If you are looking for the origin of black noses in Shorthorns, you better go back to the origin of the breed and start there. While black noses in some of today's Shorthorns can be traced to appendix heritage, there is probably as many black noses in Shorthorns that can be traced back to their origin in Scotland. My grandfather established our Shorthorn herd in 1917 and I can still remember him telling a story of the best bull he ever raised, who was born in 1927 from parents born in Scotland. This bull had a black nose and was pretty well worthless as a breeding animal in that era.
Glamis Benefactor was imported to America, in the 60s and was the undefeated Champion at every British show he was ever shown at. He was such a powerful bull overall, that people felt his black nose had to be overlooked as he had so much to offer the breed. I saw Benefactor at KC Shorthorn Farms, and not only was his nose black but his entire head was black as well. He had black pigment on most of his body.
Another excellent bull that was imported from Scotland that had a black nose was Drynie Argosy. He was purchased by Remitall Cattle Co, Olds, AB when they were looking for a new herd sire in the 60s as well. Not only did Argosy have a black nose, but he was red and white in color, which was shunned as much as black noses in that day. Remitall decided to bring him to Canada despite these characteristics as they felt he was the best overall bull they could find in Scotland.
I am not sure exactly where the black noses started but I am pretty sure it goes back to the foundation of the breed. Three years ago, I had the good fortune to visit with Donald and Diana McGillvary of Calrossie, in Scotland. Donald was in his 80s but his memory was crystal clear yet. His father and grandfather had leading roles in the history of the Shorthorn breed in Scotland. In our discussion, he said that there has been many animals over the years that had questionable genetics in their makeup. We like to think of all these cattle that originated from Scotland, as being pure as fresh fallen snow, but according to Donald McGillvary, there were questionable genetics in all breeds. He also said that because the Shorthorn and Angus breeds were developed in close proximity, that there was some cross over between the breeds in the early stages of the breeds . Some of this was accidental and some was intentional by dishonest breeders who only wanted to gain success with their animals.
Cattle from the Irish strain of Shorthorns have an even higher chance of black noses. Deerpark Improver had a black nose and black noses have appeared from many other Irish animals.
I am also not sure how the black nose is inherited, as it can appear from parents who have no black noses for many many generations in their pedigree. I had an ET calf about 5 years ago that had a black nose. This calf was DNA parentage verified to parents with no appendix in their pedigree. There was some Irish breeding 7 generations back but the particular Irish animals did not have black noses.