Shaggy white dogs, once great favourites with ladies. Shakespeare mentions them (Henry V., ii. 1).
“Use and custome bath intatained ... Iceland dogges curled and rough all over, which, by reason of the length of their heire make showe neither of face nor of body.” —Fleming: Of English Dogges (1576).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894