American researchers have found that free-roaming horses can be safely fitted with GPS or VHF radio collars with minimal risk of injury.
The researchers evaluated both commercial and custom-built collars in their study, the findings of which have been published in the open-access journal, PLoS ONE.
Gail Collins, Steven Petersen, Craig Carr and Leon Pielstick said effective and safe monitoring techniques were needed by United States land managers to understand the behavior of free-roaming horses and their habitat use, and to aid in making informed management decisions.
Global positioning system (GPS) and very high frequency (VHF) radio collars can be used to provide the information on horse movements to help make such decisions, they said.
“GPS and VHF collars are a common tool used in wildlife management, but have rarely been used for free-roaming horse research and monitoring in the US,” the researchers said.
They cited several studies around the world in which collar technology had been successfully used, including studies on wild horses, Przewalski’s horses, Asiatic wild asses and zebras.
However, despite the technology’s widespread application, collars have been barred from use on free-roaming horses under the jurisdiction of the Bureau of Land Management (BLM) in the US because of previous incidents of collar-related injuries.
Problems included ill-fitting collars and, more importantly, a lack of collar removal that resulted in horses wearing collars for extended periods, causing significant injury.
The four set out in their study to evaluate the design, safety, and detachment mechanisms on GPS/VHF collars used to collect horse location and movement data.
Between 2009 and 2010, 28 domestic and feral horses were marked with commercial and custom-designed collars.
The researchers carried out their evaluation of the collars on a ranch in southeast Oregon and the 232,694 hectares of sagebrush-steppe habitat that comprises the Sheldon National Wildlife Refuge in northwest Nevada. The horses used in the Nevada phase were allowed to roam a 12,000-hectare fenced area within the refuge.
Modifications were made during the pilot study, because in about 30 percent of cases there was hair wear sufficient enough to expose the skin. However, as this took place over an extended period, the underlying skin adapted by thickening and strengthening the epidermal structure. It remained pliable with no evidence of callus formation or loss of elasticity. In no case was the skin integrity compromised.
The modifications included the addition of collar length adjustments to both sides of the collar, allowing for better alignment; the addition of foam padding to the custom collars to replicate the commercial collar’s foam padding; and repositioning of the detachment device to reduce wear along the jowl.
“Following these modifications we observed only slight wear in the hair along the neck and mane of the horses with no abrasions or calluses even after several months of wear,” they reported.
“Collar wear during the in-field [Nevada] study was as expected from that observed following the collar modifications during the pilot study.”
Collins and her colleagues said their work showed that free-roaming horses can be safely collared using an appropriately modified design with minimal to no detectable physical impact to the horse.
During their study, most of the custom-built collars failed to collect data.
“We tested the custom-built collars due to the greater cost savings,” they explained. “However, we experienced issues with their functionality, likely due to inexperience with the construction and potentially rougher handling by horses than other species.
“We observed several instances where a commercial collar took a direct kick from another horse and continued to function normally.
“For those custom-built collars we could recover, in several locations soldered joints in the electronics were broken leading us to suspect there were flaws in the construction,” the researchers said.
“The potential exists for horses to be injured when collars get caught in trees or fencing. Although we did not specifically monitor for these events, we saw no evidence of any injuries that could be attributed to horses being trapped in fencing or trees because of collars.”
Breakaway devices may provide protection against this type of injury, but more research was needed on the strength of the rubber tubing used in such a system to fully address this question. During the study, detachment devices had an 89 percent success rate.
They employed two basic types of detachment devices – a breakaway system made of perishable rubber tubing or a time-release device. All the rubber-tubing collars successfully detached. Several of the time-released devices failed, which the researchers suspect related to their attempts to reset them in the field.
“Based on our experience in this study, collar fit is an important consideration,” they said. “By maintaining a natural oval shape and fitting the collar high on the neck, collar movement and subsequent wear was significantly reduced. In addition, collar detachment devices should be installed along the collar in locations to ensure they do not cause excessive wear along the horse’s jowl.”
The study team said the use of VHF/GPS collar technology was critical to understanding how free-roaming horses, particularly in the western United States, move across the larger landscape and use increasingly scarce resources.
“Lack of this information has contributed to the management complexity of this species.
“Applying this technology to the study of free-roaming horses will provide the opportunity to better understand horse resource use, habitat preference, home range, and movement patterns,” they said.
Such investigations could be incorporated into investigations of social structure and herd or band dynamics, as well as behavioral modifications associated with reproductive management including contraceptive use and sterilization, they said.
They concluded: “This study showed that free-roaming horses can be safely marked with GPS and/or VHF collars with minimal risk of injury, and that these collars can be a useful tool for monitoring horses without creating a risk to horse health and wellness.”
Collins GH, Petersen SL, Carr CA, Pielstick L (2014) Testing VHF/GPS Collar Design and Safety in the Study of Free-Roaming Horses. PLoS ONE 9(9): e103189. doi:10.1371/journal.pone.0103189
The full study can be read here.