American Pharoah -- My Dad's Sperm Is Hotter Than Ever!

Imagine getting paid $60,000 ... just to bang.

That's how much it costs to mate with American Pharoah's father right now ... and the prices are going UP UP UP in the wake of AP dominating at the Kentucky Derby and the Preakness.

The horse that's getting all the action is Pioneerof The Nile -- who's been nailing mares professionally since 2010 ... and churning out some of the fastest ponies in the game.

TMZ Sports spoke with the people at WinStar Farms, where Pioneer lives (and bangs), who tell us ... "The phones have been ringing non-stop with people asking about him [since the Derby]."

When Pioneer first got into the baby making game, his rate was $17,500. But that was in 2010 ... before his kids started crushing it on the track. Now, his seed runs $60k-a-pop and we're told the price is expected to go WAY up.

A rep for Pioneer's owner tells us, "He was busy before. His babies were hitting the ground running. But we haven't experienced anything like this. Not even close."

So, how much higher could the prices go if Pharoah wins the Belmont Stakes and takes the first Triple Crown since 1978?

No one would give us an exact price but they did say it would provide a VERY significant boost.

After all ... "Everybody loves a winner."