there is no history of it in the parents bloodline , should i be worried about this or not.
Hm that IMHO is the breeder inferring that their dogs bloodlines are CEA free which in Rough Collies I very much doubt
The only way to guarantee dogs are CEA free is by DNA testing either both parents are genetically DNA clear or the the puppies are DNA tested clear. Screening only tells you the puppy doesn't have CEA or the degree to which it is affected. It doesn't mean the dogs are CEA free
My BC spuppy doesn't have CEA & will never have it but he carries CEA
However I personally doubt there are very many genetically clear Rough Collies & I don't think many will have been DNA tested in the UK.
Slightly affected dogs can need normal lives but I personally would never buy an affected puppy & of course they shouldn't be bred from