Ashwasena was an important part of war in ancient India. It is the cavalry wing of the ancient Hindu army. Arthashastra describes it as Chaturangabala. A complete army as per Mahabharata consists of ratha (chariot), gaja (elephant), turaga (horse) and padadi (infantry).
Ashwasena in ancient Hindu world comprised of the best quality horses.
Ashwasena was assigned in the battle very important tasks. The tasks included the supervision of the discipline of the army, protection of its sides, first attack, turning the movement of the army, pursuit and like. (Arthashastra X.4)
Horses were an indispensible part of the army during ancient times. There was a special department to look after their selection, training and upkeep under an official called Ashvadhyksha.
A register for the horses were maintained as to their breed, age, color, size etc. Special care was taken or their stabling, training and treatment of diseases.
Horses for the cavalry had to be secured from various places specifically known for different breeds such as Kamboja (Afghanistan, the kaofu of Hieun – Tsang), Sindhu (Sind), Aratta (Punjab), Balhika (Balkan States), Sauvira (Sind or Indus delta), Papeya and Taitila (Arthashastra II30).
Western horses occupied a pride of place from the time of the Mahabharata in all warfare, as these steeds were very strong.
The mettle of the horses was tested by certain measurements which Kautilya called Ashvapariksha.
Stables were built in conformity with the rules of hygiene, and the feeding of the horses received special attention. War horses received special training in the various movements required of them on the battlefield.
Source - notes taken from Encyclopedia of Hinduism Volume II page 5 - IHRF