Brands horses, without question (7)
I believe the answer is:
marques
'brands' is the definition.
('marque' can be a synonym of 'brand')
'horses without question' is the wordplay.
'horses' becomes 'mares' (mare is a kind of horse**).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'question' becomes 'qu'.
'mares' placed around 'qu' is 'MARQUES'.
(Other definitions for marques that I've seen before include "Brands (e.g. of cars)" , "Makes of car" .)