Coat Care

Re my adopted kune kune piggies (two and three years old):

For the most part all three girls' coats are in SOOO much better condition with good food, pasture, and space to wander... but Holly, and to a lesser extent Duchess, both have gotten these balding patches.  Having seen pics here in another thread of a Kune Kune with mites I wonder if somehow the girls have ended up exposed.  Could something like that have come from a purchased hay bale?  Or what else might we be looking at?  Any and all thoughts or ideas would be welcome and appreciated.  I love my piggies, they are the realization of a ten year dream for my son and I, and I want nothing but the best for them.  They have our hearts.

I've attached two pics of Holly's coat and one of Duchess.  
I'll come back and add one of Patsy, aka Two Four, with her face full of slop to cover the "cute pig tax".

nom nom nom