Dandruff on piggies?

[GuineaPigsPipPumpandJG]

All 3 of my pigs have dandruff, and have had it since I can remember. They don't seem to be unwell, they have a good diet, with dust-extracted hay, so I have no idea why they have it. My girls are half-texel, so could it be because of their breed? Any suggestions?
(They have all been treated with spot-on containing ivermectin in case of parasites.)

 

[Piggies&buns]

Some piggies can have drier skin than others but it is always best to have a vet check them over first. If you are seeing them excessively scratching or are otherwise concerned, then do see a vet. Please don’t treat on spec though, you should always get a vet diagnosis before giving any treatment