The European system is based on the American system. Then, in terms of retirement, the USA (benefiting from a much larger area of grassland) benefit from many associations and foundations that host and maintain the racehorses in retirement. These associations / foundations are financed by donations and patronage. In Australia too.
In Europe, these foundations for retirement are still few and we hope one day develop this side. On the other hand, in terms of conversion, Europe is very active.