Is this a thread about pony sweat? Because I have just the thing.
"Horses, however, have a thick, waterproofed, hairy pelt that would normally impede the rapid translocation of sweat water from the skin to the surface of the hair necessary for evaporative cooling.
"To solve this, horses appear to have evolved [this] surface-active, detergent-like protein that they release at unusually high concentrations in their sweat (human sweat is instead high in salt but low in protein).
"This protein, latherin, presumably acts by wetting the hairs to facilitate water flow for evaporation, the side effect of which is the lathering that is often observed on the pelts of sweating horses, especially where rubbing occurs."
TLDR; horses sweat soap.