I'm always interested in old farm books because they are sometimes more helpful to the small farmer than the more modern books. My cattle have been perhaps fortunate not to have a wart problem but I hear of a lot of other breeders that are seeking remedies for warts. So if nothing else is working for you here's an old treatment that you could try:
Warts. - Warts are small skin tumors that frequently appear on the neck, shoulders, and heads of young cattle. They are probably caused by an abnormal nutrition of the skin. As a rule, they are of a temporary nature and will gradually disappear of their own accord. Their disappearance, however, can be hastened by the daily application of castor oil or salty bacon fryings. Large warts can be removed by ligation with a horse hair or a strong cord. The root should then be cauterized with strong acetic acid or tincture of iodine.
"Beef Cattle" by Roscoe R. Snapp, Ph.D., originally published in 1925.