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Environment
A study conducted by Nevada researchers confirms what rangeland users have long suspected, but myths have claimed otherwise: cattle don’t actually spread invasive cheatgrass across the West through grazing. In fact, their digestive process breaks down cheatgrass seeds and effectively renders the seeds unable to germinate.
A group of researchers from the University of Nevada, Reno, published a study in the August edition of Rangelands that evaluated whether cattle spread cheatgrass seed via excrement. Results showed that not only does cheatgrass not spread through cattle’s digestion processes, but cheatgrass seeds consumed in the fall will have a slight lag in microbial degradation.
“Thus, we can conclude that seeds consumed while target grazing in the fall will be subjected to prolonged periods of ruminal fermentation, effectively eliminating germination while reducing the seed bank in afflicted areas,” the researchers wrote.
The Public Lands Council (PLC) called the study the perfect example of common sense meeting environmental realities.
“What we see in the West today is a perfect storm of mismanagement and misinformation, and this study is a huge step in the right direction in applying real solutions to real problems, like late season grazing on cheatgrass stands,” said PLC Executive Director Kaitlynn Glover.
Glover continued that if seeds can’t survive the digestion process, cattle are the ideal grazing tool. Not only does grazing reduce fuel buildup to reduce fire risk, but it also neutralizes seeds to prevent regermination and provides organic matter to support native grass stands.
“Thank you to the researchers that took the time to conduct this labor-intensive study and prove that grazing is the best conservation practice for our western landscape,” Glover said.
Study details
The spread of cheatgrass on rangelands has proven to have major implications on native ecosystems and agricultural productivity. The grass rapidly spreads and leads to an abundance of fuel buildup, increasing the risk of wildfires and limiting forage sources for livestock grazing.
Recent studies have tried to link the spread of cheatgrass to cattle grazing, but the Nevada researchers suggested that targeted grazing effectively reduces cheatgrass fuel height and seed bank without adverse impacts on the ecosystem.
In the in situ ruminal incubation portion of the study (seeds were inserted into the rumen of cannulated steers), noteworthy patterns were observed in the germination response over time in the rumen, the researchers said.
Cheatgrass seeds collected in the spring and in the fall showed a steady decline in their breakdown as time in the rumen increased. After 36 hours in the rumen, the seeds showed nearly a complete lack of germination.
“This suggests a critical timepoint beyond which the ruminal environment becomes detrimental to seed viability,” the study read.
Seeds collected in the fall also took longer to break down and stayed intact for a longer duration than spring-harvested seeds. This is because the mature cheatgrass in the fall is a lower-quality forage, which leads to longer retention times in the rumen and slower passage rates.
The study authors do note that while the lack of seed germination in the fecal germination trial is promising, there are still factors to consider. “Nevertheless, our findings offer a deeper insight into the detrimental effects ruminal conditions have on cheatgrass seed and may ease concerns surrounding cattle as endozoochorous cheatgrass dispersal agents,” the authors concluded.
The study was funded by a grant from the Bureau of Land Management, Nevada State Office. — Anna Miller, WLJ managing editor
