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We describe 4 years of an experimental rotation in ecosystem health offered to senior veterinary students in Canada. Faculty from the 4 Canadian veterinary colleges collaborated in offering the rotation once annually at 1 of the colleges. The 1st rotation was held in Guelph in 1993, followed in successive years by rotations at Saskatoon, Saint-Hyacinthe, and Charlottetown. The rotation is a predominantly field-based experience that allows students to work with veterinary and other role models who are actively engaged in clinical research related to ecosystem health. Five specific field studies that worked particularly well during the rotations are presented. These studies involved investigating mortality in wildlife due to botulism, designing an environmental surveillance system around herds of beef cattle, using belugas to evaluate the health of the St. Lawrence River, dealing with competition for water use by aquaculture and agriculture, and exploring the role of veterinarians during major coastal oil spills. The experience has resulted in our developing the subject matter, field examples, teaching approach, and confidence necessary to make ecosystem health the focus of a productive clinical rotation for senior year veterinary students.

The objectives of this study were to describe the serological prevalence of maedi-visna in a sample of Ontario sheep flocks, and to identify management and demographic variables that were associated with seroprevalence for maedi-visna. A sample of 103 sheep flocks in Ontario was randomly selected from those flocks participating in the Red Meat Plan. The owners of these flocks were surveyed regarding management procedures on their farms, and blood samples were taken from a random sample of ewes in each flock. At least one ewe tested serologically positive, based on the agar gel immuno-diffusion test, in 69.9% of the farms. Positive serological reactions occurred in 20.9% of the 3880 sheep tested. Flock demographics and farm management variables were considered in a multiple regression model, and several factors were positively associated with higher maedi-visna seroprevalence rates. These included the average age of the flock, the number of years the owner had been sheep farming, the practice of using foster ewes, the practice of allowing lambs to have contact with other ewes that are lambing, and the average pasture acreage per ewe.

A survey was done of 150 systematically selected United States animal care agencies and 74 Canadian humane societies to determine the prevalence of animal assisted therapy (AAT) programs; concerns about, and experience with, zoonotic diseases; and precautions taken to prevent zoonotic disease transmission. Of the 69 US agencies and 49 Canadian societies that reported having AAT programs, 94% used dogs and/or cats in their programs, 28% used rabbits, 15% used "pocket pets" (hamsters, gerbils, mice, guinea pigs), and 10% used birds (excluding poultry). About two-thirds of the programs were involved with the elderly in nursing homes, about a quarter of them worked with schools, and a quarter worked with hospitals. Half of the respondents had concerns about zoonotic disease control. Rabies, ringworm, and external parasitism were the most commonly cited zoonotic diseases of concern. Few concerns were based on actual experience. Fewer than half of the programs consulted a health professional about prevention of zoonotic diseases. Only 10% of the respondents reported having printed guidelines about the prevention of zoonotic disease transmission. Practising veterinarians are encouraged to make their expertise available to local AAT programs.

In a random sample of 103 sheep farms in Ontario, 99% of the farms had some sheep serologically positive for Toxoplasma gondii, based on an enzymelinked immunosorbent assay (ELISA). The percent of sheep affected within farms ranged from 3.8% to 97.8%, with an average flock prevalence of 57.6%. When farm management variables were considered in a multivariate analysis, significantly lower rates of serologically positive sheep were associated with neutering of female cats and clipping of ewes' perineums before lambing; significantly higher prevalence rates were found on farms where sheep were purchased from other flocks, pigs were raised on the same farm, sheep shared pasture with other animals, flowing water was available at pasture, and pastured replacements had access to housing. As well, in univariate analyses, higher prevalence was positively associated with an increasing number of cat litters born over the previous two years and offering creep feed or forage to lambs, and inversely with the amount of labor expended on sheep rearing.

Veterinarians are integrally involved in the maintenance of a safe and sufficient food supply; this involvement may be put to the test when a crisis - particularly a nuclear crisis - occurs. Few people can be said to be experts in how to ensure a safe food supply in a nuclear crisis. However, a working knowledge of radionuclides and how they behave in the food system, and the ability to identify high-risk foods and high-risk consumers in a crisis situation should be a part of the education of all veterinarians. In this paper I review those features of postdisaster radionuclide contamination of the food chain most relevant to veterinary activities in ensuring a safe food supply.

Evidence from chemistry, physics, the biological sciences and the earth sciences is now accumulating that the earth functions as a living organism, with all the implications of circulatory and homeostatic systems which that implies. As veterinarians, we are more than simply handmaidens to agribusiness, the academic, pet and food industries, or government regulatory agencies. While our jobs may be specific, dependent, and circumscribed, our vocation can be nothing less than the health-care of all animal life - and hence by direct implication, the care of the earth, as a living organism, itself.

Risk assessment from 2 x 2 tables can be very useful for both clinicians and researchers. The measures described go beyond demonstrating a statistical association between some factor and disease or death, and attempt to assess, in real world terms, just how important a particular factor may be. Five measures of risk are explained by means of a veterinary example. The odds ratio compares the odds of animals succumbing to disease or death if they are exposed to a factor, compared to the odds of succumbing if they are not exposed. Attributable rate and attributable proportion (risk) measure the amount of disease or death in the exposed group which can actually be attributed to the factor under study. Population attributable rate and population attributable proportion (risk) extend these measures to the real world: how much of the disease or death on the farm might we be able to prevent? Calculation of measures of risk from a data set requires that a number assumptions be met, and that the data used be of the highest quality.

Calf-related drug use was studied on 104 randomly selected Holstein dairy farms in southwestern Ontario between October 1980 and July 1983. About 20% of dairy farmers were observed to administer antimicrobials preventively to healthy newborn calves (primarily as commercial "cocktails" of various antimicrobials, vitamins and minerals given in an oral bolus form) at some time during the year. About 30% of the farmers were observed to use vitamins (primarily vitamins A,D and E) preventively. The pattern of types of antimicrobials used preventively appeared to be different from the pattern seen for therapeutic use. Chloramphenicol was the single most commonly used therapeutic antimicrobial in this population of calves, accounting for some 30% of overall therapeutic antimicrobial use. In this study population, the prophylactic use of antimicrobials was associated with a decreased risk of being treated for pneumonia, and of dying, but an increased risk of being treated for scours. Case fatality rates for calves treated therapeutically varied, depending on the antimicrobial used and the routine of treatment. Calves treated with penicillin consistently suffered the highest case fatality rates. Case fatality rates for calves treated with chloramphenicol were considerably higher for calves treated once per day than for calves treated twice per day. For instance, calves first treated for scours with chloramphenicol, if treated once per day, suffered a case fatality rate of 22%. For scouring calves treated twice per day the case fatality rate was just under five percent. Clinical field trials of specific antimicrobials used preventively and therapeutically are required to delineate the conditions under which they might be useful.

A five year survey of mortality in an Ontario waterfowl park was conducted. The highest mortality rate was in birds under seven weeks of age, with infectious disease most frequently diagnosed. In older birds, amyloidosis and gout were most common. Associations were found between the presence of amyloid and the diagnoses of gout, enteritis, and arthritis. Specific data collection requirements for studies of this type, and the difficulties involved, are outlined. Recommendations for increasing productivity, including the implementation of sanitation programs, and improvements to the record-keeping system, are made.

An unusually high incidence of urinary calculi in a group of feeder cattle is described. Necropsy findings in one affected animal suggested that oxalates in the feed, specifically in fescue (Festuca spp.) seed screenings, may have been the cause. Low dietary calcium and decreased water intake by the cattle appear to have been predisposing factors. Control measures are discussed.