I used a bit of chaste berry with my old boy when nec but not needed it for Jess yet, but mostly just keeping stress levels low, keeping them out and moving and on low sugar & starch, high fibre, plus oil when nec. diets and managing weight through exercise and grass restriction. I also keep an eye for indications of the immune system becoming compromised and boost with herbs like echinacea and use more specific homeopathy depending on what's going on.
Phoenix was typical uber hairy so I clipped him year round and kept him well rugged, I lost him at about age 35 (he was a rescue so that was the vets best guess) and he never had lami in his years with me, he went when his body was no longer compliant rather than anything ppid related.
Jess has been diagnosed young (a bit over 2 years ago as a 10 year old), I've done the same with her now and not had lami but the work element is very critical for her as she really likes to eat! If she began showing symptomatic changes I would re-check her ACTH (I'm doing that periodically anyway) and prasend won't be excluded as an option but it will be my last choice as I don't like the idea of her being on drugs for the next 20 years possibly.