Antibiotic resistance genes (ARGs) may be introduced to agricultural soil through the land application of cattle manure. During a rainfall event, manure-borne ARGs may infiltrate into subsurface soil and leach into groundwater. The objective of this study was to characterize and model the vertical transport of manure-borne ARGs through soil following the land application of beef cattle manure on soil surface. In this study, soil column experiments were conducted to evaluate the influence of manure application on subsurface transport of four ARGs: erm(C), erm(F), tet(O) and tet(Q). An attachment-detachment model with the decay of ARGs in the soil was used to simulate the breakthrough of ARGs in leachates from the control column (without manure) and treatment (with manure) soil columns. Results showed that the first-order attachment coefficient (kₐ) was five to six orders of magnitude higher in the treatment column than in the control column. Conversely, the first-order detachment and decay coefficients (kd and μₛ) were not significantly changed due to manure application. These findings suggest that in areas where manure is land-applied, some manure-borne bacteria-associated ARGs will be attached to the soil, instead of leaching to groundwater in near terms.

Beef cattle feedyards have been identified as sources of large amounts of particulate matter (PM) which may transport affiliated chemicals including steroids, beta agonists, and antibiotics from feedyards into the environment. This study is the first to examine persistence of PM-affiliated pharmaceuticals downwind of feedyards using multiple downwind samples collected at increasing distances from feedyard boundaries (n = 5). Concentrations of antibiotics and ractopamine per gram of PM remained consistent at all downwind locations (out to 4.8 km) whereas concentrations per m³ air decreased significantly at distances between 0.1 and 0.7 km downwind, corresponding to significant decreases in mass of PM. Monensin was present in the highest concentrations of any measured pharmaceutical, with concentrations of 37 μg/g PM (376 ng/m³) air in samples collected within 0.1 km downwind of feedyards. Total copy count of tetracycline resistance genes (tetW, tetQ, tetO, tetM, tetL, and tetB) were also significantly increased in samples collected within 0.1 km downwind of feedyards (10⁶ copies) as compared to samples collected upwind (10³ copies) and farther downwind (10⁴ copies) of feedyard boundaries. These results suggest that transport of pharmaceutical-laden PM into the terrestrial environment is occurring primarily via PM deposition within 0.7 km of the feedyard, while aerial transport persists over longer distances (>4.8 km).

Hormonal growth promoters (HGPs), widely used in beef cattle production globally, make their way into the environment as agricultural effluent—with potential impacts on aquatic ecosystems. One HPG of particular concern is 17β-trenbolone, which is persistent in freshwater habitats and can affect the development, morphology and reproductive behaviors of aquatic organisms. Despite this, few studies have investigated impacts of 17β-trenbolone on non-reproductive behaviors linked to growth and survival, like boldness and predator avoidance. None consider the interaction between 17β-trenbolone and other environmental stressors, such as temperature, although environmental challenges confronting animals in the wild seldom, if ever, occur in isolation. Accordingly, this study aimed to test the interactive effects of trenbolone and temperature on organismal behavior. To do this, eastern mosquitofish (Gambusia holbrooki) were subjected to an environmentally-relevant concentration of 17β-trenbolone (average measured concentration 3.0 ± 0.2 ng/L) or freshwater (i.e. control) for 21 days under one of two temperatures (20 and 30 °C), after which the predator escape, boldness and exploration behavior of fish were tested. Predator escape behavior was assayed by subjecting fish to a simulated predator strike, while boldness and exploration were assessed in a separate maze experiment. We found that trenbolone exposure increased boldness behavior. Interestingly, some behavioral effects of trenbolone depended on temperature, sex, or both. Specifically, significant effects of trenbolone on male predator escape behavior were only noted at 30 °C, with males becoming less reactive to the simulated threat. Further, in the maze experiment, trenbolone-exposed fish explored the maze faster than control fish, but only at 20 °C. We conclude that field detected concentrations of 17β-trenbolone can impact ecologically important behaviors of fish, and such effects can be temperature dependent. Such findings underscore the importance of considering the potentially interactive effects of other environmental stressors when investigating behavioral effects of environmental contaminants.

Cavity nesting bees are proficient and important pollinators that can augment or replace honey bee pollination services for some crops. Relatively little is known about specific pesticide concentrations present in cavity nesting insect reed matrices and associated potential risks to cavity nesting bees. Nesting substrates (Phragmites australis reeds in bundles) were deployed in an agriculturally intensive landscape to evaluate colonization and agrochemical exposure among cavity nesting pollinators over two consecutive field seasons. Composition of insect species colonizing reeds within nest bundles varied considerably; those placed near beef cattle feed yards were dominated by wasps (93% of the total number of individuals occupying reed nest bundles), whereas nest bundles deployed in cropland-dominated landscapes were colonized primarily by leaf cutter bees (71%). All nesting/brood matrices in reeds (mud, leaves, brood, pollen) contained agrochemicals. Mud used in brood chamber construction at feed yard sites contained 21 of 23 agrochemicals included in analysis and >70% of leaf substrate stored in reeds contained at least one agrochemical. Moxidectin was most frequently detected across all reed matrices from feed yard sites, and moxidectin concentrations in nonviable larvae were more than four times higher than those quantified in viable larvae. Agrochemical concentrations in leaf material and pollen were also quantified at levels that may have induced toxic effects among developing larvae. To our knowledge, this is the first study to characterize agrochemical concentrations in multiple reed matrices provisioned by cavity-nesting insects. Use of nest bundles revealed that cavity nesting pollinators in agriculturally intensive regions are exposed to agrochemicals during all life stages, at relatively high frequencies, and at potentially lethal concentrations. These results demonstrate the utility of nest bundles for characterizing risks to cavity nesting insects inhabiting agriculturally intensive regions.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous analysis of 6 ectoparasiticides – 2 synthetic pyrethroids (deltamethrin, cypermethrin) and 4 macrocyclic lactones (abamectin, doramectin, ivermectin and eprinomectin) in biosolids. The method was used to investigate the occurrence of these ectoparasiticides in beef cattle feedlot wastes in Australia from 5 commercial feedlot operations which employ varying waste management practices. Deltamethrin and cypermethrin were not detected in any of the samples while abamectin, ivermectin, doramectin and eprinomectin were detected in some of the samples with concentrations ranging from 1 to 36 μg/kg dry weight (d.w.) freeze dried feedlot waste. Levels of macrocyclic lactones detected in the feedlot wastes varied and were dependent on sample type. The effect of seasonal variations and waste management practices were also investigated in this study.

Levels of antibiotic resistance genes (ARGs) and the fractions of antibiotic resistant bacteria (ARB) among culturable heterotrophic bacteria were compared in outdoor air near conventional (n = 3) and organic (n = 3) cattle rearing facilities. DNA extracts from filters taken from 18 locations were analyzed by quantitative polymerase chain reaction (qPCR) for five ARGs. At the reference (non-agricultural) site, all genes were below detection. ARGs sul1, bla SHV, erm(B), and bla TEM were more frequently detected and at higher levels (up to 870 copies m⁻³ for bla SHV and 750 copies m⁻³ for sul1) near conventional farms compared to organic locations while the opposite was observed for erm(F) (up to 210 copies m⁻³). Isolates of airborne heterotrophic bacteria (n = 1295) collected from the sites were tested for growth in the presence of six antibiotics. By disk diffusion on a subset of isolates, the fractions of ARB were higher for conventional sites compared to organic farms for penicillin (0.9 versus 0.63), cloxacillin (0.74 versus 0.23), cefoperazone (0.58 versus 0.14), and sulfamethazine (0.50 versus 0.33) for isolates on nutrient agar. All isolates’ ΔA600ₚᵣₑₛ/ΔA600ₐbₛ were measured for each of the six tested antibiotics; isolates from farms downwind of organic sites had a lower average ΔA600ₚᵣₑₛ/ΔA600ₐbₛ for most antibiotics. In general, all three analyses used to indicate microbial resistance to antibiotics showed increases in air samples nearby conventional versus organic cattle rearing facilities. Regular surveillance of airborne ARB and ARGs near conventional and organic beef cattle farms is suggested.

While some countries disaggregate N₂O emission factors for urine and dung deposited onto pastures, in Canada, distinct N₂O emission factors for beef cattle urine and dung have not been defined. To help address this knowledge gap, we conducted a 1-year study to quantify N₂O fluxes from beef cattle urine and dung patches on a semiarid tame pasture in western Canada, as well as to quantify the N₂O emission factors (EF3) for urine and dung as the percentage of applied N emitted as N₂O-N. Urine and dung were deposited when soil water-filled pore space was nearly 60%, a wet soil condition for the grazing season in the semiarid study region, which led to a burst of N₂O from urine in the first 14 days of the study (42% of total N emitted). Urine emitted more cumulative N₂O (P < 0.001) and had a greater N₂O emission factor (P = 0.002) than dung. The urine patch emitted 1.30 ± 0.47 g N₂O-N m⁻² year⁻¹, while the dung patch emitted 0.083 ± 0.020 g N₂O-N m⁻² year⁻¹ (mean values ± SD). The N₂O emission factor for urine was 1.32 ± 0.49%, while for dung it was 0.03 ± 0.02%. We conclude that more study is needed to determine if distinct N₂O emission factors are required for urine and dung deposited onto pasture in western Canada to more accurately estimate national N₂O inventories.

Livestock manure and compost are commonly used to supply nutrients for crops and improve soil quality. However, excess application may increase the risk of nutrient loss and eutrophication. We investigated the potential leaching losses of nitrogen (N), phosphorus (P), and non-purgeable organic carbon (NPOC) over 105 days in the laboratory. Soils were amended with four treatments: (1) manure (BM) and (2) compost (BC) from cattle fed a typical finishing diet, (3) manure (DDGSM), and (4) compost (DDGSC) from cattle fed diets containing 60 % wheat dried distillers’ grains with solubles (DDGS) replacing barley grain. A non-amended control soil was included for comparison. Leachate samples were collected 0, 7, 21, 42, 70, and 105 days after amendment application. Amendment application significantly increased leaching loss of total nitrogen (TN), NO₃ ⁻-N, NH₄ ⁺-N, total phosphorus (TP), ortho-P (PO₄ ³⁻-P), and NPOC from soils by 2.2 to 154.8 times compared with the control. Regardless of whether DDGS was included in cattle diet, cumulative leaching losses of TN, NO₃ ⁻-N, TP, and PO₄ ³⁻-P were significantly higher, while NH₄ ⁺-N and NPOC were lower from compost-amended soil than manure-amended soil. The proportion of cumulative N leaching losses relative to the total N applied was greater with DDGSM and DDGSC than BM and BC, while a greater proportion of total P was leached from DDGSM and DDGSC than BM. Based on the results, more attention should be paid to the potential risk of soil nutrient leaching posed after applying manure and compost, and the higher risk of N and P leaching losses from soil amended with DDGS manure and compost than manure from beef cattle fed typical finishing diets.

Grazing can accelerate and alter the timing of nutrient transfer, and could increase the amount of extractable phosphorus (P) cycle from soils to plants. The effects of grazing management and/or forage type that control P cycling and distribution in pasture's resources have not been sufficiently evaluated. Our ability to estimate the levels and changes of soil-extractable P and other crop nutrients in subtropical beef cattle pastures has the potential to improve our understanding of P dynamics and nutrient cycling at the landscape level. To date, very little attention has been paid to evaluating transfers of extractable P in pasture with varying grazing management and different forage type. Whether or not P losses from grazed pastures are significantly greater than background losses and how these losses are affected by soil, forage management, or stocking density are not well understood. The objective of this study was to evaluate the effect of grazing management (rotational versus “zero” grazing) and forage types (FT; bahiagrass, Paspalum notatum, Flugge versus rhizoma peanuts, Arachis glabrata, Benth) on the levels of extractable soil P and degree of P saturation in beef cattle pastures. This study (2004–2007) was conducted at the Subtropical Agricultural Research Station, US Department of Agriculture–Agricultural Research Service located 7 miles north of Brooksville, FL. Soil (Candler fine sand) at this location was described as well-drained hyperthermic uncoated Typic Quartzipsamments. A split plot arrangement in a completely randomized block design was used and each treatment was replicated four times. The main plot was represented by grazing management (grazing vs. no grazing) while forage types (bahiagrass vs. perennial peanut) as the sub-plot treatment. Eight steel exclosures (10 × 10 m) were used in the study. Four exclosures were placed and established in four pastures with bahiagrass and four exclosures were established in four pastures with rhizoma peanuts to represent the “zero” grazing treatment. The levels of soil-extractable P and degree of P saturation (averaged across FT and soil depth) of 22.1 mg kg⁻¹and 11.6 % in pastures with zero grazing were not significantly (p ≤ 0.05) different from the levels of soil-extractable P and degree of P saturation of 22.8 mg kg⁻¹and 12.9 % in pastures with rotational grazing, respectively. On the effect of FT, levels of soil-extractable P and degree of P saturation were significantly higher in pastures with rhizoma peanuts than in pastures with bahiagrass. There was no net gain of soil-extractable P due to the presence of animals in pastures with rotational grazing. Averaged across years, soil-extractable P in pastures with rotational grazing and with “zero” grazing was less than 150 mg kg⁻¹, the water quality protection. There had been no movement of soil-extractable P into the soil pedon since average degree of P saturation in the upper 15 cm was 14.3 % while the average degree of P saturation in soils at 15–30 cm was about 9.9 %. Overall, average extractable P did not exceed the crop requirement threshold of 50 mg P kg⁻¹and the soil P saturation threshold of 25 %, suggesting that reactive P is not a problem. Our study revealed that rhizoma peanuts and bahiagrass differ both in their capacity to acquire nutrients from the soil and in the amount of nutrients they need per unit growth. Rhizoma peanuts, which are leguminous forage, would require higher amounts of P compared with bahiagrass. The difference in the amount of P needed by these forages could have a profound effect on their P uptake that can be translated to the remaining amount of P in the soils. Periodic applications of additional P may be necessary especially for pastures with rhizoma peanuts to sustain their agronomic needs and to potentially offset the export of P due to animal production. Addition of organic amendments could represent an important strategy to protect pasture lands from excessive soil resources exploitation.

The synthetic growth-promoting hormones trenbolone and melengestrol acetate have been detected in the environment near beef cattle feedlots and are reportedly transported via wind-borne particulate matter. Therefore, movement of synthetic hormones from beef cattle feedlots to water bodies via particulate matter is possible. Our objective was to evaluate potential effects of 17α-trenbolone (17α-TB), melengestrol acetate (MGA), and combinations of both on growth, development, and survival of Xenopus laevis larvae. On post-hatch day 2 (stage 33/34), X. laevis larvae were exposed to three nominal concentrations of 17α-TB (10, 100, and 500 ng/L), MGA (1, 10, and 100 ng/L), a combination of both (1/10, 10/100, and 100/500 ng/L MGA/17α-TB), frog embryo teratogenesis assay-Xenopus medium, or a solvent control. Significant increases in all X. laevis growth metrics were observed among larvae in the 1 ng/L MGA + 10 ng/L 17α-TB and 10 ng/L MGA + 100 ng/L 17α-TB treatments. Stage of development was increased among larvae in the 1 ng/L MGA + 10 ng/L 17α-TB treatment group and significantly decreased among those in the 500 ng/L 17α-TB treatment. Total body mass and snout–vent length of X. laevis larvae were significantly reduced in the 100 ng/L MGA and 100 ng/L MGA + 500 ng/L 17α-TB treatment groups. Larvae exposed to 500 ng/L 17α-TB had decreased total body mass, snout–vent length, and total length. In general, growth measurements decreased with increasing concentration of MGA, 17α-TB, or a combination of both. Survival among all treatments was not significantly different from controls. Amphibians exposed to MGA and 17α-TB in the environment may experience alterations in growth and development.