Study shows cows prefer grazing clean grass


GPS Collars Help Missouri Researcher Track Grazing Preferences.

A recent study by Kevin Bradley, University of Missouri Extension weed scientist, confirms that cattle prefer clean, weed-free grass when given the choice.
The study tracked grazing patterns across three continuously grazed locations in Missouri. A mix of broadleaf weeds or broadleaf weeds and woody brush infested each site, which ranged from 50 to 100 acres in size.

“We sprayed half of each pasture with herbicides and left the other half untreated,” Bradley says. Depending on the undesirable species present, the site received an application of GrazonNext herbicide or a tank mix of Grazon P+D plus Remedy Ultra herbicide. The herbicide treatment eliminated most of the clover.
A month before spraying, Bradley established the baseline. He fitted three cows at each site with GPS collars to track grazing habits. A special, up-down indicator on the collars documented when the cows were actively grazing. The collars recorded their activity at one-hour intervals throughout the season. Prior to weed control, cows grazed the pasture relatively uniformly and continued to do so during the first month after treatment.

Two months after the herbicide application, grazing patterns shifted. Cows grazed 77% of the time on the treated half and only 23 percent of the time on the untreated area. Those results remained constant throughout the duration of the grazing season. In untreated areas, weeds accounted for as much as half the total forage yield, including clover.

“When we compared the grazing preference data with the weed density data, the cows clearly preferred the treated half of the pasture where there was far less weed pressure,” Bradley says.

Other key findings:
• Spraying improved pasture productivity — nearly 2 pounds of grass replaced every pound of broadleaf weeds and woody plants controlled.

• Pasture utilization improved. Cattle more uniformly grazed the entire treated area, while they avoided weeds and brush on the untreated portion.

• Grass volume remained relatively constant and was greater in the treated area at the end of the season, even though it received most of the grazing pressure.
Cows apparently prefer weed-free grass more than they do a weedy pasture that contains clover.

Bottom line
When weed density is significant, spraying presents a real opportunity to improve productivity.

“We see the grass production increase,” Bradley says. “We likely can increase our carrying capacity as well.”
Solve a weed problem first and then bring back the clover, he advises. Many soils will have a native supply of seed that will produce a year after you stop spraying. If not, spend a few dollars and seed new clover into the system.

To learn more about Bradley’s work, visit

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