If you've been around horses long enough, you've surely seen one of these big cubical white tubs of Orvus Paste/Shampoo. They last FOREVER, so you might have seen the same one for years and years. It is a shampoo that gets the job done, especially for white horses that are so hard to get clean. There are no 'flavours' to choose from--it only comes in the 'original' shampoo form. But as generations of horse, cattle, sheep, goat, dog, etc. owners will tell you, it WORKS.
The first and main thing you need to know about Orvus is that it is concentrated. A little goes a long way. A cap full can do a whole horse. One time I went out to the wash rack and found a girl using this who didn't understand the concept of 'concentrated’. She had rubbed a HANDFUL of ORVUS into ONE side of her horse's neck!!! It took 30 minutes of rinsing just to get it all out of his hair!!!! She got the concept after that. As I said, one tub will last you years, especially if you have just one horse and you don't wash them all the time.
The contents of the shampoo are sodium lauryl sulfate, lauryl alcohol, sodium sulfate, and water. Sounds really artificial and loaded with chemicals, but this is actually recommended by preservationists for use in cleaning historical linens, quilts, and other fine natural fabrics. It is made for cleaning rugs, upholstery, hand washing delicate fabrics, and, oh yeah, washing livestock too (seems rather odd--delicate fabrics and 1500 pound cattle). If you check the quilting websites, the quilters swear by this stuff. They sell it as "quilt paste" and then put (an equine shampoo) beside the name to describe what it is. Funny.
It can't be too harsh if it is recommended as a preservative for historic fabrics, and it isn't. Horses come out nice and clean and shiny. It is great for getting green grass stains and manure stains out of horse hair, and it just picks up the dirt and washes it away (it is a surfactant, like the dish soap Dawn - takes grease out of your way). It rinses clean quickly (especially if you don't put 60 times too much on the horse).
In the winter, the shampoo becomes more like a paste--white and thick. In the summer, it is more syrup-y and yellow, but in either form it works just fine (it's just easier to work with in the summer). It takes a lot of normal shampoo or dish soap to clean a horse, compared to the amount it takes to clean a horse with Orvus. Besides, if you actually finish a jar of Orvus, it makes a great jar for stashing horse treats that came in an unsealable bag