I hear that the Global Herbs do a suplement that regulates hormones in male horses. My mate gave it to her stallion who would get over excited to the point that he rarely 'put it away' You have nothing to loose if you phone their advice line and talk to their vet.
If it was my horse I would probably get bloods done because testosterone can be produced by certain types of tumor... tiz probably just the joys of spring though.
he's driving me and himself nuts! He's 14 so gelding probably isn't an option but he is pacing constantly, has injured himself through it, has been on box rest, jumped out but got stuck over the door and we had to take the door off to free him and consequently he nearly gelded himself in the process. He's dropping weight at an alarming rate through stress I'm assuming......vet is coming out today so I'll see what he has to say.
Is the Globalherbs supplement you mentioned the "rigcalm"?