Under certain circumstances cattle can cause negative effects on natural water sources by shedding zoonotic pathogens into the environment (34
). Being ruminants, sheep carry and shed many of the same zoonotic organisms as cattle including E. coli
), and Yersinia enterocolitica
). One of the factors that make cattle a risk for transmission of pathogens into water sources is how they use riparian areas and their behavior in and around water sources (37
). Even though sheep may pose similar risks, there are few data available on the impact of sheep production on natural water sources, and to the authors’ knowledge there have been no previous studies on how sheep behavior may affect zoonotic pathogen load in surface water and riparian areas.
Ruminants, particularly cattle, are considered the main reservoirs for E. coli O157:H7. In the present study, no E. coli O157:H7 was recovered from the water, the soil or the sheep feces. Reliance on biochemical tests alone to identify and differentiate E. coli O157:H7 from other organisms and E. coli types would have resulted in a number of false positives. However, further confirmation with PCR eliminated all suspects. The objective of this study was to determine which organisms sheep are contributing to their environment, rather than to measure the prevalence of zoonotic organisms in the sheep per se. Therefore, the flocks studied may have been colonized with E. coli O157:H7, but at levels not detected in this study.
Other factors that have been shown to contribute to shedding of E. coli
O157:H7 by ruminants are sudden changes in diet, environment, or antimicrobial therapy (6
). These factors were not present in any of the flocks studied. Furthermore, levels of E. coli
O157:H7 are lower in feces from sheep and cattle fed forage rather than concentrate diet (6
), which is typical of pastured sheep production in general and of the flocks studied here specifically. Hence, results from the present study support the hypothesis that the amount of E. coli
O157:H7 contributed to the environment by pastured sheep is low.
was detected in this experiment; again this is likely a function of study design, sample type, and the low prevalence expected in pastured sheep. Similar to E. coli
animals fed a pasture or forage-based diet shed less Salmonella
in their feces than those fed concentrate based diets (11
). Further study on the epidemiology of Salmonella
in sheep would be useful for determining how to manage this pathogen in sheep flocks.
were recovered in this study from sheep feces, water, and soil samples. Campylobacter
spp. are found frequently in all animals including wild birds and poultry (14
), which may contribute to environmental levels of Campylobacter.
One study found that 42% of wild geese and other waterfowl feces were contaminated with Campylobacter jejuni
). In the present study, wild geese were observed near the water sources on each of the farms. The hypothesis that wildfowl are at least partly responsible for the environmental contamination is supported by the fact that there was no significant difference in levels of Campylobacter
between soil that had never been grazed by sheep (the roadside control) and soil where sheep grazed and camped. Therefore it would seem likely the Campylobacter
recovered from the soil and water was not exclusively from ovine sources. Again, stress such as lambing or calving, moving animals, weaning, transport or changing feed can cause an increase in the shedding of Campylobacter
). None of these were factors in the study herein.
In the present study, more Yersinia spp. was recovered from soils where the sheep had access than from roadside soil; however, there were no differences in levels of Yersinia enterocolitica from the different soil locations. This suggests that sheep are at least partially responsible for contaminating the environment and the water, but serotypes of Yersinia that were shed are unlikely to cause disease in humans. There has been little or no research on the effect of feeding and management in the shedding of Yersinia from ruminants, and therefore it is not clear how management affects Yersinia prevalence, if at all.
The lack of association between amount of time that sheep spent in one location and the levels of pathogens in samples from that location was not expected. This lack of association was also found in the related behavioral component to our study (24
). To the authors’ knowledge, no other studies have examined these parameters with regards to sheep production. Soils where sheep camp receive higher levels of feces relative to noncamp areas (40
) and, therefore, would be expected to have higher levels of pathogens. Also higher levels of pathogens would be expected in the water on farms where the sheep spent more time near the water compared with farms where the sheep were never seen near the water. These results indicate that under the management conditions observed, sheep do not have a significant impact on foodborne zoonotic pathogen levels in riparian areas and surface waters. This result is likely due to a combination of the organisms and levels that sheep typically shed, the behavior patterns specific to sheep, and the typical management of sheep in Ontario.
In conclusion, sheep on pasture in Ontario do not appear to be an important source of water contamination with Escherichia coli O157:H7 or Salmonella. Although in this study Campylobacter and Yersinia were recovered from samples of sheep feces, soil, and water; there was insufficient evidence to implicate sheep as an important cause of environmental contamination with these pathogens. The lack of association between prevalence of these pathogens and behavior of sheep supports the hypothesis that grazing sheep are not a major risk factor in the transmission of foodborne zoonotic pathogens to water sources.