Environmental Aspects of Ethical Animal Production1 J. M. Siegford,*2 W. Powers,* and H. G. Grimes-Casey† *Department of Animal Science, Michigan State University, East Lansing 48824; and †School of Natural Resources and Environment, University of Michigan, Ann Arbor 48109 greater nutrient inputs to reach the same production end point, resulting in less efficient nutrient use and greater losses to the environment. Dual systems might additionally increase environmental contamination by pathogens. When swine are housed in welfare-friendly huts, Salmonella may cycle more freely between swine and their environment; however, population numbers of pathogenic bacteria may not be different between the indoor and outdoor systems evaluated. Alternatively, these dual purpose systems may reduce antibiotic and hormonal releases to the environment. Finally, intensity of resource use may be different under welfare-friendly and organic practices. In most situations, welfare-friendly production will require more land area per animal or per unit of product. Energy inputs into such systems, from feed production to rearing to product distribution, may also differ from prevalent industrial production practices. Clearly, consumers and producers considering the benefits and costs of ethical animal production practices need to understand the system-wide environmental impacts of these approaches to meeting demand for animal products.

ABSTRACT Livestock and poultry producers face a number of challenges including pressure from the public to be good environmental stewards and adopt welfarefriendly practices. In response, producers often implement practices beyond those required for regulatory compliance to meet consumer demands. However, environmental stewardship and animal welfare may have conflicting objectives. Examples include pasture-based dairy and beef cattle production where high-fiber diets increase methane emissions compared with grain feeding practices in confinement. Grazing systems can contribute to nitrate contamination of surface and groundwater in some areas of the world where grazing is the predominant land use. Similarly, hoop housing for sows, an alternative to indoor gestation crates, can increase the risk of nutrient leaching into soil and groundwater. Direct air emissions may also increase with unconfined animal production as a result of less opportunity to trap and treat emissions, as well as the result of increased cage space and greater surface area per mass of excreta. Coupling welfarefriendly and organic production practices may require

Key words: environment, ethics, animal welfare, animal well-being, extensive 2008 Poultry Science 87:380–386 doi:10.3382/ps.2007-00351

acterize agricultural practices that promote quality of life for animals and healthy environments. Many consumers picture pastoral, nonconfined systems when they picture agriculture that is environmentally sustainable or promotes good animal welfare. On the other hand, consumer ideas related to sustainability include the notion that intense animal production systems are inherently linked with environmental degradation and poor animal welfare (Petit and van der Werf, 2003). Producers would likely prefer to adapt their current model of production to address such problems while maintaining production yields, but the public may prefer to see alternative production models developed to address these issues (Petit and van der Werf, 2003). In some cases, the different aims of environmental stewardship and animal welfare can create conflict within a production system. As an example, many organic standards for food product certification have goals aimed at promoting environmental health and animal welfare (USDA, 2007). One typical environmental aim is to reduce

INTRODUCTION Livestock and poultry producers face a number of challenges including pressure from the public to be good environmental stewards and to adopt welfare-friendly practices. In both arenas, producers often implement practices beyond those required from a regulatory standpoint to meet the demands of consumers. Animal welfare and environmentally friendly are emotionally laden, socially acceptable terms that are often used in the market as buzzwords to sell niche products. Often, consumers do not have accurate or specific definitions for these terms, but rather have a vague idea that these terms char-

©2008 Poultry Science Association Inc. Received August 22, 2007. Accepted October 4, 2007. 1 Symposium paper from Bioethics Symposia at the 2007 Joint Annual Meeting of ADSA-PSA-AMPA-ASAS. 2 Corresponding author: [email protected]

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or eliminate synthetic and chemical inputs used in production. A typical animal welfare-related aim is to allow animals access to pasture. Yet, many organic standards and producers using the standards do not have clear strategies for meeting these goals simultaneously because it assumed that working toward meeting one goal will lead to fulfillment of the other. Systems designed to promote good animal welfare do not always promote good environmental health and vice versa. There may be conflicts related to the most appropriate rearing practice relative to allowing expression of the innate behavior of the animals, to reducing the risk of pollution from production, and to the ultimate aim of producing animal products in sufficient quantities (Hermansen et al., 2004). This paper reviews and compiles the relevant environment, ethics, and animal behavior literature to consider the potential for recent environmental and ethical animal production goals to result in conflicting impacts to the animal-based industrial system and the environment.

The Impact of Animal Behavior Pasture-based systems that promote the natural behavior of animals have the potential to increase environmental degradation and pathogen exposure, depending on the species, design, or location of the system. In all situations, animal behaviors and their environmental impacts must be considered when designing facilities to accommodate animal welfare and environmental goals. Some factors related to facility design that must be considered include consideration of appropriate stocking densities, appropriate vegetative ground cover or forage options; terrain, soil, and climate conditions; and design and location of shelters, drinkers, and feeders. In the end, systems that meet welfare and environmental goals may be easier to create for some species than others due to incompatibilities between animal behavior, environmental stewardship, and production. Pasturebased systems for raising beef and lamb are likely similar or better in terms of their environmental impact relative to confinement operations while typically promoting good animal welfare (Kumm, 2002). Conversely, the most common outdoor systems used for intensive organic production of pigs and poultry have significant environmental impacts, including increased risk of nitrogen-leaching and ammonia volatilization, as well as negative consequences for animal welfare, such as nose-ringing of pigs (Hermansen et al., 2004). Consider some of the problems associated with common outdoor systems used for intensive organic production of pigs. Pigs spend a great deal of their time foraging and exploring—and engage in rooting as part of these behaviors. Pigs on pasture can spend up to a quarter of their day rooting, which is an important foraging and exploratory behavior. Pigs appear highly motivated to root, and when prevented show evidence of frustration (Jensen and Toates, 1993; Studnitz et al., 2003a,b). Pigs that are kept outdoors will also wallow in mud or water to utilize evaporative cooling to thermoregulate in hot

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weather (Culver et al., 1960; Huynh et al., 2005). Rooting and wallowing behaviors result in bare, compacted ground in pastures, intensifying nutrient leaching (Hermansen et al., 2004; Eriksen et al., 2006). Overstocking of pigs in outdoor production systems further increases the damage to soil and vegetation in paddocks caused by rooting, wallowing, and grazing (Eriksen et al., 2006). These natural behaviors have environmental consequences when pigs are kept on pasture, including increased risk of nitrogen-leaching and ammonia volatilization. Nose ringing of pigs on pasture is often assumed to be essential to maintaining good grass cover in pastures (Hermansen et al., 2004). However, nose ringing presents several welfare problems by causing frustration in pigs by preventing them from rooting, and by causing pain to the animal as well as creating a possible site of infection. Several studies recently have found that nose ringing does not prevent sows from reducing the grass cover in pasture (Larsen and Kongsted, 2000). Ringing may also not be related to the content of highly soluble nitrogen in the soil (Hermansen et al., 2004). Therefore, ringing may not be effective at maintaining grass cover or reducing leaching of nutrients from soil. Thus, alternatives such as reducing stocking density of pastures or providing sows with foraging material high in fiber such as straw to fulfill their need to engage in rooting and exploratory behavior may be more effective (Brouns et al., 1994; Braund et al., 1998; Hermansen et al., 2004). All agricultural production systems, even those in bucolic pasture settings, have impacts on the environment including nutrient loading and leaching, air emissions, and pathogen transfer. The environmental impacts of extensive, pasture-based systems may be different than those of confined operations. In some cases, the environmental impacts may be greater, and in other cases the impacts may be less relative to those of intense confinement operations.

Nutrient Loading and Leaching Combined welfare-friendly and organic systems may require greater nutrient inputs to reach the same production end point, resulting in less efficient nutrient utilization and greater losses to the environment. For example, animals in pasture-based systems often require supplemental feed to optimize production (Williams et al., 2000; Hermansen et al., 2004). There are energetic and landbase requirements for producing this additional feed, and in many cases surplus nutrients from supplemental feed can also be lost to the environment. Nutrients from supplemental feed can be responsible for much of the environmental impact of outdoor pig production units (Eriksen et al., 2002; Hermansen et al., 2004). When nitrogen inputs, outputs and losses from different outdoor pig farming systems are examined, nitrogen inputs exceed outputs and losses in all cases and result in nitrogen surpluses in the systems (Williams et al., 2000). These surpluses are hypothesized to exacerbate

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nitrate leaching losses from the soil in future seasons (Williams et al., 2000). Grazing systems can contribute to nitrate leaching to groundwater in some areas of the world where grazing is the predominant land use or where soils are susceptible to leaching (Burden, 1982; Fraters et al., 1998; Stout et al., 2000; Verloop et al., 2006). However, beef cattle congregation sites such as mineral feeders, water troughs, and shade areas in Florida pastures did not contribute more nutrients to surface or groundwater supplies than other pasture locations (Sigua and Coleman, 2006). Additionally, a study in the North Appalachian Experimental Watershed in Ohio has demonstrated that in unfertilized grass pastures, both rotational grazing and removal of grass as hay can effectively reduce high NO3-N concentrations resulting from highfertility, high-stocking-density grazing systems (Owens and Bonta, 2004). These findings suggest that site specific factors may be influential in determining groundwater pollution potential. Nutrients released on pasture during grazing can result in surface water and stream contamination as nonpoint sources of emission are more difficult to contain or control on pasture than when they are emitted into a fully contained facility (Howell et al., 1995; Quinn and Stroud, 2002). Surface water impacts are of issue when grazed animals have unrestricted access to streams. In such cases, there can be direct contamination of water by excreta in addition to well documented damage to stream banks and beds causing erosion, reduced water clarity, and eutrophication of streams (Kauffman et al., 1983; Belsky et al., 1999; Zaimes et al., 2004). It may be possible to reduce such impacts by providing animals on pasture with offstream water sources or by restricting access to streams. In fact, providing off-stream water sources for grazing cattle can effectively reduce erosion, nutrient contamination, and presence of fecal coliform and fecal Streptococcus in adjacent streams (Sheffield et al., 1997). Cattle prefer to drink from a water trough when one is provided, even in pastures that lack stream bank fencing (Miner et al., 1992; Clawson, 1993; Sheffield et al., 1997). As a consequence of shifting their drinking from the stream to a trough, the cattle spend less time standing on the stream bank or in the stream, reducing their opportunity to deposit urine and feces directly into the stream (Miner et al., 1992; Clawson, 1993). Outdoor production of pigs can increase the risks of nutrient leaching into soil and groundwater contamination (e.g., Jongbloed and Lenis, 1998; Petersen et al., 2001; Eriksen et al., 2002). Hoop housing for sows, as an alternative to indoor gestation crates, increases the risk of nutrient leaching into soil and groundwater contamination if sites are not suitably prepared. However, even in intensive systems designed to be nondischarge operations, there are still problems associated with nutrient leaching into surrounding catchments and water supplies (Karr et al., 2001). In sum, low nitrogen-use efficiency and adverse effects of nitrogen leaching on the environment conflict with the sustainability of outdoor pig production. Changes in

management are therefore needed to improve the efficiency of nitrogen use and lead to less surplus nitrogen being excreted and lost in outdoor pork production. Management changes could include moving feeders and sheds to evenly distribute manure and allow it to be taken up by forages or crops in the pasture (Eriksen and Kristensen, 2001), reducing dietary nitrogen from supplemental sources (Eriksen et al., 2002; Williams et al., 2000; Hermansen et al., 2004) and lowering stocking densities (Worthington and Danks, 1992; Eriksen et al., 2002).

Emissions into Air Emissions into the air by any animal production system can be problematic in terms of pollutants and toxicity and in terms of odor and perception of air quality by human neighbors. Methane (a greenhouse gas) and ammonia are 2 of the most widely studied air emissions for animal agriculture. At the system level, methane and ammonia emissions from pasture-based systems can increase relative to confined systems because it is harder to trap and treat emissions released in outdoor settings vs. those released in confinement buildings. Additionally, increasing the available space per animal increases surface area per mass of excreta, which also leads to increased emissions (Monteny et al., 2001). At the level of the animal, emission of methane and ammonia gases can be impacted by diet, stress, and genetics of the animals (Smits et al., 2003; Leifeld and Fuhrer, 2005; Hegarty et al., 2007). Typically cattle grazing on pasture have diets high in fiber, which increases methane production compared with grain feeding practices in confinement (Johnson and Johnson, 1995; Harper et al., 1999). However, The Swiss REP program (required standards for ecological performance), which promotes integrated agricultural production with limits on stocking densities as well as organic farming, has been linked to a decline in overall methane from animal agriculture (Leifeld and Fuhrer, 2005).The authors hypothesize that trends of declining forage and increasing grain and oilseed-based feed will further reduce methane production (Leifeld and Fuhrer, 2005). Another animal agriculture trend in feeding also may reduce methane production. Cattle selected for lower residual feed intake are managed such that the difference between actual intake and expected feed requirements is minimized for greater feed efficiency, resulting in lower daily methane production rates (Hegarty et al., 2007). In Australia, use of residual feed intake-selected bulls is estimated to decrease methane production by cattle by 3.1% in 2025 compared with levels in 2002. More efficient cattle that need less feed will also produce less manure, which could potentially reduce the amount of nitrous oxide, another greenhouse gas, and other gaseous emissions liberated from the manure of these animals. Finally, ammonia emissions are reduced when cattle are grazed rather than confined. This is largely because urine deposited on pasture by grazing cattle is quickly absorbed into the soil, reducing the chance that ammonia

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will volatilize to the air (Webb et al., 2005). Thus, while some gaseous emissions may be reduced in animal welfare friendly systems, others may increase, requiring a thorough evaluation of the air quality impact when assessing production systems.

Pathogenic Release Pasture-based systems with organic and welfarefriendly aims might increase environmental contamination by pathogens. Theoretically, with equal total inputs, less Escherichia coli should pollute surface water from daily small grazing inputs to a pasture than from a single large slurry input (Vinten et al., 2004). However, practically, the proportion of E. coli actually entering surface water from grazing inputs spread out over time appears equal to that from a single application of slurry (Vinten et al., 2004). This may be due to the fact that slurry is typically stored before being applied to the land, during which time the E. coli initially present in the feces die off (Larsen and Munch, 1983; Vinten et al., 2002). Additionally, E. coli removal from soil becomes more difficult as time from deposition increases (Vinten et al., 2004). This reduces the relative longer term risk of E. coli continuing to leach into surface water from a single slurry application compared with grazing because inputs of fresh feces will daily deposit E. coli that are more readily mobilized. Cattle excrete more E. coli in spring and late summer, and though this seasonality is not fully understood, changing feed from hay to grain and general stress have both been found to dramatically increase the presence of virulent strains of E. coli, such as E. coli O157, numbers in cattle feces (Diez-Gonzalez et al., 1998; Jones, 1999; Russell and Rychlik, 2001). Thus pasture-based systems could have conflicting effects on the amount of harmful E. coli excreted. On the one hand, cattle kept on pasture year round will be fed more natural diets and will not be subjected to the stresses of confinement or changes in housing. On the other hand, manure containing E. coli will be excreted directly onto the pasture, which could increase contamination rates. Further research is needed to elucidate the relationship between E. coli and pasturebased management of dairy cattle. Regular use of antibiotics on dairy farms could increase the levels of E. coli O157 found on farms. A study of Wisconsin dairy farms found that antimicrobial use could be a risk factor associated with shedding of E. coli O157 into the environment and that this hypothesis required further research (Shere et al., 1998). Additionally, feeding cattle grain-based diets can increase the incidence of E. coli O157 and increase the number of acid-resistant bacteria capable of surviving the acidity of the human stomach by 1,000- to 1,000,000-fold. Feeding cattle hay even for a brief period before slaughter can significantly reduce shedding of E. coli and reduce numbers of acid-resistant bacteria (Russell and Rychlik, 2001). In contrast, there may be some basis for hypothesizing that E. coli O157 could be less common in organic than in conventional livestock systems because several core practices and prin-

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ciples of organic farming could be expected to reduce the levels of O157 on organic farms (Patriquin, 2000). Such practices include the infrequent use of antibiotic and the emphasis on probiotics and maintenance of healthy microflora in livestock (and people) and of high levels of microbial activity in soils (Ma¨der et al., 2002). Sows housed outdoors for farrowing form wallows near their farrowing huts. These wallows become contaminated with pig feces and can harbor organisms such as Salmonella and E. coli that can cycle between the environment and the pigs (Callaway et al., 2005). However, population numbers of pathogenic bacteria were not different between the indoor and outdoor systems evaluated. In organic and many welfare-friendly systems, there are restrictions on the use of supplementary, synthetic, or recombinant hormones and antibiotics, or a combination of these, resulting in little or no release of these compounds to the environment through excreta. In conventional swine production, antimicrobials can be used for purposes of growth promotion and prophylaxis. However, despite the common use of antimicrobials in animal agriculture, the impact of these practices on antimicrobial resistance only recently has been examined. The evidence suggests that as little as 10 parts per billion of antimicrobial drugs can increase the resistance of an indicator organism, Staphylococcus aureus ATCC 9144 (Kleiner et al., 2007). When the organism was exposed to multiple drugs at the same time, the resistance to the antimicrobial drugs in general increased dramatically (Kleiner et al., 2007). Organic and welfare friendly systems, by restricting or prohibiting use of these substances, could result in transmission of fewer microbes with antimicrobial resistance to the environment. Samples collected near lagoons for manure storage and treatment at swine confinement facilities reveal higher detection rates for tetracycline-resistant genes near and down-gradient from the lagoons than at distant sites (Mackie et al., 2006). In a similar study, fecal Streptococcus bacteria were detected in the groundwater near swine confinement facilities, suggesting that the filtration of bacteria by soil surrounding deep-pit manure storage systems may not be as effective as is commonly assumed. Together, these results suggest that the groundwater at swine confinement facilities may persistently harbor tetracycline-resistant genes, which could affect the safety of this water (Krapac et al., 2002; Mackie et al., 2006). In a comparison of resistance against 2 common antimicrobials on conventional and organic swine farms, conventional farm samples had the highest levels of resistance despite differences in antimicrobial usage among farms (Jindal et al., 2006). In contrast, the levels of resistance in organic farm samples, where no antimicrobials were used, were very low (Jindal et al., 2006). Interestingly, the resistance levels at the conventional farms remained high throughout the waste treatment systems, suggesting a potential impact on environmental levels of resistance when treated wastes and waste treatment byproducts are applied to agricultural land (Jindal et al., 2006). In a comparison of antimicrobial resistance at conventional vs. organic dairy farms, samples from conven-

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tional dairy farms had E. coli with significantly higher resistance to 7 common antimicrobials, including ampicillin, streptomycin, and kanamycin than samples from organic dairies (Sato et al., 2005). Similarly, conventional dairy farms were more likely than organic dairy farms to have Salmonella isolates that were more resistant to streptomycin and other antimicrobial agents (Ray et al., 2006).

Resource Intensity The intensity of resource use relates total consumption of a resource to the amount of output enabled by its use; higher resource intensity implies greater inputs of energy, water, nutrients, etc. are required to provide a unit of product. When these inputs are scarce or associated with toxic, hazardous, or otherwise detrimental processes or by-products, resource intensity can be linked to environmental damages. A recent paper acknowledges the damages caused by utilizing 40% of the world’s land area to food production, including damages such as deforestation, loss of biodiversity, and soil and water pollution and degradation (Elferink and Nonhebel, 2007). The authors consider opportunities to reduce the intensity of land use in producing typical, industrialized animal food products in the Netherlands. They find that optimizing feed composition for highest yield feed crops and choosing high-yield regional sources for feed will reduce land area requirements for pork, chicken, and beef, but acknowledge that the world’s optimal feed production regions are insufficient to meet the world’s meat demand with reduced land use intensity (Elferink and Nonhebel, 2007). Therefore, the results suggest that moving toward an animal-friendly agriculture system of reduced confinement and more “natural” diet while maintaining demand for animal products will require greater land resources than conventional animal systems. It has already been noted that producing higher quality, high-yield feed crops for improving animal diets could reduce some air emissions and reduce overall land requirements in animal agriculture. However, these crops generally require greater inputs of fossil-fuel-based fertilizer, pesticides, and irrigation water to achieve high yields (Ward et al., 1993). These upstream inputs of chemicals and energy will contribute to the environmental, humanhealth, and ecological impacts of an animal-based production system. Clearly, if welfare-friendly production systems require more land units per animal or per unit of product, conflict could arise where open land is scarce, where land and habitat conservation is a factor, or where human habitation or recreational use compete with use of land for agriculture. Extensive pasture-based systems also make existing practices of collection and beneficial reuse of animal waste materials much more difficult. However, pasture-based systems, particularly those that are organic, in general may also promote greater biodiversity in soils

as well as greater soil fertility, reducing the need for fertilizer and pesticide inputs (Ma¨der et al., 2002). Cleveland (1995) notes that energy productivity of industrial agriculture in the United States (the reverse of energy intensity, measured as output per unit of energy input) was lower as of the 1990s (although on an increasing trend since the 1970s) than at the turn of the century, despite great improvements in farm product yields. Fossil fuel inputs in farm equipment production, farm operation and maintenance, and product distribution increased much faster than the physical or economic yields of agricultural products. Whether environmental or ethical approaches to animal-based agriculture can significantly change the trends for energy and resource intensity will depend on how these alternative animal product systems vary relative to the norm for conventional animal agriculture.

DISCUSSION Consumers, producers, and even government organizations are becoming more interested in the ecological footprints left by animal-based agriculture and the consequences for animal and human welfare. Recent and forthcoming organic, environmental, or animal-friendly certifications may be shifting the practices and components of production, distribution, and land use that make up animal product systems. A variety of animal products are now available to many US consumers, and the systems that provide them are themselves being showcased as “locally farmed”, “small farm”, “sustainably harvested”, “organic”, and numerous variations on those themes. These systems may eschew machinery, fossil fuels, and commercial distribution in favor of human labor and renewable energy for a “slow food” approach, or alternatively celebrate their highly automated, efficient, global operations. The preceding review highlights the opportunities for improved environmental and ethical management and for even greater degradation under animalfriendly or organic guidelines, or both, for animal food products. It also illustrates the need for better understanding of how these concerns and benefits will be manifested under existing and future animal production models. It will therefore be imperative to develop measures of product and system level performance given environmental, ecological, and social sustainability requirements) to assess and compare the ability of conventional, organic, and other extensive systems to meet the needs of our animal and human populations.

CONCLUSIONS As with conventional agriculture, we must be aware that agriculture that meets goals of social responsibility in terms of animal welfare or other societal concerns may also have some negative impacts on the environment that must be recognized in order to be addressed. Therefore, when considering ethical animal production practices, special consideration needs to be given to the impacts of

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the system on the environment. In some cases, environmentally friendly management practices will need to be deliberately incorporated into organic or welfare-friendly systems. Stocking densities of animals must be appropriate for soil characteristics, vegetation, terrain, and weather conditions. Feeding practices must minimize waste and external inputs while maximizing intake. Vegetative cover should be maintained continuously in pastures to prevent erosion and nutrient leaching. In addition, different approaches need to be considered to develop sustainable agricultural practices for livestock that are both environmentally and welfare friendly. As an example, the behavior of animals can be approached from a perspective of using behaviors that animals are strongly motivated to perform in constructive ways rather than from a perspective of controlling behaviors viewed as undesirable. Systems could be designed to take advantage of the natural behavior of animals in ways that promote productivity of the animals as well as the productivity of other crops incorporated into the systems (Hermansen et al., 2004). As an example, the rooting tendencies of pigs could be harnessed to help cultivate land in preparation for a crop, whereas the pecking drive of geese and chickens may be used in orchards to control weeds and insects. Ultimately, analysis and research at the interface between the environment and animal welfare are now needed to determine the environmental vs. welfare costs through the lifecycle of animal-based products to gain a better understanding of the environmental costs of ethical animal production.

ACKNOWLEDGMENTS The authors would like to thank the Department of Animal Science and College of Agriculture and Natural Resources at Michigan State University, the School of Natural Resources and Environment at the University of Michigan, and the Alcoa Foundation for their support. We would also like to thank Richard Reynnells of the USDA for his support of bioethics.

REFERENCES Belsky, A. J., A. Matzke, and S. Uselman. 1999. Survey of livestock influences on stream and riparian ecosystems in the western United States. J. Soil Water Conserv. 54:419–431. Braund, J. P., S. A. Edwards, I. Riddoch, and L. J. Buckner. 1998. Modification of foraging behaviour and pasture damage by dietary manipulation in outdoor sows. Appl. Anim. Behav. Sci. 56:173–186. Brouns, F., S. A. Edwards, and P. R. English. 1994. Effect of dietary fibre and feeding system on activity and oral behaviour of group housed gilts. Appl. Anim. Behav. Sci. 39:215–223. Burden, R. J. 1982. Nitrate contamination of New Zealand aquifers: A review. N. Z. J. Sci. 25:205–220. Callaway, T. R., J. L. Morrow, A. K. Johnson, J. W. Dailey, F. M. Wallace, E. A. Wagstrom, J. J. McGlone, A. R. Lewis, S. E. Dowd, T. L. Poole, T. S. Edrington, R. C. Anderson, K. J. Genovese, J. A. Byrd, R. B. Harvey, and D. J. Nisbet. 2005. Environmental prevalence and persistence of Salmonella spp. in outdoor swine wallows. Foodborne Pathog. Dis. 2:263–296.

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Clawson, J. E. 1993. The use of off-stream water developments and various water gap configurations to modify the watering behavior of grazing cattle. MS Thesis. Oregon State University, Corvallis. Cleveland, C. 1995. The direct and indirect use of fossil fuels and electricity in USA agriculture, 1910-1990. Agric. Ecosyst. Environ. 55:111–121. Culver, A. A., F. N. Andrews, J. H. Conrad, and T. L. Noffsinger. 1960. Effectiveness of water sprays and a wallow on the cooling and growth of swine in a normal summer environment. J. Anim. Sci. 19:421–428. Diez-Gonzalez, F., T. R. Callaway, M. G. Kizoulis, J. B. Russell. 1998. Grain feeding and the dissemination of acid-resistant Escherichia coli from cattle. Science 281:1666–1668. Elferink, E. V., and S. Nonhebel. 2007. Variation in land requirements for meat production. Cleaner Prod. 15:1778–1786. Eriksen, J., J. E. Hermansen, K. Strudsholm, and K. Kristensen. 2006. Potential loss of nutrients from different rearing strategies for fattening pigs on pasture. Soil Use Manage. 22:256–266. Eriksen, J., and K. Kristensen. 2001. Nutrient excretion by outdoor pigs: A case study of distribution, utilization and potential for environmental impact. Soil Use Manage. 17:21–29. Eriksen, J., S. O. Petersen, and S. G. Sommer. 2002. The fate of nitrogen in outdoor pig production. Agronomie 22:863–867. Fraters, D., L. J. M. Boumansa, G. van Drechta, T. de Haab, and W. D. de Hoop. 1998. Nitrogen monitoring in groundwater in the sandy regions of the Netherlands. Environ. Pollut. 102:479–485. Harper, L. A., O. T. Denmead, J. R. Freney, and F. M. Byers. 1999. Direct measurements of methane emissions from grazing and feedlot cattle. J. Anim. Sci. 77:1392–1401. Hegarty, R. S., J. P. Goopy, R. M. Herd, and B. McCorkell. 2007. Cattle selected for lower residual feed intake have reduced daily methane production. J. Anim. Sci. 85:1479–1486. Hermansen, J. E., K. Strudsholm, and K. Horsted. 2004. Integration of organic animal production into land use with special reference to swine and poultry. Livest. Prod. Sci. 90:11–26. Howell, J. M., M. S. Coyne, and P. Cornelius. 1995. Fecal bacteria in agricultural waters of the Bluegrass region of Kentucky. J. Environ. Qual. 24:411–419. Huynh, T. T. T., A. J. A. Aarnink, W. J. J. Gerrits, M. J. H. Heetkamp, T. T. Canh, H. A. M. Spoolder, B. Kemp, and M. W. A. Verstegen. 2005. Thermal behaviour of growing pigs in response to high temperature and humidity. Appl. Anim. Behav. Sci. 91:1–16. Jensen, P., and F. Toates. 1993. Who needs “behavioural needs”? Motivational aspects of the needs of animals. Appl. Anim. Behav. Sci. 37:161–181. Jindal, A., S. Kocherginskaya, A. Mehboob, M. Robert, R. I. Mackie, L. Raskin, and J. L. Zilles. 2006. Antimicrobial use and resistance in swine waste treatment systems. Appl. Environ. Microbiol. 72:7813–7820. Johnson, K. A., and D. E. Johnson. 1995. Methane emissions from cattle. J. Anim. Sci. 73:2483–2492. Jones, D. L. 1999. Potential health risks associated with the persistence of Escherichia coli O157 in agricultural environments. Soil Use Manage. 15:76–83. Jongbloed, A. W., and N. P. Lenis. 1998. Environmental concerns about animal manure. J. Anim. Sci. 76:2641–24648. Kauffman, J. B., W. C. Krueger, and M. Vavra. 1983. Impacts of cattle on streambanks in Northeastern Oregon. J. Range Manage. 36:683–685. Karr, J. D., W. J. Showers, J. W. Gilliam, and A. S. Andres. 2001. Tracing nitrate transport and environmental impact from intensive swine farming using delta nitrogen-15. J. Environ. Qual. 30:1163–1175. Kleiner, D. K., S. E. Katz, and P. M. Ward. 2007. Development of in vitro antimicrobial resistance in bacteria exposed to residue level exposures of antimicrobial drugs, pesticides and veterinary drugs. Chemotherapy 53:132–136.

386

SIEGFORD ET AL.

Krapac, I. G., W. S. Dey, W. R. Roy, C. A. Smyth, E. Storment, S. L. Sargent, and J. D. Steele. 2002. Impacts of swine manure pits on groundwater quality. Environ. Pollut. 1202:475–492. Kumm, I.-J. 2002. Sustainability of organic meat production under Swedish conditions. Agric. Ecosyst. Environ. 88:95–101. Larsen, H. E., and B. Munch. 1983. Practical applications of knowledge on the survival of pathogenic and indicator bacteria in aerated and non-aerated slurry. Pages 20–34 in Hygienic Problems of Animal Manures. D. Strach, ed. University of Hohenheim, Stuttgart, Germany. Larsen, V. A., and A. G. Kongsted. 2000. Sows on pasture. Pages 99–105 in Ecological Animal Husbandry in the Nordic Countries, DARCOF Report, vol. 2. J. E. Hermansen, V. Lund, and E. Thuen, ed. Tjele, Denmark. Leifeld, J., and J. Fuhrer. 2005. Greenhouse gas emissions from Swiss agriculture since 1990: Implications for environmental policies to mitigate global warming. Environ. Sci. Policy 8:410–417. Mackie, R. I., S. Koike, I. Krapac, J. Chee-Sanford, S. Maxwell, and R. I. Aminov. 2006. Tetracycline residues and tetracycline resistance genes in groundwater impacted by swine production facilities. Anim. Biotechnol. 17:157–176. Ma¨der, P., A. Fliessbach, D. Dubois, L. Gunst, P. Fried, and U. Niggli. 2002. Soil fertility and biodiversity in organic farming. Science 296:1694–1697. Miner, J. R., J. C. Buckhouse, and J. A. Moore. 1992. Will a water trough reduce the amount of time hay-fed livestock spend in the stream (and therefore improve water quality)? Rangelands 14:35–38. Monteny, G. J., C. M. Groenestein, and M. A. Hilhorst. 2001. Interactions and coupling between emissions of methane and nitrous oxide from animal husbandry. Nutr. Cycling Agroecosystems 60:123–132. Owens, L. B., and J. V. Bonta. 2004. Reduction of nitrate leaching with haying or grazing and omission of nitrogen fertilizer. J. Environ. Qual. 33:1230–1237. Patriquin, D. G. 2000. Reducing risks from E. coli O157 on the organic farm. Canadian Organic Growers. Summer 2000. http://www.cog.ca/efgsummer2000.htm#REDUCING Accessed Aug. 2007. Petersen, S. O., K. Kristensen, and J. Eriksen. 2001. Denitrification losses from outdoor piglet production: Spatial and temporal variability. J. Environ. Qual. 30:1051–1058. Petit, J., and H. M. G. van der Werf. 2003. Perception of the environmental impacts of current and alternative modes of pig production by stakeholder groups. J. Environ. Manage. 68:377–386. Quinn, J. M., and M. J. Stroud. 2002. Water quality and sediment and nutrient export from New Zealand hill-land catchments of contrasting land use. N. Z. J. Mar. Freshwater Res. 36:409–429. Ray, K. A., L. D. Warnick, R. M. Mitchell, J. B. Kaneene, P. L. Ruegg, S. J. Wells, C. P. Fossler, L. W. Halbert, and K. May. 2006. Antimicrobial susceptibility of Salmonella from organic and conventional dairy farms. J. Dairy Sci. 89:2038–2050. Russell, J. B., and J. L. Rychlik. 2001. Factors that alter rumen microbial ecology. Science 292:1119–1122. Sato, K., P. C. Bartlett, and M. A. Saeed. 2005. Antimicrobial susceptibility of Escherichia coli isolates from dairy farms us-

ing organic versus conventional production methods. J. Am. Vet. Med. Assoc. 226:589–594. Sheffield, R. E., S. Mostaghimi, D. H. Vaughan, E. R. Collins, Jr., and V. G. Allen. 1997. Off-stream water sources for grazing cattle as a stream bank stabilization and water quality BMP. Trans. ASAE 40:595–604. Shere, J. A., K. J. Bartlett, and C. W. Kaspar. 1998. Longitudinal study of Escherichia coli O157:H7 dissemination on four dairy farms in Wisconsin. Appl. Environ. Microbiol. 64:1390–1399. Sigua, G. C., and S. W. Coleman. 2006. Sustainable management of nutrients in forage-based pasture soils: Effect of animal congregation sites. J. Soils Sediments 6:249–253. Smits, M. C. J., G. J. Monteny, and G. van Duinkerken. 2003. Effect of nutrition and management factors on ammonia emission from dairy cow herds: Models and field observations. Livest. Prod. Sci. 84:113–123. Stout, W. L., S. L. Fales, L. D. Muller, R. R. Schnabel, and S. R. Weaver. 2000. Water quality implications of nitrate leaching from intensively grazed pasture swards in the northeast US. Agric. Ecosyst. Environ. 77:203—210. Studnitz, M., K. H. Jensen, and E. Jørgensen. 2003a. The effect of nose rings on the exploratory behaviour of outdoor gilts exposed to different tests. Appl. Anim. Behav. Sci. 84:41–57. Studnitz, M., K. H. Jensen, E. Jørgensen, and K. K. Jensen. 2003b. The effect of nose ringing on explorative behaviour in gilts. Anim. Welf. 12:109–118. USDA. 2007. USDA’s National Organic Program. United States Department of Agriculture. http://www.ams.usda.gov/ NOP/FactSheets/Backgrounder.html Accessed Aug. 2007. Verloop, J., L. J. M. Boumans, H. van Keulen, J. Oenema, G. J. Hilhorst, H. F. M. Aarts, and L. B. J. Sebek. 2006. Reducing nitrate leaching to groundwater in an intensive dairy farming system. Nutr. Cycling Agroecosystems. 74:59–74. Vinten, A. J. A., J. T. Douglas, D. R. Lewis, M. N. Aitken, and D. R. Fenlon. 2004. Relative risk of surface water pollution by E. coli derived from faeces of grazing animals compared to slurry application. Soil Use Manage. 20:13–22. Vinten, A. J. A., D. R. Lewis, D. R. Fenlon, K. A. Leach, R. Howard, I. Svoboda, and I. D. Ogden. 2002. Fate of E. coli and E. coli O157 in soils and drainage water following cattle slurry application at three sites in southern Scotland. Soil Use Manage. 18:1–9. Ward, G. M., K. G. Doxtader, W. C. Miller, and D. E. Johnson. 1993. Effects of intensification of agricultural practices on emission of greenhouse gases. Chemosphere 26:87–93. Webb, J., S. G. Anthony, L. Brown, H. Lyons-Visser, C. Ross, B. Cottrill, P. Johnson, and D. Scholefield. 2005. The impact of increasing the length of the cattle grazing season on emissions and ammonia and nitrous oxide and on nitrate leaching in England and Wales. Agric. Ecosyst. Environ. 105:307–321. Williams, J. R., B. J. Chambers, A. R. Hartley, S. Ellis, and H. J. Guise. 2000. Nitrogen losses from outdoor pig farming systems. Soil Use Manage. 16:237–243. Worthington, T. R., and P. W. Danks. 1992. Nitrate leaching and intensive outdoor pig production. Soil Use Manage. 8:56–60. Zaimes, G. N., R. C. Schultz, and T. M. Isenhart. 2004. Stream bank erosion adjacent to riparian forest buffers, row-crop fields, and continuously-grazed pastures along Bear Creek in central Iowa. J. Soil Water Conserv. 59:19–27.