![\"\"](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/image-edited.jpeg\")
Horse manure. (Courtney Buchanan)<\/p>\nTouring the West during the height of the COVID pandemic, Courtney Buchanan lived out of her truck, slept wherever she ended up and lived off propone-stove-cooked meals.<\/p>\n
The then-University of Wyoming researcher was a nomad with a purpose, combing Western rangelands for free-roaming horses and the dung they left behind in search of clues about what they were eating and how they were faring. During surveys across seven Western states, she was struck by how the animals were consistently in good shape. She found the fattest horses in the Bighorn Basin, not far from home.<\/p>\n
\u201cThe McCullough Peaks horses were in the best condition out of any of the horses I visited,\u201d Buchanan told WyoFile. \u201cIt was wild to me, being out on the range, seeing them. Some of them are actually overweight \u2014 fat, chunky horses.\u201d\u00a0<\/p>\n
Horse manure. (Courtney Buchanan)<\/p>\n
The findings of Buchanan\u2019s recently completed study help explain why. The University of Wyoming Ph.D. graduate examined the composition of horses\u2019 diet, how much it varied by season, and how much it varied from one reach of the equines\u2019 Western range to another. She found great variation on all fronts.\u00a0<\/p>\n
\u201cOur big takeaway was that in different environments and different places and in different seasons, they can really switch up what they\u2019re doing and still be successful,\u201d Buchanan said. \u201cIf they\u2019re able to vary their diet that much and still maintain body condition, that sets them up for success.\u201d\u00a0<\/p>\n
The dietary flexibility, she said, could help explain why rangewide free-roaming horse and burro populations are \u201cso high\u201d \u2014 at roughly 73,000<\/a>, they number nearly three times land managers\u2019 goal.<\/p>\n Buchanan studied under UW ecology professor Jeff Beck, who\u2019s researched free-roaming horses for a decade, including how the large herbivores are negatively influencing sage grouse survival rates<\/a>.\u00a0<\/p>\n The study on diet and body condition, which looked at 16 herds in seven states, was recently published<\/a> in the journal of Rangeland Ecology and Management. In their concluding remarks, Buchanan and Beck suggested that range managers could use their findings to help strike a balance between free-roaming horses, livestock and wildlife.\u00a0<\/p>\n \u201cWhile studies in individual locations and a meta-analysis of western North America<\/a> have indicated low potential for direct dietary competition with free-roaming horses and wild ungulates that consume woody species such as mule deer and pronghorn, our findings indicate that there may be more potential for dietary overlap and competition during winter,\u201d they wrote.<\/p>\n Going into the study, the ecologists sought to test the common view that horses are true grazers. Old research from the 1970s had found that horses in most herds ate predominantly grass, Buchanan said, though there were some exceptions and herds that also concentrated on other plant families.\u00a0<\/p>\n In the lab a half century later, Wyoming researchers tested the horse manure Buchanan collected using a technology called DNA metabarcoding. That technique narrowed the contents of the feces down to the plant family level, though results weren\u2019t accurate enough to reliably predict the species, Beck said.\u00a0<\/p>\n Buchanan found that some herds fit the horses-are-grazers reputation. For example, the Adobe Town Herd \u2014 part of the historic \u201ccheckerboard\u201d horse dispute<\/a> \u2014 ate predominantly Poacae, the grass family, regardless of the season. But diets varied wildly and, in many places, grasses were less than half of horse diets, especially in the winter.\u00a0<\/p>\n \u201cEach herd\u2019s kind of doing a different thing,\u201d Buchanan said.\u00a0<\/p>\n The plump McCullough Peaks horses, for example, homed in on legumes in the summer, but come winter switched to eating more from the Chenopodiaceae family \u2014 spinach-adjacent plants \u2014 than anything else.\u00a0<\/p>\n![\"\"\/](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/DSCN4167-scaled.jpg\")
Horses from the Adobe Town Herd in the winter of 2020-21. (Courtney Buchanan)<\/p>\n![\"\"](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/Herd-diet-composition-summer-and-winter.jpg\")
What wild horses eat varies dramatically, both seasonally and across their range, as illustrated in this graph of 16 herds\u2019 diet composition. Summer is up top, winter is down low and the scientific names of plant families are on the legend at right. (Rangeland Ecology and Management)<\/p>\n