Cows and Water Quality

It's a long-held belief of pasture management: Give cattle access to streams and they will stir up a nasty brew of fecal matter, biological contamination, sediment and nutrient loadings. The solution to watering cattle has been to pump it upland to troughs located away from the streams and creeks.

Jim Russell, professor of animal science at Iowa State University, has been working to develop cattle- and pasture-management practices that allow cattle to drink from the streams but also encourage them not to lounge in the water. Russell and his research team have come upon these ideas by observing through GPS collars cow location in a given area of pasture. From those observations, they have evidence showing that a well-designed pasture-management plan may allow cattle access to streams and creeks with minimal damage to water quality. What's more, these management practices are competitive with the cost of exclusion fencing and water pumps.

NOT SO MUCH

In 30-acre pastures on a farm in south-central Iowa, Russell's team has found that cattle really don't hang out in the water as much as expected.

"The [percent of time] they are in the water is lower than people might think," Russell said. During the summer, with full access to the stream, the cattle Russell's team tracked spent about 2% of the time in water. Even during the hottest summer months, they averaged 4% of their time standing in the stream. At night, the cattle tended to stay out of the water. Russell also found the cattle in these pastures spent no more than 14% of their time within 110 feet of the stream.

Further experiments have shown the impact of pasture size on these measurements. Cows in smaller, 10-acre pastures spent more time in the water, nearly 10%, and close to 30% of their time within 110 feet of the stream.

Near the water, not in it. When the cattle are confined to riparian (streamside) paddocks -- in this study, 110-foot strips on both sides of the stream ­— for limited periods of times as part of a rotational grazing system, they spent no more than 0.2% of their time in the water. But limiting the time spent there is important. The cows can create nutrient, erosion and runoff threats to the quality of the water if they are allowed to graze in a piece of pasture long enough so that they create bare spots and allow manure to accumulate.

By limiting the grazing along the streams -- Russell calls it "flash grazing" -- the damage is greatly reduced. Flash grazing means the paddock is never grazed more than four days, and the grass is grazed no lower than 4 inches in height.

The proximity of the cattle to the stream bank does not seem to create a significant erosion problem as long as access is managed. Cutbank erosion to streams, Russell argues, is due more to the velocity of moving water than to grazing.

To test the idea, Russell designed a stabilized crossing structure that allows cattle limited access to streams. These are crossings stabilized with a fiber mat and polyethylene webbing, covered with stones. The crossings are about 16 feet wide, with electric fencing along the sides. Beyond the limits of the fencing are grassed buffer strips to control precipitation runoff. Fenced lanes, a couple of hundred feet long, lead up and away from the crossing.

CONSIDER THE INVESTMENT

In 2004, construction of a 16- by 80-foot crossing cost $4,347, not including labor. The cost for 6-inch webbing is still $1.50 per square foot today, as it was then. The price of the other crossing supplies also have changed little in the years since. Additional investments in crushed rock are necessary to maintain the crossings annually.

In comparison, installing underground PVC pipe and frost-free faucets to bring water to the cattle costs about $2.30 per foot.

With the crossing installed, Russell found the cattle spent little time (less than 1%) actually standing in the water. "They drink and move on," he said. "The stabilized crossing seemed to be effective when used with the riparian buffer, whether in large or small pastures."

Russell has tested stream water flowing into and out of an area of managed pastures on 13 cooperating farms in southern Iowa. He finds little difference in water quality.

This does not mean the water is uncontaminated, only that those cattle don't appear to be a new and significant source of contamination under managed grazing programs. Russell does believe that upstream contamination, when no cattle are present, may come from wildlife, companion animals (horses, dogs), humans and their septic systems.

Furthermore, there was no correlation between streambank erosion and the stocking rate of the pasture, further demonstrating the greater importance of stream hydrology on bank erosion than grazing.

SHADE FACTOR

On five of these farms, Russell observed that major factors affecting the time cattle spent in streams were the size, shape and shade distribution in a pasture. In a subsequent study, as temperatures increased, cattle preferred to locate in upland shade in 30-acre pastures, but preferred to locate in riparian shade in 10-acre pastures. So, while management practices utilizing fencing to keep cattle out of streams may be useful in small pastures, they are less important in large pastures.

Russell's research is financed by the USDA Cooperative State Research, Education and Extension Service (CSREES) and the Leopold Center for Sustainable Agriculture. Also working with Russell are Mat Haan, former research associate, and Doug Bear, Kirk Schwarte and Justin Bisinger, former graduate students at Iowa State University.

BUILD A STREAM CROSSING

Here's a way to limit your cattle to a single stream crossing. Consider locating the crossing away from mineral- and hay-feeding areas, as that might encourage the livestock to loiter near the stream.

This particular crossing was designed by a county office of the Tennessee Natural Resources Conservation Service (NRCS). This design calls for smoothing out steep slopes so the creek could also be crossed with equipment.

The plan called for excavating an 8-inch-deep path across the bottom of the creek. Then geotextile fabric was placed on the bottom of this path and anchored into the stream bed with pins and 1.5-inch rocks. These rocks were topped off by a 2-inch-thick layer of smaller, crusher run rocks. Cattle are reluctant to walk over large rocks, so the fine rocks used in this crossing encourage cows to quickly cross

the stream.

The size of the rock needed is determined by stream flow. The heavier the stream flow, the bigger the rocks need to be. This crossing, for example, was designed to withstand an intense, once-in-25-years storm, as calculated from weather history for this part of Tennessee.

NARROW CROSSING

If possible, it's best to locate stream crossings in the narrower portions of a stream. Crossings about 8-feet wide will keep cattle from loitering. Although, if you want the ford to accommodate equipment and livestock, its width may have to be adjustment to allow for that dual use.

Several conservation programs, such as the Environmental Quality Incentives Program (EQIP), may provide cost and engineering assistance for building stream crossings. Contact the NRCS office in your area for more information.

(VM/CZ)

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