Pics not required - it is probably lice.
You can get all sorts of things to treat it - call your local feed store or veteranarian - they will have something that works - all you need is a wallet and cash.
Or you can do nothing and it will eventually go away on its own.
Happens at this time of the year - every year - and even in so called closed herds - it is completely natural and some people go crazy worrying about it.
Once the winter coat sheds out the sun kills the lice.
Bez