RHODES – Doug Bear engaged the four-wheel drive of the Iowa State University pickup truck, apologized in advance for the bumpy ride, creeping in low gear down a pasture drive deeply rutted from the recent heavy rains.
He continued his dialogue. “We have 30 acres, divided into six pastures, each managed differently. Some of the pastures give the cows unlimited access to the stream and two restrict access to 16-foot-wide crossings.
“These are all fall-calving cows, which is good because it gives us a good three months of data without the cows having a calf on them.”
Bear is a graduate student assisting ISU animal science professor Jim Russell in a study that determines how long cattle actually spend in or around a stream bed and determine what factors lead the cattle to spending time in the water.
The study is also looking at stream bank erosion with the cattle given unlimited access to the water, compared to bank erosion in restricted pastures.
Another portion of the study is simulating rainfall, assessing the amount of nutrient runoff from bare ground into the nearby stream.
Russell has been studying cattle water source preferences for three years as part of a research project supported by the Leopold Center for Sustainable Agriculture. He uses global positioning systems attached to cattle collars to track each animal’s movements within a pasture over two-week periods of time.
“There are three cows with the collars per pasture,” Bear explained, “just in case there is trouble with one.”
Each GPS device takes six readings of the cow’s position each hour, tracked by 26 satellites throughout the day. The information is recorded on a computer chip. The three C-cell batteries last just two weeks, Bear described, so the collared cattle are round up, led to a cattle barn where the batteries are changed and the information on the chip is downloaded into a laptop. The chip is reinserted and the cows are led back to their appropriate pastures.
“It only takes about 10 minutes to do this part,” Bear said, “but a lot longer to bring the cattle up as gently as possible and take them back.”
“We wanted to find out how much time cattle really were spending near waterways and if they were, why,” said Russell. “After three years, we noticed that they don’t spend nearly as much time in or near the water as people generally think.”
Bear said that a similar project in southern Iowa found cattle spending just 2 percent of their time in or by the water. Which was an encouraging discovery, he added, “because where the cows are, they excrete their nutrients.”
Nutrients is academia speak for manure.
The location of cattle in relation to creeks or other sources of water is important information for the Leopold Center’s grazing research program. It was assumed that cattle in pasture-based systems are large contributors to the levels of sediment, nutrients and pathogens found in surface water.
Findings showed that the amount of time cattle spend in waterways varies according to specific pasture conditions. For example, size and shape are most important and smaller pastures generally mean more time in the water. But if all pastures are the same size, the shape will determine how long animals stay in the water. If all pastures are similar in size and shape, then shade placement becomes an important variable that influences more or less time in waterways.
Bear said that so far research indicates that shade and ambient temperature doesn’t play as big of a role in cattle standing in water as does the size of the pasture. “The smaller the pasture, the more often they’re in the water,” Bear said.
Staked along the creek banks are white fiberglass rods posted 100 feet from each other, originally staked 5 feet from the edge of the stream bank. There are also fiberglass pins insert at one-foot levels from the foot of the bank to its top.
Periodically, the rods’ distances from the bank are measured; and pins’ locations are noted.
“So far,” Bear said, “it seems that the rate of erosion is the same, whether the cows have access to them or not.”
There is evidence of fresh erosion in both restricted and unlimited access pastures.
“We think its more hydrology than it is the cows,” Bear said.
Placed strategically in what Bear called pasture 2 is a weather station continuously measuring several atmospheric activities including ambient temperature, humidity, wind speed and direction and precipitation.
Setting close to the measuring devices is a black globe attached to the top of pole. The globe is about 4 feet off the ground. Bear said this device measures the solar radiation in the ambient temperatures. It replicates, he added, how the ambient temperature feels to the black cattle. Researchers are watching to see if these solar impacts cause the animals to seek the water or shade
Up above the weather station is what Bear described as “an off-stream water source.” That’s research speak for a water tank. Half of the tank gives unrestricted access to the cows in pasture 1, while the tank in pasture 2 has a gate that can block water from the cattle. On this day, the gate was closed, meaning the only source of water for the herd in pasture 2 was the stream.
Bear said the reason for the gate is to determine if the cattle are opportunistic water drinkers or if they prefer the stream to the standing water in the tank. Opportunism seems to the key factor, Bear indicated.
“Actually I have seen them just drink out a puddle after it rained.”
For the past two years, Russell and various assistants have conducted what they call rainfall simulations in the months of April, June, August and October. This involves a device set up on bare ground with water falling on it for 90 minutes. The runoff is sampled to see how much nutrient reaches the stream from bare ground.
In the trials performed in southern Iowa, Bear said, by touring 13 producers’ fields, they confirmed that the ratio of bare ground is created by herd size. And the larger the bare spot, the more nutrient-ladened runoff reaches the water.
“We’re trying to answer everyone’s questions,” Bear said. “If they ask ‘did you try this?’ we can say, ‘yes we did that.'”
What to do
Russell believes that cattle producers can take several steps immediately from what he’s learned through his research.
“Creating buffer strips between pastures, providing off-stream water sources or stable crossing points, or using rotational grazing are good places to start,” he said. “The size and shape of pastures does matter, and cattle don’t spend as much time in the water as we hypothesized so other factors may be contributing to the water quality, such as wildlife or even septic tank leakage.
“Sediment in the water is caused more by the hydrology than by cattle kicking it around.”
Contact Larry Kershner at (515) 573-2141, Ext. 453 or by e-mail at firstname.lastname@example.org.
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