K-State graduate student explores cattle grazing as invasive grass management tool

Growing up on a Nebraska cow-calf operation, Tasha Macholan saw how drought and changing pasture conditions could complicate livestock management.

Now a Kansas State University graduate student in the Department of Animal Science and Industry, she is studying whether one routine management decision — where producers place cattle supplement — could improve calf performance while helping manage invasive Old World bluestem.

"I became really passionate about working to mitigate drought effects through cattle management and looking at pasture health overall," Macholan said. "The past few years have been difficult for producers with varying weather and drought conditions."

Macholan recently earned her bachelor's degree in animal science from South Dakota State University. She is now a second-year master's student at K-State studying ruminant nutrition with a focus on rangeland management.

Her research at K-State's Agricultural Research Center-Hays — under the guidance of Professor KC Olson and in collaboration with Keith Harmoney, professor and range scientist, and Emma Briggs, assistant professor and beef cattle systems specialist — brings those interests together by examining both animal performance and pasture response.

A practical pasture question

The roughly 150-day grazing season in western Kansas can be divided into early and late periods. As native forage matures later in the season, its quality declines, often limiting cattle gains. Protein supplementation can help calves continue gaining weight during that period.

Macholan's project examines dried distillers grains, a protein-rich byproduct commonly used in cattle diets.

Previous K-State research compared distillers grains fed in bunks with feed delivered directly on the pasture surface.

Feeding directly on the ground may be more practical in remote or difficult-to-access pastures, but cattle searching for the supplement also trample, graze and disturb the vegetation beneath them.

That disturbance prompted a new question: Could producers direct it toward patches of Old World bluestem, an invasive grass that competes with desirable native species?

"There have been studies looking at burning it and using chemicals to control it," Macholan said. "My project is a little bit different. We're looking at on-ground supplementation."

Old World bluestem was introduced for forage production and soil conservation, but it can spread quickly and form dense stands. It also matures earlier than many native grasses, becoming less palatable as the season progresses. Cattle may avoid it while grazing desirable native plants more heavily.

"You start to see it take over areas in the native grass," Macholan said.

Directing cattle to targeted patches

The multi-year study uses approximately 100 fall-born stocker calves divided among eight pastures, averaging about 34 acres each.

During the latter half of the grazing season, cattle in six pastures receive dried distillers grains twice per week. Three groups are fed in bunks, while the supplement for the other three is placed directly on the ground. Two additional pastures receive no supplement and serve as controls.

Within the ground-fed pastures, Macholan identified patches dominated by either Old World bluestem or blue grama, a desirable native shortgrass. Those areas were divided into weekly feeding plots, with supplement placed in the center of a different plot during each of the study's 10 weeks.

Once the feed reached the ground, the cattle concentrated around it.

Images taken before and after feeding show clear sections where tall, mature Old World bluestem had been grazed and trampled nearly to bare soil. The cattle consumed vegetation they would ordinarily avoid at that stage of maturity while searching for the dried distillers grains.

"They were basically taking it down to the bare soil in those areas," Macholan said. "It was interesting to see them eating a grass species they don't usually touch thattime of year."

Following the cattle and the grass

Macholan tracked calf weights when the animals entered the pasture in May, before supplementation began in July and again at the end of the grazing season in October.

She also measured changes in the plant community.

A falling plate meter helped estimate forage height and biomass, while clipped vegetation samples were dried and weighed to calculate forage yield. Macholan also used gridded frames to measure how frequently blue grama or Old World bluestem appeared within each plot and recorded plant cover and bare ground.

The first year's results showed that supplemented calves tended to gain more than calves that received no supplement. The cattle fed on the ground performed similarly to those fed in bunks, suggesting that ground feeding did not cause a measurable loss in gain or feeding efficiency during that year.

The vegetation response was particularly notable.

Old World bluestem initially appeared in an average of about 74% of the small sampling squares within its designated plots. Its frequency declined to approximately 45% after the supplementation period and fell further when researchers evaluated regrowth the following year.

Macholan said the heavy grazing and hoof action exposed the plants' roots, potentially making the less cold-tolerant invasive grass more vulnerable during winter.

The following spring, cattle also returned readily to the previously disturbed patches.

"The areas that were grazed on the ground were a lot greener and a lot shorter," she said. "The calves were drawn to them more."

Looking beyond one season

For producers, the question extends beyond whether calves gain weight.

Feeding directly on the ground may reduce the need to transport, place and maintain bunks in difficult pasture locations. But producers also need to understand how that practice affects desirable native grasses, invasive species and long-term pasture productivity.

"How is feeding on the ground versus bunk feeding going to affect your efficiency and gain in your calves?" Macholan said. "And then, looking at long-term pasture management, how is this going to affect the pasture and its growth? Could it help control invasive species like Old World bluestem, or will it negatively affect native grasses?"

Because the research is continuing across multiple years, Macholan is careful not to draw broad conclusions from the first season. Additional groups of calves and repeated vegetation measurements will help determine whether the initial reduction in Old World bluestem persists and how native grasses respond over time.

"The next year is really going to be the big part of the project," she said. "We'll see what grows back, how the grass and ground were affected and what happens to the biodiversity."

A new side of Kansas agriculture

The Agricultural Research Center-Hays gives Macholan the opportunity to study those questions in the same shortgrass and native rangeland systems western Kansas producers manage.

"It gives you a more diverse side of Kansas agriculture than what you see around Manhattan," she said. "It's native grasslands and shortgrass pastures, and it's very different from what I grew up with in Nebraska or even South Dakota."

She said the center's facilities, pastures and staff have helped her translate her interest in cattle nutrition into research that considers the entire grazing system.

"It's been awesome working out here," said. "The people at the station are wonderful, and the setup has been really great for me and my research."

For Macholan, that is the larger purpose of the project: developing management strategies that account for calf performance, pasture health and the uncertainty producers face from year to year.

"I grew up with a cow-calf background," she said. "Over the years, I became passionate about mitigating drought effects through cattle management and looking at pasture health overall."