What is the slobber strap and why do vaquero-trained horses wear them?

A slobber strap is a short leather strap — typically four to six inches long — that attaches between the bit ring and the rein on a vaquero-style bridle. The name comes from the fact that these straps were traditionally made from soaked rawhide that dried stiff, though the term now applies to similar straps made from leather or other materials. The slobber strap serves several practical functions in vaquero and California reined horse training. The primary mechanical purpose is to add weight below the bit ring, which makes the rein hang with a natural drape and swing. When the rein is dropped to a loose rein after communication, the slobber strap's weight pulls the rein gently back to its resting position against the horse's neck, which provides a consistent tactile signal to the horse that the communication has ended and the rein is slack. The slobber strap also protects the rein from the horse's saliva — a horse working correctly in a correctly fitted bit will salivate, which is a sign of relaxation and correct jaw release. Traditional braided rawhide reins are degraded by moisture, and the slobber strap keeps the rein out of direct contact with the wet area near the horse's mouth. From a training communication perspective, vaquero trainers used the slobber strap as part of developing the horse's sensitivity to the rein's weight and swing. A horse trained to respond to the weight and swing of the rein — which changes subtly as the slobber strap swings — is more finely tuned to the rein's movement than a horse trained only to respond to direct pressure. This is consistent with the vaquero ideal of a horse so light that the weight of the rein communicates rather than active hand pressure.