126 The Canadian Journal of Veterinary Research 2000;64:0–00
chain. Each of these organisms can be carried and shed by sheep,
and can be transmitted to humans through water. However, there
is a paucity of information regarding the risks of sheep production
to nearby water supplies.
The World Health Organization estimates that 2 million deaths per
year result from drinking water that is contaminated with bacterial
pathogens (2). Pathogens from livestock feces are the source of some
of the water contamination. After direct feces deposition by grazing
animals or manure application on farm fields, pathogens can move
from manure to waterways or riparian areas (3). In Canada, a study
has shown that 32% of farm wells in Ontario exceed the maximum
acceptable concentrations of coliforms (4).
Mead et al (5) estimated that 0.5% of all foodborne infections and
3% of deaths from foodborne infections in the United States were due
to E. coli O157:H7. The main reservoir species for E. coli O157:H7 are
ruminants, such as cattle and sheep (6). Pollution of groundwater
with livestock manure can be an important cause of E. coli O157:H7
outbreaks (7); however, the risk from sheep production is unclear.
Estimates of overall prevalence of E. coli O157:H7 in sheep range
from 0 to 60% (8,9), with differences stemming from animal age,
production type, and season.
Salmonella is thought to be responsible for the highest cost per case
of foodborne gastroenteritis in Canada and the US (1). A study in the
United States estimated that 9.7% of foodborne infections and 31%
of deaths were due to nontyphoidal Salmonella (5). There has been
no study on the prevalence of Salmonella in sheep in Canada. A sur-
vey in Great Britain by Davies et al (10) found a fecal prevalence
of Salmonella in sheep of only 0.1%. However, Hutchinson et al (11)
found that 8% to 11% of sheep manure samples contained Salmonella.
Contamination of the environment by manure outflow may lead to
significant levels of this pathogen in surface water. Johnson et al
(12) found that 6.2% of river water samples in Alberta, Canada were
positive for Salmonella.
Campylobacter, particularly C. jejuni and C. coli, is the most com-
mon foodborne pathogen in the developed world. These organisms
cause gastroenteritis, but this is usually not fatal (13). The main
reservoirs of these bacteria are poultry and wild birds (14,15), but
they are commonly found in ruminants and other production ani-
mal species. A study of sheep on pasture in the UK found that the
prevalence of shedding of Campylobacter varied from 0 to 100%, with
the highest prevalence following lambing and very low shedding
during other times (16). There has been no study on the prevalence
of Campylobacter in sheep in Canada. Commonly transmitted by
water, Campylobacter has been found in 50% of river water samples
in New Zealand (17). Contamination of streams, rivers, ponds, and
groundwater is strongly associated with upstream agricultural loca-
tions, or sewage contamination (15).
There is a much higher prevalence of Y. enterocolitica in pigs than
in ruminants, and serotypes associated with human disease are more
likely to be isolated from pigs (18). Estimates of the prevalence of
Yersinia infection in humans in Canada are not available. There has
been no study on the prevalence of Yersinia in sheep from Canada.
In the UK, McNally et al (18) found 10.7% of samples from slaughter
sheep feces were positive for Yersinia enterocolitica. Yersinia survives
well in spring, river, or groundwater (19), and is often isolated from
According to recent figures (21), there are 230 000 sheep in Ontario,
which comprises 27% of the national flock. There is increasing con-
cern in Ontario and elsewhere regarding the health risks of livestock
grazing near waterways and riparian areas. This is partly due to
large outbreaks of human disease associated with cattle manure (22).
However, it is known that sheep and cattle exhibit different behav-
ior patterns on pasture (23). Combined with the lack of foodborne
pathogen data associated with sheep, it has been difficult to estimate
the risk of transmission of zoonotic pathogens from sheep.
The objective of this study was to determine whether sheep
pastured near riparian areas are an important risk factor for the
contamination of water with foodborne zoonotic pathogens.
Materials and methods
Study design and sample collection
Written surveys were mailed to all producers in the Ontario Sheep
Marketing Agency District 5 to determine the existence of riparian
areas on sheep farms (24). Ten farms were selected to participate in
the study, based on proximity to laboratory facilities, presence of a
suitable waterway, and willingness to participate. From the period
of May 30th until August 19th, 2005, each of the 10 farms was vis-
ited weekly. Order of visits was formally randomized for day of the
week and time of day (morning or afternoon). Over the course of
this study period, each farm received 5 morning visits (07:30–11:30)
and 5 afternoon visits (15:30–19:30), during which time behavioral
observations were taken for an associated study.
Soil, water, and fecal samples were collected each day after the
end of the morning behavioral observations. Water samples (50 mL)
were collected within 30 cm of the water’s edge, in open water,
using a sterile conical tube. Because of their strong flocking behav-
ior, sheep typically access water sources from particular locations.
Hence, water samples were collected from 3 different locations,
1 taken at the location where sheep access the stream (access),
1 taken 10 m upstream from the access point (upstream), and 1 taken
10 m downstream from the access point (downstream). If the sheep
were contaminating the water source, pathogen levels would be
higher at the access and downstream locations than at the upstream
Soil samples were collected from 5 locations, and a minimum of
of soil, free of vegetation, was collected using a sterile scupula.
One sample was taken at the edge of the water at the sheep access
point (Access), 1 in the open field where the sheep were observed to
graze (field), and 1 from the road edge where sheep had never had
access (roadside). The behavior of pastured sheep includes grazing
bouts interspersed with camping bouts where sheep congregate to
lie down, ruminate, and rest. Therefore, 2 samples were collected
from each camping area. On farms where sheep had barn access,
camping tended to occur in the barn with a 2nd camping site located
in the pasture.
Two fecal samples of approximately 5–10 g each were collected
from the ground at the sheep camping site. Where possible, feces
were collected immediately after excretion. If the sheep were not on
the camping site at the end of the observation period, the freshest
feces were collected.