reactive P loads (kg ha(-1)) in runoff. Composting reduced total P and molybdate-reactive P loads in runoff, and adding Fe and Al to compost reduced total P but not molybdate-reactive P loads in runoff. Molybdate-reactive P in runoff (mg box(-1)) was well correlated to water-extractable P applied to boxes (mg box(-1)) in manures and composts. Therefore, the final environmental impact of dietary phytase will depend on the management of poultry diets, manure, and farm-scale P balances.

A consensus protocol for the determination of the threshold doses for allergenic foods: how much is too much?

BACKGROUND: While the ingestion of small amounts of an offending food can elicit adverse reactions in individuals with IgE-mediated food allergies, little information is known regarding these threshold doses for specific allergenic foods. While low-dose challenge trials have been conducted on an appreciable number of allergic individuals, a variety of different clinical protocols were used making the estimation of the threshold dose very difficult. OBJECTIVE: A roundtable conference was convened to develop a consensus clinical protocol for low-dose challenge trials for the estimation of threshold doses for specific allergenic foods. METHODS: In May 2002, 20 clinical allergists and other interested parties were invited to participate in a roundtable conference to develop consensus of the key elements of a clinical protocol for low-dose challenge trials. RESULTS: A consensus protocol was developed. Patients with convincing histories of food allergies and supporting diagnostic evidence including past challenge trials or high CAP-RAST scores can be enrolled in low-dose challenge trials. Care must be taken with younger patients to assure that they have not outgrown their food allergy. An approach was developed for the medication status of patients entering such trials. Challenge materials must be standardized, for example, partially defatted peanut flour composed of equal amounts of the three major varieties of peanuts (Florunner, Virginia, Spanish). Challenge materials must be appropriately blinded with sensory evaluation used to confirm the adequacy of blinding. A double-blind, placebo-controlled design should be used for low-dose challenge trials. Low-dose challenge trials would begin at doses of 10 microg of the allergenic food and would continue with doses of 100 microg and 1 mg followed by specific higher doses up to 100 mg depending upon the expert judgement of the physician; even higher doses might be applied to assure that the patient is indeed reactive to the particular food. A 30-min time interval would be used between doses, and reactive doses would be expressed as both discrete and cumulative doses. The goal of each challenge would be to develop objective symptoms; trials should not be discontinued on the basis of subjective symptoms only. Statistically, a minimum of 29 patients would be enrolled in low-dose challenge trials for each allergenic food because 0 reactors out of 29 patients at a particular dose allow the conclusion that there is 95% certainty that 90% of allergic individuals will not react to that dose. CONCLUSION: A consensus protocol was developed. Using this protocol, it will be possible to estimate threshold doses for allergenic foods, the lowest amount that elicits mild, objective symptoms in highly sensitive individuals.

A simple method to predict dissolved phosphorus in runoff from surface-applied manures.

Computer models are a rapid, inexpensive way to identify agricultural areas with a high potential for P loss, but most models poorly simulate dissolved P release from surface-applied manures to runoff. We developed a simple approach to predict dissolved P release from manures based on observed trends in laboratory extraction of P in dairy, poultry, and swine manures with water over different water to manure ratios. The approach predicted well dissolved inorganic (R2 = 0.70) and organic (R2 = 0.73) P release from manures and composts for data from leaching experiments with simulated rainfall. However, it predicted poorly (R2 = 0.18) dissolved inorganic P concentrations in runoff from soil boxes where dairy, poultry, and swine manures had been surface-applied and subjected to simulated rainfall. Multiplying predicted runoff P concentrations by the ratio of runoff to rainfall improved the relationship between measured and predicted runoff P concentrations, but runoff P was still overpredicted for dairy and swine manures. We attributed this overprediction to immediate infiltration of dissolved P in the freely draining water of dairy and swine manure slurries upon their application to soils. Further multiplying predicted runoff dissolved inorganic P concentrations by 0.35 for dairy and 0.60 for swine manures resulted in an accurate prediction of dissolved P in runoff (R2 = 0.71). The ability of our relatively simple approach to predict dissolved inorganic P concentrations in runoff from surface-applied manures indicates its potential to improve water quality models, but field testing of the approach is necessary first.