That known as ‘tread’ is caused by the shoe on the opposite foot, and may happen in a variety of ways.  More often than not it is met with in the feet of heavy draught animals, and is there caused by the calkin, either when being violently backed or suddenly turned round.  It may also occur in horses with itchy legs, as a result of the animal rubbing the leg with the shoe of the opposite limb.  The irritation in this case is nearly always due to parasitic infection (Symbiotes equi), and becomes sometimes so unbearable as to render the animal unmindful of the injury he may be inflicting so long as he experiences the relief obtained by the rubbing.

Self-inflicted tread is also sometimes met with when horses are worked abreast at plough.  The animal in the furrow, with one foot sometimes in and sometimes out of the hollow, is caused to make a false step, and so brings the injury about.

Animals worked in pairs are further liable to receive a tread from the foot of their companion.  This is commonly seen in heavy animals at agricultural labour in fields, where the walking is uneven, and abrupt turning constant.  It is not uncommon either in animals at work in vans in town, and is occasionally met with in the feet of carriage-horses.

‘Overreach’ is the term used to indicate the injury inflicted on the coronary portion of the heel of the fore-foot by the shoe of the hind.  Ordinarily, overreach occurs when the animal is at a gallop, and is thus met with in its severest form in hunters and steeplechasers.  It can only occur when the fore-foot is raised from the ground and the hind-foot of the same side reached right forward.  When the feet separate the injury takes place.  In its movement backwards the inner border of the shoe of the hind-foot catches the coronet of the fore, and tears it backwards with it.  Quite frequently a portion of the skin is removed entirely, but often it hangs as a triangular flap.  The flap in such a case is always attached by its hindermost edge, and indicates plainly enough that the direction of the blow that cut it must have been from before backwards.

Although ordinarily inflicted at the gallop, the same injury may, nevertheless, be caused by allowing a fast trotter, and one with extreme freedom of action behind, to push forward at the utmost limit of his pace.  The outside heel is the one most subject to the injury.

While the common form of injury to the coronet is, as we have described, that occasioned by the animal’s own shoe, or that of a companion, it is evident that the foot is also open to similar injuries from quite outside sources.  Falls of the shafts when unyoking animals from a heavy cart, blows or wounds from the stable fork, wounds resulting from the foot becoming fixed in a gate or a fence, either may equally well set up the mischief.