I've heard of people rubbing WD-40 on their joints for arthritis... and they swore by it, too.
As for feet, as TMom pointed out, the hoof is dead - good feet come from the inside, with lots of sulphur-containing aminoacids (cysteine and methionine), or other sources of bioavailable sulphur, which are used to build the keratin of the hoof. Plain gelatin works well - or can also use flavoured Jello (my farrier swears by this). However, cheap-o, lanolin-based hand cream does help, when put on the coronary band. Petroleum-based products are not recommended, because they actually encourage the growth of horn-eating bacteria. Also, when put out in the sun, mineral-oil (petroleum) based products tend to actually dry out the hoof.
To this day, my 93 year old grandmother, who is the daughter of a farrier, swears by putting bacon grease on a horse's feet. I tried it, but it stinks - and attracts ants

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