The Fa'side flock was started by Susan and Ian Brash, with their purchase of three Black Wensleydale foundation ewes, and has grown to include a separate flock of White Wensleydale sheep. The Rare Breed Survival Trust lists Wensleydale sheep as "at risk" on their register, meaning there are between 900 and 1,500 registered sheep in Britain. Fa'side Wensleydales are meticulously bred and registered each year, with the hope of preserving and growing the breed. The 15th century Fa'side castle and estate is also home to a Warmblood horse herd, which produces a yearly crop of well-bred foals that go on to become successful dressage, show jumping, and eventing horses around the world. 

The Wensleydale breed originated in North Yorkshire in the early 19th century with the crossing of a since extinct local longwool ewe, and a Dishley Leicester tup. Unlike most sheep breeds, the lineage can be traced directly back to one ram, Bluecap, born in East Appleton, five miles from Bedale in North Yorkshire. Developed as a dual use breed, Wensleydales still carry the characteristics of the founding tup: dark skin, excellent quality of wool, and large size.

A separate register was started in 1994 for black lambs, and the number of registered ewes has been quite volatile, with 88 registered in 1999, which has since declined. The black wool colour is a double recessive trait and is impossible to predict within a white herd. Historically the dark lambs were culled to avoid contaminating the valuable clip with their dark fibres. However, these unpredictable black lambs from white herds have become a valuable resource for the small number of Black Wensleydale herds, as they widen the gene pool and lessen the likelihood of inbreeding.