Something to consider before starting your young horse on a daily dewormer:
There is evidence that the use of a daily dewormer in your youngsters grain ration may interfere with the development of an acquired immunity to strongyles. The daily dewormer kills the migratory/invasive stages of the parasite, which normally trigger an immune response. If kept on the dewormer, the young horse would in fact be protected. However, if there were a break in the regimen this individual could be vulnerable to parasitic disease if exposed, since he would have no natural immunity.

It may be wiser in the long run to have some exposure to infective larval stages as a youngster to acquire a natural immunity, which would protect him throughout his life. Normal deworming of your youngster would keep the parasite levels under control while allowing his immune system to develop.

Of course, if your pasture burdens are heavy I think daily dewormers are a good idea. Empirically, weanlings kept on daily dewormers often look better than weanlings not on daily dewormers, but again they may be set up for problems later in life.