The Royal Steeds are any number of mounted animals used by the Royal Guard and Knights of Daventry and kept in the royal stables.
They may include horses (a number of puns point to possible horses "neigh-sayer", but many of them are dog-like Snutes.
Behind the scenes[]
Chapter 1 makes reference to the race of steeds being 'snutes'. However, ch2 puns for the "Royal Steeds' also seems to make reference to horse related material as well.