Pathogen Pathways − Contamination of water bodies via artificial drainage
6. Conclusions
The potential of dairy farms to be sources of Campylobacter, Cryptosporidium and Giardia for the contamination of drainage and runoff waters depends firstly on the levels of infection in the herd. In this study, we again report concentrations of Campylobacter in all fresh dung spots that were highly variable, confirming earlier observations that individual cow shedding of Campylobacter is highly individualistic.
In this study, fresh faeces did not contain Cryptosporidium oocysts or Giardia cysts. Giardia cysts were identified in runoff and drainage waters. In one experiment, higher Giardia cysts concentrations typically occurred in water samples collected immediately after grazing. In this case the cyst source is presumably the soil (older dung spots or bird faeces) disturbed by the grazing cow and not fresh dung.
Campylobacter concentrations in drainage and runoff declined with time (days) after grazing. However, lower numbers of organisms remained present in drainage and surface-runoff occurring days and even weeks after grazings. The source of this ongoing contamination of water with Campylobacter could either be due to the survival of Campylobacter in old dung spots and the associated soil environment or could be from other sources (for example, wild birds).
The formation of the water-stable skins on dung pats the same day they are deposited, is believed to be a major factor reducing the contamination of rain water as it moves into and across the soil, reducing the Campylobacter concentrations in drainage and runoff water.
The results from these grazing trials may be unique to the cool moist conditions that occurred during the experimental period. Some experiments will be repeated with early winter drainage events in 2004 to confirm findings that suggest that prudent herd management prior to heavy rain and careful scheduling of post-grazing irrigation and effluent applications may provide mitigation strategies which reduce the risk of pathogens contaminating surface water bodies.
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