Horse Hoof Pick
A hoof pick is a small took (usually made of metal) used to clean the hoof, specifically to remove mud, manure, dirt, ice or snow, and stones from the hooves of a horse. It has a blunt point (the pick) to clean the hoof and often has a small stiff brush on the side opposite from the point. Following is a photo of a very simple hoof pick (courtesy wikipedia).
Regular use of a pick helps to keep the hooves healthy, as well as removing objects or dirt clumps which can make walking uncomfortable or even painful for the horse. Removal of mud and manure prevents illnesses such as thrush, while removal or stones helps to prevent bruises and abcesses.
Aside from the actual benefits of cleaning the hooves, it provides an opportunity to carefully inspect all four hooves for injury, illness or excessive wear (e.g. from walking or running on hard or abrassive surfaces).
It is recommended that the hooves be cleaned daily and that they should be cleaned before and after each ride. To make this take easier, the horse should be trained from a young age to pick up its foot when a person runs their hand down its fetlock (lower leg) and gently lifts. If these does not work, most horses will pick up their hoof if the fendons behind their cannon bone are squeezed (squeeze the back of the leg, just above the hoof).
The point of a hoof pick should be blunt, to prevent accidental injury to the horse or the person using it. For further safety, one can work from the back of the hoof to the front (less chance of slipping and poking a leg). Some picks have a stiff brush, which is useful for brushing out small bits, such as in the photo below.