I have a tb schoolmaster who was diagnosed with cushings in 2010. A strong management program is key to keeping her up and running. My main issues have been keeping weight and muscle on her, as well as coping with the scruffy, long coat.
First, she is checked by my vet every 6 month to monitor how she is getting along on the pergolide (which Smartpak has the cheapest as of now). She gets 1mg/daily.
For the weight/muscle: she gets 8 lbs daily of Triple Crown Senior. With cushings horses, you want to watch the starch, or NSC, content of your food. Unfortunately, most of the more palatable feeds have high NSC values. The TC senior, and the TC LoW Starch, are the best feeds I have found through trial and error. You may want to also consider getting your hay tested. If you have a starchy hay, soaking for 30-60 minutes before feeding can cut down on the starch content. My mare also goes out on grass a few times a week, and gets daily turnout. She is ridden 4-6 days a week to keep her fit, and I have yet to see a lameness issue with this routine.
For the gnarly coat: I supplement with Omega Horseshine. It is a little expensive, but it works! And it is safe for Cushings horses. The OHS helps her shed out sooner, and keeps some shine in her coat. Off of it, she looked terrible. Very mousy, and her coat was actually rough to the touch (think wire-haired terrier hair). She is also body clipped about every 2.5 months- in the summer I clip her to keep her from over heating, and in the winter to help her cool out faster and not get chilled. If you do clip in the winter, it is important to monitor blanketing, as the cushings messes with a horse’s ability to thermoregulate.
Some miscellaneous things to think about- cushings horses are more likely to be immunocompromised, so issue like colds take longer to heal. Consider starting your horse on an immune supplement. Wounds and fungus also have significantly longer healing times, especially if you have an older horse. Promptly treat anything that pops up, and keep at it until you are 115% sure the issue is resolved.
Cushings horses also drink more water and urinate more- I insist on 2 full buckets as well as the auto waterer, and her stall gets cleaned and picked multiple times daily to remove any soiled bedding.