The finding was contained in a report released by the Unwanted Horse Coalition into the survey, conducted by an independent market research company.
The coalition says its study is the first of its kind to assess the causes and magnitude of the unwanted horse population in the US.
More than 90% of participants believed the number of unwanted horses, as well as those neglected and abused, is increasing.
Among respondents, 87% felt that in the past year, the issue of unwanted horses had become "a big problem", compared with 22% who said the problem was important three years ago.
Respondents also reported that the number of horses being euthanized is increasing.
The poor US economy was considered to be a significant contributor to the unwanted horse problem. The closing of the nation's processing facilities, changes in breed demand/indiscriminate breeding, as well as the high costs of euthanasia and carcass disposal are also cited by respondents as major contributors.
Exploring placement options, 63% of equine rescue/retirement facilities polled reported they were full, or nearly full, and, on average, turned away 38% of the horses brought to them.
Survey respondents believe the top solutions for solving the problem of unwanted horses are to educate owners to purchase and own responsibly, increase the ability of private rescue and retirement facilities to care for unwanted horses, reopen US processing plants, and increase options and resources for euthanizing and disposing of unwanted horses.
"One of the highlights of the survey is the willingness by all respondents to resolve the unwanted horse problem," said Tom Lenz, chairman of the coalition.
"We believe these findings will be useful in identifying common ground for all interested groups and aid us in developing solutions that will have a profound and lasting impact on the lives of unwanted horses and the horse industry at large."
The survey was conducted from November 2008 to January 2009.