There are numerous designs for expansion collars in the biological literature. Most designs incorporate a tensioning element that allows the collar to expand as the neck circumference increases. Virtually all of these designs have been used successfully. All of these designs also have limitations. In the case of juvenile animals the neck circumference increases and then remains constant. The elastic material need only expand once. However, if these collars are used on males that undergo "rut" or "roaring" the elastic may be so permanently stretched during the period when neck girth is maximum and that the material may not be able to return to the original dimension post rut. Another concern is that any collar that can stretch may allow a calf to slip a leg through the collar and become entangled. Alternatively, a tree branch may snag in the collar and trap the animal. All these concerns should be addressed by the study team prior to considering the use of this technology in the study. Telonics also recommends that the researchers contact and consult with individuals who have experience using this technology on the species. Careful monitoring of animals that wear expansion collars is also recommended. Several "standard expansion/breakaway collars" are described below and standard pricing is available for each design. Custom expansion breakaway collars are also available. Please consult with the factory regarding implementing custom designs and to obtain a quotation for the collar.