Do some ponies not itch at all

[corabella]

I have been reading this and other boards and it seems that itching is very common. Is it a spectrum with sweet itch at one end but all equines itching in some circumstances? Do some ponies never seem to be affected and if so why? Is the predisposition inherited or is it mainly environmental?
It does seem awful to have to rug native breed ponies during summer months. How effective is brewers yeast in prevention. Presumably nothing is totally effective as there are so many products on the market for this.

[valerie n scout]

My Scout isn't a Dales but is a "professional" scratcher...and is therefore rugged all year round. I got skin scrapings and he doesnt suffer from the traditionsl sweet itch but is allergic to the "dust" that lifts when there is ploughing or harvesting...its a bally pain, he was sweating this year but rubs himself till he bleeds,so MUST be covered x
Ive tried all sorts and nothing does it but covering does so....