Skip to Content

The Weekly News Source for Wyoming's Ranchers, Farmers and AgriBusiness Community

Study analyzes targeted grazing impacts

by Wyoming Livestock Roundup

The impact of invasive and poisonous species on rangelands can be detrimental, and livestock species can be severely impacted. As a result, Julia Workman, a master’s degree candidate at University of Wyoming, decided to look into the impacts of targeted grazing to control those species. 

Workman’s study looked at a targeted grazing to control Dalmatian toadflax. 

Inside targeted grazing

“There are a few things to think about when looking at targeted grazing,” Workman notes. “We can control what animal will be grazing, how much time and how many animals we use and the frequency of grazing.”

First, animal selection is important. Not all species graze all plants in the same manner. 

“We want the animals we are using to eat the species we are targeting,” she explains. “If we are looking to reduce cheatgrass, we probably don’t want to select a goat, which only has about 12 percent of its diet made up of grass. If we have shrubs that we want to target, we likely won’t use a cow, which eats 75 percent grasses.”

Since her study targeted forbs, Workman elected to utilize sheep, which consume about 34 percent of their diet as forbs and other browse. 

“Selectivity is the next thing we have to look at,” Workman continues. “Cows can go in and sweep in a whole bunch of grass, whereas a sheep or goat has a smaller mouth and more flexible mouth parts that can select very specific parts of the plant.”

Timing and intensity

She also looked at the importance of timing in targeted grazing efforts. 

“Most plants are generally less palatable over time, as they build more lignin and structural carbohydrates,” Workman explains. “They also increase in susceptibility to grazing, up to a point.”

By selecting the right time for grazing, targeted species can be more effectively grazed. 

“We want to graze our weeds when they are very susceptible to grazing, pretty palatable to our animals and, ideally, when our desirable species are not susceptible and not very palatable,” Workman says. “This can get complicated pretty quickly when we have a whole bunch of species like we often do in our rangeland communities.” 

Finally, Workman mentions that intensity of grazing can also make a difference. 

“Intensity describes how much pressure we are putting on the system,” she adds. 

Dalmatian toadflax

Workman notes that the weed she selected to study has an impact on Wyoming’s rangelands.

“Dalmatian toadflax is a nasty species,” she says. “It is native to the Mediterranean, and like many invasives, it was introduced as an ornamental and has long-since escaped cultivation.”

The weed is considered noxious in Wyoming and 15 North American states, as well as in Canada. 

“Toadflax is spread vegetatively, which makes is super competitive,” Workman notes. “It can also produce a lot of seed. It is perennial and short-lived, so it has a lot of things going on.”

In previous studies, primarily mowing and clipping studies, the impact of grazing has been simulated with varying results. 

“There are mixed reviews on whether we can get an impact on Dalmatian toadflax with enough repetition,” she says. “Another question is, will animals actually eat it? We have observed that they will.”


“We decided to look at targeted grazing compared to herbicides, because that is the standard right now,” Workman says. “We are able to draw comparisons between the two methods.”

The study has been underway for one year, and Workman says they are able to begin drawing some conclusions from the impacts. 

Seven treatments were applied at each of four grazing sites. Four of those treatments were grazing treatments, with varied density and timing. 

“We did a 12-hour grazing treatment in the spring and summer, a six-hour treatment twice in the spring and summer and a four-hour treatment in the spring, summer and fall,” Workman explains. 

Data collection

“We did our main data collection event in mid-summer at peak biomass,” Workman explains. 

Workman counted the number of individual toadflax stems before and after grazing. After grazing, only the stems not impacted by the sheep were counted.

She also measured the height of the plants and recovered biomass at various times. 

“Many of the toadflax stems had the tops bitten off, while others had the leaves stripped or were bent over or crushed,” Workman describes. 


“We really did see impacts on toadflax stems,” Workman continues. “When we increased grazing pressure, we had almost 100 percent of the stems impacted.”

Results in the six-hour and four-hour treatments were slightly less, but still high impact. 

Differences in biomass by weight weren’t detected with as much significance, but Workman notes that may be because often, the heavy, woody stems were left ungrazed. 

“Selective defoliation appears to reduce Dalmatian toadflax growth,” Workman adds. “Grazing may be a useful management tool, particularly in combination with other control measures.”

Further studies will continue into the future.

Targeted grazing

Targeted grazing has become more popular in recent years, says Julia Workman, a student at the University of Wyoming. 

“We hear more about targeted grazing for a number of reasons,” she says. “If we can use animals to control weeds and accomplish those goals using animals, we also get the forage. That is a good deal.”

The grazing strategy also can be more effective in difficult to access, steep or rocky terrain. 

“We like the idea of targeted grazing, in general, because it is very natural,” Workman says. “Many people like the idea of animals on the range eating nasty weeds because it is a natural process.”

“Targeted grazing makes sense economically in some cases, as well,” she adds. “There are studies out there that also show it is effective.”


Workman presented her study during the 70th Annual Wyoming Weed and Pest Conference held in Rock Springs at the beginning of November 2014. 

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

Back to top