A breastcollar is a Y-shaped piece of tack that prevents the saddle from sliding backwards.
It has a strap that goes between the front legs and attaches to the cinch, and two straps that attach to the saddle on each site.
The breastcollar may be attached to the riggings or the d-rings on the saddle.

Breastcollars are often used in fast-paced events such as barrel racing, roping, and reining. They keep the saddle from slipping and, in the event that a cinch fails or comes loose, can provide support.

Breastcollars are often made of leather or nylon. Breastcollars used in showing or parades are often more decorative and may include fancy engraved leather and silver plates. Some functional breastcollars are decorated with beads or colored inlays.

Breastcollar straps are a connective piece that goes over the horse's withers and holds the breastcollar high enough so that it will not interfere with the movement of the horse's shoulder. This is especially important in fast-paced performance events where the horse needs to have full movement to complete events. Some people will tie a piece of twine across, but some breastcollars come with straps. Or, almost any kind of strap with clips can be used-- for example, a small double-clipped dog walking leash works well.

English riders use a similar piece of tack called breastplates or breastgirths.