When I was a kid I worked as a hot walker at a SB barn. Horses were washed with warm water and soap after every workout. They came in hot, sweaty, covered in track crud. After cooling out, they were washed --and rinsed, of course. I THINK the soap may have been Orvis. As far as conditioner for the coat --we used none (that I recall). This was early 1970s.
I wash my horses a couple of times a month --always before a competition and once or twice in between because I like to ride a well-turned out horse. I use Cowboy Magic products (Orvis is a pain to rinse out --takes forever --and I use conditioner and PEPE coat shine before we go out. I really like Carr and Daily products --but hard to find around here. And kind of costly for my boys who show where turn out means nothing —
I have heard the “soap washes out oils” before. Not sure I agree. I showed with some pretty high up (World/Congress) QH people --I was never at that level --but their kids were friends with my kids and we held our own at local shows --they washed their horses same as I did. I am sure that over use of harsh soaps will damage a coat, but I don’t think that’s true of the products designed for horses --if it were, no one would use them.
I have two bays --one true bay and one roan. They are slick looking --coats like seals. I don’t think it is washing/not washing that makes a difference; I think it’s what I feed them —good quality alfalfa hay and good feed. And I brush each one about 15-20 minutes each day. I was working as a ring steward at a small local show. It was a youth class in Showmanship. The judge said , " I can always tell which kid brushes his horse every day." He was right.