There's no reason this info should NOT be in the PPs. Almost all tracks announce it as a program change, and then next time the horse runs he'll be listed as a gelding in the PPs versus a colt, horse or ridgling. This means, obviously, the database field for the horse's sex is updated. Why not add a comment? For the players, it would be nice to mark the start when a horse was gelded, as it often does mark a form reversal.
Another blatant example of how the industry puts the player at the bottom...