The wild horses share their habitat with many native animals. They found their way into balanced ecosystems and upset that balance. During lush years, there was enough food and water for all the animals. However, when times were hard, they not only ate much of the food needed by other grazing animals, but they destroyed much of the plant base in their desperate effort to get enough food. Thus, in an unmanaged state, the horses could (and did) have a very negative impact on the ecology of many areas.

In the better grazing areas the horses competed with another "introduced species;" beef cattle. The west has had a long standing tradition of growing beef cattle on rangeland. Being more active than cows, horses eat more food. The cattle ranchers are well aware of this fact and therefore for their personal financial interests, they saw a need to keep the growing numbers of horses in check.

"The biggest problem with the wild horses is that as a reintroduced species, nature had not developed all the necessary checks and balances in the ecosystem to deal with them."

Before 1971, there were few controls in place as to how wild horses would be managed. They were considered prairie pests. They were hunted and captured by whomever wanted to go after them. Cowboys known as mustangers would would gather them up by the thousands, oftentimes using cruel methods. A handful would be saved for riding horses and rodeo stock, but the balance would be shipped off to the slaughterhouses.