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Tufts OpenCourseware
Author: One Health Students

Fall 2008
Gretchen Kaufman, DVM
Cummings School of Veterinary Medicine at Tufts University

1. Animal Health Perspective – Student Work

1.1. Basic Concepts

What is Herd Health Management?

In any livestock production system, certain diseases and production constraints can be anticipated on the basis of accumulated experiences. Herd health management and preventive medicine programs are designed to minimize potential adverse effects of these predictable constraints and to protect against unexpected ones. The goal of the program is to improve the herd's productivity through general husbandry, nutritional management, parasite control, vaccination, and environmental management.

Many herd health programs fail in their objectives because too much reliance is put on vaccinations and other treatments. A comprehensive herd health program recognizes vaccination as an important tool, but not a cure-all. Effective programs integrate medicine and management to prevent disease. Three major factors should be considered in attempting to keep disease losses to a minimum:

  1. Prevent Exposure to Disease. Purchase and quarantine procedures should be employed to decrease the likelihood of disease introduction into the existing herd. In high intensity operations, increasing confinement means increasing exposure to disease-causing organisms that exist in all groups of animals. Such operations need more intensive preventive programs.

  2. Keep Disease Resistance High. Nutrition, management, and housing programs should be designed to keep resistance to disease high at all times. Preventing or minimizing animal stress is a necessity for maintaining good resistance. In addition to these measures, resistance to specific diseases can sometimes be accomplished by vaccination.

  3. If Disease Occurs, Prevent Its Spread. Segregate affected animals immediately. Have a diagnosis made, and take recommended action as soon as possible.

Dairy Herd Health

  • well-recognized measures of individual animal and herd health exist (see PowerPoint and references)

  • measures provide an objective way to compare organic and conventional herds

Wildlife Health

  • diseases may spread from wildlife to cattle and from cattle to wildlife

  • wildlife affected by farm land use

  • little information on effects of organic vs. conventional farming on wildlife

Domesticated Animal Health

  • pets and other livestock on farms may interact with dairy herd

  • potential for disease spread among these groups

  • little information for effects of organic vs. conventional farming on these groups of animals

Herd Health Indicators

  • mastitis: BTSCC, CMT

  • reproductive diseases: abortion, infertility, metritis

  • lameness

  • calf health

  • internal parasites

  • animal welfare: management, comfort, hygiene

1.2. Disciplinary Gaps and Research Questions from the Animal Health Perspective

General: How can we compare organic and conventional farming in terms of their influence on the health of wildlife and other domestic animals? What role does the animal health specialist play in improving awareness of the economic, social, and human health effects of animal diseases? What is the role of industry in animal health: food producers, drug makers, product packagers, and how can they work together with the other disciplines to improve health?

  • Do organic and conventional dairy farms have different impacts on the health of wildlife and other domesticated animals?

    • Method: Prevalence study: Measure disease prevalence among domestic animals and wildlife as compared to dairy herd: Relevant information has to be obtained from the wildlife department in the region. Define what diseases affect wild animals and domestic animals the most and see how relevant these are to the dairy herd: Which ones are zoonotic and how prevalent are they?

    • Hypothesis: Diseases of domestic animals and wildlife might have a bigger impact on the organic farmer than on the conventional farmer, since the organic farmer focuses more on disease prevention. Wildlife and other domestic animals are important in the zoonotic transmission of diseases to the dairy herd. The organic farm focuses more on disease control because use of antibiotics is limited. Knowing what disease can be transmitted from the wildlife/domestic animals is important in herd health disease management and prevention.

  • How sustainable is organic farming in relation to production in New England?

    • Method: Survey: select particular organic farms and compare their production in relation to their input to measure how much profit they make from their farms and compare these with similar sized conventional farms. Distinct measures that need to be done will include cost of feed, medicine, farm labor.

    • Hypothesis: Organic farming is as profitable as conventional farming. There is an increasing interest for sustainable forms of livestock production systems, which will provide a balanced relationship between environmental, socio-cultural and economic factors. Economic sustainability is a key issue in determining whether many farms would in the long run turn to organic farming.

  • Does milk quality differ between organic and conventional herds?

    • Method: Using indicators that define the quality of milk such as percentage of cream, total protein, level of mastitis and other diseases, compare milk obtained from a conventional farm and that from an organic farm.

    • Hypothesis: Numerous studies show that one of the main motives for the purchase of organic food is either the belief that it was intrinsically "healthier" than conventional food or through fear of pesticide and chemical residues, (Sachs et al., 1987; McGuirk et al., 1990; Tregear et al., 1993; Smailwood, 1989; Kramer, 1990; van Ravenswaay, 1990; Lamb, 1991, 1993; James, 1993). Some studies as reported in Bourn (1994) have found increased concentrations of vitamin C and minerals with lower nitrate levels in organic compared to conventionally produced food. A similar study should be done with milk as well.

  • Are the management practices on organic farms quantifiably better than those on conventional farms.

    • Method: Surveys/ experimental studies that examine management practices on the two farming systems. One of the key characteristics of organic farming is the extensive management of livestock, paying full regard to their evolutionary adaptations behavioral needs and animal welfare issues with respect to nutrition, housing, health, breeding and rearing.

    • Hypothesis: That livestock management on organic farms is better than those on conventional farms. Livestock husbandry on organic farms depends on three major principles. These include: systems in which animals are kept must conform to the highest welfare standards; animals must be fed in a way suited to their physiology, using food largely produced on the farm; veterinary treatment should always avoid routine prophylactic drug use. Livestock health should be maintained through good preventive husbandry, animal welfare and appropriate housing and feeding systems. Organic farming systems aim to keep livestock healthy, however the attainment of this aim has often been questioned by some people.

  • What is the role of industry in animal health: food producers, drug makers, product packagers, and how can they work together with the other disciplines to improve health? (Animal)

  • Industry plays a major role in dairy farming. The feed and drug makers and the consumer are at both ends of the cycle.

    • Method: Surveys/interviews: interview and talk to feed and drug companies and consumers about their role in dairy. Identify if it is just a financial benefit or if they are interested in environmental impact of their products. Are consumers more interested in organic products or in cheap products.

    • Hypothesis: That feed and drug companies will support conventional farming easily because of the profit factor, but that consumers on the other hand are more interested in a healthier product.

1.3. Terms

Animal rights
The right of animals not to be exploited by humans. This viewpoint generally holds that it is not morally acceptable for humans to use or claim animals as property.

Animal welfare
Protection of the health and well-being of animals - including comfort, hygiene, stress, etc. This viewpoint generally accepts that it is morally acceptable for humans to use animals for food, research, clothing, etc, as long as unnecessary suffering is avoided.

Bulk tank somatic cell count
A measure of somatic cells per milliliter of milk taken from the farm bulk tank. The bulk tank is the central holding tank where milk from all cows on the farm is collected. Samples of milk from the bulk tank are reflective of the entire herd, not individual cows. The BTSCC is a good indicator of udder health in the herd: a high BTSCC indicates higher levels of udder disease, specifically subclinical mastitis.

California Mastitis Test-CMT
A rapid, cow-side test to assess the somatic cell count of an individual cow. Milk from each quarter is mixed in a small tray with the reagent, and results read immediately by assessing the thickness of the milk-reagent mixture after swirling. The more gel-like the mixture, the more somatic cells are present. The CMT is a good indicator of subclinical mastitis in the individual cow. (See D/D100.htm for fun pictures.)

Disability or disease of limbs or feet that interferes with normal and pain-free movement

Organic farming
Organic agriculture is a production system that sustains the health of soils, ecosystems and people. It relies on ecological processes, biodiversity and cycles adapted to local conditions, rather than the use of inputs with adverse effects. Organic agriculture combines tradition, innovation and science to benefit the shared environment and promote fair relationships and a good quality of life for all involved." (from IFOAM)

Subclinical mastitis
Mastitis which is not clinically recognizable. The udders and teats appear normal and milk appears grossly normal.

Sustainable farming
As it pertains to agriculture, sustainable describes farming systems that are "capable of maintaining their productivity and usefulness to society indefinitely. Such systems... must be resource-conserving, socially supportive, commercially competitive, and environmentally sound." (from USDA website)
The mammary gland of bovines. (Also used for sheep and goats.) The udder of a cow is divided into quarters.

Zoonotic diseases
Infectious diseases that can be transmitted between animals and humans or that may infect both humans and animals; anthrax, equine encephalitis , BSE, Brucellosis

1.4. Stereotypes about the Animal Health Perspective

1.5. Animal Health Presentation Materials

Animal Health Perspective slide presentation

Animal Health Disciplinary Concept Ma (VUE)

Animal Health Disciplinary Concept Map (PDF)

1.6. Animal Health Perspectives Annotated Bibliography

Bidokhti MR, Tråvèn M, Fall N, Emanuelson U, Alenius S. Reduced likelihood of bovine corona virus and bovine respiratory syncitial virus infection on organic compared to conventional dairy farms. Division of Ruminant Medicine and Veterinary Epidemiology, Department of Clinical Science, Swedish University of Agricultural Sciences, Box 7019, SE-750 07 Uppsala, Sweden.
The prevalence of antibodies to bovine coronavirus (BCV) and bovine respiratory syncytial virus (BRSV) infections was studied in 20 conventional and 20 organic dairy herds. The organic farms had produced 'certified' milk for at least 2 years. On two occasions, with a 1-year interval, 699 serum samples from 624 peri-parturient cows were tested by ELISA for antibodies to BCV and BRSV. Accompanying data relating to the sampled animals were collected in order to identify potential factors associated with increased antibody prevalence. The antibody prevalence was high at both sampling times with approximately 85% and 80% of animals positive for antibodies to BCV and to BRSV, respectively. Conventional herds had a significantly higher mean antibody prevalence to BCV and BRSV than the organically managed herds (P<0.01). Animal age was significantly associated with increased antibody prevalence (P<0.001). The findings of this study suggest that organic farm management may be effective in reducing the seroprevalence of these viruses relative to conventional farming methods.

There are very few studies comparing disease prevalence in organic farms and conventional farms and this study does that.

Byström Sara, Jonsson, Simon, Martinsson, Kjell. Organic versus conventional dairy farming - studies from the Öjebyn Project. Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences, Patrons Allè 10, S-943 31 Öjebyn, Sweden
A study (the Öjebyn Project) was conducted to determine differences between organic and conventional dairy farming systems. Comparisons of feed intake, milk production, live weight (LW), feed efficiency and animal health were conducted, based on records from 145 dairy cows (238 parities). A lower daily metabolisable energy (ME) intake, lower milk yield and a higher protein content was recorded in the organic herd during the first ten weeks of lactation. No differences were recorded between the systems in either average total DM intake or efficiency of feed conversion, calculated as MJ of feed/kg of energy-corrected milk (ECM). There were a trend to lower LW change and better health in the organic herd. Most differences between the systems were recorded during the early lactation period.

Conn DB, Weaver J, Tamang L, Graczyk TK. Synanthropic flies as vectors of Cryptosporidium and Giardia among livestock and wildlife in a multispecies agricultural complex. Vector Borne Zoonotic Dis. 2007 Winter
The authors use fluorescent in situ hybridization and immunofluorescent antibody techniques to examine flies as carriers of cryptosporidium and giardia. They find that flies from the families Calliphoridae, Sarcophagidae, and Muscidae all carried oocysts or cysts internally and externally and deposited them on surfaces in both livestock and wildlife areas.

This article illustrates one mechanism of disease spread among different groups of animals and pulls in the importance of the idea that wild and domestic populations affect each other.

Coorevits A, De Jonghe V, Vandroemme J, Reekmans R, Heyrman J, Messens W, De Vos P, Heyndrickx M.{}Comparative analysis of the diversity of aerobic spore forming bacteria in raw milk from organic and conventional dairy farms. Syst Appl Microbiol. 2008 Jun;31(2):126-40. Epub 2008 Apr 10
Bacterial contamination of raw milk can originate from different sources: air, milking equipment, feed, soil, feces and grass. It is hypothesized that differences in feeding and housing strategies of cows may influence the microbial quality of milk. This assumption was investigated through comparison of the aerobic spore-forming flora in milk from organic and conventional dairy farms. Laboratory pasteurized milk samples from five conventional and five organic dairy farms, sampled in late summer/autumn and in winter, were plated on a standard medium and two differential media, one screening for phospholipolytic and the other for proteolytic activity of bacteria.

Although the overall diversity of aerobic spore-forming bacteria in milk from organic vs. conventional dairy farms was highly similar, some differences between both were observed: a relatively higher number of thermotolerant organisms in milk from conventional dairy farms compared to organic farms (41.2% vs. 25.9%), and (ii) a relatively higher number of B. cereus group organisms in milk from organic (81.3%) and Ureibacillus thermosphaericus in milk from conventional (85.7%) dairy farms. One of these differences, the higher occurrence of B. cereus group organisms in milk from organic dairy farms, may be linked to differences in housing strategy between the two types of dairy farming. However, no plausible clarification was found for the relatively higher number of thermotolerant organisms and the higher occurrence of U. thermosphaericus in milk from conventional dairy farms. Possibly this is due to differences in feeding strategy but no decisive indications were found to support this assumption.

Stephan Dabbert, Department of Farm Economics, University of Hohenheim, Stuttgart, Germany 705932006 Plant Management Network. Measuring and Communicating the Environmental Benefits of Organic Food Production
Perceived environmental advantages are a key motivation for the interest in organic farming. The comparison between the environmental effects of organic and conventional farming poses a number of methodological challenges. Empirical evidence shows that organic farming is ranked at least equal, and in a number of instances better, than conventional farming for key environmental indicators. In communicating these advantages to consumers, the concept of credence characteristics is important; attempts to sell organic products to consumers on their non-use values alone are likely to fail. The positive environmental effects of organic farming can, under certain circumstances, justify policy intervention. Organic farming as an agro-environmental policy instrument is particularly useful where the goal is overall improvement of a large number of environmental indicators; in such instances its comparatively lower transaction cost is a distinct advantage. However, organic farming cannot address all agro-environmental problems.

Ellis KA, Innocent GT, Mihm M, Cripps P, McLean WG, Howard CV, Grove-White D. Dairy cow cleanliness and milk quality on organic and conventional farms in the UK. J Dairy Res. 2007 Aug;74(3):302-10. Epub 2007 Apr 24
A longitudinal study was done to assess a subjective cow cleanliness scoring system which was validated and used to assess the cleanliness score of dairy cows at different times in the year. There was a link between cow cleanliness scores and milk quality, with herds having lower bulk tank somatic cell counts (BTSCC) tending to have a lower (cleaner) median cow cleanliness score; with this relationship strongest for the organic herds. No major mastitis pathogens were cultured from bulk tank milk samples from the quartile of herds with the cleanest cows in contrast to the quartile of herds with the dirtiest cows, where significant mastitis pathogens were cultured.

Organic farms are forced to maintain a higher level of cleanliness than conventional farms because they are restricted on the use of antibiotics. These stringent measures therefore also indicate a reduction in disease.

Ellis KA, Monteiro A, Innocent GT, Grove-White D, Cripps P, McLean WG, Howard CV, Mihm M. J Dairy Res. 2007 Nov;74(4):484-91. Epub 2007 Oct 9. Investigation of the vitamins A and E and beta- carotene content in milk from UK organic and conventional dairy farms
During a 12-month longitudinal study, bulk-tank milk was collected from organic (n=17) and conventional (n=19) dairy farms in the UK. Milk samples were analysed for vitamin A (retinol), vitamin E (alpha-tocopherol) and beta-carotene content. The farming system type, herd production level and nutritional factors affecting the milk fat vitamin content were investigated by use of mixed model analyses. Conventionally produced milk fat had a higher mean content of vitamin A than organically produced milk fat, although there were no significant differences in the vitamin E or beta-carotene contents between the two types of milk fat. Apart from farming system, other key factors that affected milk fat vitamin content were season, herd yield and concentrate feeding level. Milk vitamin content increased in the summer months and in association with increased concentrate feeding, whilst higher-yielding herds had a lower milk vitamin E and beta-carotene content. Thus, conventional dairy farms in the UK produced milk with a higher vitamin A content, possibly owing to increased vitamin A supplementation in concentrate feeds. However, knowledge of the effects of season, access to fresh grazing or specific silage types and herd production level may also be used by all producers and processors to enhance the vitamin content in milk.

Fall N, Grohn YT, Forslund K, Essen-Gustafsson B, Niskanen R, Emanuelson U. An observational study on early-lactation metabolic profiles in Swedish organically and conventionally managed dairy cows. J Dairy Sci. 2008 Oct
Metabolic profiles of cows on organic and conventionally managed farms in Sweden are compared by measuring the blood parameters nonesterified fatty acids, β-hydroxybutyrate, glucose, and insulin. The general purpose of the study was to determine any difference between herds that may be due to management practices. The authors report no significant difference.

Organically managed dairy herds often use different feeding management practices than conventional farms. The biggest difference is a higher roughage:grain ratio used on organic farms, and animal scientists and veterinarians have questioned whether or not this type of diet can support high production demands, or if it might be detrimental to animal health due to metabolic derangement. This article provides some evidence that there is no metabolic difference despite different diets.

Garcia, Alvaro. Indicators of animal welfare, cow comfort and its economic impact. South Dakota State University
This is a presentation by a veterinarian relating to measuring cow comfort on dairy farms and how it relates to herd health and has economic impacts for the farm. Some of the best physical indicators of cow comfort suggested in this source are lameness, cow hygiene, and teat condition. The author also provides methods for calculating measures such as the cow comfort index and stall use index.

This source is very useful for practical ways to quickly evaluate a dairy herd for cow comfort measures which relate to health and productivity of the herd. Reference charts, images, scoring guides and formulas for the indices are provided and could all be used at an actual herd visit.

Hamilton C, Emanuelson U, Forslund K, Hansson I, Ekman T. Mastitis and Related Management Factors in Certified Organic Dairy Herds in Sweden. Acta Vet Scand. 2006 Jul 17; 48:11
This paper demonstrated that organic herds were found to have a lower incidence of clinical mastitis, teat injuries, and a lower proportion of cows with a high somatic cell count (as indicated by the UDS, Udder Disease Score) compared to conventional herds. The main management factor that was different from conventional herds was the proportion of concentrates fed i.e., the feeding strategy, where organic herds used a larger share of forage. This led them to conclude that udder health in Swedish organic herds appears to be better than in conventional herds of comparable size and production.

Many studies have rarely demonstrated a major difference in diseases incidence among organic and conventional farms.

Hamilton C, Emanuelson U, Forslund K, Hansson I, Ekman T. Health of cows, calves and young stock on 26 organic dairy herds in Sweden. Vet Rec., Apr 2002; 150: 503 - 508
This paper studied the health and housing of the stock on 26 organic dairy herds in four counties in eastern Sweden for one year. The herds ranged in size from 12 to 64 cows, and their milk production from 3772 to10,334 kg per cow per year. The incidence of diseases treated by a veterinarian was lower in the organic herds than the average for the conventional herds in the local dairy association. The findings at the farm visits supported these data, and it is evident that a good standard of health and welfare can be achieved in organic dairy herds.

F. Hardeng and V. L. Edge: Mastitis, Ketosis, and Milk Fever in 31 Organic and 93 Conventional Norwegian Dairy Herds. J. Dairy Sci. 84:2673-2679 American Dairy Science Association, 2001
The aim of this study was to investigate differences in disease incidence between organic and conventional herds. The study was based on data from the Norwegian. Dairy Herd Recording, which includes the Norwegian Cattle Health Recording System. Factors influencing disease incidence were studied by means of a generalized linear model approach. Management system had a highly significant effect on disease incidence. Odds ratios for organic compared with conventional herds were as follows: mastitis, 0.38; ketosis, 0.33; and milk fever, 0.60. Other significant factors that emerged in modeling the three diseases were year and lactation category for mastitis; lactation category, maximum milk yield, and season for ketosis; and lactation category and milk yield for milk fever. There was no marked difference in milk somatic cell count (SCC) between organic and conventional herds. However, cows in organic herds had lower SCC in lactation two and greater counts in lactations six and higher.

Kebreab, E.: Model for estimating enteric methane emissions from United States dairy and feedlot cattle. J Anim Sci. 2008.86:2738-2748
Measuring the gases produced and released by cattle in the process of rumination has been a difficult task, and for this reason, it is difficult to really compare different feeding strategies or different herds. This article describes a method for estimating specifically methane emissions in US cattle. Using methods such as this may allow future comparison between organic and conventional farms.

Kwan PS, Barrigas M, Bolton FJ. Molecular epidemiology of Campylobacter jejuni populations in dairy cattle, wildlife, and the environment in a farmland area. Appl Environ Microbiol. 2008 Aug;74(16):5130-8. Epub 2008 Jun 27
Isolates of Campylobacter jejuni from dairy cattle, wildlife and the environment are characterized to explore animal reservoirs and possible routes of human infection. The authors find that isolates are widely distributed among the dairy cattle, wild mammals, wild birds, and environmental water samples. The findings suggest that wildlife and the environment may be reservoirs for dairy cattle and that humans may be exposed from any of these independent sources.

While C. jejuni is not my idea of an important cattle disease, it is the most common bacterial pathogen causing food-borne GI illness in humans, usually with zoonotic implications. I like this article because it seems to thoroughly explore the idea that zoonotic disease interactions are very complex and that human and animal exposure can come from multiple sources. I think that a similar approach of investigating livestock, wildlife in the environment, and environmental sources is a way we could approach other cattle disease interactions in discussion.

S. J. LeBlanc1, K. D. Lissemore, D. F. Kelton, T. F. Duffield and K. E. Leslie. Major Advances in Disease Prevention in Dairy Cattle Population Medicine, Ontario Veterinary College, University of Guelph, Ontario, Canada N1G 2W1: J. Dairy Sci. 89:1267-127. American Dairy Science Association, 2006
This paper describes some of the major points of progress and challenges in health management of dairy cattle in the last 25 years. A selection of the leading contributors in the field is acknowledged. Specific advances in the areas of transition cow management, epidemiology, udder health, applied immunology, housing design, calf health, and health-monitoring tools are described. The greatest advances in dairy health in the last 25 yr have been the shifts to disease prevention, rather than treatment, as well as from focus on individual animals to groups and herds. A fundamental advancement has been recognition of the multifactorial nature of almost all diseases of importance in dairy cattle. Another major advance has been redefining disease more broadly, to include subclinical conditions (e.g., subclinical mastitis, ketosis, rumen acidosis, and endometritis). Links between cattle and people through consideration of environmental or ecosystem health are likely to further expand the concept of disease prevention in the future.

Notable successes are decreases in the incidence of milk fever, clinical respiratory disease in adults, contagious mastitis, and clinical parasitism. There has also been improved protection through vaccination against coliform mastitis and bovine virus diarrhea.

Lund V.: Research on animal health and welfare in organic farming---a literature review. Livestock Production Science, Volume 80, Issue 2, 2003 age 55
Organic standards aim at good livestock health and welfare. A literature search on organic animal health and welfare was performed in October-November 2001 to investigate how well these aims compare with reality, and to see what areas have been researched. The search also made it apparent that national and historical differences in organic standards and in the way organic farming is understood must be considered when comparing results from different studies. The reasons for this are further discussed. Only 22 peer-reviewed papers were found in the search, mainly dealing with dairy cattle health and parasitology. Ten were comparative studies. In addition, two overviews were found. No papers focused on welfare issues other than health. The small number of papers published is not surprising in light of the development of organic farming and its philosophy. For example, organic researchers have been more interested in solving practical problems than publishing papers. However, this makes it impossible to draw general conclusions regarding the health and welfare of organic livestock. None of the published articles found indications that health and welfare are worse in organic than in conventional livestock farming, with the exception of parasite-related diseases. A cautious conclusion based on this material is that except for parasite-related diseases, health and welfare in organic herds are the same as or better than in conventional herds.

Lyautey E, Hartmann A, Pagotto F, Tyler K, Lapen DR, Wilkes G, Piveteau P, Rieu A, et al. Characteristics and frequency of detection of fecal Listeria monocytogenes shed by livestock, wildlife, and humans. Can J Microbiol. 2007 Oct;53(10):1158-67
Fecal samples from livestock, wildlife, and humans were tested for presence of Listeria monocytogenes. The goals of the study were to describe the prevalence and characteristics of L. monocytogenes strains in the various species. In total, 84 strains were isolated. The authors found that the strains from each set of species were distinct but still overlapping, and surface water was a possible source of contamination and may have been related to the overlapping populations of L. monocytogenes strains.

Scott A. McEwen1 and Paula J. Fedorka-Cray2. Antimicrobial Use and Resistance in Animals. Clinical Infectious Diseases 2002; 34:S93-S106
Antimicrobial resistance has emerged in zoonotic entero- pathogens such as salmonella, E. coli, campylobacter. This is because food animals in the United States are often exposed to antimicrobials to treat and prevent infectious diseases or to promote growth. Many of these antimicrobials are identical or closely resemble drugs used in humans. This is mostly done on conventional farms. Microbial resistances have emerged, and there is subsequent transfer of resistance genes and bacteria among animals and animal products and the environment.

A . Nardone , G . Zervas , B . Ronchi. Sustainability of small ruminant organic systems of production. Livestock Production Science, Volume 90, Issue 1, Pages 27 - 39
There is an increasing interest for sustainable forms of livestock production systems, which will provide a balanced relationship between environmental, socio-cultural and economic factors. This paper examines the small ruminant sector, analyzing the special role that organic farming plays to meet the demands of sustainability. The small ruminant sector is examined with particular focus on the possibilities of improving the sustainability of small ruminant systems and on the possible role of organic production to meet the demand of sustainability. Current regulations highlighting different approaches and interpretation of organic farming among countries are reviewed. Regulations concerning organic livestock production between the US and the EU are compared. For the future development of organic farming, a strong harmonisation of rules and legislation at international and national level is needed.

Pol M, Ruegg PL. Treatment practices and quantification of antimicrobial drug usage in conventional and organic dairy farms in Wisconsin. J Dairy Sci. 2007 Jan;90(1):249-61.
Antimicrobial drug usage and treatment practices for various diseases are compared in groups of conventional and organic Wisconsin dairy farms. The authors find that the overall prevalence of the diseases compared (mastitis, metritis, respiratory and foot disease) are higher on conventional farms. Conventional farms tended to use antimicrobial drugs for the treatment of many of these diseases, whereas organic farms tended to use nonantimicrobial methods to treat and prevent disease.

This article relates to our discussion of sustainable farming practices because it specifically compares management practices between organic and conventional farms for several important dairy cow diseases. Organic farms cannot use antibiotics on their animals and sell the products as organic, so they often seek other methods of disease prevention and treatment. Some methods presented in the article include filtered whey based products, vitamin/mineral supplement, garlic tincture, aloe vera, aspirin, corticosteroids, and vegetable oils. These methods could be compared for efficacy in sustainable farming.

B. Ronchi. Contribution of organic farming to increase sustainability of Mediterranean small ruminants livestock systems. Livestock Production Science, Volume 80, Issue 2, Page 17 B
The aim of the paper is to evaluate the feasibility and constraints of organic farming to increase the sustainability of Mediterranean small ruminant livestock systems. The paper analyzes the factors affecting sustainability of small ruminant livestock systems in the Mediterranean basin, such as seasonal forage availability or suboptimal pasture utilisation due to overgrazing but also the factor of undergrazing. The paper considers how the application of practices of organic farming may contribute to promoting sustainable land use and improving environment conservation, animal welfare, and product quality. Also the prospects of new information-based technologies, like geographic information systems and global positioning systems, to improve sustainability are presented. A model of pasture-based dairy sheep production system is proposed, with special emphasis on the organisation of a farm forage system to meet animal nutritional requirement

Rotz, CA. Organic Dairy Production Systems in Pennsylvania: A Case Study Evaluation. J. Dairy Sci. 90:3961-3979
This study was performed to study the relative profitability of organic dairy farms in Pennsylvania. They were particularly interested in describing how small farms' profits would be affected by switching to organic methods. They used 4 organic farms, doing analyses of farm profits with a number of factors simulated over 25 years. This study determined that transition to organic farming is an economically viable option for small Pennsylvania dairies.

Rozzi P, Miglior F, Hand KJ. A total merit selection index for Ontario organic dairy farmers. J Dairy Sci. 2007 Mar;90(3):1584-93.
The authors describe a "total merit" index for scoring traits in cows on organic dairies in Ontario. They find that, compared to conventional dairies, organic herds tend to have lower milk production, lower culling rates, increased somatic cell counts, increased crossbreeding, and fewer reported health problems. Organic herds tend to select individuals for breeding based on health and conformational traits, with much less importance placed on production traits than conventional herds.

This article provides information about how animal breeding practices contribute greatly to the farm's overall sustainability. Due to the regulations involved in organic dairy farming, the farmers are selecting animals based on health traits, and while this has generally decreased milk production by organic herds, the overall health of the cows has increased. This article documents how the organic herds have significantly reduced clinical mastitis, foot and limb problems, and have greatly reduced their culling rates over conventional herds. Animal health can be increased in herds transitioning to organic by selecting individuals with high health traits over production traits and incorporating these genetics into the herd.

Rutherford, KMD, et al. Hock Injury Prevalence and Associated Risk Factors on Organic and Nonorganic Dairy Farms in the United Kingdom. J. Dairy Sci. 91:2265-2274
Hock injury prevalence was assessed in 40 organic and 40 conventional farms in the UK. Organic farms had a lower prevalence of hock injuries, and the authors also found that hock injuries were greater in the spring and in barns using free-stalls as opposed to straw bedding. The authors point out that the prevalence of hock injuries was greater than what is acceptable on both organic and conventional farms in terms of cow comfort.

Sischo W. M, Atwill, E. R. Lanyon L. E. and George J. Cryptosporidia on dairy farms and the role these farms may have in contaminating surface water supplies in the northeastern United States Preventive Veterinary Medicine. Volume 43, Issue 4, 29 Feb 2000, 253-267
Cryptosporidium parvum (the parasite responsible for causing cryptosporidiosis) is a major worldwide public-health concern in both rural and urban settings. In particular, C. parvum has been implicated as the cause of numerous outbreaks associated with contaminated food and water supplies. This study examined the prevalence and risk factors for shedding of cryptosporidia by dairy cattle and calves and the prevalence and risk factors for cryptosporidia in surface waters associated with dairy farms for a well-defined watershed in the northeastern United States. Eleven dairy farms were enrolled in the study and subjected to monthly sampling over a 6-month period. 91% of the dairy farms in the study had Cryptosporidium on their premises. The single risk factor for detecting cryptosporidia in surface water was increasing frequency of spreading of manure on fields.

About 75% of the new diseases that have affected humans over the past 10 years have been caused by pathogens originating from an animal or from products of animal origin. Identifying and evaluating microbiological hazards to human health of animal origin: new, emerging and re-emerging zoonotic diseases, and foodborne diseases, including those due to antimicrobial resistant bacteria. Crpotosporidium is one such disease that is emerging and becoming a greater threat to human health.

Vicini, J. Survey of Retail Milk Composition as Affected by Label Claims Regarding Farm-Management Practices. J. Am. Dietetic Assoc. July 2008.
The authors of this article investigated milk quality between dairy products labeled conventional, rBST free, or organic. They sampled retail milk samples in 48 states and tested them for bacterial counts, nutritional value and hormone composition. The authors find minimal differences, with conventional milk having lowest bacterial counts, estrogen and progesterone, and organic milk having higher protein, but the differences were not biologically meaningful. They conclude no meaningful difference in the milks sampled based on label claims.

Walsh C, Fanning S. Antimicrobial resistance in foodborne pathogens--a cause for concern. Current Drug Targets. 2008 Sep;9(9):808-15
The emergence of antibiotic resistant zoonotic bacteria is associated with the widespread use of antibiotics in food animal production systems . Antibiotic resistant bacterial infections have a negative impact on public health, due to an increased incidence of treatment failure and severity of disease. This paper looks at current food preservation systems especially the increasing reliance on biocides for pathogen control that can lead to biocide resistant strains. And cross resistance to other antibiotics.

Weller R.F and Bowling P.J. Health status of dairy herds in organic farming. Vet Rec., Jan 2000; 146: 80 - 81
Changing to organic farming has implications for the management of the dairy herd as no long-acting antibiotics are used during the dry period, and either all of the majority of cases requiring treatment during lactation are. This study showed that although no long-acting antibiotics were used during the dry period and many cases of clinical mastitis during lactation were treated without using antibiotics, the incidence of clinical mastitis was no higher than in conventional herds.

Williams ES. Sharing the Range - What Diseases Do Wild Ruminants and Beef Cattle Share? Proceedings - The Range Beef Cow Symposium XVI
This symposium article provides a nice overview of some of the major diseases which may be transmitted between cattle and wild ruminants in North America. It gives basic information about each disease and its overall importance. Since this article was published, the entire United States has achieved brucellosis free status, but the disease does still exist in wild ruminants in the Yellowstone area.

While the article was written with range beef cattle in mind, I think the diseases are applicable to dairy herds as well, especially those on pasture. As the article points out, many of the diseases are unlikely to be a significant problem when considering wildlife and livestock disease interactions, but I think they should be considered when planning vaccine protocols, disease prevention strategies, and disease surveillance systems. Farmers should be aware of which wildlife species exist in their area and which infectious diseases may affect their herd.

Wiliams ES, Barker IK. Infectious Diseases of Wild Mammals Third Edition, Blackwell Publishing, 2001
This text book is a great reference on infectious diseases of wild mammals and provides information on a wide range of diseases, how they are transmitted, host range, and pathogenesis. Diseases are grouped together by type making it an easy book to use to find quick facts about a disease.

Since the book provides information on domestic species which may also be affected by a disease, this makes an especially good reference for diseases which may be transmitted between cattle and wildlife.