“The only thing he missed—besides Hemming—was Wyoming itself, its extravagant flatness, its trees so deeply green they looked blue, the sugar-and-turd apple-and-peat smell of a horse after it had been rubbed down for the night.”]]]]
Turd: a piece of the solid brown waste material you pass from your body.
Peat: a black substance formed from decaying plants under the surface of the ground in some areas, which can be burned as a fuel, or mixed with soil to help plants grow well.
Here it may refers to the smell of excrement of horse, let assumed it, why it would related to sugar, apple.
Question: what the meaning of 'sugar-turd Apple-and-peat" and "rubbed down"