Few studies have examined the N kinetics of individual feeds with stable isotope tracing. We hypothesized that N partitioning to milk and excreta pools as well as the rates of the processes that drive this partitioning would differ for alfalfa silage, corn silage, corn grain, and soybean meal. Feed ingredients were endogenously labeled with 15N and included in 4 diets to create treatments with the same dietary composition and different labeled feed. Diets were fed to 12 late-lactation dairy cows for 4 d (96 h) and feces, urine, and milk collection proceeded during the 4 d of 15N enrichment and for 3 d (80 h) after cessation of label feeding. Nonlinear models of 15N enrichment and decay were fit to milk (MN), urine (UN), and fecal N (FN) in R with the nlme package and feed-specific parameter estimates were compared. The estimated proportions of feed N that were excreted in feces supported our understanding that N from soybean meal and corn grain is more digestible than N from alfalfa and corn silage. Estimates for the N partitioning between milk (MN) and urine (UN) from the 2 concentrate feeds (soybean meal and corn grain) indicated that UN:MN ratios were less than or equal to 1:1 indicating either more or equal nitrogen partitioning to milk compared with urine. It is important to maintain factual accuracy in representing the results rather than implying a desired outcome unsupported by the data. In contrast, UN:MN ratios for forage feeds (corn and alfalfa silage) were > 1:1, indicating more N partitioning to urine than milk. The modeled proportion of total FN that originated from feed N was 82.2% which is in line with previous research using a similar 15N measurement timeframe. However, the proportion of urinary and MN originating from feed N was much lower (60.5% for urine, 57.9% for milk), suggesting that approximately 40% of urinary and MN directly originate from body N sources related to protein turnover.

Growing concerns about environmental impacts of dairy farms have driven producers to address greenhouse gas (GHG) emissions and nitrogen (N) losses from soil following land application of dairy manure. Tannin dietary additives have proved to be a successful intervention for mitigating GHG and ammonia (NH3 ) emissions at the barn scale. However, it is unknown how land application of dairy manure from cows fed tannin diets affects crop-soil nitrogen dynamics and soil GHG flux. To test this, cows were fed diets at three levels of tannins (0.0%, 0.4%, and 1.8% of dry matter intake) and their manure was field applied at two N rates (240 and 360 kg N ha-1 ). Soil NH4 + -N, NO3 - -N, corn silage yield, and soil GHG flux were then measured over a full growing season. Soils amended with tannin manure had lower initial NH4 + -N concentrations and lower total mineral N (NH4 + -N + NO3 - -N) concentrations 19 days after application, compared to soils amended with no tannin manures. Despite lower early season N availability in tannin-fertilized plots, there were no differences in corn silage yield. No differences in soil GHG and NH3 emissions were observed between manure-amended treatments. These results demonstrate that while tannin addition to dairy cow feed does not offer short-term GHG or NH3 emissions reductions after field manure application, it can promote slower soil N mineralization that may reduce reactive N loss after initial application.

Improving nutrient management in grazing system dairy farms requires determining nutrient flows through animals, the placement of cows within farms and potential for collection, and the re-use and loss of nutrients. We applied a model incorporating data collected at a range of temporal and spatial scales to quantify nutrient excretion in all locations that lactating herds visited on five days over a year on 43 conventional and organic grazing system dairy farms. The calculated nutrient loads excreted by cows in different places were highly skewed; while N, P and K deposited loads were consistent across the year, S, Ca and Mg loads varied between sampling times and seasons. The greatest mean and range in nutrient loads were deposited in paddocks, with the smallest amounts deposited in dairy sheds. All excreted nutrient loads increased with farm and herd sizes and milk production. Mean daily loads of 112, 15, 85, 11, 22 and 13 kg of N, P, K, S, Ca and Mg were deposited by the herds which, when standardised to a 305-day lactation, amounted to 24, 4, 20, 3, 5 and 3 t excreted annually, respectively. In addition to routine manure collection in dairy sheds, ensuring collection and recycling of nutrients excreted on feed pads and holding areas would decrease potential nutrient losses by 29% on average. Non-collected, recycled nutrients were disproportionately returned to paddocks in which cows spent time overnight, and except for S and Ca, nutrient loading rates were greater than rates applied as fertilisers. These data demonstrate the extent of excreted nutrients in grazing dairy systems and indicate the need to account for these nutrients in nutrient management plans for Australian dairy farms. We propose incorporating excretion data in current budgeting tools using data currently collected on most Australian grazing system dairy farms.

Estimating excreted nutrients is important for farm nutrient management, but seldom occurs on commercial grazing system farms due to difficulties in quantifying pasture intake. Nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) intake, excretion and use efficiency of 43 commercial dairy herds grazing pasture were calculated to understand the range in nutrient intake and excretion in these systems. Milk production, feed (grazed and supplement), as well as farm and herd management data were collected quarterly on representative farms located in temperate, arid, subtropical and tropical regions of Australia. Lactating herd sizes on these farms averaged 267 (30 to 1350) cows, with an average daily milk yield of 22 (9 to 36) kg/cow per day and the herds walked from <0.01 to 4 km/day on a variety of terrains. The mean total metabolizable energy (ME) required by cows in the herds was estimated to be 195 (116 to 289) MJ/cow per day. Although these farms are considered grazing systems, feeding strategies ranged from total dependence on pasture to total mixed rations (TMRTMR) and consisted of a wide variety of nutrient and energy contents. Mean pasture dry matter intake (DMI) (9 kg/cow per day, from 0.1 to 22 kg/cow per day) was just over half of total DMI. Dietary concentration of crude protein, P, K, S, Ca and Mg concentrations were, on average, 19%, 0.45%, 2.1%, 0.29%, 0.65%, and 0.3%, respectively, for all herds and, except for N, supplement nutrient concentrations were always more variable than pasture. Approximately 72% and 88% of diets provided greater than recommended P and N intakes, respectively. Calculated mean N, P, K, S, Ca and Mg excretions were 433, 61, 341, 44, 92 and 52 g/cow per day, respectively. Of the farm characteristics examined, residual maximum likelihood (REML) analysis indicated that daily excreted N, P and S were significantly related to per ha milk production, and excreted P, K and Mg were related to percentage of herd DMI provided as supplement. Mean use efficiencies by cows of N, P, K, S, Ca and Mg were 21%, 25%, 9%, 16%, 23% and 4%, respectively. These estimates of nutrient excretion and feed nutrient use efficiencies can be used to improve nutrient management on grazing system commercial dairy farms.

Nitrogen (N) and phosphorus (P) loss from agriculture persists as a water quality issue, and outdoor cattle lots can have a high loss potential. We monitored nutrient concentrations in leachate and runoff from constructed dairy heifer lots. Lots were about 42 m(2), excavated to 1.1 m deep, and backfilled with three surface materials (soil, sand, and bark mulch). Plots were lined with a rubber membrane to allow total collection of all leachate. Runoff was collected from soil plots only. Runoff and leachate were monitored for dissolved and total N and P from 2010 to 2015. Dairy heifers were placed on plots several times per year for a week at a time. The percentage of annual precipitation collected as leachate averaged 34% for soil, 75% for sand, and 64% for mulch plots. For soil plots, the percentage of annual precipitation collected as runoff ranged from 13% to 44%, with the percentage increasing with precipitation. Leachate N concentrations in soil and sand plots behaved similarly, with ammonium-N (NH4-N) much less than nitrate-N (NO3-N) and total N. Leachate N concentrations were generally least from mulch, suggesting more microbial N retention. Soil had the least and sand plots had the greatest P concentrations in leachate, with mulch in between. In runoff from soil plots, particulate N and P were well related to sediment concentrations. Compared with leachate from soil and sand, soil runoff NO3-N concentrations were typically less, but were similar to leachate in mulch plots. Conversely, soil runoff NH4-N concentrations were typically greater than in leachate for any treatment. Soil runoff dissolved P concentrations increased slightly over time, with most runoff P when cows were recently on plots, and were typically greater than in leachate for any treatment. Overall, nutrient dynamics in sand and soil plots appeared controlled by mineral processes, while biological processes dominated more in mulch plots. Sand plots had the most nutrients in leachate, implying more potential to recover nutrients in liquid form. Soil and mulch retained more nutrients within plot materials, which means on-farm nutrient use would require transfer of materials to cropland or growing crops directly in previous cattle lots.

Abstract.On dairy farms, outdoor lots where cows spend substantial time can be areas of high nutrient deposition in manure. This represents an inefficient use of farm nutrients, if the nutrients are not recovered, and a potential for nutrient loss to the environment. Management of barnyards to recover nutrients can have environmental and production benefits. We monitored nitrogen (N) and phosphorus (P) fate for five years in dairy heifer barnyard plots constructed with soil, sand, or bark mulch surfaces. The plots were stocked with heifers several times per year for about a week at a time. We monitored N and P loss in runoff (soil plots only), leachate, and gas emissions. Of the total N inputs to the plots through heifer excretion, 6% to 8% of inputs were lost in runoff (~2%), leachate (~3% to 4%), and gas emissions (~3% to 4%) from the soil and mulch plots. Most of the N inputs remained in the surface materials. For the sand plots, more N inputs were lost in leachate (~13%) and gas emissions (~6%), but most of the N remained in the surface material. Of total P inputs to the plots through heifer excretion, 4% to 6% of inputs were lost in runoff and leachate, with most of the P remaining in the surface materials. The results suggest that most of the nutrients deposited by heifers onto barnyards could be recovered and used as fertilizer for crop growth by excavating the surface materials and spreading them on cropland, by including animal holding areas in land used for crop rotation so crops can recover nutrients , or by corralling animals directly on cropland. Keywords: Barnyards, Cattle, Leaching, Nutrients, Runoff.

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.

The increased global demand for milk and other dairy products over the past decades is a cause for concern due to the potential for environmental impact. Ammonia produced by housed dairy cows can contribute to the formation of particulate matter and nitrous oxide which both contribute to the greenhouse effect. The methane produced by these cows also contributes to the greenhouse effect. Scientists and engineers face the challenge of developing methods to reduce the environmental impact of dairy production while not inhibiting the ability of producers to keep up with demand. Emission of methane and ammonia are highly dependent on feed composition, barn design and operation, manure management making this a challenging topic to study experimentally. Using computational models to simulate the generation and dispersion of gaseous species within dairy housing can facilitate the exploration of cost-effective gas mitigation strategies. Thus a steady-state computational fluid dynamics (CFD) model capable of simulating biologically based generation of methane, ammonia, and heat and their transport within the domain was developed and validated. The effect of buoyancy forces on the accuracy and stability of the solutions was explored. The model was validated with experimental data collected from emission chambers located at USDA-ARS Dairy Forage Research Center in Wisconsin, USA. Concentration of ammonia and methane, due to controlled injections from cylinders and biological generations from a dairy cow, were measured in the chambers using a FTIR gas analyzer. Results of the validated CFD model could be used to predict gaseous emissions under a range of environmental, design, and experimental treatment parameters.

A resilient US dairy industry will be underpinned by forage and crop production systems that are economically, environmentally, and socially sustainable. Land use for production of perennial and annual forages and grains for dairy cattle must evolve in response to multiple food security and environmental sustainability issues. These include increasing global populations; higher incomes and demand for dairy and other animal products; climate change with associated temperature and moisture changes; necessary reductions in carbon and water footprints; maintenance of soil quality and soil nutrient concerns; and competition for land. Likewise, maintaining producer profitability and utilizing practices accepted by consumers and society generally must also be considered. Predicted changes in climate and water availability will likely challenge current feed and dairy production systems and their national spatial distribution, particularly the western migration of dairy production in the late 20th century. To maintain and stabilize profitability while reducing carbon footprint, particularly reductions in methane emission and enhancements in soil carbon sequestration, dairy production will need to capitalize on genetic and management innovations that enhance forage and grain production and nutritive value. Improved regional and on-farm integration of feed production and manure utilization is needed to reduce environmental nitrogen and phosphorus losses and mitigate greenhouse gas emissions. Resilient and flexible feed production strategies are needed to address each of these challenges and opportunities to ensure profitable feeding of dairy cattle and a sustainable dairy industry.

The objective of this study was to determine the relative partitioning of N in individual feed within a diet (alfalfa silage [AS], corn silage [CS], corn grain [CG] and soybean meal [SBM]) into milk, urinary and fecal N in lactating dairy cows. For 11 days, twelve multiparous Holstein cows (means +/- SD; 264 +/- 18 DIM) were fed once a day an unlabeled TMR formulated to contain (DM basis) 335, 325, 190, 125 and 25 g/kg of CS, AS, CG, SBM and a mineral-and-vitamin premix, respectively. On the morning of day 12, cows were blocked by milk yield and randomly assigned within block to one of four dietary treatments constructed by replacing one feed ingredient of the unlabeled TMR with its corresponding N-15-labeled ingredient (grown with N-15-labeled fertilizers). Cows were fed dietary treatments for four days (day 12-15) and the unlabeled TMR from day 16-19. Feed intake and lactation performance were measured daily whereas total fecal and urinary collections were conducted on each cow every 6 h from day 12-19. Feeding N-15-labeled ingredients had no effect on DMI (mean +/- SD; 22.0 +/- 2.0 kg/d), milk yield (26.4 +/- 5.2 kg/d), N intake (631 +/- 25 g/d), milk protein concentration (34.7 +/- 3.3 g/kg), and N use efficiency (milk N/intake N; 235 46 g/kg). By the end of sampling, 61% of N-15 was recovered in milk (13.6%), urine (24.1%) and feces (23.3%) suggesting substantial distribution of 15N in tissues with slow turnover rates or growing actively (e.g., fetal tissues). The ratio of N-15 atom% excess (APE) in urine to N-15 APE in milk and the ratio of N-15 APE in feces to N-15 APE in milk measured on the fourth day of feeding the treatment TMR were used as indicators of relative N partitioning. The N-15 APE urine/milk ratio was greater for AS (1.51) than for'CS (1.30), which in turn was greater than for the concentrates (1.02 for CG and 0.94 for SBM). In addition, the APE N-15 feces/milk ratio was greater in silages than concentrates (2.12 vs. 1.20, respectively). Interestingly, the main route of N-15 excretion from AS was fecal rather than urinary. Overall results suggested more excretion of urinary N and fecal N relative to milk N secretion for silages than for concentrates.

Manure management at dairy production facilities, including anaerobic digestion (AD) and solid-liquid separation (SLS), has shown strong potential for the abatement of greenhouse gas (GHG) and ammonia (NH3) emissions. However, previous study results are inconsistent and the combined effect of AD + SLS remains to be quantified. This study evaluated the effects of AD, SLS, and AD + SLS on GHG and NH3 emissions during manure storage through land application over nine months. AD and SLS alone significantly (P < 0.05) reduced total GHG emissions for storage and land application compared to untreated manure slurries by 25% and 31%, respectively. The majority of that reduction was from methane during storage. SLS had a greater potential for methane reduction in storage than AD, but the variability in digester performance likely impacts the reduction potential. Digestion with subsequent separation further decreased CH4 emissions from 3.9 g CO2-eq to 1.3 g CO2-eq, but increased emissions of nitrous oxide (N2O) from 0.6 g CO2-eq to 2.0 g CO2-eq during storage eliminating a further reduction of GHG emissions as compared to AD alone. AD resulted in a gas emission tradeoff as it increased NH3 emissions by 81% during storage, which could be mitigated by subsequent SLS, manure storage covers, or other beneficial management practices. (C) 2017 The Authors. Published by Elsevier B.V.

The increased global demand for milk and other dairy products over the past decade has heightened concerns about the potential for increased environmental impacts. Accurate measurement of gas emissions from dairy cows is essential to assess the effects of cow diets and other management practices on both the composition and rate of gas emissions. In this article, methodologies are described to instrument, calibrate, and assess the uncertainty of gas emissions by cows housed in chambers that simulate production settings. The supply and exhaust ducts of each chamber were equipped with pitot tubes, temperature and relative humidity probes, and gas samplers to monitor airflow rates, gas composition, and gas emission rates. A Fourier transform infrared spectroscopy (FTIR) instrument was used to quantify gaseous concentrations in the gas samples on a semi-continuous basis. The measurement uncertainty of the rate of gaseous emission from the chambers was quantified, and gas concentration and differential pressure, as measured by the pitot tubes, were identified as the primary parameters contributing to gas emission uncertainties. Mass recovery tests determined that the recovery of methane from each chamber was within 10% of the released mass. Fan operating curves were experimentally determined to identify optimum differential chamber pressures to minimize gas leakage from the chambers. A computational fluid dynamics model was developed to assess air mixing patterns and define steady-state conditions. The model was validated with experimental data of air velocity within each chamber. These procedures will facilitate accurate measurement of gas emissions from housed dairy cows and provide a laboratory to test various gas mitigation treatments.

Large N surpluses are a feature of most dairy farms worldwide. Despite the predominance of grazing systems in Australia, increasing animal densities and greater reliance on purchased feed mean that feed nutrient inputs and the role of grazing animals in N flows and deposited loads have grown. However, quantifying nutrient intakes and N excretion is difficult on commercial farms due to challenges in estimating pasture dry matter (DM) intake by grazing cattle. The aim of the present study was to quantify for commercial dairy farms, N excreted by lactating herds, the relative amounts of excreta N versus farm N inputs, and N loads deposited to different within-farm locations. Data were collected on at least five occasions from 43 diverse grazing system farms located in different climatic zones. An animal performance method for estimating annual DM intake was modified to calculate daily N intake and excretion and animal feed N use efficiency (NUE; milk N secreted/feed N intake). On average, these herds received 52% of their energy requirements from supplementary feeds despite the grazing base. Mean N intake (545 g cow–1 day–1), which greatly exceeded recommended dietary intakes, resulted in mean excretion of 433 g N cow–1 day–1 and low mean NUE (21%; range 11–39%). Calculated annual N flows through the lactating herds were equivalent to 69% of total N inputs onto these farms. When excreted N was apportioned to the locations visited by the lactating herds, deposition to pasture paddocks was not uniform. Almost 50% more excreted N was deposited to paddocks that were closer to the dairy shed, and approximately twice as much N was returned to feedpads and holding areas as deposited in dairy sheds and yards, with the potential for N accumulation and loss in these places. On average, 20% more N was deposited as excreta on pasture paddocks by the lactating herd than was applied as commercial fertiliser (168 vs 141 kg N ha–1 respectively). These results demonstrate that quantifying excreta N loads and spatial nutrient distribution by lactating cows can assist in improving N management in grazing system dairy farms.

Crops and livestock transform a general range of 20% to 50% of applied nitrogen (N) into product N (e.g., grain, forage, meat, milk). Most N not incorporated into agricultural products is lost to the environment. The objective of this study was to quantify soil N input (fertilizerN, biologically fixed-N) incorporation into the major diet components fed to dairy cows, diet component N secretions in milk N and excretion in manure N constituents, and manure N recycled back through the feed supply. Alfalfa for silage (AS), corn for silage (CS), corn grain (CG) and soybeans (SB, eventually solvent-extracted into soybean meal, SBM) were enriched in the field with fertilizers containing the stable isotope 15N. Each 15N-labeled diet component was fed individually to twelve mid-lactation cows (3 cows per 15N-enriched diet component) as part of a total mixed ration (TMR). Proportions of each component’s 15N intake (15NI) recovered in milk, feces, fecal undigested dietary N, urine, urinary urea and retained by cows were determined during a 4-day 15N feeding period and 4days thereafter. Diet component 15N manure was applied to field plots and 15N uptake by corn for silage was determined over two succeeding years. The wide range in total 15N recoveries (% 15NI), greatest from cows fed AS (67) followed by CS (61), SBM (61) and CG (54) indicate significant differences in diet component 15N retention by cows. Relative 15N recoveries (% of total 15N recovered) in milk were greater (and statistically similar) from cows fed CG and SBM (average of 29.2) than from cows fed AS and CS (also statistically similar, average of 18.4). Relative 15N recoveries in feces were greater (and statistically similar) from cows fed AS and CS (average of 42.2) than from cows fed CG and SBM (also statistically similar, average of 30.7), and 15N recoveries as fecal undigested dietary N were greatest from cows fed CG (2.5) followed by AS and CS (average of 2.2) and SBM (<1). Relative 15N recoveries in urine (average of 39.7) and urinary urea (average 34.0) were similar across all diet components. Over the 2-year field study period, greatest manure 15NUE (% of applied manure 15N recovered as corn silage 15N) was obtained in plots amended with manure 15N derived from SBM (38.2) and lowest from CS (30.5). The greater total N use efficiency (percent N inputs incorporated into milk N plus corn silage N) for SBM (68.3) and AS (51.5) than for CG (47.4) and CS (40.6) can be attributed mostly to differences in N use efficiencies of the biologically-fixed-N and fertilizer N to grow diet components. A balance between corn, alfalfa and soybeans in dairy cropping systems should be encouraged to not only enhance N use efficiency in feed and milk production and manure N recycling, but also to capture many of the long-term benefits associated with corn-legume rotations.

Nitrogen (N) is invaluable for maintaining agricultural production, but its use, and particularly inefficient use, can lead to environmental losses. This paper reviews N use efficiency (NUE) and N surplus indicators for dairy production systems to assess their utility for optimising N use outcomes and minimising environmental N losses. Using case-study examples, we also assess realistic goals for these indicators and discuss key issues associated with their use. Published whole-farm NUE and whole-farm N surplus values ranged within 10–65% and 40–700 kg N ha–1 year–1 respectively. In a study of five catchments across New Zealand, whole-farm NUE was more strongly affected by catchment differences in soil and climatic conditions than by differences in management. In contrast, whole-farm N surplus differed both between- and within-catchments and was a good indicator of N losses to water. Realistic goals for both NUE and N surplus thus depend on the agro-climatic context of the dairy system and on its economic and environmental goals. Crop and animal NUE values can be valuable indicators for optimising fertiliser and feed use and minimising N losses. However, global or national whole-farm NUE values appear of limited value if the ultimate goal for setting targets is to reduce the environmental impact of N use; whole-farm level targets based on N surplus would be a more useful indicator for this purpose. Our review also reinforces the importance of standardising the variables that should be used to estimate NUE and N surplus values, to ensure equitable comparisons between different systems. Finally, NUE and N surplus targets should also be set in the context of other agro-environmental considerations.

Manipulating dietary ingredients may effect greenhouse gas emissions by dairy cows. The objective was to determine CH4 and NH3 emissions of lactating cows fed canola meal (CM) or soybean meal (SBM) as the main protein source at either a high (HI; 17.6%) or low (LO; 15.4%) CP concentration. Twenty-four multiparous Holstein cows (mean ± SD; 120.5 ± 3.24 DIM; 2.71 ± 0.81 parity) were assigned 1 of 4 treatment diets at calving in a randomized complete block design with a 2 × 2 factorial arrangement of treatments. After wk 16 of lactation, cows were randomly assigned to 1 of 4 air-flow controlled chambers. Cows remained in the chamber for 6 d. Performance and emission data were measured on the last 3 d of each block. Diets were formulated to contain 55.0% forage (39.6% corn silage, 15.4% alfalfa silage) and 45% concentrate on DM basis. CM was included at 19.4% and 11.9% DM and SBM was included at 14.5% and 8.9% DM for the HI and LO diets, respectively. Soyhulls were included to balance nutrients and alter CP concentration. All other ingredients were the same across diets. Data were analyzed using the MIXED procedure of SAS. Cows fed either source or CP concentration of protein did not differ in DMI (mean ± SEM; 26.67 ± 0.75) or 4% fat-corrected milk (FCM; 53.89 ± 2.04 kg/d). Milk yield (59.1 vs. 53.3 ± 2.48 kg/d; P = 0.095) and feed efficiency (FCM/DMI; 2.11 vs. 1.95 ± 0.09; P = 0.082) tended to be greater for cows consuming HI protein compared to LO protein diets. Milk urea N (MUN) was lower for cows fed LO protein compared to HI protein (9.14 vs. 12.93 mg/dL; P < 0.001). There was a source × CP concentration interaction for CH4 emission. Cows fed HICM produced less CH4 than those consuming HISBM and LOCM (465.7 vs. 528.5 and 537.9 ± 28.7 g/d; P = 0.036). CH4 expressed per unit of DMI (19.3 ± 1.24) or FCM (9.23 ± 0.71) did not differ among treatments. NH3 tended to be higher for cows fed HI protein compared to LO protein (29.5 vs. 24.6 ± 2.31 g/d; P = 0.062). Milk N (g/d) and NH3 emission expressed per unit of milk N was not affected by diet. NH3 tends to increase with added protein inclusion in the diet and CM may reduce methane under specific feeding strategies.

Dairy cattle spend considerable time in outside barnyards. Nine barnyards were constructed to examine impacts of surface materials (bark, sand, soil) and timing of cattle corralling (before and after 3–14-day corralling periods) on fluxes of carbon dioxide (CO2), methane (CH4), ammonia (NH3), nitrous oxide (N2O) and CO2 equivalents (CO2eq). Surface, year, and surface*year interactions accounted for 64%, 6% and 16% of CO2 flux variability. Average CO2 flux from bark (2552 mg/m2.h) was 3.1–3.9 times greater than from sand or soil, especially after bark replenishment. Timing, year, timing*year and surface*year accounted for 40%, 17%, 14%, and 17% of CH4 variability. Average CH4 flux after corralling (10.6 mg/m2.h) was 3.8 times greater than before corralling, and 5.2 times greater the year following bark replenishment. Timing accounted for 67% of NH3 variability. After corralling, NH3 fluxes (1622 µg/m2.h) were 95 times greater than before corralling. Timing, surface, surface*timing and timing*year accounted for 33%, 10%, 24% and 13% of N2O variability. Average N2O flux after corralling (2252 µg/m2.h) was 3.7 times greater than before corralling. Surface and surface*year accounted for 71% and 16% of CO2eq variability. Average CO2eq flux from bark (3188 mg/m2.h) was 2.5–3.0 times greater than sand or soil. Greatest CO2eq flux occurred the year after bark replenishment. Tradeoffs between gas emissions, nutrient runoff and leaching, and cow comfort and health need to be assessed more fully before recommending beneficial practices for barnyard surface type and management.

Nitrogen use efficiency (NUE), the ratio between N outputs in products over N inputs, is often used to evaluate N use outcomes of an agricultural system and/or the risk of environmental N losses. In this paper we address the question what NUE goals are realistic for dairy production systems. We use the following definitions of NUE: Crop NUE, defined as the percentage of the total N inputs taken up by crops or pasture; Animal NUE, defined as the percentage of total feed N intake incorporated into milk and meat; and Whole farm NUE, defined as the percentage of total N inputs to the farm that is exported in animal products and/or exported feed. Nitrogen surpluses (i.e. N inputs minus N outputs) are also reviewed. Published values of Crop NUE and N surplus generally ranged between 55-90% and 25-230 kg N/ha/year, respectively, while commonly reported Animal NUE and N surplus values ranged between 15-35% and 110-450 kg N/ha/year. Whole farm NUE and N surplus values ranged between 10-65% and 40-700 kg N/ha/year. In a NZ catchment study, Whole farm NUE was affected more strongly by differences between catchments (e.g. soil and climatic conditions) than by differences in management. In contrast, N surplus values differed both between-catchment and within-catchment and were good indicators of N losses to water. Realistic goals for NUE will therefore depend on the agro-climatic context in which a dairy system operates and on the economic and environmental goals the system aims to achieve. Crop and Animal NUE values can be valuable indicators for optimising fertiliser and feed use, and minimizing N losses. However, global or even national Whole-farm NUE values appear to be of limited value if the ultimate goal for setting targets is to reduce the environmental impact of N use. Whole-farm level targets based on N surplus would be a more useful indicator for this. Regardless of the metric used all metrics are calculated based on estimates of N inputs and N outputs, so it is important to agree on which items should be included in the input and output terms, and that all inputs and outputs are measured or adequately estimated. For systems that import large amounts of purchased feeds, this should include the N inputs required to produce this feed. Any NUE goals targets should be set in the context of other agro-environmental indicators such as losses of phosphorus and faecal organisms to water, carbon footprints, and energy and water use efficiencies.

Dairy cows are responsible for significant emissions of enteric methane (CH4) and produce nitrous oxide (N2O) and ammonia (NH3) gas from manure. As an abatement strategy, we explored the effects of long-term condensed tannin (Quebracho and chestnut extracts) addition to dairy cow diets. Previous studies have demonstrated that tannins in cow diets reduce methane and ammonia efflux, but none have done so over a >1-month time period. A modified stanchion barn equipped with gas analysis instrumentation measured CH4, N2O, and NH3 fluxes into and from the barn, at the onset of the experiment, and 45 and 90 days after feeding groups of lactating dairy cows a control diet or two levels of tannin extract at 0.45 and 1.8 % of dietary dry matter. Few statistical differences among treatments were observed, likely a consequence of high variability and low sample size necessary for conducting a study of this duration. However, on a per-cow basis, low and high tannin diets lowered CH4 emissions by 56 g cow−1 day−1 and by 48 g cow day−1, respectively. Diet tannin additions lowered CH4 (33 %), NH3 (23 %), and N2O (70 %) per unit milk corrected emissions in the high tannin treatment compared to the control at the end of the experiment, without significant loss in milk production. These results suggest that relatively low concentrations of diet tannin additions can reduce ruminant CH4 and gaseous N emissions from manure. The tannin effect observed after 90 days is a starting point for considering tannin additions as a potential long-term strategy for improving the environmental footprint of milk production.

The objective of this study was to determine how feeding diets that differed in dietary ruminal in vitro NDF digestibility (IVNDFD) affected DMI, milk production, and CH4 emission from lactating dairy cows. Twenty four multiparous Holstein cows (mean ± SD; 717 ± 67 kg of BW; 160 ± 49 d in milk) were randomly assigned to four dietary treatments in a randomized complete block design study. Four levels of dietary IVNDFD (digestibility determine after 30 h of incubation) were achieved by substituting corn stover (15% of dietary DM) with alkaline-treated corn stover (at 7.0% Ca(OH)2 of stover DM; stover DM was 50%) in stepwise increments (0, 5, 10, and 15% of dietary DM). Following a 2-wk covariate adjustment period, cows were assigned to dietary treatments for 6 wk. Cows were fed a total mixed ration with (DM basis) 55% forage, 45% concentrate, 16.6% crude protein, 28.7% NDF, and 23.7% starch once daily. Replacing untreated corn stover with 5, 10, and 15% treated corn stover increased dietary IVNDFD by 2.2, 4.3, and 6.2% units, respectively. Performance and CH4 emission measurements were conducted in four tie-stall emission chambers during three consecutive days the last week of the covariate and experimental periods. Treatment effects are presented as covariate-adjusted least squares means (± SEM). Increasing IVNDFD in the diet had no effect on DMI (21.3 ± 1.3 kg/d), milk yield (32.1 ± 2.2 kg/d), fat-and-protein corrected milk yield (FPCM; 29.9 ± 2.3 kg/d), FPCM/DMI (1.42 ± 0.1), CH4 emission (524 ± 35 kg/d), and CH4/FPCM (18.4 g/kg ± 1.7). However, with increasing levels of IVNDFD in the diet there was a linear decrease (P = 0.02) in CH4/DMI from 26.4 to 23.3 (g/kg) and a tendency (P = 0.06) to reduce CH4/milk from 18.8 to 14.4 (g/kg). Also, a tendency (P = 0.08) for a quadratic response was observed for CH4/milk; increasing dietary IVNDFD by 2.2 and 6.2% units decreased CH4/milk to 17.7 and 14.4 g/kg respectively, compared with 15% untreated corn stover diet (18.8 g/kg), but a 4.4% increase on IVNDFD resulted in the highest yield of CH4/milk (20.0 g/kg). Under the conditions of this study increasing IVNDFD in the diet by as much as 6.2% units had little impact on performance or emission of CH4 (g/d), but decrease CH4 emission per unit of DMI by 12% and decreased CH4 emission per unit milk by 23%.