How many runs can be considered too many for a horse without winning a race?

[moody]

How many runs without winning can a horse be considered to be on a long losing run or hard to win with? Also, if a horse has changed trainer, for example, within the last two races, and it didn't have a win since 10 runs ago, should we still take into account this runs without winning? Or the new trainer sort of 'resets' those runs and we should count the runs without winning for the new trainer?

[Hendredenny]

I had a share in a horse a couple of years ago. He never won for me, but came 2nd several times at Bath . He was tried over 5, 6, 7 furlongs and no matter the distance he would run a promising second but never wanted to lead at the finish. For all his faults he was a really nice animal, but I never backed him !