Does any one encounter this situation?
After modifying the horse pool under the schedule file, the no. of horses is keep decreasing over the years
I modify the pool to 21000, have 12000 horses in my debut season
it decrease to around 10000 in second season
Now is less than 7000 in my third season
Are there any solutions to tackle this issue?

I might be having this issue too, I've noticed my races are practically empty, even the ones that are coded in the schedule to have big fields. Even including international horses, I don't have 20,000 horses in my game; it's not just that they're not racing. I'm on my third season and I have 7679 horses in Australia (my main country).