mounted escort, groom
騶 centers on a person who manages or accompanies horses: a mounted escort or a groom who cares for horses.
騶 combines 馬 (horse) with 芻, which likely contributes the sound and relates to cutting grass or fodder, fitting the groom or escort role.
A horse 馬 needs a groom to cut and bring fresh grass 芻. Picture a mounted escort feeding his horse with freshly cut fodder.
For シュウ, imagine the groom giving a sharp 'shoo!' sound to shoo away flies while escorting the horse: shoo -> シュウ.