This New York Times article mentions how harness racing faces the same problem as t-bred racing: breeding is way more lucrative than racing. But someone on the sulky side has an idea:
It seems like a good idea on-paper/on-line but will it catch on?
Officials are mulling changing the conditions for many rich stakes races, barring competitors sired by a horse who was 4 years old or younger at the time of conception. That would make a 4-year-old sire less valuable and more likely to remain in competition another year before entering into the lucrative breeding industry.