It's belived that the Bulgarians were the first who brought the stirrups to Europe(стремена.
...and they borrowed this from Mongol Keshiks. I think this is true for the proto-bulgarian Asparuh's army. Later, the horsemen were more like heavy cavalry. Look here
...част от прабългарската конница е била изцяло тежко въоръжена и е представлявала основно ударно ядро, чиято цел е била мощен фронтален или флангов удар срещу добре въоръжена пехота или конница в открито сражение...
Also some other weapons might be used by the horsemen, such as swords.
...this makes them heavy cavalry, armed not only with bows, but with swords, shields, spears and maces....