Sheep grazing targets larkspur

Poisonous plants can present many challenges to livestock producers. In Wyoming, larkspur, locoweed, halogeton and death camas are a few examples of dangerous plants found on rangelands.  

New University of Wyoming (UW) research utilizes grazing practices to target one of the most toxic plants to livestock – larkspur. UW Sheep Extension Specialist Whit Stewart and UW Rangeland Extension Specialist Derek Scasta, as well as Graduate Student Hannah Fraley began studying the ability of sheep to remove larkspur from the landscape through grazing.  

“Larkspur is one of the most problematic toxic plants in the West because it is native on some of our public lands,” Scasta explained to producers at the Wyoming Stock Growers Association (WSGA) Winter Roundup on Dec. 13. “We can’t just go spray with herbicide, as it is not always effective or economical. So, we’re trying to understand integrated sheep and cattle grazing.”  

Grazing research 

This study originated as previous research noted sheep have a greater tolerance of alkaloids, a toxic chemical compound found within larkspur plants. In fact, sheep’s tolerance of the compound is roughly four to six times the tolerance of cattle – in other words, sheep are about four times as resistant to avoid alkaloid toxicity over cattle.  

In addition to differences in toxin tolerance, Scasta and Stewart shared sheep have different dietary preferences compared to cattle.  

“Sheep are more willing to eat weeds, shrubs and forbs,” Scasta said, adding to the rationale behind this study.  

The sheep on trial, provided by WSGA Young Producers Assembly President Sage Askin, grazed at multiple sites across the High Plains Grassland Research Center outside of Cheyenne where larkspur was prevalent. Scasta noted in early May, when the grazing period began, vegetation was sparse and livestock are not allowed as much dietary diversity.  

“Livestock consume higher amounts of larkspur because at this time of year, it’s the most vegetated plant,” Scasta said. “This is when those toxicity events occur.” 

One goal of this research was to determine if sheep could safely and efficiently graze to remove larkspur and decrease the risk of toxicity to cattle grazing the same land. In what these researchers called “integrated grazing mitigation strategy,” yearling cattle grazed the same plots following the sheep.  

“One of the challenges we have in controlling this invasive species is how we target it in a significant time of year where the burden of the plant can be reduced without decreasing the stocking rate,” noted Stewart.  

Study results 

In the early parts of the growing season, Scasta and Stewart shared the toxicity of larkspur is higher as alkaloids concentrate in the flowers and pores. This, along with the maturity of other vegetation in the area, made it difficult to target larkspur on the scale the researchers were looking for. 

“It takes a lot of pressure early on for us to get the sheep to consume larkspur,” Scasta shared.  “The other aspect is palatability increases as the stage of maturity goes up, so we really had to put a lot of grazing intensity on plots to get animals to consume larkspur.” 

Stewart added, “Getting the grazing pressure early on required a lot of sheep, and larkspur was not the first plant sheep sought out in the early vegetative stage.”  

Though later in the season, sheep appeared to have a higher preference during the bud and flowering stages.  

Throughout the season, Fraley tracked larkspur response to grazing, measured bite counts and took plant samples to determine alkaloid concentrations at different stages, as well as other data collection efforts including sheep weights. 

Data from the first year of the study suggests sheep grazing from mid-May to late-June didn’t display any symptoms of toxicity, and sheep gained on averaged 12 pounds throughout the six-week study. A figure Scasta shared during the presentation highlighted larkspur prevalence before and after targeted sheep grazing and showed post-grazing larkspur prevalence was negligent.  

“By the time yearling cattle came on, there was regrowth of other vegetation and there wasn’t any loss of capacity for the yearling cattle operation,” Scasta explained.   

“Moving forward, our hope is to not only understand how we can use this as a biological control tool, but also characterize the health and well-being of sheep. So in these co-grazing situations where stockers go through afterwards, we know what kind of benefit there is,” Stewart added. 

Averi Hales is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.