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UW graduate student studies free-roaming horse adaptations

by Wyoming Livestock Roundup

 The Bureau of Land Management (BLM) estimates approximately 95,114 wild and free-roaming horses across 10 western states as of March 1, 2020. The population in Wyoming is estimated at 8,706 horses. 

Wild and free-roaming horses have adapted to many different environments, including areas with low forage availability, according to Courtney Buchanan. 

Varying environments

Buchanan, a graduate student at the University of Wyoming (UW) in the Department of Ecosystem Science and Management, is working to understand how gut microbes in wild and free-roaming horses adapt to different environments and if certain microbe populations encourage greater body condition. She graduated with a degree in animal science from Utah State University before coming to UW to continue her education. 

Buchanan collected fecal samples from horse populations in 15 different BLM Herd Management Areas (HMAs) this summer. The samples will provide information on what kinds of plants the horses consume and what bacteria is present in their digestive system. 

HMA environments in her study range from grass-dominated ecosystems to riparian areas and from pinyon pine and juniper ecosystems to the Mojave Desert and shrub/grass environments. 

“Horses have overpopulation issues in many areas,” Buchanan explains. “We want to learn how these horses are adapting so well to their environments.” 

Body condition 

Buchanan’s study also compares horse body condition score to the amount of forage available or herbaceous cover.  While collecting fecal samples, Buchanan scored the horses based on visual appearance of bones and fat cover. 

“In our preliminary results, there is a slight trend that environments with higher herbaceous cover contain horses with higher body condition scores,” Buchanan explains. 

The score for most horses fell in the moderate range. 

The study relates body condition to forage species richness and diversity, according to Buchanan. 

“Horses are generally thought to eat a diet of mostly grass,” notes Buchanan. “There have been some studies in the past showing horses eating high amounts of different forbs and sometimes browse.” 

Logically, inadequate grass supply leads to lower body condition scores, according to Buchanan. She also will determine if the horse diet consists of a greater proportion of browse where herbaceous cover is less. 

Seasonal work

Buchanan hopes to be revisit the same HMAs this winter to determine potential seasonal diet shifts from summer to winter associated with shifts in the fecal microbiome. 

“We have the potential to see a greater difference in microbial communities coinciding with seasonal diet shifts,” she shares. 

Buchanan’s study is part of a grant studying the gut microbiome of other species, including pronghorn and mule deer and the toxin tolerance of these species to connect information to different demographics.

Buchanan is advised by Dr. Jeffrey Beck, a professor in the Department of Ecosystem Science and Management. Beck’s research focus is wildlife habitat ecology and restoration ecology with a focus on restoring function and structure of wildlife habitats in disturbed rangeland systems, with particular focus on sagebrush habitats. 

The project is funded by the Genomes Underlying Toxic Tolerance–Community (GUTT-C) Grant Program with Boise State University and the University of Nevada–Reno as major collaborators with UW. The research team would like to thank the National Science Foundation (NSF) Track Two Wyoming Experimental Program to Stimulate Competitive Research (EPSCoR) Program award number OIA-1826801 for support. 

Averi Hales is the editor for the Wyoming Livestock Roundup. Send comments on this article to

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