trotting poles

I have ridden from the age of 3 competitively and NEVER had this problem. My horse will not TROT over trot poles, he’ll walk them under saddle, walk trot & canter them on the lunge, walk trot and canter a single pole under saddle but any more then 3 poles he goes back down to a walk to finish...

Waaaaah. Got a sense for how much the ex-racehorse at my riding stables used to love jump racing on Sunday. Exercise in the school was to trot from H-C, trot poles from C-A, track left at A and pick up a canter before F, back to trot at M, trot poles C-A, track right at A, and trot back to E...