Microbial tracking - Tate looks at cattle impact on microbial loadingWritten by Saige Albert
Sheridan – Water quality concerns remain paramount for many across Wyoming, and the Wyoming Association of Conservation Districts (WACD) heard from researchers at the University of California, Davis about research that has looked at the impacts of cattle grazing on microbial loading of waters.
“We’ve been doing research over the last 20 years on sustaining livestock, water quality, habitat and sensitive species on rangeland watershed in California,” commented Ken Tate, a UC Davis researcher. “Leslie Roche and I represent a group out of California that focuses on rangeland management.”
Tate and Roche presented at the Wyoming Association of Conservation Districts Annual Convention Nov. 18-20 in Sheridan.
California ranchers graze on nearly 57 million acres of rangeland that are divided between public and private ownership.
“We have about 1 million acres of irrigated forage, and it is essential to our livestock acreage,” Tate said. “These acres are in a very diverse ecosystem with hundreds of vertebrates and thousands of invertebrate and plant species.”
In addition, 85 percent of surface waters in the state are used for municipal purposes. Water reservoirs for San Francisco are surrounded by vast tracts of rangelands, which are used for cattle grazing to control plant species.
In the early 80s, concern was expressed by the environmental community and regulatory agencies about rangeland watershed and clean water, particularly focused on human health.
“The big water topic that won’t go away for us is microbial water quality as it relates to livestock production,” Tate said. “When I arrived at UC Davis in April 1995, I began testifying at the Public Utilities Commission in San Francisco in the midst of an ongoing debate being held in the news media as to whether or not livestock were the source of a protozoan pathogen called Cryptosporidium parvum.”
The pathogen had shown up in the water source and impacted the human health of San Francisco, making it a large concern. At the same time, testing for the species is difficult and expensive, chlorination doesn’t kill the protozoa, and filtration systems capable of addressing the pathogen are expensive.
“From that event, our group started a 20-year journey of trying to understand as much as we could about the ecology and biology of microbial pollutants,” Tate noted.
One aspect of Tate’s research looked at how many microbes are produced in the fecal matter of cattle.
“When we look at fecal coliforms, we see that fresh, right-out-of-the-cow, 10 million plus colony forming units are present per gram of manure,” he said. “A cow produces about 7 trillion E. coli a day. If we look at indicator E. coli, they put out about 1 million or more per gram of feces.”
Looking at Cryptosporidium parvum, Tate noted that 15 to 20 percent of calves at three to four months of age are infected, and they shed the microbe at a rate of approximately 100 eggs per gram.
“Less than five percent of the cows in rangelands have C. parvum, and they shed it at a low rate – about one to 100 eggs per gram,” he said. “That is a small population of cows.”
“We were surprised that indicator bacteria are not correlated to the pathogen at the creek, but they aren’t correlated at the end of the cow,” Tate continued. “E. coli is not a good indicator for pathogen contributions from livestock.”
At the same time, new research has also indicated that the species of Cryptosporidium creating human health problems isn’t the same as that present in cattle.
“With better taxonomic skills and better technology, we went back out and sampled 450 cow/calf pairs,” Tate said. “We found that 14 percent were infected with Cryptosporidium, but zero percent were C. parvum, which was the species we were worried about.”
Though the other species may be minimally infectious to humans, he noted that cattle “might not be the public health threat that we thought. Other scientists still need to follow and confirm this work.”
Tate further looked at the survival of pathogens in the environment, noting that the survival of many bacteria is very poor after leaving the host.
“One of the first best management practices that was voiced when it comes to livestock production and microbial water quality is how far back from water sources do we need to build the fences,” Tate said. “We didn’t know if it needed to be 100 feet or 400 feet.”
A subsequent research project modeled temperature of cattle fecal pats during the day in a variety of conditions. The data was then mimicked in water baths in a laboratory. Known amounts of bacteria were added to the water baths and survival rates were measured.
“If temperatures hit 104 degrees at some point during the day, it only took one day for 90 percent of C. parvum to die,” Tate noted. “At about 78 degrees ambient temperature, fecal pats reached 104 degrees.”
“We get a lot of 78-degree days in California, so we have a lot of days in the spring, summer and fall where the range is acting as an autoclave,” he continued, noting that the only period of concern is during the winter, when cooler temperatures mean that bacteria would survive longer.
Further, Tate noted that once the microbes leave the host, their ability to move in the environment is limited.
“Based on 40 to 50 storm events in 36 runoff plots, we looked at E. coli, Cryptosporidium and Salmonella,” he said. “If we get 16 storm events over the course of the season, 90 percent or more of the E. coli is still in the fecal pat or within 10 centimeters of it.”
Each meter away from the fecal pat, leaching of bacteria and protozoa is reduced an additional 79 to 99.99 percent.
As a result of their findings, Tate said management actions associated are quite simple.
For example, calving in dry areas away from wet corrals and creeks reduces the survival of microbes.
Additionally, Tate commented that because the microbes don’t move away from the fecal pats readily, keeping cattle out of creeks is often sufficient to reduce loading. Fences around creeks and riparian areas only need to be several meters from the banks.
“High stocking rates can lead to increased livestock water loads because there is more fecal matter out there,” he said. “We also need to avoid reduced infiltration due to compaction.”
As water seeps into the soil, filtration is increased, and the prevalence of microbes is reduced.
“I believe in working landscapes, and livestock are an important part of the landscape,” Tate added. “Not everyone in California agrees with me, though.”
University of California, Davis researcher Ken Tate noted that often, indicator bacteria, such as Escherichia coli, are used to determine if water is safe to drink.
“The fecal indicator bacteria are things we regulate on and things that we tend to monitor,” he explained. “We hope that monitoring for those bacteria, which is cheap and relatively simple, will indicate the presence of fecal material and potential for pathogen.”
Tate’s team looked at whether or not such a correlation was true for western rangelands.
After months of research sampling irrigated pastures and meadows, he noted, “We continue to see a lack of relationship between indicator bacteria and pathogens.”
“It is a little disheartening,” Tate commented. “The relationships are a lot stronger in an urban watershed, and if the fecal source is more dominated by humans, the relationship get better.”
However, he noted that they continue to look for a way to detect potential harmful bacteria, commenting, “Maybe it is worth the money to start looking at the actual pathogens we are concerned about.”
Look for information from Leslie Roche’s presentation at the WACD Annual Convention in an upcoming edition of the Roundup.