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ISU studies ‘mob grazing’

By Staff | Dec 9, 2011

Angus cattle munch on fresh grass in a paddock during a mob-grazing research project at Iowa State University.

AMES (LCSA) – Four times a day, Margaret Dunn walks out to a field at the Iowa State University Beef Nutrition Farm, strings electric wire around a new strip of pasture, and whistles for the cows.

Dunn is an ISU graduate student researching the effects of mob grazing, a strategy for improving the quality of a pasture by stocking a large number of cattle for a short period of time.

The project, led by ISU Department of Animal Science professor Jim Russell, received funding from the Leopold Center for Sustainable Agriculture’s Ecology Initiative in 2010. It is featured in a new Leopold Centervideo, “Cattle Grazing for Healthier Pastures.”

“One of the keys to sustainability is to have perennial forage on the ground,” Russell said. “In order to maintain and increase the amount of land that we have planted in perennial forage, we need to find ways to increase the profit that we can obtain by it.”

Profitable cattle production offers an incentive to landowners to keep land planted in perennial forages, which offer year-round benefits for soil, water and air quality. However, grazing management is key.

The mob grazing system features running cattle on small paddocks and moving them four times daily.

In continuous grazing systems, cattle will select the most palatable plants to eat, resulting in a decline in forage productivity. Cattle graze less selectively when they “mob” a small pasture. This “high-intensity, low-frequency” system provides more balanced pasture utilization and fosters plant diversity.

Management-intensive grazing systems are increasing in Iowa.

In 1992 only one percent of the state’s cow-calf producers used a grazing system that required cattle movement once a week. That number has risen sharply in some regions of Iowa, according to a recent survey of 27 cow-calf producers conducted by one of Russell’s graduate students, Angela Richardson. Richardson found that 60 percent of the surveyed producers in western Iowa graze intensively, as do 75 percent in northeast Iowa.

Richardson points out that rotational grazing has the potential to ease the strain of limited land availability because it increases forage production and allows higher stocking rates. In southeast Iowa, 100 percent of the surveyed producers cited the lack of available land as the most important factor limiting their expansion, but only 14 percent of the surveyed producers rotate cattle in intensive grazing systems.

Russell’s project at the ISU Beef Nutrition Farm can help close this gap. The project compares three types of management-intensive grazing systems: mob, strip and rotational. Each 10-acre tall fescue pasture, seeded with red clover, is stocked with 10 fall-calving Angus cows in the spring. Mob grazing cattle move to a new strip of pasture four times a day, compared to strip grazing (once daily) and rotational grazing (once every few days).

Dunn explained that the cattle in each experiment receive the same amount of forage each day, but at different times. In mob grazing, she said, “they get four meals a day as opposed to one big meal a day, or a whole acre of land every several days.”

The researchers monitor the weight of the cows and calves, take forage samples, and measure the selectivity of grazing. They also sample the soil to assess carbon content, compaction and water infiltration. Studies suggest that mob grazing improves the quality of the pasture by increasing legumes, evenly spreading manure, minimizing soil erosion and maximizing carbon sequestration. In another Leopold Center project at the ISU McNay Research and Demonstration farm in south-central Iowa, Russell is studying the potential of mob grazing to improve wildlife habitat.

“In the end, this has to make economic sense,” Dunn said. The research will help provide vital information to cow-calf producers about the costs and rewards of mob grazing and other management-intensive systems that aim to create successful, sustainable operations in Iowa.

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