I've been doing alot of research on how far back Irish Setters have been mushing. I've come across a few mentions of the breed in Mushing.com magazine aswell.
This guy is running 14 with a cart...boy is he brave http://smythirishsetters.com/dogsledding.html
Yes they were nearly wiped out the Red Setter overtook the Red and White in popularity. This was in some part in the 1880's to the rising fashion for the red dog in the United States, and a continuing demand for red dogs in Ireland, for which good prices could be obtained. Consequently, the breed came close to extinction. Thanks to the efforts of an early 20th century by a Northern Ireland Clergyman the breed survived but only in small numbers in the island of Ireland. From around 1970 there was a planned revival of the breed, and the numbers began to increase slowly. By the 1980s IRWS were being imported into Great Britain, where the breed was developed more as a show dog. In contrast to these British IRWS, the breed has continued to be primarily a working and field trial dog in Ireland