Sucking Horses are not born with stable vices, it is man and domesticity which has brung about these problems, it is therefore important in the early years of a horses training, not to give a horse an excuse to find himself a vice.
Horses can develop stable vices at anytime however.
Most stable vices are caused through boredom and are extremely if not impossible in some cases to cure. Vices can also be learnt from other horses and copied. In some cases vices are possible to cure. There are several different vices a horse can pick up on to entertain himself while he is bored and undoubtedly several more that are either rare or unique and have not been given a label as such yet, because we are not fully aware of the horses way of thinking. It is because of this reason horses need to be treated as an individual, they do not all develop the same vice for exactly the same reason.