I'm having the same problem here: two years old kune kune and the small one is loosing hair. The neighbour being a farmer I got some " pour. On" Ivermectin for mange. I was feeding them kitchen leftover which seems to be not good, so I switched to one cup of soaked oats per pig per day. They have access to plenty of grass.
I'm starting to suspect pressure treated wood that is around. I'll address the wood problem and do my best to come back here if there's improvement.
