The horse collar was one of the few important technical feudal innovations. I believe the Avars among others used it. It did not come into general use in Europe until 11th – 12th centuries. It’s impact was massive since the previous yokes or harnesses had decreased the pulling power of a horse to little more than an ox. This collar enabled the horse to use its full strength without choking. This meant that horses could pull a much heavier plough. The heavy plough produced much better crops and Europe enjoyed an increase in population generally as more land was put under cultivation. The increase in production led to greater surpluses as the growth in trade and towns and everything that went with it ( the 12th century “ renaissance “).
This growth came to a sudden halt because of the plague ( the Black Death). Because of the increased demand for labourers it also led ( particularly in England) to the undermining of feudal serfdom because lords were willing to poach peasant labourers by offering cash wages as increasing rates. This tendency increased after the Black Death because of the shortage of labour. So indirectly the horse collar led to the growth of capitalism.