The 9 years I've had peafowl I've continued worming my peafowl with Ivermectin or Safeguard in water twice a year with no problems. I don't see any indication it's ever disturbed their molting or feathers growing back. I have beautiful healthy peafowl with gorgeous full feathering. Have lost none to worms or illnesses. Did loose a peahen in flight breaking her neck on a ceiling post, a male taken by hybrid red wolves and 2 peahens killed by predators while nesting on our 5 acres. Hens now go in a safe aviary during breeding season. I do feed them WELL giving them more then just the Purina Gamebird Feed (20% protein)..........healthy veggies and fruit, Audubon Supreme Birdseed Blend and Farmers Helper UltraKibble (read the ingredients in it). OH, they also get Purina Cat Chow once a week. The gamebird feed is available all the time with the others filling in as healthy treats. My birds are happy....not stressed in tight quarters. Maybe here in the Texas Hill Country with all the rocks and limestone we don't have the worm problem others do but as I dig rocks out and more mulch decays into dirt I am seeing some huge earthworms that makes me want to go fishing, LOL! Another thing that might help is I use seasoned cedar mulch on the ground in the open aviaries (bugs don't like cedar). Never in a closed area like the peachick house. The oil in cedar is not good for birds. We've used piles from mulching the cedar trees on out property so it's dried out a lot. If I purchase bags of it I dump them outside the aviaries and let it set there for a month or more airing/drying out before using.
If I weren't a senior woman taking care of my birds by myself I'd probably worm my peafowl orally but it would be very stressful for them and me. They don't like being caught and it's not an easy task. I read all the time to give the wormer on a piece of bread. Mine can taste it, they shake their head and drop it. IN A GRAPE? Please explain to me how you can add liquid to the inside of a grape full of juice. Which brings up another healthy treat my birds get....cooked sweet potato. That I can mix meds in. They love their sweet potatoes. Last year I had a White peacock attacked by a raccoon. Sweet potato was a Godsend to get his antibiotics in him. Have also used sweet potato to give peahens acting like maybe eggbound some vitamin E or fish oil.
OK, I've rambled on enough. Through years of reading and talking to people I've compiled the above that works for me. Can't say it will work for everyone. I also have a few pheasant and 2 Black Australian swans. I do worm the pheasant the same way. Have not as yet wormed Gracie and Gunther, not quite a year old yet. Some worm, some don't. I'd worm them if I were sure what and how but can't even find a local Veterinarian that knows for sure.
LOVE MY HOBBY, LOVE MY BIRDS!