A wild horse herd in Wyoming. © BLM
Equine Welfare Alliance spokesman John Holland described some of the plans laid out by the Bureau of Land Management (BLM), which is responsible for the wild herds, as bloodless genocide.
"The reckless abandon with which the BLM has accelerated its gather programme is breathtaking," Holland said.
"It has, however, had one effect that nobody could have predicted. It is so outrageous and unjustified in its implementation and so staggering in its consequences that it has galvanised and united the entire wild equine community to a level we have never seen before."
The Equine Welfare Alliance, an umbrella organisation representing more than groups, has called for a moratorium on wild horse gathers.
A recent Associated Press report suggests BLM officials have rejected the idea.
The alliance will now consider its legal options.
Holland said the equine welfare community in general and the wild equine advocates, in particular, have long been a fractious, independent bunch and difficult to bring together.
"Moreover, the anti-slaughter effort has traditionally been a different set of advocates than the wild equine movement. The same can be said of other areas of animal advocacy.
Wild horses from the Onaqui Herd in Utah. © BLM
The alliance is critical of the so-called Salazar plan, which proposes more aggressive use of long-term contraceptives and relocating wild horses to up to seven new horse reserves on more productive land further east of the western rangelands.
"As to the Salazar plan specifically, we see it as a bloodless genocide at best," Holland said.
He said Interior Secretary Ken Salazar has attempted to alter the discussion of what to do with the horses in long-term holding into a discussion of what to do with all the wild horses.