Answer

By Your Horse

Farrier Glyn Trundle says:

The frog acts as a pump to help blood circulation. It provides protection for the inner, more sensitive hoof structures, acts as an anti-concussion mechanism and prevents slipping (more so in unshod feet).
The frog, which is part of the hoof, has a similar make-up to the horny wall and sole but a much softer consistency, accounted for by its higher moisture content – around 40% compared with the hoof wall, which contains 25% moisture. It has to have the softer, more elastic horn to fulfil its anti-concussion role and help pump blood around the leg.
The frog helps compress veins (when the leg bears weight onto other surrounding structures) and squeeze blood back up the leg (blood pressure is often low in the legs due to gravity). This is why some horses’ legs swell when they stand in the stable a lot.
The frog’s wedge shape also acts as an effective brake in the unshod foot as it increases drag on the hoof in soft conditions and its soft ‘rubbery’ consistency provides friction on
hard surfaces.
Good care should be taken of the frog so it remains healthy and strong and can fulfil its role.