Environmental Consequences of Pasturing Dairy Heifers near Small Open Water Sources: Microbiological Impacts.

In Ontario, Canada, dairy farmers often opt to graze their replacement heifers when the weather allows. Because of the increased consumer awareness and environmental concerns this grazing practice calls for environmental monitoring and studies that quantify the actual impact on water quality.
We are investigating the pathogenic risk entering a small, open water source (Barnes Creek, Ontario, Canada (Lat= 45º, 00’, 22.22”, Long= 75º, 37’,33.64” ) from grazing Holstein heifers of approximately 500 Kg of body weight (BW). The study was designed to test the effect that placing a water trough on the grazing paddock had on the recovery of E. coli, Salmonella spp., Streptococcus spp., and Clostridium perfringens in the water samples. In a complete randomized design of a treatment (Trough) compared to a control (NoTrough), the animals were observed in 4 hours shifts, for 12 hours, 4 days per week, for 8 weeks, from mid May to late August, for 3 years.  Their drinking and manuring (defecating) incidents during the observations periods were recorded and analyzed using standard statistics. Water for microbiological and nutrient analysis was collected at points before, at and after the experimental site, twice a week, starting two weeks prior to animal arrival and ending two weeks after the animals left the site.  
Results indicated that physical parameters of stream water, such as temperature, pH, together with nutrient concentration all had considerable impact on the microbiological quality of the water resource that was independent of the immediate animal practices.